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UBC Theses and Dissertations

Study of self-supporting deuterated polyethylene targets Makosky, Lyle M. 1969

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A STUDY OF SELF-SUPPORTING DEUTERATED POLYETHYLENE TARGETS LYLE M. MAKOSKY •Sc. (Hons.) U n i v e r s i t y o f Western O n t a r i o , 1 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE In the Department o f PHYSICS We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY rfF BRITISH COLUMBIA June, 1969 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y of B r i t i s h C olumbia, I a g r e e t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and Study. I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g of t h i s t h e s i s f o r s c h o l a r l y p u rposes may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n of t h i s thes,is f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department of y f 3 ^ Y S / C £ The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date ^f^ft? - I i -ABSTRACT T h i n s e l f - s u p p o r t i n g d e u t e r a t e d p o l y e t h y l e n e t a r g e t s f o r use w i t h t h e r e a c t i o n 2 H ( 3 H e , p ) 4 H e have been i n v e s t i g a t e d . Both p o u r i n g and e v a p o r a t i n g t e c h n i q u e s f o r the c o n s t r u c t i o n o f t h e p o l y e t h y l e n e f i l m were t e s t e d . S t a b l e t a r g e t s , c a p a b l e of w i t h s t a n d i n g 690 keV 3He beam c u r r e n t d e n s i t i e s o f more than 10 yA/cm 2, were c o n s t r u c t e d by e v a p o r a t i n g 10 yg/cm 2 t h i c k c arbon l a y e r s o n t o both s i d e s o f t h e ( C 2 D i + ) n f i l m ("sandwich" t a r g e t s ) . T a r g e t s p r e p a r e d by the p o u r i n g t e c h n i q u e were found t o be m e c h a n i c a l l y s t r o n g e r than the " s a n d w i c h " t a r g e t s p r e p a r e d by e v a p o r a t i o n o f ( C ^ D i J n . The t a r g e t s e x h i b i t an i n i t i a l r a p i d d e c r e a s e i n the d e u t e r i u m c o n t e n t d u r i n g the f i r s t 150 yc o f 3He beam on the t a r g e t . T h i s e f f e c t i s a t t r i b u t e d . t o breakdown o f the C^D^molecules i n t o t h e i r a t o m i c c o n s t i t u e n t s and subsequent d i f f u s i o n o f the d e u t e r i u m out o f t h e t a r g e t . A f t e r t h i s i n i t i a l e f f e c t , t h e t a r g e t s d e t e r i o r a t e by l e s s than 0.05% per y c . The t a r g e t s were d e v e l o p e d f o r use f o r t o t a l p r o t o n r e a c t i o n c r o s s s e c t i o n measurements by t h e a s s o c i a t e d p a r t i c l e t e c h n i q u e . The beam p r o f i l e s o f the 15.8 MeV p r o t o n s from the r e a c t i o n 2H ( 3He,p)^He, wh i c h a r e r e l e v a n t t o t h i s t e c h n i q u e , were measured. The amount of e l a s t i c s c a t t e r i n g s u f f e r e d by t h e p r o t o n s i n the p r e s e n t t a r g e t s was s m a l l e r than t h a t o b s e r v e d w i t h the copper backed heavy i c e t a r g e t s used i n p r e v i o u s c r o s s s e c t i o n measurements (Ho 68). The d e u t e r i u m c o n t e n t o f the t a r g e t was found t o be a l i n e a r f u n c t i o n o f the t h i c k n e s s o f t h e carbon l a y e r s c o m p r i s i n g t h e t a r g e t " s a n d w i c h " . The a l p h a y i e l d f r o m the r e a c t i o n 2H ( 3He,p)^He i n c r e a s e d by a f a c t o r of 1.83 - 0.35 per 10 yg/cm 2 carbon l a y e r on t h e "back" of the t a r g e t , and by a f a c t o r o f - i i i -1.38 - 0.26 per 10 yg/cm 2 carbon l a y e r on the " f r o n t " o f the t a r g e t . As a p o s s i b l e e x p l a n a t i o n o f t h i s e f f e c t i t i s proposed t h a t d e u t e r i u m , r e p l e a s e d from t h e p o l y e t h y l e n e by the beam, d i f f u s e s t h r o u g h o u t the t a r g e t and i s t r a p p e d by the ca r b o n t o a c o n c e n t r a t i o n o f 0.11 d e u t e r i u m atoms per carbon atom. i v -TABLE OF CONTENTS ABSTRACT i i TABLE OF CONTENTS i v LIST OF TABLES v] LIST OF FIGURES v i i ACKNOWLEDGEMENTS x CHAPTER I INTRODUCTION 1.1 G e n e r a l I n t r o d u c t i o n 1 1.2 P r e v i o u s Work w i t h P o l y e t h y l e n e T a r g e t s 8 1.3 P r e s e n t Work w i t h P o l y e t h y l e n e T a r g e t s 10 CHAPTER II EXPERIMENTAL METHOD AND DESIGN 2.1 G e n e r a l I n t r o d u c t i o n ... 13 2.2 T a r g e t P r e p a r a t i o n 2.2.1 C a l i b r a t i o n o f T h i c k n e s s M o n i t o r 1** 2.2.2 Poured P o l y e t h y l e n e T a r g e t s 18 2.2.3 E v a p o r a t e d P o l y e t h y l e n e T a r g e t s 23 2.2.4 T a r g e t S t r e n g t h e n i n g Through R a d i a t i o n .. 25 2.3 A l p h a Y i e l d Measurements 2.3.1 Method 2 7 2.3.2 A p p a r a t u s 30 2.4 T a r g e t T h i c k n e s s Measurements By Energy Loss AE 2.4.1 Method 36 2.4.2 A p p a r a t u s 39 - v -CHAPTER II EXPERIMENTAL METHOD AND DESIGN c o n t i n u e d 2.5 P r o t o n Beam P r o f i l e Measurements 2.5.1 " C o i n c i d e n c e " E l e c t r o n i c s 42 2.5.2 Other A p p a r a t u s and Method 45 CHAPTER I I I EXPERIMENTAL OBSERVATIONS AND CALCULATIONS 3-1 G e n e r a l I n t r o d u c t i o n 52 3.2 S e l f - S u p p o r t e d T a r g e t P r e p a r a t i o n 52 3.3 T a r g e t Performance Under the 3He Beam 3.3.1 A l p h a Y i e l d and Energy Loss T h i c k n e s s f o r R e g u l a r Runs 56 3.3.2 A l p h a Y i e l d f o r Carbon L a y e r V a r i a t i o n s . 65 3.4 P r o t o n Beam P r o f i l e 3.4.1 O p t i m i z a t i o n o f Measurement Parameters .. 76 3.4.2 H o r i z o n t a l P r o f i l e 82 3.4.3 V e r t i c a l P r o f i l e 85 CHAPTER IV CONCLUSIONS AND SUGGESTIONS 4.1 G e n e r a l C o n c l u s i o n s 88 4.2 S u g g e s t i o n s f o r F u r t h e r Study 94 BIBLIOGRAPHY 96 APPENDIX A (C 2D [ +)n THICKNESS REQUIREMENT 97 APPENDIX B ENERGY LOSS OF THE 3He BEAM IN A CARBON FILM 99 APPENDIX C THE "EQUIVALENT POLYETHYLENE THICKNESS" AS A FUNCTION OF THE ALPHA YIELD (COUNTS/yc) 1 Q1 APPENDIX D "EQUIVALENT CARBON THICKNESS" OF TARGET MATERIAL CALCULATED FROM THE 1 9 F RESONANCE SHIFT IO1* - v i LIST OF TABLES TABLE 1. L a y e r t h i c k n e s s e s and t h e i r e r r o r s f o r the " s a n d w i c h " t a r g e t s 5** 2. A summary o f t h e a l p h a y i e l d and energy l o s s t h i c k n e s s t e s t i n g c a r r i e d out on t h e b a s i c " s a n d w i c h " t a r g e t samples.. 58 3. A summary o f the a l p h a y i e l d s t u d y on t a r g e t s w i t h d i f f e r e n t c a r b o n l a y e r t h i c k n e s s e s 66 A t t e n u a t i o n o f the p r o t o n beam (due t o s c a t t e r i n g ) f o r d i f f e r e n t h a l f a n g l e s subtended by the p r o t o n d e t e c t o r 92 - v i i LIST OF FIGURES FIGURE 1. 2H ( 3He,p) t*He r e a c t i o n k i n e m a t i c s 2 2. 2 H ( 3 H e , p ) l t H e r e a c t i o n k i n e m a t i c s 3 3 . 2H ( 3He,p) 1 +He r e a c t i o n k i n e m a t i c s k k. Geometry o f ca r b o n e v a p o r a t i o n a p p a r a t u s 17 5 . S e l e c t i v e e v a p o r a t i o n , p o u r i n g and w e i g h i n g p r o c e d u r e s f o r *»5 yg/cm 2 t h i c k poured (C2Dtf)n t a r g e t s 20 6. S c h e m a t i c d i a g r a m o f t h e " s i n g l e g r a i n box s o u r c e " ........ 2A 7 . S c h e m a t i c d i a g r a m o f polymer s t r e n g t h e n i n g t h r o u g h gamma r a d i a t i o n 26 8. S c h e m a t i c d r a w i n g o f t h e chamber s e t - u p f o r a l p h a y i e l d measurements 31 9. B l o c k d i a g r a m o f t h e e l e c t r o n i c s f o r the a l p h a y i e l d measurements 33 1 0 . S c h e m a t i c d i a g r a m o f t h e chamber s e t - u p used i n t a r g e t t h i c k n e s s measurements by energy l o s s ^0 11. B l o c k d i a g r a m o f t h e e l e c t r o n i c s used f o r t a r g e t t h i c k n e s s measurements by energy l o s s M 1 2 . B l o c k d i a g r a m o f the e l e c t r o n i c s used i n the p r o t o n beam p r o f i l e measurements ^ 3 1 3 . S c h e m a t i c d i a g r a m o f the chamber s e t - u p used i n the p r o t o n beam p r o f i l e measurements ^6 1^ 4. Diagram of c o l l i m a t o r d e v i c e f o r measuring t h e h o r i z o n t a l and v e r t i c a l p r o t o n beam p r o f i l e s 50 - v i i i FIGURE 15- A t y p i c a l s o l i d s t a t e d e t e c t o r s p e c t r u m f o r t h e a l p h a y i e l d measurements 57 16. A l p h a y i e l d as a f u n c t i o n o f t h e t o t a l i n t e g r a t e d beam c u r r e n t on t a r g e t f o r t h e t a r g e t s IBS(2) and IBS(3) 61 17. A l p h a y i e l d as a f u n c t i o n o f t h e t o t a l i n t e g r a t e d beam c u r r e n t on t a r g e t f o r t h e t a r g e t s I I IAS (1) and IVo 64 18. A l p h a y i e l d as a f u n c t i o n o f t h e t o t a l i n t e g r a t e d beam c u r r e n t on t a r g e t f o r t h e t a r g e t s I I A S ( l ) and I IAS (2) 68 19. A l p h a y i e l d as a f u n c t i o n o f the t o t a l i n t e g r a t e d beam c u r r e n t on t a r g e t f o r t h e t a r g e t s I I B S ( l ) , I IBS(2) and I IBS (3) ' 69 20. A l p h a y i e l d as a f u n c t i o n o f t h e t o t a l i n t e g r a t e d beam c u r r e n t on t a r g e t f o r t h e t a r g e t s I I C S ( l ) , I ICS (2)R and I ICS (3) 70 21. A l p h a y i e l d as a f u n c t i o n o f t h e t o t a l i n t e g r a t e d beam c u r r e n t on t a r g e t f o r t h e t a r g e t s I I I B S ( l ) and I I I B S ( 2 ) R . . . 71 22. F i n a l a l p h a y i e l d as a f u n c t i o n o f the number o f lOpg/cm 2 c a r b o n l a y e r s on t h e "back" o f the t a r g e t 73 23. The r a t i o o f the " f i n a l a l p h a y i e l d " f o r a g i v e n number o f ca r b o n l a y e r s on t h e "back" t o t h e " f i n a l a l p h a y i e l d " f o r t h e same t a r g e t i n i t s o r i g i n a l " b a s i c " sandwich form, as a f u n c t i o n o f the number o f carbon l a y e r s 74 24. The r a t i o o f a n t i c o i n c i d e n c e t o c o i n c i d e n c e c o u n t s as a f u n c t i o n o f the s o l i d s t a t e d e t e c t o r assembly a n g l e 77 - i x -FIGURE 25- The r a t i o o f a n t i c o i n c i d e n c e t o c o i n c i d e n c e c o u n t s as a f u n c t i o n o f t h e s o l i d s t a t e d e t e c t o r h e i g h t 78 2 6 . The r a t i o o f a n t i c o i n c i d e n c e t o c o i n c i d e n c e c o u n t s as a f u n c t i o n o f t h e ti m e d e l a y f o r t h e p r o t o n p u l s e s 79 2 7 . The r a t i o o f a n t i c o i n c i d e n c e t o c o i n c i d e n c e c o u n t s as a f u n c t i o n o f t h e base l i n e s e t t i n g f o r the 100 keV window ., 80 2 8 . H o r i z o n t a l p r o f i l e s o f p r o t o n beam 83 2 9 - V e r t i c a l p r o f i l e s o f p r o t o n beam 86 - X ACKNOWLEDGEMENTS I w i s h t o e x p r e s s my s i n c e r e g r a t i t u d e t o Dr. C.F. H o j v a t f o r h i s p a t i e n c e and u n d e r s t a n d i n g o f t h e problems i n v o l v e d d u r i n g t h e c o u r s e o f t h i s r e s e a r c h and f o r h i s s u p e r v i s i o n and a s s i s t a n c e t h r o u g h o u t the e x p e r i m e n t a l work. I am a l s o g r a t e f u l t o Dr. G.M. G r i f f i t h s f o r h i s s u p e r v i s i o n o f my c o u r s e o f s t u d y and f o r h i s h e l p f u l s u g g e s t i o n s on the w r i t i n g o f t h i s thes i s. The a s s i s t a n c e o f the s t u d e n t s , t e c h n i c i a n s and f a c u l t y o f t h e Van de G r a a f f group i s t h a n k f u l l y acknowledged. I am i n d e b t e d t o the N a t i o n a l R e s e a r c h C o u n c i l f o r the r e c e i p t o f t h e i r s c h o l a r s h i p d u r i n g t h i s work. - 1 -CHAPTER I INTRODUCTION 1 .1 Gene r a l I n t r o d u c t i o n The r e a c t i o n 2H ( 3He,p)^He, Q = 18.352 MeV, i s used as a s o u r c e o f p r o t o n s f o r t h e measurement o f t o t a l p r o t o n r e a c t i o n c r o s s s e c t i o n s by t h e a s s o c i a t e d p a r t i c l e t e c h n i q u e (Ho 6 8 ) . The a s s o c i a t e d p a r t i c l e t e c h n i -que p e r m i t s t h e measurement o f the p r o t o n s removed by an a b s o r b e r from a p r o t o n beam ( i e p r o t o n beam a t t e n u a t i o n ) where t h e p r o t o n beam i s d e f i n e d by t h e d e t e c t i o n o f t h e a s s o c i a t e d ^He p a r t i c l e s . In a n u c l e a r r e a c t i o n w i t h two p a r t i c l e s i n the f i n a l s t a t e , t h e p r i n c i p l e s o f c o n s e r v a t i o n o f energy and momentum p e r m i t the c o r r e l a t i o n o f the two p r o d u c t s i n an unambiguous way. I f one o f t h e p a r t i c l e s i s d e t e c t e d a t some a n g l e w i t h r e s p e c t t o t h e d i r e c t i o n o f the incoming p r i m a r y beam, the energy and a n g l e o f e m i s s i o n o f the a s s o c i a t e d p a r t i c l e i s d e f i n e d b y . the parameters o f the r e a c t i o n . The parameters a r e the masses o f t h e i n i t i a l and f i n a l p r o d u c t s and the Q-value f o r the r e a c t i o n . K i n e m a t i c a l r e l a t i o n s h i p s can then be w r i t t e n , f o r a p a r t i c u l a r r e a c t i o n , c o r r e l a t i n g t h e a n g l e s and e n e r g i e s o f the outcoming p a r t i c l e s u s i n g , f o r example, t h e i n c i d e n t energy i n the i n p u t channel as a pa r a m e t e r . The r e l e v a n t k i n e -m a t i c a l r e l a t i o n s h i p s f o r t h e r e a c t i o n 2H ( 3He,p) 4He a r e p r e s e n t e d i n F i g u r e s 1, 2 and 3. D e t e c t i o n o f one o f t h e p r o d u c t s not o n l y d e f i n e s t h e k i n e m a t i c a l a s p e c t s o f t h e a s s o c i a t e d one but a l s o y i e l d s u s e f u l temporal . i n f o r m a t i o n . For example, i t p r o v i d e s a means o f knowing when the a s s o c i a t e d A L P H A E N E R G Y (Mev) Figure 3: PROTON ANGLE 2H(3He,p)4He reaction kinematics - 5 -p a r t i c l e was produced o r i s e x p e c t e d t o a r r i v e . In the t e c h n i q u e d e v e l o p e d by H o j v a t and Jones (Ho 68), t h e 4He p a r t i c l e s o f energy 3.3 MeV emerging from the t a r g e t a t an a n g l e o f 96.2° w i t h r e s p e c t t o the i n c i d e n t 3He beam were d e t e c t e d i n a s i l i c o n s u r f a c e b a r r i e r d e t e c t o r . The kinematica 1 1y c o r r e s p o n d i n g 15.8 MeV p r o t o n s emerging a t an a n g l e o f 63.5° were d e t e c t e d i n a C s l s c i n t i l l a t i o n c o u n t e r a f t e r t r a v e r s i n g t h e sample a b s o r b e r t o be measured. Both t h e s p a t i a l c o l l i m a t i o n and t h e tim e o f a r r i v a l o f t h e p r o t o n were d e f i n e d by t h e d e t e c t i o n o f t h e a s s o c i a t e d ^He p a r t i c l e . Thus, removal o f a p r o t o n from t h e p r o t o n "beam" was i d e n t i f i e d by an a n t i c o i n c i d e n c e between the ^He and p r o t o n c o u n t e r s , whereas p r o t o n t r a n s m i s s i o n was i d e n t i f i e d by a c o i n c i d e n c e . T h i s a s s o c i a t e d p a r t i c l e t e c h n i q u e was used t o measure t h e t o t a l p r o t o n r e a c t i o n c r o s s s e c t i o n o f d i f f e r e n t a b s o r b e r s . The p a r t i c l e f l u x a v a i l a b l e i n t h e a s s o c i a t e d p r o t o n beam depends on the c r o s s s e c t i o n f o r t h e 2 H ( 3He,p) t fHe s o u r c e r e a c t i o n . The c r o s s s e c t i o n as measured by Kunz (Ku 55) has a r e s o n a n t c r o s s s e c t i o n o f 695 - m i l l i b a r n s a t an i n c i d e n t 3He energy o f ShO keV. As d i s c u s s e d i n t h e o r i g i n a l work, as maximum energy l o s s o f 100 keV by the 3He beam i n t h e s o u r c e t a r g e t i s c o m p a t i b l e w i t h good c o l l i m a t i o n i n the p r o t o n beam (Ho 68). The l i m i t a t i o n on the p r o t o n f l u x e s then a r i s e s not i n the f l u x e s a v a i l a b l e i n the p r i m a r y beam fr o m a p a r t i c l e a c c e l e r a t o r , but i n the problems i n v o l v e d i n the d e s i g n o f s o u r c e t a r g e t s c a p a b l e o f w i t h -s t a n d i n g the n e c e s s a r y beam c u r r e n t d e n s i t i e s w i t h o u t i n t r o d u c i n g unwanted s c a t t e r i n g m a t e r i a l i n t h e p r o t o n and 4He p a t h s . - 6 -In t h e o r i g i n a l work a heavy i c e D20 t a r g e t on a 120 x 10~6 i n c h t h i c k copper b a c k i n g f o i l was employed. The copper b a c k i n g f o i l , k ept i n c o n t a c t w i t h a l i q u i d n i t r o g e n r e s e r v o i r was used t o f r e e z e heavy w a t e r vapour ( i n j e c t e d i n t o t h e t a r g e t chamber) i n t o a l a y e r o f D20 i c e . The copper b a c k i n g however i n t r o d u c e d e l a s t i c s c a t t e r i n g o f t h e p r o t o n beam. P r o t o n s s c a t t e r e d o u t o f t h e a n g l e subtended by the p r o t o n d e t e c t o r w i l l be d e t e c t e d as " f a l s e " o r background a n t i c o i n c i d e n c e s . T h i s w i l l c o n t r i -b ute t o the "background a t t e n u a t i o n " o f the p r o t o n beam i e t h a t a t t e n u a -t i o n o f the p r o t o n beam wh i c h i s due t o s o u r c e s o t h e r than t h e a b s o r b e r sample b e i n g measured. T h i s background, due t o t h e copper b a c k i n g s c a t t e r i n g , can be reduced by s u b t e n d i n g a l a r g e r s o l i d a n g l e w i t h t h e p r o t o n d e t e c t o r . The r a t i o o f the d e t e c t e d c o i n c i d e n t p r o t o n s ( i e d e t e c t e d c o i n c i d e n t w i t h t h e m o n i t o r e d ^He p a r t i c l e s ) t o t h e n o n - c o i n c i d e n t ones i s d e t e r m i n e d by the a n g l e subtended by t h e p r o t o n d e t e c t o r . The p r o t o n d e t e c t o r s o l i d a n g l e i s chosen so t h a t the s c a t t e r i n g o f the p r o t o n beam i n the s o u r c e t a r g e t does not c o n t r i b u t e s i g n i f i c a n t l y t o the a t t e n u a t i o n background. For t h e case o f the copper backed t a r g e t s , f o r an a t t e n u a t i o n o f <5 x 10 5 due t o t h e e l a s t i c s c a t t e r i n g , the h a l f - a n g l e subtended by the p r o t o n de-t e c t o r was c a l c u l a t e d t o be 11°. For such a l a r g e a n g l e t h e r e i s a l a r g e number o f p r o t o n s d e t e c t e d w h i c h a r e not a s s o c i a t e d k i n e m a t i c a 1 l y w i t h the chosen ^He p a r t i c l e s (which o c c u r i n an a n g u l a r range o f o n l y 5°). Due t o t h e "dead t i m e " e f f e c t s p r e s e n t i n t h e d e t e c t o r s , a p a r t i c l e a r r i v i n g a t one o f t h e d e t e c t o r s w i t h i n t h e p a r a l y s i s time o f a p r e c e d i n g p u l s e e i t h e r f a i l s t o produce a p u l s e a t a l l , o r i t s p u l s e a m p l i t u d e i s degraded. The d i s a p p e a r a n c e o f a c o i n c i d e n t p u l s e from the p r o t o n d e t e c t o r w i l l r e s u l t - 7 -i n the r e c o r d i n g o f an " a c c i d e n t a l " a n t i c o i n c i d e n c e c o u n t . S i n c e t h e s e dead t i m e e f f e c t s were enhanced i n t h e p r o t o n d e t e c t o r due t o t h e l a r g e background o f n o n - c o i n c i d e n t p r o t o n s , i t was n e c e s s a r y t o p r e v e n t the a n a l y s i s o f both 4He and p r o t o n p u l s e s when the p r o t o n p u l s e s o c c u r r e d w i t h i n a p r e s e t t i m e o f a p r e v i o u s one. For t h i s purpose a " P a r a l y z a b l e Dead Time G a t e " was employed. However, t h e use o f t h i s " g a t e " may p r e -vent a n a l y s i s o f a l a r g e f r a c t i o n o f t h e ^He d e t e c t e d w i t h t h e c o r r e c t s e l e c t e d e n e r g y . For example, f o r a "dead t i m e " o f 16 yS g e n e r a t e d w i t h each p r o t o n d e t e c t e d and a t y p i c a l n o n - c o i n c i d e n t p r o t o n r a t e o f 70 x 103 S" 1, o n l y 35% o f the d e t e c t e d 4He were a n a l y z e d (Ho 68). To o b t a i n low s t a t i s t i c a l e r r o r s a l a r g e number o f c o u n t s a r e r e q u i r e d . Hence, th e "dead t i m e " r e s t r i c t i o n on t h e number o f c o u n t s a n a l y z e d , i n c r e a s e s the a n a l y s i s time r e q u i r e d f o r measurements. A measurement o f t h e h o r i z o n t a l and v e r t i c a l p r o f i l e s o f the p r o t o n beam c o n f i r m e d the s p r e a d i n g o f the beam due t o e l a s t i c s c a t t e r i n g e f f e c t s i n the copper b a c k i n g o f t h e s o u r c e t a r g e t (Ho 68). The p o s s i b i l i t y o f a d e u t e r i u m t a r g e t i n t h e form o f a s e l f - s u p p o r t i n g d e u t e r a t e d p o l y e t h y l e n e (C 2D t t)n f i l m was s u g g e s t e d (Ho 68). A t a r g e t o f t h i s type p r e p a r e d w i t h p r a c t i c a l l y no b a c k i n g f o i l a t a l l would reduce the e l a s t i c s c a t t e r i n g o f t h e p r o t o n beam c o n s i d e r a b l y . The s o l i d a n g l e subtended by the p r o t o n d e t e c t o r a t the c e n t r e o f t h e s o u r c e t a r g e t c o u l d then be reduced by a l a r g e f a c t o r . The n o n - c o i n c i d e n t p r o t o n r a t e would then be reduced by the same f a c t o r . C o n s e q u e n t l y t h e t r a n s m i s s i o n of ^He p u l s e s by t h e " P a r a l y z a b l e Dead Time G a t e " w i l l i n c r e a s e a c c o r d i n g l y . The - 8 -i n c r e a s e d number o f e v e n t s a n a l y z e d would r e s u l t i n lower s t a t i s t i c a l e r r o r s f o r the same a n a l y s i s t i m e d u r i n g t o t a l p r o t o n r e a c t i o n c r o s s s e c t i o n measurements. For an energy t h i c k n e s s o f 100 keV t o an i n c i d e n t 690 keV 3He beam, c a l c u l a t i o n s show t h a t a s e l f - s u p p o r t i n g d e u t e r a t e d p o l y e t h y l e n e t a r g e t would have a p p r o x i m a t e l y 2.5 tim e s more d e u t e r i u m atoms a v a i l a b l e than t h e heavy i c e t a r g e t . The t h i c k n e s s o f (C 2D t t)n r e q u i r e d t o produce t h i s 100 keV l o s s was c a l c u l a t e d t o be 45.5 yg/cm 2 (Appendix A ) . I t was s u g g e s t e d (Ho 68) t h a t the i n c r e a s e i n t h e r a t i o o f c o i n c i d e n t t o n o n - c o i n c i d e n t p r o t o n s p l u s the l a r g e r number o f d e u t e r i u m atoms a v a i l a b l e a t the s o u r c e t a r g e t c o u l d p r o v i d e an i n c r e a s e by a t l e a s t a f a c t o r o f k i n t h e c o i n c i d e n t c o u n t i n g r a t e t r a n s m i t t e d t hrough the dead t i m e g a t e . The u n c e r t a i n t y i n the measured c r o s s s e c t i o n v a l u e would t h e n be reduced by 50% i n t h e same measuring t i m e . 1.2 P r e v i o u s Work w i t h P o l y e t h y l e n e T a r g e t s The p r e p a r a t i o n o f 40 yg/cm 2 t h i c k d e u t e r a t e d p o l y e t h y l e n e t a r g e t s on a t h i n copper b a c k i n g was d e s c r i b e d by O l i v o and B a i l e y (01 6 7 ) . The t a r g e t s were p r e p a r e d by d i s s o l v i n g 600 yg o f ( C 2 D i t ) n i n 1 g o f b o i l i n g X y l e n e . The s o l u t i o n was g e n t l y b o i l e d f o r a t l e a s t 2 minutes and then poured o n t o a h o r i z o n t a l 15 cm 2 copper b a c k i n g . S u r f a c e t e n s i o n kept the s o l u t i o n w,ithin the c o n f i n e s o f t h e t a r g e t b a c k i n g w h i l e the X y l e n e e v a p o r a t e d . The t a r g e t s were s u b j e c t e d t o 160 keV p r o t o n s t o s t u d y the r e a c t i o n D ( p , y ) 3 H e . The t a r g e t s were found t o be r e l a t i v e l y s t a b l e and gave a h i g h e r y r a y y i e l d than d e u t e r i d e t a r g e t s (such as z i r c o n i u m d e u t e r i d e ) . A r a p i d i n i t i a l - 9 -d e t e r i o r a t i o n o f the p o l y e t h y l e n e t a r g e t s a t h i g h beam c u r r e n t d e n s i t i e s (0.3 mA/cm2) was o b s e r v e d . G.T. A r n i s o n (Ar 66) d e s c r i b e d a t e c h n i q u e f o r t h e p r e p a r a t i o n o f s e l f -s u p p o r t i n g ( C 2 D i t ) n t a r g e t s i n t h e t h i c k n e s s range I t o 20 mg/cm 2. A weighed q u a n t i t y o f (C 2 D t t ) n was d i s s o l v e d i n warm X y l e n e . The s o l u t i o n was poured o n t o a s h a l l o w s t a i n l e s s s t e e l t r a y (heated up t o 200°C) o n t o w h i c h a 100 yg/cm 2 t h i c k sodium c h l o r i d e l a y e r had been e v a p o r a t e d t o a c t as a s t r i p p i n g a g e n t . The t r a y was a l l o w e d t o c o o l and then immersed i n a d i s h o f warm w a t e r and the f i l m s l o w l y s t r i p p e d o f f . The p r e p a r a t i o n o f s e l f - s u p p o r t i n g (C 2D t t)n t a r g e t s o f a t h i c k n e s s e q u a l t o 100 yg/cm 2 was d e s c r i b e d by T r i p a r d and White (Tr 6 7 ) . They d i s s o l v e d 0.01 g o f (C2D[+)n i n 5 9 o f b o i l i n g X y l e n e . A f t e r b o i l i n g f o r 5 minutes t h e hot s o l u t i o n was poured o n t o p r o c e s s c l e a n m i c r o s l i d e s . The s l i d e s were s e t a s i d e t o d r y i n a d u s t - f r e e e n v i r o n m e n t . T h e i r p r e l i m i n a r y t e s t s i n d i c a t e d t h a t t he t a r g e t s were v e r y u n s t a b l e i n a charged p a r t i c l e beam due t o t h e i r v e r y low therma l and e l e c t r i c a l c o n d u c t i v i t y . I t was found t h a t t h e e v a p o r a t i o n o f a t h i n f i l m o f car b o n (10 yg/cm 2 t h i c k ) o n t o the p o l y e t h y l e n e improved the s t a b i l i t y a g r e a t d e a l . The p o l y e t h y l e n e f i l m w i t h i t s t h i n c a r b o n c o a t i n g was f l o a t e d o f f t h e g l a s s by l o w e r i n g the s l i d e s l o w l y i n t o t he w a t e r a t an a n g l e o f 30° t o the s u r f a c e . The f i l m s were p i c k e d up on f l a t metal frames w i t h 0.318 cm d i a m e t e r h o l e s . To measure t h e t a r g e t d e t e r i o r a t i o n , r e a c t i o n p r o t o n s from bombarding t h e t a r g e t s w i t h 2 MeV d e u t e r o n s were m o n i t o r e d . The competing r e a c t i o n s were C 1 2 ( d , p ) C 1 3 and D(d,p)T and t h e s e produced two peaks i n t h e p r o t o n - TO -energy s p e c t r u m . By m o n i t o r i n g t h e r a t i o o f t h e number o f c o u n t s i n t h e two p e a k s , i t was p o s s i b l e t o d e t e c t any d e t e r i o r a t i o n i n the d e u t e r a t e d p o l y e t h y l e n e r e s u l t i n g from m e l t i n g o r s u b l i m a t i o n . With an i n c i d e n t d e u t e r o n beam o f 200 nA t h r o u g h a 0.318 cm d i a m e t e r c o l l i m a t o r t h e r e was about a 10% d e c r e a s e i n t h e d on d p r o t o n y i e l d w i t h r e s p e c t t o t h e C 1 2 p r o t o n y i e l d a f t e r 1 hour o f bombardment. T h i s i m p l i e d a g r e a t e r l o s s o f d e u t e r i u m atoms from t h e t a r g e t t h a n c a r b o n atoms. M. White (Wh 65) d e s c r i b e d the vacuum e v a p o r a t i o n o f common s o l i d p o l y -e t h y l e n e i n t o f i l m s between 900 and 2500 A° t h i c k on g l a s s s u b s t r a t e s . E v a p o r a t i o n was c o n d u c t e d by d r o p p i n g s m a l l p i e c e s o f P o l y e t h y l e n e i n t o a n i c k e l boat p r e h e a t e d t o 290°C. I n i t i a l f i l m s appeared t o be s p o i l e d by what appeared t o be s m a l l p i e c e s o f s o l i d m a t e r i a l imbedded i n them. The i n t r o d u c t i o n o f a b a f f l e between t h e s o u r c e and s u b s t r a t e p r e v e n t e d d i r e c t d e p o s i t i o n and subsequent f i l m s were f r e e from d e f e c t . Good g e n e r a l r e v i e w s d e s c r i b i n g s e l f - s u p p o r t i n g and s o l i d backed t a r g e t p r o d u c t i o n , t h i c k n e s s measurement t e c h n i q u e s and s t r i p p i n g o f f p r o c e d u r e s (from s u b s t r a t e s ) a r e a l s o a v a i l a b l e i n t h e l i t e r a t u r e (Ko 66, Ma 67, Ya 62). 1.3 P r e s e n t Work w i t h P o l y e t h y l e n e T a r g e t s S e c t i o n 1.1 d e s c r i b e d the a s s o c i a t e d p a r t i c l e t e c h n i q u e f o r measuring t o t a l p r o t o n r e a c t i o n c r o s s s e c t i o n s o f d i f f e r e n t a b s o r b e r s u s i n g heavy i c e (D 20) w i t h a c opper b a c k i n g as the s o u r c e t a r g e t . In v i e w o f the p o s s i b l e improvements s u g g e s t e d f o r t h e s e measurements through use o f a s e l f - s u p p o r t i n g d e u t e r a t e d p o l y e t h y l e n e t a r g e t , i t was d e c i d e d t o i n v e s t i -g a t e the p r e p a r a t i o n and t e s t i n g o f such a t a r g e t . - 11 -Both poured and e v a p o r a t e d ( C 2 D t t ) n f i l m p r o d u c t i o n t e c h n i q u e s were s t u d i e d . P r e l i m i n a r y s t u d y i n d i c a t e d the n e c e s s i t y o f e v a p o r a t i n g c a r b o n l a y e r s o n t o both s i d e s o f the p o l y e t h y l e n e f i l m t o p r e v e n t the f i l m from b e i n g d e s t r o y e d under the r e q u i r e d 3He beam c u r r e n t d e n s i t i e s . P o l y e t h y l e n e f i l m s were s t u d i e d f o r a t h i c k n e s s o f kS yg/cm 2 (as r e q u i r e d f o r a 100 keV energy> l o s s o f a 690 keV 3He beam) as w e l l as f o r 135 yg/cm 2. The t h i c k e r f i l m s were s t u d i e d t o see i f t h e y would compensate f o r t h e d e u t e r i u m l o s s o b s e r v e d i n t h e t h i n n e r t a r g e t s . The d e u t e r i u m l o s s was r e f l e c t e d by a r a p i d l y d e c r e a s e d a l p h a p a r t i c l e y i e l d f r o m t h e r e a c t i o n 2H ( 3He,p) t fHe, as a f u n c t i o n o f the t o t a l i n t e g r a t e d 3He beam c u r r e n t i n c i d e n t on the t a r g e t . A l p h a y i e l d s were measured t o t e s t the u n i f o r m i t y o f the t a r g e t samples as w e l l as t o compare t h e r e l a t i v e m e r i t s o f p o u r i n g and e v a p o r a t i n g ^ D t ^ n . The two p r o c e d u r e s were a l s o compared f o r o t h e r a s p e c t s such as t h i c k n e s s a c c u r a c y , m e c h a n i c a l s t r e n g t h o f f i l m s , and ease o f p r e p a r a t i o n . Some o f the f i l m s were s u b j e c t e d t o gamma r a d i a t i o n t o t e s t the p o s s i b l e s t r e n g t h -e n i n g of t h e t a r g e t s t h r o u g h " c r o s s - l i n k i n g " (see s e c t i o n 2.2.k) o f t h e polymer c h a i n s . The h o r i z o n t a l and v e r t i c a l p r o f i l e s o f t h e a s s o c i a t e d p r o t o n beam were measured. T h i s was c a r r i e d o u t t o o b s e r v e t o what e x t e n t removal o f the copper b a c k i n g from the t a r g e t had reduced the e l a s t i c s c a t t e r i n g o f the p r o t o n s emerging from the s e l f - s u p p o r t i n g t a r g e t . The t o t a l t a r g e t t h i c k n e s s e s i n yg/cm 2 were c a l c u l a t e d from the measured energy l o s s o f an i n c i d e n t p r o t o n beam a t a g i v e n e n e r g y . - 12 -F i n a l l y , i t was d e c i d e d t o v a r y the t h i c k n e s s o f the carbon l a y e r s on e i t h e r s i d e o f the ( C ^ D i J n f i l m and t o o b s e r v e the e f f e c t on the t a r g e t p e r f o r m a n c e , as r e g a r d s a l p h a y i e l d and d e u t e r i u m l o s s , when exposed t o a 3He beam. - 13 -CHAPTER I I EXPERIMENTAL METHOD AND DESIGN 2.1 G e n e r a l I n t r o d u c t i o n P r e l i m i n a r y t e s t s i n d i c a t e d t h a t a s e l f - s u p p o r t i n g ( C ^ t j n f i l m was d e s t r o y e d i m m e d i a t e l y a f t e r e x p o s u r e t o t h e 3He beam. E v a p o r a t i o n o f a 10 yg/cm 2 t h i c k carbon l a y e r o n t o one or o t h e r s i d e o f t h e ( C 2 D i t ) n f i l m was not e f f e c t i v e i n p r e v e n t i n g d e s t r u c t i o n o f the t a r g e t . S t a b l e t a r g e t s c a p a b l e of w i t h s t a n d i n g t h e r e q u i r e d beam c u r r e n t d e n s i t i e s were o b t a i n e d by e v a p o r a t i n g 10 yg/cm 2 t h i c k carbon l a y e r s o n t o both s i d e s o f t h e ( C 2 D i + ) n f i l m ("sandwich" t a r g e t s ) . Hence a l l f u r t h e r d e s c r i p t i o n o f t a r g e t p r e p a r a t i o n i s co n c e r n e d w i t h the p r e p a r a t i o n o f t h i s " s a n d w i c h " t y p e o f t a r g e t . C h a p t e r II i s f i r s t o f a l l c oncerned w i t h t h e p r e p a r a t i o n o f the " s a n d w i c h " t a r g e t s by b o t h p o u r i n g and e v a p o r a t i n g t h e ( C 2 D 1 + ) n . The t h i c k n e s s o f both the ( C 2 D i 4 ) n l a y e r and t h e car b o n l a y e r s was d e t e r m i n e d by a w e i g h i n g t e c h n i q u e f o r t h o s e " s a n d w i c h " t a r g e t s whose (C 2 D L f ) n t h i c k n e s s was yg/cm 2. D u r i n g the c o u r s e o f t h e work a q u a r t z r e s o n a t o r t h i c k n e s s m o n i t o r became a v a i l a b l e . I t was used t o measure the t h i c k n e s s o f e v a p o r a t e d (C 2D t t)n f i l m s ( a p p r o x i m a t e l y 132 yg/cm 2 t h i c k ) . In a d d i t i o n i t s e r v e d t o a s c e r t a i n t h e t h i c k n e s s o f the car b o n f i l m s f o r t h e above mentioned e v a p o r a t e d ( C 2D L f)n t a r g e t s as w e l l as f o r the poured (C 2 D L f)n t a r g e t s (^ 132 yg/cm 2 t h i c k ) and f o r a d d i t i o n a l l a y e r s o f ca r b o n e v a p o r a t e d o n t o the t h i n n e r t a r g e t s . There i s a l s o a d i s c u s s i o n o f t h e p o s s i b l e - H -s t r e n g t h e n i n g o f the t a r g e t t h r o u g h gamma r a d i a t i o n and the method of r a d i a t i o n e x p o s u r e used. T h i s c h a p t e r then d e s c r i b e s how t h e v a r i o u s c h a r a c t e r i s t i c s o f t h e " s a n d w i c h " t a r g e t s were a s s e s s e d i n r e l a t i o n t o t h e r e a c t i o n 2 H ( 3 H e , p ) ^ H e . The i means o f assessment were a l p h a y i e l d measurements, t a r g e t t h i c k n e s s e v a l u a t i o n v i a the energy l o s s i n t h e t a r g e t o f a p r o t o n beam, and p r o t o n beam p r o f i l e measurements. 2.2 T a r g e t P r e p a r a t i o n 2.2.1 C a l i b r a t i o n o f T h i c k n e s s M o n i t o r A S l o a n DTM-3 (SI 69) t h i c k n e s s m o n i t o r was used. The t h i c k n e s s o f t h i n e v a p o r a t e d f i l m s i s measured by comparing the f r e q u e n c i e s o f two d i f f e r e n t o s c i l l a t o r s . S p e c i f i c a l l y , t h e mass o f the d e p o s i t i s measured by e v a l u a t i n g t h e change i n f r e q u e n c y o f a r e s o n a t i n g q u a r t z c r y s t a l as the d e p o s i t b u i l d s up on i t s s u r f a c e . P r i o r t o each e v a p o r a t i o n a v a r i a b l e f r e q u e n c y o s c i l l a t o r i s tuned so t h a t t h e "beat f r e q u e n c y " between i t and the c r y s t a l o s c i l l a t o r i s z e r o . An i n c r e a s e i n the mass o f the c r y s t a l w i l l r e s u l t i n a beat f r e q u e n c y change. The f r e q u e n c y s h i f t Af i s g i v e n by th e e m p i r i c a l e q u a t i o n T - 2Af/p (where T i s the t h i c k n e s s i n A° o f a. m a t e r i a l o f b u l k d e n s i t y p(g/cm 3) and Af i s i n c y c l e s / s e c ) . The e s t i m a t e d f i l m t h i c k n e s s ( u s i n g t h i s m o n i t o r ) on an a d j a c e n t s u b s t r a t e must i n c l u d e ; any c o r r e c t i o n s n e c e s s a r y i n t h e m o n i t o r T v a l u e due t o p o s s i b l e d i f f e r e n t g e o m e t r i c a l l o c a t i o n s o f t h e m o n i t o r head and s u b s t r a t e r e l a t i v e t o the e v a p o r a t i o n s o u r c e . With our equipment i t was found more c o n v e n i e n t t o - 15 -c a l i b r a t e t he T m o n i t o r s e p a r a t e l y f o r both carbon and p o l y e t h y l e n e e v a p o r a t i o n s . C a l i b r a t i o n was a c c o m p l i s h e d by f i r s t p r e w e i g h i n g 1" x 3" g l a s s s l i d e s on a microgram b a l a n c e , t h e n e v a p o r a t i n g t h e d e s i r e d s u b s t a n c e o n t o the s l i d e s and r e w e i g h i n g the g l a s s s l i d e s . A comparison o f t h e f r e q u e n c y s h i f t f rom the m o n i t o r w i t h the t h i c k n e s s o f f i l m s (measured by w e i g h i n g ) r e s u l t e d i n a T m o n i t o r c a l i b r a t i o n i n terms o f t h e number o f c y c l e s / s e c f r e q u e n c y s h i f t per yg/cm 2 f i l m t h i c k n e s s on each s l i d e . A s i z a b l e amount (of t h e o r d e r o f 1 mg on a 1" x 3" s l i d e ) was e v a p o r a t e d f o r t h e c a l i b r a t i o n t o reduce the r e l a t i v e e r r o r i n t h e w e i g h i n g i n t r o d u c e d by the b a l a n c e , ( r e s u l t i n g from ambient h u m i d i t y changes e t c . ) . With the e x p e r i m e n t a l c o n f i g u r a t i o n s used (see F i g u r e s h and 6), t h e c a l i b r a t i o n f o r carbon was 19.90 c y c l e s / s e c per yg/cm 2 c a r b o n f i l m t h i c k n e s s on t h e c e n t r e s l i d e , and f o r (C2Dtt)n the c a l i b r a t i o n was 9.83 c y c l e s / s e c per yg/cm 2 (CzDi^n f i l m t h i c k n e s s on the 2 c e n t r e s l i d e s . The h i g h t e m p e r a t u r e o f the car b o n rods and c o n t a c t p o i n t used i n t h e e v a p o r a t i o n , r e s u l t e d i n t h e r m a l shock on t h e o s c i l l a t o r c r y s t a l and the (C2nit)n f i l m s were i n danger o f b e i n g damaged. The heat r a d i a t i o n was reduced by t h e f o l l o w i n g s t e p s : ( i ) The s i z e o f the c o n t a c t p o i n t o f the car b o n rods was reduced t o l i m i t t h e e l e c t r i c power d i s s i p a t e d to t h e c o n t a c t r e g i o n t h e r e b y a l l o w i n g the car b o n t o e v a p o r a t e a t a much lower c u r r e n t v i z : F i g u r e 4. - 16 -( i i ) A t a n t a l u m s h i e l d was p l a c e d around the c a r b o n rods l e a v i n g o n l y the a r e a about the c o n t a c t p o i n t e x p o s e d , ( i i i ) Water c o o l i n g was i n c o r p o r a t e d i n t o b oth t h e c a r b o n rod h o l d e r s and t h e q u a r t z c r y s t a l mount. [Note: w a t e r c o o l i n g on the c r y s t a l mount was used f o r a l l e v a p o r a t i o n i n c l u d i n g ( C 2 D [ + ) n . ] ( i v ) An 88% - t r a n s m i s s i o n t u n g s t e n mesh r a d i a t i o n s h i e l d was mounted near t h e f a c e o f the q u a r t z c r y s t a l . These improvements a d e q u a t e l y reduced the heat r a d i a t i o n such t h a t t h e s m a l l thermal shock e x p e r i e n c e d by the c r y s t a l (of the t y p e where r e t u r n t o the normal s t a t e o c c u r s i n 10 t o 15 seconds) d i d not e f f e c t the m o n i t o r a c c u r a c y [as e x p l a i n e d i n t h e S l o a n manual (SI 6 9 ) ] . The p o l y e t h y l e n e c a l i b r a t i o n was done i n a s i m i l a r way. In t h i s case a g i v e n amount o f ( C 2 D i f ) n was e v a p o r a t e d f r o m the " s i n g l e g r a i n box s o u r c e " (see s e c t i o n 2.2.3). The ( C 2 D t t ) n t h i c k n e s s i n yg/cm 2 was d e t e r m i n e d by w e i g h i n g t h e two 1" x 3" g l a s s s l i d e s b e f o r e and a f t e r e v a p o r a t i o n . T h i s t h i c k n e s s c o r r e s p o n d e d t o a T m o n i t o r f r e q u e n c y s h i f t (as e x p l a i n e d b e f o r e ) and r e s u l t e d i n a t h i c k n e s s c a l i b r a t i o n f o r t h e m o n i t o r . With the equipment used, no c o n t r o l o f the amount o f (C 2 D i f)n e v a p o r a t e d was p o s s i b l e u n l e s s the amount was weighed b e f o r e h a n d , s i n c e c o m p l e t e e v a p o r a t i o n o f the sample o c c u r r e d each t i m e . From t h e m o n i t o r c a l i b r a t i o n and the amount o f ( C 2 D t + ) n u s e d , i t was p o s s i b l e t o c a l c u l a t e the amount o f ( C 2 D i t ) n r e q u i r e d t o p r o -duce f i l m s o f the d e s i r e d t h i c k n e s s . The f i n a l e s t i m a t e d t h i c k n e s s o f each ( C 2 D [ + ) n e v a p o r a t e d f i l m was d e t e r m i n e d by t h e measured f r e q u e n c y s h i f t . : The c a l i b r a t i o n e r r o r f o r the ( C 2 D i + ) n e v a p o r a t i o n i s e s t i m a t e d t o be 3.0" t o 3 - 3" x 1" SI i d e s C u t a w a y o f Tan ta1um S h i e l d O v e r C a r b o n R o d s 4.6" t o T M o n i t o r C u r r e n t S p e c t r o s c o p i c a 1 1 y P u r e C a r b o n R o d s N a r r o w G r o o v e t o R e d u c e L a t e r a l S l i d i n g F I G U R E 4: GEOMETRY OF CARBON E V A P O R A T I O N A P P A R A T U S - 18 -t 8.7% and i s composed o f the f o l l o w i n g : a) A w e i g h i n g e r r o r o f 2.5% due t o a s l o w d r i f t e x p e r i e n c e d by the m i c r o b a l a n c e when w e i g h i n g the s l i d e s , r e s u l t i n g from h u m i d i t y changes e t c . b) A m o n i t o r e r r o r c o n s i s t i n g o f a ± 7 c y c l e s / s e c s c a l e r e a d i n g e r r o r and a r e p r o d u c i b l e a c c u r a c y o f t 2%. c) An e r r o r o f 8% due t o t h i c k n e s s v a r i a t i o n a c r o s s t h e s l i d e f rom th e a v e r a g e t h i c k n e s s c a l c u l a t e d f o r each s l i d e ( s i n c e a l l p a r t s o f t h e s l i d e a r e not a t the same r a d i a l d i s t a n c e from t h e e v a p o r a t i o n p o i n t ) . The t o t a l e r r o r was chosen as the s q u a r e r o o t o f t h e sum o f t h e s q u a r e s o f a l l t h e p o s s i b l e e r r o r s . The u n c e r t a i n t y i n t h e c a l i b r a t i o n f o r t h e c a r b o n e v a p o r a t i o n i s composed o f the same e r r o r s as above e x c e p t t h a t t h e w e i g h i n g e r r o r was ± 5%> r e s u l t i n g i n a t o t a l c a l i b r a t i o n e r r o r o f - S.6%. In a d d i t i o n t o t h e c a l i b r a t i o n e r r o r s , a l 1 e v a p o r a t i o n s a r e s u b j e c t t o a f u r t h e r m o n i t o r e r r o r composed o f a i 21 r e p r o d u c i b l e a c c u r a c y p l u s a - 7 c y c l e / s e c s c a l e r e a d i n g e r r o r (as mentioned b e f o r e ) . 2.2.2 Poured P o l y e t h y l e n e T a r g e t s To o b s e r v e and t e s t t h e (C^ D i^n l a y e r a l o n e , a t h i n f i l m o f p o l y e t h y l e n e was p r e p a r e d by f i r s t d i s s o l v i n g a measured q u a n t i t y o f c o m m e r c i a l l y p r e -p a r e d powdered ( C 2 D t t ) n (De 69) i n a q u a n t i t y o f b o i l i n g X y l e n e s o l v e n t . The s o l u t i o n was poured o n t o a 3 " x 3 " " p r o c e s s c l e a n " s l i d e e n a b l i n g the X y l e n e t o e v a p o r a t e l e a v i n g t h e (C 2 D t ()n f i l m . A f t e r p r e l i m i n a r y t e s t i n g a - 19 -c o n c e n t r a t i o n o f 41.0 mg i n 30 ml o f X y l e n e [ i e 1.36 mg (C 2 Di +)n per ml o f X y l e n e ] was found t o produce an a v e r a g e f i l m t h i c k n e s s o f 44 yg/cm 2 t 25% ( t h i s e r r o r i s d i s c u s s e d i n s e c t i o n 3.2). T h i s t h i c k n e s s and u n c e r t a i n t y f i g u r e were a r r i v e d a t by t e s t i n g t h e above c o n c e n t r a t i o n o v e r a t o t a l o f 25 s l i d e s from 5 s e p a r a t e p o u r i n g s . The t e s t was t o weigh l a r g e a r e a ( C 2 D i t)n s e c t i o n s (2.5 cm x 2.5 cm) from the s l i d e s t o a r r i v e a t an average t h i c k n e s s f o r each s l i d e . D u r i n g p r e p a r a t i o n o f t h e 44 yg/cm 2 t h i c k (C 2 D ) +)n t a r g e t " s a n d w i c h e s " , the t h i c k n e s s m o n i t o r was not a v a i l a b l e t o measure the c a r b o n l a y e r t h i c k -n e s s e s . Hence i t was n e c e s s a r y t o d e r i v e a t e c h n i q u e whereby the t h i c k n e s s o f the c a r b o n and p o l y e t h y l e n e l a y e r s c o u l d be d e t e r m i n e d s e p a r a t e l y by w e i g h i n g . The g e o m e t r i c e v a p o r a t i o n and p o u r i n g t e c h n i q u e i s i l l u s t r a t e d i n F i g u r e 5-A carbon l a y e r o f a p p r o x i m a t e l y 10 yg/cm 2 i s f i r s t e v a p o r a t e d o v e r p a r t o f the s l i d e . The f i g u r e o f 10 yg/cm 2 was chosen because i t appeared t o be t h i c k enough t o g i v e s t a b l e t a r g e t s , w h i l e g i v i n g r i s e t o o n l y 18.8 keV energy l o s s f o r a 690 keV 3He beam (see A p p e n d i x B ) . The s l i d e s were s e t a s i d e f o r one day t o e n a b l e the c a r b o n l a y e r s t o harden. The p o l y e t h y l e n e f i l m was then p r e p a r e d o v e r the whole s l i d e , i n c l u d i n g the carbon a r e a , as fo11ows: ( i ) The measured q u a n t i t y o f (C 2 D ( +)n was p l a c e d i n a 50 ml beaker c o n t a i n i n g 30 ml of b o i l i n g X y l e n e . ; ( i i ) The s o l u t i o n was l i g h t l y b o i l e d f o r a t l e a s t 5 minutes and then poured i n t o t h e 3" x 3" g l a s s s l i d e . The q u a l i t y o f the (C 2D ( +)n — r — | — • -i TT i 1 1 ToTx_j_p 'X_LO. T^ I_PJ_XTO|X. | 01 X | o T x _ | 0 1 | c r H -_ l _ 1 i 1 f. 1 1 1 i • i A H - h r J_[_L: S t e p A . W e i g h i n g P r o c e d u r e : a ) W e i g h s a m p l e s f r o m s e c t i o n A , a v e r a g e g i v e s ^ p o l y e t h y l e n e t h i c k n e s s b ) W e i g h s a m p l e s f r o m s e c t i o n B , a v e r a g e g i v e s ^ ( p o l y + 1st c a r b o n l a y e r ) a n d s u b t r a c t i n g a ) we h a v e ^ 1st c a r b o n t h i c k n e s s c ) S i m i l a r i l y , s e c t i o n C g i v e s , ^ ( p o l y + 2nd c a r b o n l a y e r ) a n d t h e r e f o r e ^ 2nd c a r b o n l a y e r d ) S e c t i o n D g i v e s ^ ( p o l y + 1st c a r b o n + 2nd c a r b o n t o t a l t h i c k -n e s s ) a n d by s u b t r a c t i n g b ) a n d c ) we h a v e ^ p o l y t h i c k n e s s . N o t e : In s e c t i o n D, X ' s i n d i c a t e t h o s e s a m p l e s w h i c h a r e w e i g h e d t o d e t e r m i n e t h i c k -n e s s , a n d O ' s i n d i c a t e t h o s e s a m p l e s t o be u s e d f o r t h e e x p e r i m e n t . F I G U R E 5: S E L E C T I V E E V A P O R A T I O N , POURING AND WEIGHING PROCEDURE FOR k$ y q / c m 2 T H I C K POURED (C 2Di»)n T A R G E T S - 21 -f i l m s o b t a i n e d i s e x t r e m e l y s e n s i t i v e t o the p o u r i n g motion i t -s e l f . I t was found t h a t a l a r g e number o f t r i a l s were n e c e s s a r y t o d e v e l o p a s t a n d a r d i s e d p o u r i n g method. The method was t o g r a d u a l l y t i l t t he beaker about 1" above t h e h o r i z o n t a l g l a s s s l i d e u n t i l t h e s o l u t i o n began t o pour j u s t o u t s i d e the edge o f the s l i d e . The beake r was then swept d i a g o n a l l y a c r o s s the s l i d e . I t i s i m p o r t a n t t o m a i n t a i n the sweeping motion a t a c o n s t a n t speed and t h e f l u x o f s o l u t i o n p o u r i n g out o f the beaker a t a r e l a t i v e l y c o n s t a n t r a t e . The speed o f the sweeping motion i s h a r d t o measure but t h e a u t h o r found i t took a p p r o x i m a t e l y 1.5 seconds from t h e b e g i n n i n g t o the end o f t h e sweep a c r o s s the s l i d e . U s u a l l y 10 s l i d e s were p r e p a r e d r e q u i r i n g 20 ml o f s o l u t i o n ( i e 2 ml per s l i d e ) . The r e m a i n i n g 10 ml o f s o l u t i o n was d i s c a r d e d because c o o l i n g o f the s o l u t i o n r e s u l t e d i n ( C 2 D i + ) n p r e c i p i t a t i n g on t h e w a l l s o f t h e b e a k e r . A second c a r b o n l a y e r o f 10 yg/cm 2 t h i c k n e s s was then e v a p o r a t e d o n t o the p o l y e t h y l e n e f i l m o v e r p a r t o f the s l i d e as i l l u s t r a t e d i n F i g u r e 5. The s u r f a c e o f the s l i d e was then s c r i b e d ( u s i n g a s h a r p c u t t i n g t o o l ) i n t o a g r i d o f square s i z e 1 cm x 1 cm. The v a r i o u s f i l m c o m b i n a t i o n s were f l o a t e d o f f the g l a s s by l o w e r i n g t h e s l i d e s l o w l y i n t o lukewarm w a t e r a t an a n g l e o f 30° t o the w a t e r s u r f a c e . L i f t o f f i s f a c i l i t a t e d by f i r s t s c r a p i n g the edge o f the s l i d e and then a l l o w i n g t h i s edge t o j u s t t o u c h t h e w a t e r u n t i l t he f i l m b e g i n s t o l i f t . P o l y e t h y l e n e f i l m s l i f t e a s i e r than the c a r b o n p l u s (C 2D[ +)n l a y e r s but both r e q u i r e a p a t i e n t and s t e a d y - 22 -hand. As a r e s u l t o f t h e s e p a r a t e samples o f (C^D^n and (C^Di^n p l u s c a r b o n , we were a b l e t o d e t e r m i n e a v e r a g e t h i c k n e s s o f the v a r i o u s l a y e r s by w e i g h i n g the samples as d e s c r i b e d i n F i g u r e 5. The t a r g e t s used i n t h e e x p e r i m e n t were t a k e n from s e c t i o n D o f t h e lower s l i d e i n t h e f i g u r e ( s t e p k). A l t e r n a t e samples were chosen from t h e g r i d t o be weighed and the samples i n t e n d e d f o r use were a s s i g n e d a t h i c k n e s s based on a s t a t i s t i c a l a v e r a g e o f t h e measured samples about them. The t a r g e t s used i n the e x p e r i m e n t were p i c k e d up from t h e w a t e r s u r f a c e on f l a t metal (copper) h o l d e r s w i t h 0.25 i n c h d i a m e t e r h o l e s as f o l l o w s : the h o l d e r s were d i p p e d i n t o the w a t e r and r a i s e d s l o w l y a t a s t e e p a n g l e a f t e r c o n t a c t w i t h t h e edge o f a f l o a t i n g f i l m had been a f f e c t e d . When t h i s work was a l r e a d y i n p r o g r e s s , t h e t h i c k n e s s m o n i t o r became a v a i l a b l e and was used t o measure t h e two carbon l a y e r t h i c k n e s s e s when the 132 yg/cm 2 t h i c k (C 2D( +)n poured t a r g e t s were p r e p a r e d . The reason f o r p r e p a r i n g and t e s t i n g the 135 yg/cm 2 t a r g e t s i s d i s c u s s e d i n s e c t i o n 1.3. In t h i s c a s e the f i r s t c arbon l a y e r was e v a p o r a t e d o v e r the whole 3" x 3" s l i d e , t h e (C 2D l +)n f i l m was formed o v e r t h i s carbon l a y e r as d e s c r i b e d b e f o r e and a second c a r b o n l a y e r was e v a p o r a t e d o v e r the p o l y e t h y l e n e . The m o n i t o r c a l i b r a t i o n e n a b l e d one t o e s t i m a t e the c a r b o n l a y e r t h i c k n e s s t o w i t h i n r o u g h l y 10%. The (C 2D [ +)n t h i c k n e s s was d e t e r m i n e d by s c r i b i n g a g r i d l i k e the one i n F i g u r e 5 o n t o the whole s l i d e and then u t i l i z i n g a s t a g g e r e d w e i g h i n g and s e l e c t i o n p r o c e d u r e as o u t l i n e d f o r s e c t i o n D (of s t e p 4 i n F i g u r e 5). T h i s '"sandwich" t a r g e t p r o d u c t i o n p r o c e s s g i v e s 15% more a c c u r a t e t h i c k n e s s e s t i m a t i o n s f o r t h e t o t a l t h i c k n e s s than the p r o c e s s w i t h o u t the T m o n i t o r and y i e l d s a g r e a t e r number o f u s a b l e t a r g e t s p e r - 23 -s l i d e (up t o t h r e e t i m e s as many)• 2.2.3 E v a p o r a t e d P o l y e t h y l e n e T a r g e t s P r e l i m i n a r y a t t e m p t s a t e v a p o r a t i n g (C 2Di t)n from open t a n t a l u m boats o f d i f f e r e n t s i z e s and shapes produced f i l m s o f a g r a n u l a r a p p e a r a n c e , con-t a i n i n g what appeared t o be s m a l l p i e c e s o f s o l i d m a t e r i a l imbedded i n them Some powder g r a i n s seem t o be e j e c t e d from the hot boat s u r f a c e s b e f o r e complete e v a p o r a t i o n . A b a f f l e system near t h e s o u r c e was n e c e s s a r y t o e l i m i n a t e t h i s e f f e c t . A " S i n g l e G r a i n Box S o u r c e " (Ma 69) i n c o r p o r a t e s such a b a f f l e system. The s o u r c e i s i l l u s t r a t e d i n F i g u r e 6. The m a t e r i a l t o be e v a p o r a t e d i s f e d v i a t h e d e l i v e r y f u n n e l i n t o t he "box" kept a t the d e s i r e d t e m p e r a t u r e . The b a f f l e system p r e v e n t s any m a t e r i a l not f u l l y v a p o r i z e d from r e a c h i n g the e x i t chimney by f o r c i n g the m a t e r i a l t o s u f f e r m u l t i p l e c o l l i s i o n s w i t h t h e hot w a l l s o f the "box". T h i s r e s u l t s i n a s t e a d y p a r t i c l e - f r e e v a p or s t r e a m a t t h e e x i t . U n i f o r m h e a t i n g o f t h e s o u r c e o b t a i n e d by p a s s i n g c u r r e n t t h r o u g h the e n t i r e l e n g t h o f the u n i t , p r e v e n t s c o n d e n s a t i o n o f m a t e r i a l between f u n n e l and chimney. D e l i v e r y o f the (CgDi^n i n t o the hot s o u r c e had t o be e l i m i n a t e d because the m a t e r i a l tended t o adhere t o the w a l l s o f the warm f u n n e l . The technique.was changed and a weighed q u a n t i t y o f (C 2Di +)n was d e p o s i t e d i n the c o l d box v i a the f u n n e l . The f u n n e l was s e a l e d w i t h aluminum f o i l t o p r e v e n t any p o s s i b l e e v a p o r a t i o n t h r o u g h i t s o p e n i n g . The r e q u i r e d amount o f (C 2Di +)n was d e t e r m i n e d as d e s c r i b e d i n 2.2 The box was then h e a t e d up t o ro290°C (Wh 65) and e v a p o r a t i o n was completed w i t h i n t he f i r s t minute. Due t o the low e v a p o r a t i n g t e m p e r a t u r e f o r (C2^k) - 2k -2.3" t o 2 - 1" x 3" G l a s s S i i d e s D e l i v e r y Funnel E x i t Chimney C u r r e n t FIGURE 6: SCHEMATIC DIAGRAM OF THE "SINGLE GRAIN BOX SOURCE" the heat r a d i a t i o n p r o t e c t i o n f o r the T m o n i t o r c r y s t a l i s not r e q u i r e d . W i t h two 1" x 3" g l a s s s l i d e s mounted 2.3" d i r e c t l y o v e r t h e e x i t chimney, the l o s s o f e v a p o r a t e d m a t e r i a l i n t o the vacuum chamber e t c , was v e r y h i g h . U s i n g t h e c a l i b r a t i o n p r o c e d u r e as o u t l i n e d i n 2.2.1, i t was found t h a t e v a p o r a t i o n o f 16.0 mg o f ^ D i j n y i e l d e d a f i l m t h i c k n e s s o f ^135 yg/cm 2 o v e r t h e two s l i d e s . As i n t h e p o u r i n g t e c h n i q u e , a ca r b o n l a y e r o f a p p r o x i m a t e l y 10 yg/cm 2 t h i c k n e s s was f i r s t e v a p o r a t e d o n t o the g l a s s s l i d e s f o l l o w e d by an e v a p o r a t e d l a y e r o f ^135 yg/cm 2 t h i c k ( C 2 D i t ) n and f i n a l l y a second 10 yg/cm 2 c a r b o n l a y e r . The s t r i p p i n g , f l o a t i n g and p i c k - u p p r o c e d u r e s were c a r r i e d o u t i n - 25 -the same way as f o r the poured " s a n d w i c h " t a r g e t s (see s e c t i o n 2 . 2 . 2 ) . These t a r g e t s were m e c h a n i c a l l y weaker than t h e poured ones, g i v i n g r i s e t o a l a r g e f a i l u r e r a t e d u r i n g s t r i p p i n g and p i c k - u p . 2.2.H T a r g e t S t r e n g t h e n i n g Through R a d i a t i o n There i s e v i d e n c e (Pr. 67) t h a t e x p o s i n g a s u b s t a n c e , composed o f polymer c h a i n s , t o gamma r a d i a t i o n s t r e n g t h e n s t h e s u b s t a n c e t h r o u g h " c r o s s - 1 i n k i n g " o f t he polymer c h a i n s . For the s u b s t a n c e ( C 2 D i f ) n t h e degree o f p o l y -m e r i z a t i o n i s i n d i c a t e d by the s u b s c r i p t n and normal polymer c h a i n s o c c u r as hundreds o f C2®h m o l e c u l e s l i n k e d t o g e t h e r as i l l u s t r a t e d i n F i g u r e 7. The p r o c e s s o f c r o s s - 1 i n k i n g i s p o s s i b l e because t h e s e l a r g e m o l e c u l a r c h a i n s a r e i n t e r c r o s s e d and d e u t e r i u m atoms o f d i f f e r e n t c h a i n s a r e i n c l o s e p r o x i m i t y . When a gamma ray e n t e r s the s u b s t a n c e the predominant i n t e r a c t i o n ( r e l e v a n t t o c r o s s - 1 i n k i n g ) w i t h the s u b s t a n c e i s Compton s c a t t e r i n g . T h i s i n t e r a c t i o n produces h i g h energy e l e c t r o n s w h i c h , t h r o u g h m u l t i p l e c o l l i s i o n s , g i v e use t o a p p r o x i m a t e l y 20 t o 3 0 , 0 0 0 s e c o n d a r y e l e c t r o n s ("cascade" e f f e c t ) . The secondary e l e c t r o n s l o s e energy u n t i l t h e y r e a c h the resonance energy o f t h e C-H c h e m i c a l bond (of the o r d e r o f 10 e V ) . For t h i s d i s c u s s i o n we w i l l use H t o s i g n i f y a heavy hydrogen atom 2H. The se c o n d a r y e l e c t r o n s t r i k e s t h e H c a u s i n g i t t o break the C-H bond and l e a v e as a " h o t " H* ( i e k i n e t i c energy >KT). T h i s H* may then i n t e r a c t w i t h one o f the a d j a c e n t H atoms c a u s i n g i t t o break i t s C-H bond. The r e s u l t i n g C-C p a i r , l e f t w i t h o u t i'ts H atoms, forms a do u b l e bond C=C. T h i s may o c c u r w i t h i n t he polymer c h a i n i t s e l f , t h e r e b y s t r e n g t h -e n i n g t he c h a i n , o r between a d j a c e n t c h a i n s t h e r e b y b i n d i n g them t o g e t h e r . - 26 -Compton S c a t t e r i n g A ^ Y Ray <+• m e .e »e -Energy ^e E l e c t r o n \ _ / Cascade E f f e c t H H - C - C • H ^ J T H H Note: H I C • H = D (Heavy Hydrogen) H*= "Hot" Hydrogen H H C -I H H' H+H* H H H H |Jyp i ca 1 Polymer Chai n C - C - C - C - C - C -I I I I I I ' H H H H H H RESULT 4 he Double Bond C h a i n S t r e n g t h e n i n g H H H H H H C - C - C - C - C -H H H H H H Double -Bond " C r o s s -L i n k i n g " he c - c -H H H H H FIGURE 7: SCHEMATIC DIAGRAM OF POLYMER STRENGTHENING THROUGH GAMMA RADIATION - 27 -The l a t t e r c a s e i s known as " c r o s s - 1 i n k i n g " . A l t h o u g h both cases s e r v e t o s t r e n g t h e n the m a t e r i a l , " c r o s s - l i n k i n g " i s more e f f e c t i v e . As mentioned b e f o r e (2.2.3) t h e e v a p o r a t e d (C 2Di +)n " s a n d w i c h " t a r g e t s were m e c h a n i c a l l y weaker than t h e poured ones. C o n s e q u e n t l y i t was d e c i d e d t o expose the e v a p o r a t e d t a r g e t s ( w h i l e s t i l l on the g l a s s s l i d e s ) t o a s u s t a i n e d dose o f gamma r a d i a t i o n t o compare any r e s u l t i n g improvements by t h i s r a d i a t i o n t e c h n i q u e . I t was hoped t h a t the p o s s i b l e t a r g e t s t r e n g t h e n i n g might a l s o p e r m i t the t a r g e t s t o w i t h s t a n d g r e a t e r 3He beam c u r r e n t d e n s i t i e s . Two " s a n d w i c h " t a r g e t s l i d e s h a v i n g an e v a p o r a t e d \ (C2 n i t)n t h i c k n e s s a p p r o x i m a t e l y equal t o 135 yg/cm 2 were exposed t o doses o f 3 and 12 MegaRads. The s l i d e s were p l a c e d i n a "Gammacell 200" con-< t a i n i n g 6170 c u r i e s o f 6 0 C o and p r o d u c i n g a r a d i a t i o n f i e l d o f hkkO Rads/min. 2.3 A l p h a Y i e l d Measurements 2.3-1 Method As mentioned i n s e c t i o n 2.1 i t was n e c e s s a r y t o a s s e s s the performance o f t h e t a r g e t s when exposed t o the 690 keV 3He beam. One of the means o f assessment was t o measure the a l p h a y i e l d ( i n c o u n t s / y c ) from the r e a c t i o n 2H ( 3 H e , p ) 4 H e , as a f u n c t i o n o f the t o t a l i n t e g r a t e d 3He beam c u r r e n t on t a r g e t . T h i s p r o v i d e d a means o f measuring the t a r g e t d e t e r i o r a t i o n t h r o u g h d e u t e r i u m l o s s e s as w e l l as p r o v i d i n g an e s t i m a t e o f the d e u t e r i u m c o n t e n t o f the t a r g e t s a t any time d u r i n g 3He bombardment. I t i s not c l e a r i n what form the d e u t e r i u m e x i s t s a f t e r the t a r g e t has been bombarded by 3 H e . ( s e e 3.3.1). C o n s e q u e n t l y t h e d e u t e r i u m c o n t e n t a t any p o i n t d e t e r m i n e d from the a l p h a y i e l d i s g i v e n i n terms o f an " e q u i v a l e n t p o l y e t h y l e n e t h i c k n e s s " - 28 -i n yg/cm 2 i.e. t h a t ( C ^ D i J n t h i c k n e s s w h i c h would g i v e the same a l p h a y i e l d ( f o r t h e 3He beam used) as measured (see A p p e n d i x C ) . The 3He beam was s l i g h t l y d e f o c u s e d so t h a t the beam s t r i k i n g t h e t a r g e t ( v i a a c o l l i m a t o r a s s e m b l y ) had a u n i f o r m c u r r e n t d e n s i t y a c r o s s the beam s p o t . The a l p h a p a r t i c l e s produced i n the t a r g e t were d e t e c t e d i n a s o l i d s t a t e d e t e c t o r . The a p p a r a t u s i s d e s c r i b e d i n d e t a i l i n s e c t i o n 2.3-2. A c l o c k was s t a r t e d when a new t a r g e t s p o t was exposed t o the 3He beam. At f i x e d t i m e i n t e r v a l s , the t o t a l number o f a l p h a p a r t i c l e s ( e m i t t e d i n t o , t he d e t e c t o r ) f o r a p r e s e t amount o f e l e c t r i c c harge i n the 3He beam was measured. The r e s u l t s were f i r s t p l o t t e d i n the form o f a l p h a c o u n t s per yc as a f u n c t i o n o f time f o r a g i v e n beam c u r r e n t (where time r e f e r s to; the t o t a l t ime t h a t the t a r g e t had been exposed t o the beam). T h i s gave an i n d i c a t i o n o f the t a r g e t d e t e r i o r a t i o n under d i f f e r e n t beam c u r r e n t s . A l l t a r g e t s e x h i b i t e d an i n i t i a l r a p i d d e c r e a s e i n the a l p h a y i e l d (more r a p i d f o r h i g h e r beam c u r r e n t s ) f o l l o w e d by a s l o w ( e s s e n t i a l l y l i n e a r ) d e c r e a s e w i t h t i m e . U s u a l l y measurements were c o n t i n u e d f o r one hour and beam c u r r e n t s ( f o r d i f f e r e n t t a r g e t s and d i f f e r e n t t a r g e t s p o t s ) v a r i e d from 0.05 yA t o 2.0 yA w i t h most measurements c a r r i e d out a t 0.1 yA. In o r d e r t o compare the t a r g e t d e t e r i o r a t i o n from d i f f e r e n t samples and beam s p o t s , i t was assumed t h a t t h i s e f f e c t i s a f u n c t i o n o f the t o t a l number o f 3He t r a v e r s i n g the t a r g e t . The c o m p a r i s o n was e f f e c t e d by p l o t t i n g the t o t a l number o f a l p h a p a r t i c l e s d e t e c t e d f o r a g i v e n c h a r g e as a f u n c t i o n o f t h e t o t a l i n c i d e n t c h a r g e t h a t a p a r t i c u l a r beam s p o t had been exposed t o . The t o t a l i n t e g r a t e d c u r r e n t on t a r g e t was c a l c u l a t e d by - 29 -\ m u l t i p l y i n g t h e beam c u r r e n t w i t h the e l a p s e d time o f t a r g e t e x p o s u r e a t each a l p h a count measurement. The r e s u l t i n g a l p h a y i e l d c u r v e s ( d e s c r i b e d i n g r e a t e r d e t a i l i n s e c t i o n 3.3-0 s t a b i l i z e d a f t e r 150 t o 200 uc t o t a l c h a r g e on t a r g e t . Hence f o r a l l a l p h a y i e l d measurements, a n a l y s i s and c o m p a r i s o n s were c a r r i e d out a t a t o t a l i n t e g r a t e d c u r r e n t on t a r g e t o f 300 yc and t h i s was d e f i n e d as the " f i n a l a l p h a (^He) y i e l d " . A l p h a y i e l d measurements were f i r s t c a r r i e d out on t h e " s a n d w i c h " t a r g e t s w h i c h had a poured (CgDiJn t h i c k n e s s o f ^hk yg/cm 2. These samples were compared as f o l l o w s : ( i ) T e s t s were c a r r i e d out on d i f f e r e n t beam s p o t s o f the same t a r g e t sample t o measure p o s s i b l e t a r g e t v a r i a t i o n a c r o s s the 0.25" d i a m e t e r s e l f - s u p p o r t e d r e g i o n . ( i i ) T e s t s were c a r r i e d out on d i f f e r e n t t a r g e t samples from the same s l i d e t o measure t a r g e t v a r i a t i o n s a c r o s s t h e s l i d e . ( i i i ) T e s t s were c a r r i e d o u t on t a r g e t samples from d i f f e r e n t s l i d e s t o o b s e r v e t h e t a r g e t v a r i a t i o n s from s l i d e t o s l i d e . A l p h a y i e l d measurements were c a r r i e d out on " s a n d w i c h " t a r g e t s o f ^132 yg/cm 2 (C 2D( +)n t h i c k n e s s , p r e p a r e d by both e v a p o r a t i n g and p o u r i n g t h e (C 2Di+)n. T h i s was done t o compare t h e m e r i t s o f e v a p o r a t i n g and p o u r i n g the ( C 2 D i + ) n as r e g a r d s t o " f i n a l a l p h a y i e l d " . The change i n a l p h a y i e l d w i t h d i f f e r e n t carbon l a y e r t h i c k n e s s e s on t h e " s a n d w i c h " t a r g e t was s t u d i e d . The m a j o r i t y o f t e s t s were c a r r i e d out on poured ( C 2 D i t ) n t a r g e t s o f ^kk yg/cm 2 t h i c k n e s s . The t a r g e t s were t a k e n from the same s l i d e t o e n s u r e c o m p a r i s o n s between s i m i l a r t a r g e t s . I t was - 30 -p o s s i b l e t o t e s t up t o t h r e e d i f f e r e n t s p o t s per t a r g e t . Each t a r g e t was f i r s t s u b j e c t e d t o an a l p h a y i e l d measurement to measure the con-s i s t e n c y between t a r g e t s . A f t e r t h i s , more car b o n was e v a p o r a t e d o n t o t h e t a r g e t ( w h i l e on the t a r g e t h o l d e r ) and the a l p h a y i e l d measured f o r a d i f f e r e n t s p o t . Carbon was added o n t o the o r i g i n a l " s a n d w i c h " t a r g e t s i n 10 yg/cm 2 t h i c k e v a p o r a t e d l a y e r s . The t a r g e t a l p h a y i e l d was measured f o r c a r b o n l a y e r v a r i a t i o n on the "back" o f the t a r g e t ( i e the s i d e o f the t a r g e t sandwich f a r t h e s t from the i n c i d e n t beam) as w e l l as on the " f r o n t " o f the t a r g e t . Due t o the b a s i c sandwich c o n s t r u c t i o n o f the t a r g e t s , i n a l l c a s e s the a l p h a y i e l d measure-ments f o r a g i v e n number o f c a r b o n l a y e r s (on e i t h e r "back" o r " f r o n t " ) , were performed w i t h a s i n g l e 10 yg/cm 2 t h i c k carbon l a y e r on t h e s i d e o f the t a r g e t o p p o s i t e t o the v a r i e d c a r b o n l a y e r s i d e . T a r g e t s were t e s t e d f o r t o t a l s o f one, two, t h r e e and f o u r c a r b o n l a y e r s on t h e "back" and one, t h r e e and f o u r c a r b o n l a y e r s on t h e " f r o n t " . A measurement was a l s o c a r r i e d out on a t a r g e t sample o f 1^35 yg/cm 2 t h i c k poured (C2Di+)n. T h i s sample was t e s t e d f o r 3 c a r b o n l a y e r s on the "back" and 3 on t h e " f r o n t " . 2.3-2 A p p a r a t u s F i g u r e 8 i s a s c h e m a t i c d r a w i n g o f the t a r g e t chamber. I t was a t t a c h e d t o one o f the beam l i n e s on the U n i v e r s i t y o f B r i t i s h C olumbia Van de G r a a f f a c c e l e r a t o r . A s i n g l y i o n i z e d 3He beam was d i r e c t e d t o the chamber v i a two s e t s o f f o c u s i n g e l e c t r o s t a t i c q u a d r u p o l e s and s t e e r i n g magnets mounted on t h e beam l i n e . The beam e n t e r e d t h e chamber t h r o u g h the c o l l i m a t o r s a ssembly A w h i c h was composed o f two d e f i n i n g a p e r t u r e s and a skimmer F I G U R E 8.:. SCHEMATIC DIAGRAM OF THE CHAMBER S E T - U P FOR A L P H A Y I E L D MEASUREMENTS - 32 -c o r r e s p o n d i n g t o a beam d i a m e t e r p f 0.160 cm (1/16").•" The chamber had i t s own vacuum pumping system and was m a i n t a i n e d a t a vacuum o f M O 5 T o r r . A f t e r p a s s i n g t h r o u g h t h e c o l l i m a t o r s , t h e beam s t r u c k t h e s e l f - s u p p o r t i n g t a r g e t w h i c h was mounted on a w a t e r c o o l e d t a r g e t h o l d e r D. The beam p a s s i n g t h r o u g h the t a r g e t was s t o p p e d i n a Faraday cage a s s e m b l y C . A b r a s s r i n g was mounted on the f r o n t o f t h e Faraday cage (and i n s u l a t e d f r o m i t ) and m a i n t a i n e d a t a p o t e n t i a l o f -300 v o l t s t o r e p e l s e c o n d a r y e l e c t r o n s e m i t t e d from t h e back s u r f a c e o f the Faraday cage and t a r g e t a s s e m b l y . The beam c u r r e n t c o l l e c t e d by the Faraday cage was f e d i n t o .an E l d o r a d o E l e c t r o n i c s Model CI-110 c u r r e n t i n t e g r a t o r ( E l 69). A bHock d i a g r a m o f t h e e l e c t r o n i c s used i s p r e s e n t e d i n F i g u r e 9. The a l p h a p a r t i c l e s p r o duced by the r e a c t i o n o f t h e 3He beam on t h e t a r g e t were d e -t e c t e d by an O r t e c S i l i c o n s u r f a c e b a r r i e r d e t e c t o r (50 mm 2» 33 keV r e s o l u t i o n , 750 ft/cm) (Or 69) mounted on t h e back o f a c o l l i m a t o r * TUniis d e t e c t o r i s p a r t o f t h e s o l i d s t a t e d e t e c t o r a s s e m b l y B w h i c h forums ipairtt o f t h e chamber's bottom c o v e r . The a n g u l a r p o s i t i o n w i t h r e s p e c t t o t n e i n c i d e n t beam d i r e c t i o n , and t h e v e r t i c a l p o s i t i o n normal t o t n e p l a n e <8>ff F i g u r e 8 can be a d j u s t e d w i t h o u t b r e a k i n g t h e vacuum. The s o l i d s t a t e d e t e c t o r s i g n a l was f e d i n t o a c h a r g e sens 51 We, F I T 5mf>umt„ O r t e c 109A p r e a m p l i f i e r (Or 69). The o u t p u t p u l s e o f t h e pre a w i p l i i f f i i e r was f e d i n t o a C . I . 1410 l i n e a r a m p l i f i e r (Ca 69) w i t h differentiiatii<0m aroil i n t e g r a t i o n t i m e c o n s t a n t s o f 1 us f o l l o w e d by a C . I , 1^ 3$ T5ra»n§ §tlh S i n g l e Channel A n a l y z e r (Ca 69). The o u t p u t from t h e SCA was f e d i n t o am O r t e c 430 S c a l e r (Or 69). D u r i n g t h e measurements, t h e s e a l e r and tn© - 33 -K I C K S O R T E R R E A M P L I F I E R L I N E A R A M P L I F I E R S I N G L E CHANNEL A N A L Y Z E R S C A L E R S . S . D . FARADAY CAGE B I A S CURRENT INTEGRATOR OFF ON T R I G G E R O N - O F F T I M E R F I G U R E 9: BLOCK DIAGRAM OF THE E L E C T R O N I C S FOR THE A L P H A Y I E L D MEASUREMENTS - 3k -c u r r e n t i n t e g r a t o r a r e s w i t c h e d on m a n u a l l y . The s c a l e r i s s w i t c h e d o f f a u t o m a t i c a l l y a t a p r e s e t c h a r g e i n the c u r r e n t i n t e g r a t o r . Hence, a c u r r e n t i n t e g r a t i o n measurement o v e r / a g i v e n p e r i o d y i e l d s the q u a n t i t y o f c h a r g e c o l l e c t e d v i a the 3He beam as w e l l as the number o f a l p h a p a r t i c l e s o f a g i v e n energy c o l l e c t e d by • the d e t e c t o r i n the same p e r i o d . The o u t p u t from t h e l i n e a r a m p l i f i e r was a l s o f e d i n t o a N u c l e a r Data 160 M u l t i c h a n n e l P u l s e H e i g h t A n a l y z e r (Nu 6 9 ) , where the s o l i d s t a t e d e t e c t o r s p e c t r u m was r e c o r d e d . As d i s c u s s e d i n s e c t i o n 1.1, t h e k i n e m a t i c s o f the r e a c t i o n 2 H ( 3He,p) 1 +He d e t e r m i n e t h e e n e r g i e s o f the p a r t i c l e s e m i t t e d f o r g i v e n a n g l e s o f e m i s s i o n r e l a t i v e t o t h e i n c i d e n t beam d i r e c t i o n . Hence the a n g l e o f the a l p h a d e t e c t o r w i l l d e t e r m i n e t h e mean e n e r g i e s o f the p r o t o n s and a l p h a p a r -t i c l e s i n c i d e n t on i t . In a d d i t i o n t o t h e s e p r o t o n s and a l p h a p a r t i c l e s o f d e f i n e d e n e r g i e s , t h e r e was a low energy p r o t o n background due t o s c a t t e r i n g o f the h i g h energy p r o t o n s by the chamber w a l l s . In o r d e r t o reduce t h i s background the i n s i d e o f the chamber was l i n e d w i t h 0.042" t h i c k p o l y e t h y l e n e . The p o l y e t h y l e n e t h i c k n e s s b e i n g g r e a t e r than t h e e x p e c t e d range of 16 MeV p r o t o n s . A l t h o u g h reduced i n i n t e n s i t y , a low energy p r o t o n background was s t i l l o b s e r v e d . The e n e r g i e s o f t h e s e s c a t t e r e d p r o t o n s c o v e r s the range o f '•He e n e r g i e s a v a i l a b l e from the r e a c t i o n 2 H ( 3He,p)^He. The e n e r g y o f the a l p h a s d e t e c t e d depends on the a n g l e o f the d e t e c t o r . P a r t i c l e i d e n t i f i c a t i o n i s n e c e s s a r y t o d i s t i n g u i s h the p r o t o n s from the a l p h a s t o p r e v e n t t h e measurement o f an e r r o n e o u s l y l a r g e a l p h a y i e l d . A s i m i l a r e f f e c t c o u l d be produced from s l i t edge - 35 -s c a t t e r i n g on t h e c o l l i m a t o r d e f i n i n g t he s o l i d a n g l e subtended by the '•He d e t e c t o r . The h i g h energy p r o t o n s would be degraded i n energy d u r i n g g r a z i n g c o l l i s i o n s w i t h the c o l l i m a t o r on r o u t e t o the 4He d e t e c t o r . P a r t i c l e i d e n t i f i c a t i o n was o b t a i n e d by c h o o s i n g a d e p l e t i o n depth f o r the s u r f a c e b a r r i e r d e t e c t o r such t h a t the maximum p r o t o n energy d e t e c t a b l e was much lower than the a l p h a energy o f i n t e r e s t . A depth o f 50 m i c r o n s ( =20 v o l t s b i a s f o r t h e d e t e c t o r mentioned above) was chosen, c o r r e s p o n d i n g t o a range o f 2 MeV p r o t o n s and 8 MeV a l p h a p a r t i c l e s i n s i l i c o n . The energy s p e c t r u m as o b s e r v e d w i t h t h i s d e p l e t i o n depth i n t h e s o l i d s t a t e . d e t e c t o r would then c o n t a i n a s u p e r p o s i t i o n o f a p r o t o n and an a l p h a s p e c t r u m : ( i ) The p r o t o n s p e c t r u m i s a d i s t r i b u t i o n w h i c h f o l d s o v e r a t 2 MeV (the " p r o t o n e d g e " ) . I t a l s o has a peak, c o r r e s p o n d i n g t o t h e h i g h energy p r o t o n s (^]k MeV), a p p e a r i n g at low c h a n n e l s s i n c e the p r o t o n s go through the d e p l e t i o n depth l e a v i n g o n l y a s m a l l amount o f energy i n t h e d e p l e t i o n r e g i o n . ( i i ) The a l p h a s p e c t r u m i s a s i n g l e peak whose p o s i t i o n depends on the d e t e c t o r a n g l e chosen. To e n s u r e t h a t the a l p h a peak would be e a s i l y d i s t i n g u i s h a b l e from t h e p r o t o n edge, an a n g l e o f 50° was chosen f o r the a l p h a d e t e c t o r . T h i s a n g l e k i n e m a t i c a l l y d e f i n e s the a l p h a energy a t r o u g h l y 5 MeV, c l e a r l y s e p a r a t i n g i t from the 2 MeV p r o t o n edge y e t w e l l w i t h i n t he d e p l e t i o n depth maximum o f 8 MeV. A t y p i c a l s o l i d s t a t e d e t e c t o r s p e c t r u m f o r t h e s e measurements, i s i l l u s t r a t e d i n F i g u r e 15 i n C h a p t e r I I I . The " b i a s l e v e l " and - 36 -"energy window" o f the T i m i n g SCA were s e t t o admit o n l y p u l s e s on e i t h e r s i d e o f the 4He peak and above t h e p r o t o n e d g e - t h e r e b y a l l o w i n g o n l y the 4 H e p a r t i c l e s c o n c e r n e d t o be a n a l y z e d . The a n g l e o f t h e t a r g e t was s e t a t 70° t o e l i m i n a t e any p o s s i b l e s c a t t e r i n g o f the a l p h a s by t h e t a r g e t mount edges. The c o n t r i b u t i o n t o t h e p r o t o n background from t h e w a l l l i n i n g o f t h e d e t e c t o r c o l l i m a t o r was reduced by e n c l o s i n g t h e r e g i o n between t h e s o l i d s t a t e d e t e c t o r and the c o l l i m a t o r w i t h p o l y e t h y l e n e t u b i n g . To reduce t h e c o n t r i b u t i o n s from t h e c o l l i m a t o r edge s c a t t e r i n g , t h e d e t e c t o r -c o l l i m a t o r s p a c i n g was made as l a r g e as p o s s i b l e . The v e r t i c a l p o s i t i o n o f t h e '•He d e t e c t o r was o p t i m i z e d t o g i v e t h e h i g h e s t a l p h a count r a t e . 2.4 T a r g e t T h i c k n e s s Measurements By Energy Loss AE 2.4.1 Method The purpose o f t h i s p a r t o f t h e e x p e r i m e n t was t o measure the a c t u a l t a r g e t t h i c k n e s s b e f o r e and a f t e r d e t e r i o r a t i o n . T h i s was done w i t h the purpose o f d e t e r m i n i n g i f t a r g e t d e t e r i o r a t i o n was e n t i r e l y due t o l o s s o f t a r g e t m a t e r i a l . The knowledge o f t h e t a r g e t t h i c k n e s s i s i m p o r t a n t i n c o n n e c t i o n w i t h the t o t a l p r o t o n r e a c t i o n c r o s s s e c t i o n e x p e r i m e n t . The energy l o s s AE o f a p r o t o n beam i n t h e t a r g e t was measured by u t i l i z i n g t h e 873.5 keV r e s o n a n c e i n the r e a c t i o n 1 9 F ( p , k H e ) 1 6 0 * where 0*+ 0 1 6 + y ( a = 5^ 0 mb, r = 5 keV, Ey = 6 MeV). T h i s energy l o s s can be r e a d i l y - 37 -c o n v e r t e d t o t a r g e t t h i c k n e s s . A c a l c i u m f l u o r i d e t a r g e t , 12 keV t h i c k a t the resonance energy ( e v a p o r a t e d i n t o a copper b a c k i n g ) , was i n s t a l l e d " a f t e r " t h e (C2Dt|)n t a r g e t h o l d e r . The a p p a r a t u s and e l e c t r o n i c s a r e d e s c r i b e d i n d e t a i l i n s e c t i o n 2.4.2. Without a ( C 2 D 4 ) n t a r g e t on t h e beam path the y - y i e 1 d (above 2.6 MeV) was measured as a f u n c t i o n o f t h e i n c i d e n t p r o t o n energy and t h e p o s i t i o n o f the 873-5 keV resonance d e t e r m i n e d . T h i s measurement a l s o p r o v i d e s a c a l i b r a t i o n o f the machine e n e r g y . The " s a n d w i c h " t a r g e t was then p l a c e d i n f r o n t o f t h e f l u o r i n e t a r g e t and t h e p r o t o n beam a l l o w e d t o pass t h r o u g h the "sandwich t a r g e t " and s t r i k e t he 1 9 F t a r g e t . The measured energy s h i f t o f t h e resona n c e peak was a d i r e c t measure o f t h e energy l o s s AE s u f f e r e d by the p r o t o n beam. The (C 2Di +)n t a r g e t d e t e r i o r a t i o n a f t e r 3He bombardment as i n d i c a t e d by the a l p h a y i e l d measurements ( d i s c u s s e d i n d e t a i l i n s e c t i o n 3-3.1), r e -f l e c t e d g r e a t l o s s e s o f d e u t e r i u m from t h e t a r g e t m a t e r i a l t o t h e e x t e n t t h a t i t was c o n c l u d e d t h e t a r g e t m a t e r i a l was p r e d o m i n a n t l y carbon a f t e r 3He bombardment. Hence c a l c u l a t i o n s o f the t a r g e t t h i c k n e s s from t h e p r o t o n e nergy l o s s were based on an a l l c a r b o n atom t a r g e t m a t e r i a l so t h a t the t h i c k n e s s i s s t a t e d as an " e q u i v a l e n t c a r b o n t h i c k n e s s " i n yg / c m 2 . ( s e e A p p e n d i x D). I t may be noted t h a t a s i m i l a r c a l c u l a t i o n assuming t h a t the t a r g e t m a t e r i a l i s a l l (C 2D t t)n would y i e l d a t h i c k n e s s v a l u e w h i c h i s 11% l e s s than t h e " e q u i v a l e n t c a r b o n t h i c k n e s s " v a l u e . T h i s was found t o h o l d f o r a l l t h i c k n e s s measurements c a r r i e d o u t . T h i s i n d i c a t e s t h a t t h e a s s u m p t i o n o f an a l l c a r b o n t a r g e t m a t e r i a l i n t r o d u c e s - 38 -a p o s s i b l e e r r o r o f <11% i n t h e t h i c k n e s s c a l c u l a t i o n s , w i t h the s i z e o f t h e e r r o r depending on the f r a c t i o n o f t a r g e t m a t e r i a l s t i l l r e m a i n i n g as (C 2D( +)n. A t y p i c a l 1 9 F resonance s h i f t measurement was performed as f o l l o w s : ( i ) The s h i f t o f t h e 1 9 F resonance was measured on a "new" t a r g e t s p o t ( i e a s p o t p r e v i o u s l y unexposed t o 3He) u s i n g a p r o t o n beam o f low c u r r e n t d e n s i t y ( a p p r o x i m a t e l y 0.5 yA/cm 2) t o p r e -v e n t t a r g e t d e t e r i o r a t i o n . An " e q u i v a l e n t c a r b o n t h i c k n e s s " was c a l c u l a t e d from the resonance s h i f t . ( i i ) A n o t h e r 1 9 F a n a l y s i s was c a r r i e d out a f t e r t h e same t a r g e t s p o t had been exposed t o a 3He beam and a s t a b l e ^He y i e l d had been a t t a i n e d , ( t y p i c a l l y 0.1 yA o f 3He f o r one h o u r ) . An " e q u i v a l e n t c a r b o n t h i c k n e s s " was c a l c u l a t e d and hence a t h i c k n e s s l o s s i n yg/cm 2 c o u l d be c a l c u l a t e d when t h i s t h i c k n e s s was compared w i t h the r e s u l t s o f ( i ) . ( i i i ) The " e q u i v a l e n t c a r b o n t h i c k n e s s " l o s s c a l c u l a t e d from ( i ) and ( i i ) was compared w i t h the " e q u i v a l e n t p o l y e t h y l e n e t h i c k n e s s " l o s s ( t he l a t t e r h a v i n g been c a l c u l a t e d from a c o m p a r i s o n of. the i n i t i a l t h i c k n e s s by w e i g h i n g and t h e f i n a l (C 2Di +)n t h i c k n e s s by a l p h a y i e l d ) . Through t h i s c o m p a rison i t was p o s s i b l e t o d e c i d e whether the t a r g e t d e t e r i o r a t i o n o c c u r r e d as a l o s s o f the C 2Di + m o l e c u l e as a whole o r as a predominant l o s s o f t h e d e u t e r i u m . That i s t o s a y , i f the " e q u i v a l e n t (C 2Dt f)n t h i c k n e s s " l o s s , w h i c h depends on the l o s s o f d e u t e r i u m , i s s u b s t a n t i a l l y g r e a t e r t h a n the " e q u i v a l e n t C t h i c k n e s s " l o s s , then t h i s i m p l i e s a g r e a t e r ;loss - 39 -o f d e u t e r i u m atoms than c a r b o n atoms. T h i s i n t u r n i m p l i e s a l o s s o f d e u t e r i u m atoms r a t h e r than a l o s s o f t h e C 2Di,. m o l e c u l e as a whole. T h i s a n a l y s i s was c a r r i e d o u t on t h e poured ( C 2 D i J n " s a n d w i c h " t a r g e t s o f 44 yg/cm 2 and 132 pg/cm 2 t h i c k ( C 2 D i + ) n . 2.4.2 A p p a r a t u s F i g u r e 10 i s a s c h e m a t i c d i a g r a m o f the chamber used i n the t a r g e t t h i c k n e s s measurements. F i g u r e 11 i s a b l o c k d i a g r a m o f the e l e c t r o n i c s used. The p r o t o n beam a f t e r p a s s i n g t h r o u g h the c o l l i m a t o r assembly A and t h e t a r g e t D, s t r i k e s the f l u o r i n e t a r g e t mounted on the copper b a c k i n g E. Measurements were c a r r i e d o u t w i t h both the t a r g e t and h o l d e r D i n f r o n t o f t h e f l u o r i n e t a r g e t and w i t h both removed as r e q u i r e d i n s e c t i o n 2.4.1. The copper b a c k i n g was mounted on t h e f r o n t p a r t o f the Faraday cage assembly C. The p r o t o n beam c u r r e n t c o l l e c t e d on t h e f l u o r i n e t a r g e t was f e d i n t o an E l d o r a d o E l e c t r o n i c s c u r r e n t i n t e g r a t o r . The Y ~ r a y s produced i n the r e a c t i o n 1 9 F ( p , a ) 1 6 0 " were d e t e c t e d i n a NaI ( T l ) s c i n t i l l a t o r mounted on a pho.tomul t i p i i e r tube F. The c r y s t a l and tube a r e mounted o u t s i d e the chamber. A l l but the f r o n t f a c e o f t h e c r y s t a l i s c o v e r e d by 2 i n c h t h i c k l e a d s h i e l d i n g t o reduce the Y~ray background. The p h o t o m u l t i p i i e r was s u p p l i e d w i t h n e g a t i v e h i g h v o l t a g e and t h e p u l s e s from t h e anode were f e d i n t o a p r e a m p l i f i e r c o n s t r u c t e d i n t h i s l a b o r a t o r y . The o u t p u t o f the p r e -a m p l i f i e r was f e d i n t o a C . I . 1410 l i n e a r a m p l i f i e r w i t h d i f f e r e n t i a t i o n and i n t e g r a t i o n t i m e c o n s t a n t s o f 1 u s . The p u l s e from t h e l i n e a r a m p l i f i e r was f e d i n t o a C . I . 1435 T i m i n g SCA S i n g l e Channel A n a l y z e r . The "base, l i n e " P h o t o m u l t i p i i e r T u b e F I G U R E 10: SCHEMATIC DIAGRAM OF THE CHAMBER . S E T - U P USED IM TARGET T H I C K N E S S MEASUREMENTS BY ENERGY LOSS - k] -P R E A M P L I F I E R L I NEAR A M P L I F l E R S I N G L E CHANNEL A N A L Y Z E R S C A L E R Na I FARADAY C A S E H . V . CURRENT INTEGRATOR OFF ON T R I G G E R O N - O F F F I G U R E 11: BLOCK DIAGRAM OF THE E L E C T R O N I C S USED FOR TARGET T H I C K N E S S MEASUREMENTS BY ENERGY LOSS - 42 -and "energy window" o f t h e SCA were s e t t o admit p u l s e s whose gamma ray e n e r g i e s f a l l i n t h e r e g i o n 2.6 MeV t o 10 MeV. The base l i n e p o i n t o f 2.6 MeV was s e t u s i n g a Ra Th s o u r c e and was chosen t o r e j e c t room back-ground and y e t s t i l l c o l l e c t a l a r g e f r a c t i o n o f the gamma ray c o u n t s . The p u l s e s a d m i t t e d by t h e SCA were counted by an O r t e c 430 S c a l e r . The s c a l e r and c u r r e n t i n t e g r a t o r were t r i g g e r e d on and o f f s i m u l t a n e o u s l y . Hence, f o r each s e t t i n g o f t h e p r o t o n e n e r g y , the number o f 6 MeV gamma ra y s p r o d u c e d , were c o u n t e d by t h e s c a l e r f o r a p r e s e t amount o f i n t e -g r a t e d c u r r e n t s t r i k i n g the f l u o r i n e t a r g e t . 2.5 P r o t o n Beam P r o f i l e Measurements 2.5.1 " C o i n c i d e n c e " E l e c t r o n i c s The use o f t h e " a s s o c i a t e d p a r t i c l e " t e c h n i q u e f o r measurements o f t o t a l p r o t o n r e a c t i o n c r o s s s e c t i o n s r e q u i r e s " c o i n c i d e n c e " e l e c t r o n i c s (Ho 68). In s e c t i o n 1.1, i t was e x p l a i n e d how the sp r e a d o f the p r o t o n beam ( i e the beam p r o f i l e ) i n f l u e n c e d t he a n a l y s i s time o f t h e c o i n c i d e n c e e l e c -t r o n i c s . Hence t h e purpose o f t h i s p a r t o f t h e e x p e r i m e n t was t o measure the p r o t o n beam p r o f i l e t o see i f an improvement had been e f f e c t e d t h r o u g h the use o f s e l f - s u p p o r t i n g t a r g e t s r a t h e r than s o l i d D20 copper backed t a r g e t s . The measurement o f the beam p r o f i l e i n c o r p o r a t e d t h e use o f t h e b a s i c " c o i n c i d e n c e " e l e c t r o n i c s used i n t h e c r o s s s e c t i o n measurements. A b l o c k d i a g r a m o f t h e e l e c t r o n i c s used i s i l l u s t r a t e d i n F i g u r e 12. A d e t a i l e d e x p l a n a t i o n o f t h e e l e c t r o n i c s ( i n c l u d i n g t h o s e f o r c r o s s s e c t i o n measure-ments) can be found e l s e w h e r e (Ho 68). A " F a s t - S l o w " c o i n c i d e n c e system 43 P R E A M P L I F I E R 1 r L INEAR A M P L I F I E R - S.J ; . D . i B IAS NE 102 H. V . P R E A M P L I F I E R L INEAR A M P L I F I E R B IASED IAMPL I F I ER PULSE STRETCHER T I M I N G SCA K I C KSORTER T I M I N G SCA SCA SCALER FAST ANT ICO I N . GATE DELAY GENERATOR SLOW CO INC IDENCE T IM I NG SCA AC SCALER FAST CO INC IDENC I GATE DELAY GENERATOR C SCALER FAST SLOW F IGURE 12: BLOCK DIAGRAM OF THE ELECTRON ICS USED IN THE PROTON BEAM P R O F I L E MEASUREMENTS - 44 -was employed. In t h i s d i s c u s s i o n C and AC a r e t a k e n t o mean c o i n c i d e n c e and a n t i c o i n c i d e n c e r e s p e c t i v e l y . The Hie and p r o t o n s i g n a l s a f t e r t h e i r r e s p e c t i v e l i n e a r a m p l i f i e r s a r e f e d i n t o T i m i n g SCA S i n g l e Channel A n a l y z e r s t o o b t a i n f a s t t i m i n g p u l s e s . " F a s t " c o i n c i d e n c e s and a n t i -c o i n c i d e n c e s a r e then o b t a i n e d f o r a l l p u l s e s w i t h o u t energy s e l e c t i o n . The l i n e a r a m p l i f i e r o u t p u t o f the 3He s i g n a l i s a l s o f e d i n t o an O r t e c 408 B i a s e d A m p l i f i e r f o l l o w e d by an O r t e c 411 P u l s e S t r e t c h e r . The o u t -put o f the p u l s e s t r e t c h e r i s f e d i n t o a k i c k s o r t e r and a T i m i n g SCA S i n g l e Channel A n a l y z e r . T h i s b i a s e d a m p l i f i e r and p u l s e s t r e t c h e r p e r m i t the s p r e a d o f the a l p h a peak o v e r t h e 0 t o 10 V i n p u t range o f the SCA. The t i m i n g SCA i s s e t w i t h a 100 keV energy "window" c e n t e r e d on the alpha-peak. The window p o s i t i o n i s checked by f e e d i n g the SCA l o g i c o u t p u t i n t o the c o i n c i d e n c e i n p u t o f t h e k i c k s o r t e r and o b s e r v i n g the s o l i d s t a t e d e t e c t o r s p e c t r u m i n t h e ON c o i n c i d e n c e and OFF c o i n c i d e n c e modes. The 100 keV window c e n t e r e d on the a l p h a peak p r o v i d e s " K i n e m a t i c a l c o l l i m a t i o n " o f the a s s o c i a t e d p r o t o n s . That i s to s a y , s e l e c t i o n o f a g i v e n range o f a l p h a e n e r g i e s at a g i v e n a n g l e k i n e m a t i c a 1 1 y r e s t r i c t s the p o s s i b l e range o f a n g l e s (and hence e n e r g i e s ) o f t h e a s s o c i a t e d p r o t o n s . The o u t p u t o f the SCA i s a l s o f e d i n t o a S c a l e r ( l a b e l l e d SCA S c a l e r ) and a "Slow C o i n c i -dence" c h a n n e l . In t h i s channel two p r o c e s s e s o c c u r : ( i ) The o u t p u t o f the " F a s t C o i n c i d e n c e " g a t e was r e q u i r e d t o be i n c o i n c i d e n c e w i t h the o u t p u t o f the SCA t h a t had s e l e c t e d the a l p h a p u l s e s i n t h e s p e c i f i e d energy range. In t h i s second c o i n c i d e n c e g a t e the p u l s e r a t e s were much lower due t o the f i r s t " f a s t " s e l e c t i o n , thus l o n g e r r e s o l v i n g times and l e s s p r e c i s e t i m i n g a r e - k5 -permissab1e. The o u t p u t o f t h i s "Slow C o i n c i d e n c e " g a t e was f e d i n t o a S c a l e r l a b e l l e d "C S c a l e r " , ( i i ) The o u t p u t o f t h e " F a s t A n t i c o i n c i d e n c e " g a t e was a l s o r e q u i r e d t o be i n c o i n c i d e n c e w i t h the SCA o u t p u t as above. The o u t p u t o f t h i s "Slow C o i n c i d e n c e " g a t e i s f e d i n t o a S c a l e r l a b e l l e d "AC S c a l e r " . C o n s e q u e n t l y t h e r e a r e t h r e e s c a l e r s m o n i t o r e d : a) The "SCA S c a l e r " w h i c h g i v e s the t o t a l number o f a l p h a p a r t i c l e s d e t e c t e d a t the d e s i r e d d i r e c t i o n and o f the s e l e c t e d 100 keV energy range. b) The "C S c a l e r " which g i v e s the t o t a l number o f a l p h a p a r t i c l e s d e t e c t e d w i t h the s e l e c t e d d i r e c t i o n and energy t h a t a r e c o i n c i d e n t w i t h a p r o t o n . c) The "AC S c a l e r " w h i c h g i v e s the t o t a l number o f a l p h a p a r t i c l e s d e t e c t e d w i t h the s e l e c t e d d i r e c t i o n and energy t h a t do not have a c o i n c i d e n t p r o t o n . The q u a n t i t y measured by the "SCA S c a l e r " s h o u l d v e r y n e a r l y equal the sum o f the o t h e r two s c a l e r q u a n t i t i e s . 2.5.2 Other A p p a r a t u s and Method F i g u r e 13 i s a s c h e m a t i c d i a g r a m o f the chamber s e t - u p used i n t h e s e measure-ments. As mentioned i n s e c t i o n 1.1 and e l s e w h e r e (Ho 68), the a l p h a and p r o t o n d e t e c t o r s were p l a c e d a t kinematica11y c o r r e s p o n d i n g a n g l e s o f 96.2° and 63.5° r e s p e c t i v e l y ( r e l a t i v e t o t h e i n c i d e n t 3He d i r e c t i o n ) . For t h e s e d i r e c t i o n s the a l p h a s and p r o t o n s had e n e r g i e s o f 3.3 and 15-7 MeV r e s p e c t i v e l y . 3 He BEAM =.----A ' J_ A = B = D = G = H = J = ZL C o l l i m a t o r s A s s e m b l y S o l i d S t a t e D e t e c t o r A s s e m b l y T a r g e t o n W a t e r C o o l e d T a r g e t H o l d e r NE 102 P l a s t i c S c i n t i l l a t i o n C r y s t a l a n d P h o t o m u 1 t i p 1 i e r T u b e M o v a b l e C o l l i m a t o r D e v i c e f o r M e a s u r i n g P + Beam P r o f i1e F a r a d a y C a g e NOTE F I G U R E 13: SCHEMATIC DIAGRAM OF THE CHAMBER S E T - U P USED IN THE PROTON BEAM P R O F I L E MEASUREMENTS To C u r r e n t I n t e g r a t o r .e-n s u l a t o r s 96 2 3 - ^ 30' \y63.5' \ - kl -The c h o i c e o f the sandwich t a r g e t (D) a n g l e i n f l u e n c e s the amount o f t a r g e t m a t e r i a l t h r o u g h w h i c h the a l p h a p a r t i c l e s must pass when produced w i t h i n t h e t a r g e t . The use o f k i n e m a t i c a l c o l l i m a t i o n t o o b t a i n a s m a l l a n g u l a r d i v e r g e n c e depends on d e t e c t i n g the . tya beam w i t h good energy r e s o l u t i o n and s m a l l s c a t t e r i n g e f f e c t s on i t s o r i g i n a l a n g l e o f e m i s s i o n . T h e r e f o r e i t i s d e s i r a b l e t o have as l i t t l e t a r g e t m a t e r i a l as p o s s i b l e i n the d i r e c t i o n o f the ^He p a r t i c l e s . An a n g l e o f 30° was chosen as a com-promise between the d e s i r e d minimum t a r g e t t h i c k n e s s e s i n the a l p h a p a r t i c l e and He beam d i r e c t i o n s . S i n c e the a x i s o f the NE102 p l a s t i c s c i n t i l l a t o r c r y s t a l and p h o t o m u l t i p i i e r tube were f i x e d a t 63-5° , t h e s o l i d s t a t e d e t e c t o r assembly was movable and l o c a t e d a t t h e k i n e m a t i c a l l y c o r r e c t a n g l e o f 96.2°. A s m a l l (0.125 i n c h d i a m e t e r ) c o l l i m a t o r mounted on the f r o n t c e n t r e o f the p r o t o n d e t e c t o r was used t o d e f i n e a s m a l l range o f p r o t o n e n e r g i e s and was employed i n l o c a t i n g the c o r r e c t p o s i t i o n o f the s o l i d s t a t e d e t e c t o r . The a l p h a d e t e c t o r p o s i t i o n was found as f o l l o w s : ( i ) The a l p h a d e t e c t o r was l o c a t e d a t a p p r o x i m a t e l y t h e c o r r e c t a n g l e o f 96° ts°. ( i i ) The 3He beam was a l l o w e d t o s t r i k e the t a r g e t and u s i n g t h e c o i n c i -dence e l e c t r o n i c s as d e s c r i b e d i n s e c t i o n 2 .5-1, the SCA, AC and C S c a l e r s were m o n i t o r e d . The s c a l e r s were a l l o w e d t o count f o r a s u f f i c i e n t number o f co u n t s t o g i v e a maximum 3-5% s t a t i s t i c a l e r r o r per s c a l e r i n the r e g i o n o f i n t e r e s t , ( i i i ) The r a t i o AC/C was measured as a f u n c t i o n o f the a l p h a d e t e c t o r assembly a n g l e , w i t h r e s p e c t t o the i n c i d e n t beam d i r e c t i o n , , i n -s t e p s o f 1° t 0.2°. For each a n g u l a r p o s i t i o n , t he 100 keV window - hS -o f the a l p h a channel T i m i n g SCA was c e n t e r e d on the a l p h a peak. The minimum AC/C r a t i o c o r r e s p o n d s t o the h i g h e s t r a t i o o f c o i n c i d e n c e t o a n t i c o i n c i d e n c e c o u n t s w h i c h i n d i c a t e s the k i n e -m a t i c a l l y b e s t p o s i t i o n . The p r o c e s s was r e p e a t e d w i t h a n g u l a r s t p s o f 0 . 5 ° - 0 . 2 ° t a k e n about the d e t e c t o r assembly a n g l e found above. A f t e r s e t t i n g the c o r r e c t a n g u l a r p o s i t i o n , the a l p h a d e t e c t o r must be l o c a t e d i n the p l a n e d e f i n e d by the i n c i d e n t 3He beam and the p r o t o n d e t e c t o r . The same p r o c e s s o f m i n i m i z i n g the AC/C r a t i o was c a r r i e d out as a f u n c t i o n o f the d e t e c t o r " h e i g h t " ( i e the v e r t i c a l p o s i t i o n r e l a t i v e t o the p l a n e def i n e d a b o v e ) . T i m i n g p u l s e s from " c o i n c i d e n t " e v e n t s d e t e c t e d i n t h e s o l i d s t a t e d e t e c t o r and p l a s t i c s c i n t i a l l t o r o c c u r r e d a t d i f f e r e n t times due t o the unequal p u l s e shapes. I t was n e c e s s a r y t o e n s u r e t h a t the " z e r o c r o s s o v e r " p o i n t s o f " c o i n c i d e n t " p r o t o n and a l p h a p u l s e s o c c u r r e d a t the same t i m e , s i n c e i t i s the " z e r o c r o s s o v e r " p o i n t w h i c h t r i g g e r e d the l o g i c out put p u l s e o f the T i m i n g SCA. The f a s t decay time o f the p l a s t i c s c i n t i l l a t o r r e s u l t e d i n a " p r o t o n " t i m i n g p u l s e o c c u r i n g e a r l i e r than the c o r r e s p o n d i n g " a l p h a " one. Hence i t was n e c e s s a r y t o d e l a y the p r o t o n p u l s e t o match the " z e r o - c r o s s o v e r " p o i n t s . The t i m e d e l a y on the T i m i n g SCA ( f o l l o w i n g t h e p r o t o n channel l i n e a r a m p l i f i e r ) was v a r i e d . The AC/C r a t i o was measured as a f u n c t i o n o f the t i m e d e l a y and a d e l a y was chosen t o c o r r e s p o n d t o the c e n t r e o f the f l a t v a l l e y on the AC/C r a t i o . To check more a c c u r a t e l y the a n g u l a r p o s i t i o n of t h e a l p h a d e t e c t o r , i t was - 49 -n e c e s s a r y t o a s c e r t a i n whether t h e minimum AC/C r a t i o c o r r e s p o n d e d t o t h e 100 keV window b e i n g c e n t e r e d on the a l p h a peak as the window was swept a c r o s s the peak. The a n g u l a r p o s i t i o n o f the a l p h a d e t e c t o r assembly was r e a d j u s t e d u n t i l t he AC/C r a t i o minimum c o r r e s p o n d e d t o the 100 keV window c e n t e r e d on t h e a l p h a peak. T h i s a n g l e o f the a l p h a d e t e c t o r was a c c e p t e d as the c o r r e c t one k i n e m a t i c a l l y . A f t e r the a l p h a d e t e c t o r was l o c a t e d and t h e r i g h t time d e l a y d e t e r m i n e d , a movable c o l l i m a t o r d e v i c e c o n s i s t i n g o f two o v e r l a p p i n g p l a t e s , as shown i n F i g u r e 14, was i n s t a l l e d on t h e f r o n t o f the p l a s t i c s c i n t i l l a t o r t o measure the p r o t o n beam p r o f i l e s . The c i r c u l a r h o l e s i n s e c t i o n s C and D were 0.125" i n d i a m e t e r and subtended an a n g l e o f 3-70° a t t h e c e n t r e o f the s e l f - s u p p o r t i n g ( C 2 D i 4 ) n t a r g e t . The v e r t i c a l p r o f i l e was measured by l o c k i n g s e c t i o n B o f p l a t e I o v e r the c e n t r e o f the s c i n t i l l a t o r and t h e n s l i d i n g p l a t e II o v e r p l a t e I u n t i l one o f the h o l e s o f s e c t i o n C was s i t u a t e d o v e r the v e r t i c a l s l o t o f s e c t i o n B. C o i n c i d e n c e measurements were then t a k e n f o r each o f t h e s u c c e e d i n g v e r t i c a l c o l l i m a t o r p o s i t i o n s 1, 2, 3» 4 and 5 as p l a t e II was moved t o the l e f t . T h i s y i e l d e d an i n t e n s i t y v a l u e f o r each o f the c o l l i m a t o r p o s i t i o n s about t h e c e n t r e l i n e o f t h e p r o t o n d e t e c t o r i n t h e v e r t i c a l d i r e c t i o n . These a n g u l a r p o s i t i o n s were 0°, t 3.69°, -7.35°. The r e l a t i v e i n t e n s i t y v a l u e was d e t e r m i n e d by c a l c u l a t i n g the r a t i o l v = C/(C + AC) f o r each c o l l i m a t o r p o s i t i o n where the C and AC v a l u e s were t a k e n from t h e i r r e s p e c t i v e s c a l e r s a f t e r s e v e r a l thousand c o u n t s . The r e l a t i v e i n t e n s i t i e s were n o r m a l i z e d t o a peak i n t e n s i t y o f 1 and t h e norm-a l i z e d i n t e n s i t y as a f u n c t i o n o f the v e r t i c a l a n g u l a r p o s i t i o n s i s p r e s e n t e d - 50 -, 1 1 - M o v a b l e P l a t e s Open S e c t i o n i n P l a t e - Open V e r t i c a l S l o t - 5 Open H o l e s (Diam = 0.125") - 1 Open H o l e (Diam = 0.125") FIGURE 14: DIAGRAM OF COLLIMATOR DEVICE FOR MEASURING HORIZONTAL AND VERTICAL PROTON BEAM PROFILES - 51 -i n s e c t i o n 3-^-3-The h o r i z o n t a l p r o f i l e was measured by f i r s t l o c k i n g s e c t i o n A o f p l a t e I ov e r the c e n t r e o f t h e p l a s t i c s c i n t i l l a t o r . P l a t e II was then s l i d o v e r p l a t e I u n t i l the 0.125° d i a m e t e r h o l e o f s e c t i o n D was l o c a t e d on the extreme r i g h t o f the open s e c t i o n A. P l a t e I I was then moved t o t h e l e f t i n s m a l l s t e p s . C o i n c i d e n c e measurements were taken f o r h o r i z o n t a l a n g u l a r p o s i t i o n s (about the c e n t r e l i n e ) o f 0 ° , ± 0.921°, t 2 .762° , - 4 .579° , +6.396° 18.179° and -9 -958° . As i n t h e c a s e o f the v e r t i c a l p r o f i l e , t he r e l a t i v e i n t e n s i t i e s 1^  = C/(C + AC) were n o r m a l i z e d t o a peak o f 1 and p l o t t e d as a f u n c t i o n o f the h o r i z o n t a l a n g u l a r p o s i t i o n . The r e s u l t s a r e p r e s e n t e d i n s e c t i o n 3.4.2. - 5 2 -CHAPTER I I I EXPERIMENTAL OBSERVATIONS AND CALCULATIONS 3 . 1 G e n e r a l I n t r o d u c t i o n T h i s c h a p t e r p r e s e n t s t h e e x p e r i m e n t a l o b s e r v a t i o n s c o n c e r n i n g t h e d i f f e r e n t p r e p a r a t i o n t e c h n i q u e s o f t h e s e l f - s u p p o r t i n g (C 2D^)n " s a n d w i c h " t a r g e t s and t h e i r p e r f o r m a n c e when s u b j e c t e d t o t h e 3He beam o f 6 9 0 keV. Performance i s a s c e r t a i n e d by a l p h a y i e l d measurements (of the a l p h a s from the r e a c t i o n 2 H ( 3 H e , p ) 4 H e ) , as w e l l as t a r g e t t h i c k n e s s measurements by the energy l o s s t e c h n i q u e ( i e the 1 9 F resonance s h i f t ) . The t a r g e t performance s t u d y was exte n d e d t o i n c l u d e a l p h a y i e l d measurements as a f u n c t i o n o f the car b o n l a y e r t h i c k n e s s i n t h e " s a n d w i c h " t a r g e t . The r e s u l t s o f t h i s extended s t u d y a r e a l s o p r e s e n t e d i n t h i s c h a p t e r . F i a n l l y t h e measurements o f the v e r t i c a l and h o r i z o n t a l p r o t o n beam p r o f i l e s a r e p r e s e n t e d and t h e p r o f i l e s compared w i t h t h o s e o b t a i n e d f o r s o l i d D2 0 copper backed t a r g e t s (Ho 6 8 ) . 3 . 2 S e l f - S u p p o r t i n g T a r g e t P r e p a r a t i o n Both poured and e v a p o r a t e d (C 2D 4)n f i l m s were f i r s t t e s t e d on c l e a r s l i d e s w i t h o u t the p r e s e n c e o f c a r b o n l a y e r s . The poured f i l m s appeared v e r y u n i f o r m and s l i g h t l y m i l k y i n c o l o u r w h i l e t h e e v a p o r a t e d f i l m s appeared e x t r e m e l y u n i f o r m and t r a n s p a r e n t . As e x p l a i n e d i n s e c t i o n 2 . 2 . 2 , t e s t i n g o f the (C 2D 4)n f i l m a l o n e was used t o d e t e r m i n e t h e ave r a g e p o l y e t h y l e n e t h i c k n e s s f o r a s l i d e as a f u n c t i o n o f t h e c o n c e n t r a t i o n o f (C 2Di t)n i n X y l e n e . U s i n g the c o n c e n t r a t i o n o f 1 . 3 6 mg (C 2Di +)n per ml o f X y l e n e , t h e poured samples o f a g i v e n s l i d e showed a maximum o f 1 5 % v a r i a t i o n from t h e ave r a g e p o l y e t h y l e n e t h i c k n e s s f o r t h e s l i d e . T h i s appeared t o be due t o the manner i n whi c h the - 53 -hot s o l u t i o n s p r e a d i t s e l f a c r o s s t h e s l i d e , c o n t r o l o f wh i c h was d i f f i c u l t . In a d d i t i o n , t h e a v e r a g e p o l y e t h y l e n e f i l m t h i c k n e s s showed a 10% maximum v a r i a t i o n from s l i d e t o s l i d e , p r o b a b l y due t o the speed o f t h e hand sweeping m o t i o n a c r o s s t h e s l i d e . Hence the o b s e r v e d a v e r a g e p o l y e t h y l e n e t h i c k n e s s o f 44 yg/cm 2 i s s u b j e c t t o a p o s s i b l e v a r i a t i o n o f t 25% ( i e i 11 y g / c m 2 ) . T h i s u n c e r t a i n t y e s t i m a t e i n c l u d e s w e i g h i n g and a r e a measure-ment e r r o r s . An example o f the r e ' a t i v e u n i f o r m i t y o f t h e p o u r i n g p r o c e s s was o b s e r v e d i n t h e t h i c k e r poured p o l y e t h y l e n e f i l m s . Here a c o n c e n t r a t i o n o f 4.08 mg (C 2D H)n per ml o f X y l e n e ( i e t h r e e t i m e s the c o n c e n t r a t i o n mentioned above) y i e l d e d t a r g e t samples o f an aver a g e (C^D^n t h i c k n e s s equal t o 132 yg/cm 2 - 25% ( i e 3 x 44 yg/cm 2 t h i c k ) . Due t o the c a l i b r a t i o n and m o n i t o r e r r o r s o f t h e e v a p o r a t i o n p r o c e s s (see s e c t i o n 2.2.1), the e v a p o r a t e d (C 2Dt +)n f i l m s o f 135 yg/cm 2 were s u b j e c t t o an u n c e r t a i n t y o f t 12 yg/cm 2. The c a r b o n l a y e r t h i c k n e s s e s o f the " s a n d w i c h " t a r g e t s , f o r t h e 44 yg/cm 2 t h i c k (C 2Di t)n, were each s u b j e c t t o an t 17% e r r o r due t o w e i g h i n g e r r o r , c a r b o n t h i c k n e s s v a r i a t i o n and (C 2Di +)n v a r i a t i o n a c r o s s the s l i d e . The (C 2D [ |)n v a r i a t i o n c o n t r i b u t e d t o the c a r b o n t h i c k n e s s e r r o r s i n c e the w e i g h i n g o f a c a r b o n l a y e r s e c t i o n i n c l u d e d the (C 2Di t)n l a y e r (as i l l u s t r a t e d i n F i g u r e 5). A l l c a r b o n l a y e r s e v a p o r a t e d o v e r the b a s i c t a r g e t sandwich f o r t he c a r b o n l a y e r v a r i a t i o n s t u d y and e v a p o r a t e d f o r t h e 135 yg/cm 2, t h i c k (C 2D l t)n " s a n d w i c h " t a r g e t s , were measured by the t h i c k n e s s m o n i t o r . Hence - 5k -t h e y were s u b j e c t t o a s m a l l e r e r r o r composed o f t h e c a l i b r a t i o n and m o n i t o r e r r o r s as e x p l a i n e d i n s e c t i o n 2.2.2. T h i s amounted t o t 10% f o r the e v a p o r a t i o n o f a s i n g l e 10 pg/cm 2 c a r b o n l a y e r . A summary o f the p o s s i b l e e r r o r s i n t h e e s t i m a t e s o f t h e v a r i o u s l a y e r t h i c k n e s s e s f o r t h e "sandwich" t a r g e t s i s shown i n T a b l e 1. TABLE 1: L a y e r T h i c k n e s s e s and t h e i r E r r o r s f o r t h e "Sandwich" T a r g e t s (C 2 D t t)n T h i c k n e s s ( C 2 D i + ) n l a y e r e r r o r S i n g l e c a r b o n l a y e r (10 yg/cm 2 t h i c k ) e r r o r kk yg/cm 2 (poured) + 15% + 17% (weighed) 132 yg/cm 2 (poured) + 14% + 10% (T mon i t o r ) 135 yg/cm 2 ( e v a p o r a t e d ) + 8.3% + 10% (T m o n i t o r ) Compared w i t h t h e w e i g h i n g t e c h n i q u e , use o f the t h i c k n e s s m o n i t o r p e r m i t t e d an immediate e s t i m a t e o f t h e ca r b o n l a y e r t h i c k n e s s as w e l l as y i e l d i n g a lower u n c e r t a i n t y f o r the t h i c k n e s s . In a d d i t i o n a more a c c u r a t e e s t i m a t e o f the t h i c k n e s s o f t h e poured ( C 2 n u ) n l a y e r was o b t a i n e d a f t e r w e i g h i n g t h e " s a n d w i c h " t a r g e t samples. The e r r o r i n t h e measurement o f t h e carbon l a y e r t h i c k n e s s would be reduced t h r o u g h b e t t e r e v a p o r a t i o n "geometry" (as mentioned i n s e c t i o n 2.2.1), t h e r e b y r e d u c i n g the e r r o r i n the measurement of t h e (C 2D L f)n l a y e r t h i c k n e s s f o r poured t a r g e t s . By u s i n g the " t h i c k n e s s m o n i t o r " t o m o n i t o r the ca r b o n e v a p o r a t i o n t o the o r d e r o f t k%, f o l l o w e d by w e i g h i n g l a r g e a r e a s (e.g. 2 cm x 2 cm) o f t a r g e t sandwich samples, the e r r o r i n the - 55 -t h i c k n e s s o f t h e (C 2D t t)n l a y e r c o u l d be reduced t o t h e o r d e r o f t 8%. The c a r b o n l a y e r s appeared v e r y u n i f o r m i n c o l o u r and t e x t u r e . To co m p l e t e the " s a n d w i c h " s t r u c t u r e , t he ca r b o n e v a p o r a t i o n , c a r r i e d o u t w i t h the minimum p o s s i b l e heat r a d i a t i o n (as d e s c r i b e d i n s e c t i o n 2.2.1), d i d not appear t o damage the exposed p o l y e t h y l e n e f i l m on t h e s l i d e . The poured (C 2Dt t)n t a r g e t sandwiches were m e c h a n i c a l l y much s t r o n g e r than the e v a p o r a t e d ones o f the same t h i c k n e s s . The e v a p o r a t e d t a r g e t s had o n l y a 10% s u c c e s s r a t e o f s t r i p p i n g from t h e g l a s s s l i d e s and p i c k - u p from the wa t e r s u r f a c e . T h i s i s much l e s s than t h e 75% s u c c e s s r a t e f o r the poured t a r g e t s . The l a r g e f a i l u r e r a t e w i t h the e v a p o r a t e d t a r g e t may have been d e c r e a s e d by s t r i p p i n g and p i c k i n g - u p i n a medium o f lower s u r f a c e t e n s i o n than w a t e r . The c u r r e n t market p r i c e o f (C 2D t f)n i s $155-00 per g (De 69). C o n s i d e r i n g the s u c c e s s r a t e s , amount o f (C 2Di t)n r e q u i r e d e t c . , the p r i c e per u s a b l e t a r g e t sample [ f o r 44 yg/cm 2 t h i c k (C 2D ) +)n] was 7 c e n t s f o r the poured (C 2D t +)n p r o c e s s w i t h o u t u s i n g t h e T m o n i t o r and 41 c e n t s f o r the e v a p o r a t e d p o l y e t h y l e n e p r o c e s s . U s i n g t h e T m o n i t o r f o r c a r b o n e v p o r a t i o n , 3 t i m e s as many u s a b l e t a r g e t s would be a v a i l a b l e from the p o u r i n g p r o c e s s due t o the l e s s e x t e n s i v e w e i g h i n g s needed f o r t h i c k n e s s e s t i m a t e s . Hence, the p r i c e would be reduced t o 2.3 c e n t s per u s a b l e t a r g e t sample. Two s l i d e s h o l d i n g e v a p o r a t e d ( C ^ i ^ n sandwich t a r g e t s were s u b j e c t e d t o gamma r a d i a t i o n t o o b s e r v e the p o s s i b i l i t y o f i m p r o v i n g t h e t a r g e t s t r e n g t h t h r o u g h " c r o s s - 1 i n k i n g " (see s e c t i o n 2.2.4). The t a r g e t samples t a k e n from the s l i d e s u b j e c t e d t o 3 Megarads showed no v i s i b l e improvement i n t h e i r - 56 -m e c h a n i c a l s t r e n g t h and e x p e r i e n c e d t h e same low 10% s u c c e s s r a t e d u r i n g s t r i p p i n g and p i c k - u p . The " s a n d w i c h " t a r g e t f i l m s u b j e c t e d t o 12 Megarads c o u l d not be s t r i p p e d from the g l a s s s u b s t r a t e . T h i s i m p l i e d a t y p e o f i n t e r a c t i o n i n which t h e f i l m was hardened o n t o the s u b s t r a t e . T h i s t e s t , by no means c o n c l u s i v e , d i d i n d i c a t e t h a t t h e t a r g e t s t r e n g t h might be improved t h r o u g h " c r o s s - 1 i n k i n g " . E v a p o r a t i n g a s t r i p p i n g agent o n t o t h e ; g l a s s s l i d e b e f o r e t a r g e t p r e p a r a t i o n c o u l d a i d i n s t r i p p i n g o f f such "hardened" f i l m s from the g l a s s s l i d e s a f t e r e x t e n s i v e r a d i a t i o n e x p o s u r e . Such s t r i p p i n g a g e n t s might be Na C I , d e t e r g e n t s o r s o l u b l e o r g a n i c com-pounds (Ko 66). 3.3 T a r g e t P e r f o r m a n c e Under t h e 3He Beam 3.3-1 A l p h a Y i e l d and Energy Loss T h i c k n e s s f o r R e g u l a r Runs A t y p i c a l s o l i d s t a t e d e t e c t o r s p e c t r u m f o r the a l p h a y i e l d measurements i s p r e s e n t e d i n F i g u r e 15- The c h a r a c t e r i s t i c s o f the s p e c t r u m were d i s c u s s e d i n s e c t i o n 2.3-2. For c o n v e n i e n c e a p a r t i c u l a r t a r g e t i s i d e n t i f i e d by 3 o r k symbols. The f i r s t symbol ( I , I I , I I I o r I V Q ) i n d i c a t e s the p a r t i c u l a r s l i d e from w h i c h the sample was t a k e n . The second symbol (A, B, C e t c ) i n d i c a t e s the p a r t i c u l a r t a r g e t sample from t h e g i v e n s l i d e . The t h i r d symbol [ S ( l ) , S(2), o r S(3)] d e f i n e s one o f the beam s p o t s on t h i s t a r g e t sample, up t o 3 s p o t s per sample. The f o u r t h o p t i o n a l symbol R i n d i c a t e s t h a t the t a r g e t has been r e v e r s e d i n p o s i t i o n r e l a t i v e t o the 3He beam d i r e c t i o n a f t e r i t s f i r s t t e s t i n g . T a b l e 2 i s a summary o f the t e s t i n g c a r r i e d o ut on t h e b a s i c " s a n d w i c h " t a r g e t s a mples. I t i n c l u d e s the " f i n a l a l p h a y i e l d " ( i e a f t e r 300 yc o f 3He on t a r g e t ) 57 I O O K P I O K I K z z < X o \ cn £ 1 0 0 O o 1 0 i r i r 16.7 MeV P r o t o n s 5 MeV 4 H e •; P r o t o n E d g e 4 8 9 6 144 192 2 4 0 C H A N N E L N U M B E R F I G U R E 15= A T Y P I C A L S O L I D S T A T E DETECTOR SPECTRUM FOR THE A L P H A Y I E L D MEASUREMENTS TABLE 2: A SUMMARY OF THE ALPHA YIELD AND ENERGY LOSS THICKNESS TESTING CARRIED OUT ON THE BASIC "SANDWICH" TARGET SAMPLES TARGET (C 2Di+)n THICKNESS (yg/cm 2) BACK C LAYER THICKNESS (yg/cm 2) FRONT C LAYER THICKNESS (yg/cm 2) "EQUIVALENT CARBON THICKNESS" BY 1 9 F ANALYSIS (yg/cm 2) AT "FINAL ALPHA YIELD" (COUNTS/yC) AFTER "EQUIVALENT POLYETHYLENE THICKNESS" (yg/cm 2) 3He BEAM CURRENT (pA) t = 0 min, t AFTER TARGET RECEIVED 3He E 60 y c , E 300 yc 60 yC 300 yC 1 AS (1 ) 40. 0 i 6 . 0 10.oil.7 8 . O i l . 4 42.0+12.0 1300i36 7.83 +0.22 0.05 1BS ( I ) 40.0+6.0 10.0^1.7 8.oi l.4 41.2+12.0 1780+42 10.7^0.25 0.015 IBS(2) 40.0i6.0 10.0±1.7 8.0+1 .4 6 0 . 0 i l 2 . 0 3 7 . 2 il2.0 453±21 2.73*0.13 0.09 IBS (3) 40.0±6.0 10.0±1.7 8 . O i l . 4 63.2±12.0 42 0 i 2 0 2.53+0.12 0.24 1 IAS (1) 38.0+5.8 1 0 . O i l . 7 8.0±1.4 189±13 1.15i0.08 0.15 1 I B S ( l ) 38.0+5.8 1 0 . O i l . 7 8.oil.4 217+15 1.31+0.09 0.12 1 ICS ( l ) 4o.0±6.0 10.0±1.7 8 . O i l . 4 2 1 i i i 4 1.27i0.08 0. 14 1 1 IAS(1) 125.0±17.5 io.oti.o 11.0+1.1 ioooi32 6.02+0.19 0.08 I V o 136.0*12.1 11.0+1.1 12.0±1.2 1050+32 6.32i0.20 0.10 1 1 ICS(1) 125.0+17.5 io.oi l .o 11. o i l . ! 132.0+12.0 i oo.oii2 .o 1110+33 6.69i0.20 0.08 Note: t = time - 59 -measurements and the " e q u i v a l e n t c a r b o n t h i c k n e s s " d e t e r m i n a t i o n s by the 1 9 F resonance s h i f t method (see s e c t i o n 2.k). Two samples were o n l y t e s t e d up t o 60 y c o f 3He as a p r e l i m i n a r y t e s t o f the a l p h a y i e l d . The e r r o r s quoted i n a l l t he a l p h a y i e l d s a r e the s t a t i s t i c a l e r r o r s i n the number o f c o u n t s . The " e q u i v a l e n t p o l y e t h y l e n e t h i c k n e s s " e r r o r s a r e de t e r m i n e d from the r e l a t i v e e r r o r s i n t r o d u c e d by t h e a l p h a y i e l d q u a n t i t i e s . The e r r o r s i n the " e q u i v a l e n t carbon t h i c k n e s s e s " a r e based on a p o s s i b l e r e s o n a n c e s h i f t measurement e r r o r o f - 3 keV. The t a b l e a l s o c o n t a i n s the e s t i m a t e s o f the v a r i o u s c o m p o s i t e l a y e r t h i c k n e s s e s f o r t h e " s a n d w i c h " t a r g e t samples as w e l l as the u n c e r t a i n t i e s i n each l a y e r . The i n c i d e n t 3He beam c u r r e n t s (on a c i r c u l a r beam spot o f 0.160 cm) f o r a l l t a r g e t s a r e l i s t e d . T a r g e t s from s l i d e s I , II and I I I a l l c o n t a i n poured p o l y e t h y l e n e f i l m s . The t a r g e t from s l i d e I V Q c o n t a i n s an e v a p o r a t e d p o l y e t h y l e n e f i l m and had been s u b j e c t e d t o 3 Megarads o f gamma r a d i a t i o n b e f o r e 3He beam bombardment. The t e s t i n g o f t h e t a r g e t s composed o f a p p o x i m a t e l y hk yg/cm 2 t h i c k poured p o l y e t h y l e n e may be summarized as f o l l o w s : A) F i n a l d e u t e r i u m c o n t e n t and t o t a l t h i c k n e s s T a r g e t s IAS (1) and I B S ( l ) were compared a f t e r they had been bombarded w i t h 60 yc o f 3He. The a l p h a y i e l d s had d e c r e a s e d such t h a t t he " e q u i v a l e n t (r.2Di+)n t h i c k n e s s e s " were 7.83 and 10.7 yg/cm 2 r e s p e c t i v e -l y . The s u b s t a n t i a l l y lower " e q u i v a l e n t p o l y e t h y l e n e t h i c k n e s s e s " as compared w i t h the " e q u i v a l e n t c a r b o n t h i c k n e s s e s " i m p l i e s a g r e a t e r l o s s o f d e u t e r i u m atoms than c a r b o n atoms w h i c h i n t u r n i m p l i e s a predominant l o s s o f d e u t e r i u m atoms r a t h e r than a l o s s o f the G2D14 - 60 -m o l e c u l e as a w h o l e . The a l p h a y i e l d d e t e r i o r a t i o n was s t i l l t o o u n s t a b l e t o make a comparison o f the t a r g e t s f o r t h i c k n e s s uni f o r m i t y . T a r g e t u n i f o r m i t y Comparison o f the a l p h a y i e l d c u r v e s f o r t a r g e t s IBS (2) and IBS(3), as i l l u s t r a t e d i n F i g u r e 16, s e r v e d as a co m p a r i s o n between d i f -f e r e n t beam s p o t s on the same t a r g e t sample. The p l o t t e d y i e l d c u r v e s a r e s e p a r a t e d because o f the d i f f e r e n t y - a x i s y c s e t t i n g s f o r w h i c h each a l p h a count was m o n i t o r e d . The c u r v e s a r e r o u g h l y p a r a l l e l and the " f i n a l a l p h a y i e l d s " (at 300 yc) i n c o u n t s / y c a g r e e t o w i t h i n t h e s t a t i s t i c a l e r r o r (see T a b l e 2). Hence when the two c u r v e s a r e n o r m a l i z e d t o the same yc v a l u e , the c u r v e s a r e i d e n t i c a l w i t h i n the e x p e r i m e n t a l u n c e r t a i n t i e s . The t a r g e t samples t h e n , a r e v e r y u n i f o r m a c r o s s the 0.25" s e l f - s u p p o r t i n g r e g i o n and the t a r g e t d e t e r i o r a t i o n as a f u n c t i o n o f t h e t o t a l i n t e g r a t e d c h a r g e on t h e t a r g e t i s c o n s i s t e n t a c r o s s t h i s r e g i o n . C h a r a c t e r i s t i c s o f the c u r v e s a r e : a r a p i d d e c r e a s e i n the a l p h a y i e l d o v e r the f i r s t 60 t o 100 y c ; s t a b i l i z i n g o f the d e t e r i o r a t i o n by 150 yc w i t h the c u r v e r e f l e c t i n g a s l o w subsequent d e c r e a s e i n the a l p h a y i e l d . The " e q u i v a l e n t C t h i c k n e s s " f o r t a r g e t IBS (2) as c a l c u l a t e d by the 1 9 F a n a l y s i s was 60.0 t 12.0 yg/cm 2 a t time t = 0 min. c o n s i s t e n t w i t h the e s t i m a t e d t o t a l t h i c k n e s s o f 58.0 t 9-1 yg/cm 2 by w e i g h i n g . A f t e r 300 yc o f 3He on t a r g e t , t h e " e q u i v a l e n t C t h i c k n e s s " was 37.2 t 12.0 yg/cm 2. T h i s i s s u b s t a n t i a l l y g r e a t e r than the " e q u i v a l e n t 10*-9 -8-7-& -^ 5-O m - 5-1 Q Z < 2-^  O to |Oa-| O 1 3 ._, U J V < I CL 5-4 4-3-* - l 10' i r i 1 1 (1) = T a r g e t IBS ( 3 ) , Q = 4.5 yC (2) = T a r g e t IBS ( 2 ) , Q. = 1.5 uC * 4 4 O O ess oo A I I I I (I) 1 I I I 1 1 I T 1 1 I I I eo JL_L ° ° O O B o o o o l l i I i j , j 1 3 1 I I I II I I i I (2) _L 0 10 20 5 0 100 150 2 0 0 2 5 0 3 0 0 3 5 0 ON 1 TOTAL INTEGRATED BEAM CURRENT i^C) F I G U R E 16: A L P H A Y I E L D A S A F U N C T I O N OF THE T O T A L INTEGRATED BEAM CURRENT ON T A R G E T FOR THE T A R G E T S I B S(2) AND I B S(3) " - 62 -(C 2D t t)n t h i c k n e s s " o f 2.73 i 0.13 yg/cm 2 w h i c h i m p l i e s (as mentioned i n A) a predominant l o s s o f d e u t e r i u m atoms r a t h e r than a l o s s o f t h e C2D4 m o l e c u l e as a whole. The " e q u i v a l e n t C t h i c k -n e s s " o f t a r g e t IBS(3) a t t = 0 min was 63.2 t 12.0 yg/cm 2 w h i c h a g r e e s w i t h t a r g e t IBS(2) w i t h i n the p o s s i b l e e r r o r . C) Comparison o f samples from t h e same s l i d e Comparison o f the a l p h a y i e l d d e t e r i o r a t i o n s f o r t a r g e t s I I A S ( l ) , I I B S ( l ) and I I C S ( l ) , as i l l u s t r a t e d i n F i g u r e 18, 19 and 20 r e s p e c t i v e l y ( i n s e c t i o n 3-3.2), s e r v e d as a co m p a r i s o n between d i f f e r e n t t a r g e t samples from t h e same s l i d e . The c u r v e s a r e r o u g h l y p a r a l l e l and the " f i n a l a l p h a y i e l d s " agree w i t h i n the s t a t i s t i c a l e r r o r s . T h i s i l l u s t r a t e s t h a t the t a r g e t samples a r e v e r y u n i f o r m a c r o s s t h e whole s l i d e and the t a r g e t d e t e r i o r a t i o n s a r e c o n s i s t e n t from sample t o sample. The same c u r v e c h a r a c t e r -i s t i c s a p p l y as d i s c u s s e d i n B ) . D) Comparison o f samples from d i f f e r e n t s l i d e s Comparison o f t h e r e s u l t s from C) w i t h t h o s e from B) s e r v e d as a com p a r i s o n between t a r g e t samples from d i f f e r e n t s l i d e s . In t h i s c a s e the y i e l d c u r v e s s t i l l appeared r o u g h l y p a r a l l e l . The " f i n a l a l p h a y i e l d " v a l u e s d i f f e r e d by more than the s t a t i s t i c a l e r r o r s i n d i c a t i n g t h a t t h e p o u r i n g p r o c e s s does not y i e l d e x a c t l y the same t h i c k n e s s f i l m s from s l i d e t o s l i d e . The b e h a v i o u r o f t h e t a r g e t s composed o f a p p r o x i m a t e l y 135 yg/cm 2 t h i c k p o l y e t h y l e n e (both poured and e v a p o r a t e d ) may be summarized as f o l l o w s : - 63 -i ) E v a p o r a t i o n vs P o u r i n g Measurement o f the a l p h a y i e l d d e t e r i o r a t i o n f o r t a r g e t s I I I A S ( l ) and I V 0 s e r v e d as a comparison o f the m e r i t s o f e v a p o r a t i n g and p o u r i n g (C 2Dtt)n as r e g a r d s t o t a r g e t d e t e r i o r a t i o n . The c u r v e s a r e i l l u s t r a t e d i n F i g u r e 17- The two c u r v e s a r e i d e n t i c a l w i t h i n t h e e x p e r i m e n t a l e r r o r s . The t a r g e t b e h a v i o u r i s v e r y s i m i l a r t o t h a t o f the " t h i n n e r " t a r g e t s d e s c r i b e d i n B ) . T a r g e t d e t e r i o r a t i o n and the " f i n a l a l p h a y i e l d s " appear t o be independent o f the method o f p r e p a r a t i o n o f the " s a n d w i c h " t a r g e t - whether by the p o u r i n g o r e v a p o r a t i n g t e c h n i q u e , i i ) E f f e c t o f " c r o s s - l i n k i n g " S u b j e c t i n g the e v a p o r a t e d ( C 2 D 4 ) n " s a n d w i c h " t a r g e t s t o 3 Megarads gamma r a d i a t i o n d i d not appear t o modify the t a r g e t d e t e r i o r a t i o n o r f i n a l a l p h a y i e l d as compared w i t h the poured t a r g e t o f s i m i l a r t h i c k n e s s . The t e s t however was by no means c o n c l u s i v e and a g r e a t e r dose o f r a d i a t i o n may a i d i n i m p r o v i n g t a r g e t p e r f o r m a n c e , i i i ) F i n a l d e u t e r i u m c o n t e n t and t o t a l t h i c k n e s s A t h i r d t a r g e t , M I C S ( l ) , was t e s t e d . The " e q u i v a l e n t C t h i c k n e s s " d e t e r m i n e d a t t = 0 min. was 132.0 t 12.0 yg/cm 2 w h i c h i s c o n s i s -t e n t w i t h the t o t a l e s t i m a t e d " s a n d w i c h " t a r g e t t h i c k n e s s o f 146.0 t 14.4 yg/cm 2 (by w e i g h i n g and T m o n i t o r ) . A f t e r s u b j e c t i n g the t a r g e t t o 300 yc o f 3He, a n o t h e r 1 9 F a n a l y s i s was c a r r i e d o u t . T h i s y i e l d e d an " e q u i v a l e n t C t h i c k n e s s " o f 100.0 t 12.0 yg/cm 2. The f i n a l a l p h a y i e l d c o r r e s p o n d e d t o an " e q u i v a l e n t (C 2Dtf)n t h i c k -n e s s " o f 6.69 yg/cm 2. A g a i n , as w i t h t h e t h i n n e r t a r g e t s , the l a r g e d i f f e r e n c e i n t h e s e f i n a l " e q u i v a l e n t t h i c k n e s s e s " i m p l i e s a 9 -8-1 — 6 -S -4 -^ 3 O tn h-z § i o 4 . U J < X Q. 6-5 -3 J 2-^ io-~~I 1 O = T a r g e t I V 0 A = T a r g e t I I I AS (1) \ o o o G A A A A A 1 o ° ° A © I 1 i h I I _I_JL ON 0 10 20 50 100 150 200 250 300 350 TOTAL INTEGRATED BEAM CURRENT (^tC) F I G U R E 17: A L P H A Y I E L D A S A F U N C T I O N OF THE TOTAL INTEGRATED BEAM CURRENT ON T A R G E T FOR THE T A R G E T S I I IAS(1) AND I V Q - 65 -predominant l o s s o f d e u t e r i u m atoms r a t h e r than a l o s s o f the C2D4 m o l e c u l e as a whole. The p r o c e s s i n v o l v e d d u r i n g t a r g e t d e t e r i o r a t i o n appears t o be t h e same as i n t h e case o f the t h i n n e r t a r g e t s . i v ) A c o m p a r i s o n o f " t h i n " and " t h i c k " t a r g e t s A f t e r 300 y c o f 3He on a g i v e n t a r g e t , the r a t i o o f the " e q u i v a l e n t ( C 2 D i + ) n t h i c k n e s s " (which depends on t h e c o n c e n t r a t i o n o f d e u t e r i u m atoms) t o the " e q u i v a l e n t c a r b o n t h i c k n e s s " (which depends on t h e c o n c e n t r a t i o n o f car b o n atoms) i s an i n d i c a t i o n o f t h e r a t i o o f d e u t e r i u m c o n c e n t r a t i o n t o car b o n c o n c e n t r a t i o n i n t h e t o t a l t a r g e t , m a t e r i a l . T h i s r a t i o f o r t a r g e t IBS (2) ( " t h i n " t a r g e t ) was 7.34 x I O - 2 t 2.1 x I O - 2 and f o r t a r g e t I I ICS (1) ( " t h i c k " . t a r g e t ) was 6 . 6 9 x 10~ 2 t 1.00 x 1 0 " 2 . These r a t i o s agree w i t h i n the e x p e r i m e n t a l e r r o r . From the " e q u i v a l e n t t h i c k n e s s " v a l u e s , the number o f atoms per cm 2 f o r b o t h d e u t e r i u m and c a r b o n may. be c a l -c u l a t e d ( u s i n g t h e f o r m u l a e d e v e l o p e d i n A p p e n d i c e s B and C ) . The r a t i o o f t h e s e two numbers th e n g i v e s t h e c o n c e n t r a t i o n o f the number o f d e u t e r i u m atoms per car b o n atom i n t h e t a r g e t m a t e r i a l . T h i s r a t i o f o r t a r g e t IBS(2) was 0 . 1 1 0 - 0 . 0 3 9 d e u t e r i u m atoms per ca r b o n atom and f o r t a r g e t I I I C S ( l ) was 0 . 1 0 0 - 0 . 0 1 5 . The agree^-ment, w i t h i n the e x p e r i m e n t a l e r r o r , o f t h e s e c o n c e n t r a t i o n s i n d i c a t e s t h a t t h e " f i n a l " c o n c e n t r a t i o n ( i e a f t e r 3He bombardment) of deu-t e r i u m t o c a r b o n i s the same f o r both t h e " t h i n " and " t h i c k " t a r g e t s . 3 . 3 . 2 A l p h a Y i e l d f o r Carbon L a y e r V a r i a t i o n s T a b l e 3 i s a summary o f the a l p h a y i e l d s t u d y c a r r i e d out on t a r g e t s w i t h TABLE 3: A SUMMARY OF THE ALPHA YIELD STUDY ON TARGETS WITH DIFFERENT CARBON LAYER THICKNESSES TARGET (C 2 D i t ) n THICKNESS (yg/cm 2) 1st C LAYER THICKNESS (ON BACK) (yg/cm 2) 1st C LAYER THICKNESS (ON FRONT) (yg/cm 2) NO. OF 10 yg/cm 2 CARBON LAYERS "FINAL ALPHA YIELD" AFTER 300 yC o f 3He (COUNTS/0.9 yC) FACTOR INCREASE IN FINAL YIELD (RELATIVE TO FINAL YIELD FOR "BASIC SANDWICH" TARGET) 3 He BEAM CURRENT ( uA) ON BACK ON FRONT 1 IAS (1) 38.0±5.8 10.Oil.7 8.0+1.4 1.0*0.17 1.0±0.17 170±13 1 .0 0.15 1 IAS (2) 38.0+5.8 10.0+1.7 8.011.4 3.0±0.26 1.OlO.17 930+13 5.47+0.60 0.18 1 I B S ( l ) 38.0±5.8 10.0±1.7 8.Oil.4 1 .0±0.17 1.0±0.17 195-1^  1 .0 0.12 1 IBS(2) 38.0±5.3 10.0+1.7 8.Oil.4 2.0±0.20 1.0l0.17 750128 3.84+0.42 0.12 1 IBS(3) 38.0+5.8 10.0+1.7 8.011.4 ii.OtO.28 1.oio.17 1375138 7.05±0.70 0.08 1 ICS (1) 40.016.0 10.Oil.7 8.011.4 i.oio.17 1.0+0.17 190ll3 1 .0 0.14 1ICS(2)R 40.0*6.0 10.0±1.7 8.0+1.4 •1 .0+0.17 4.0+0.35 1050132 5.52+0.54 0.09 1 ICS (3) 40.016.0 10.Oil.7 8.Oil.4 ^.010.35 1.oio.17 1350137 7.1+0.67 0.07 1 1 IBS (1) 125.0+17.5 10.oil.0 11.0+1.1 3.oio.26 1.oio.17 2950154 - 0.09 1 1 1 BS (2)R 125.0+17.5 io.oil.o n . o i i . i i.oio.17 3.oio.26 2300±48 - 0.09 - 67 -d i f f e r e n t c a r b o n l a y e r t h i c k n e s s e s . The t a b l e c o n t a i n s a l i s t o f the " b a s i c s a n d w i c h " t a r g e t s and t h e t h i c k n e s s e s o f t h e i n i t i a l l a y e r s com-p r i s i n g t h e " s a n d w i c h e s " . The number o f 10 yg/cm 2 c a r b o n l a y e r s on the " b a c k " and on t h e " f r o n t " o f each t a r g e t i n c l u d e s both the i n i t i a l c a r b o n l a y e r s and t h e e x t r a c a r b o n l a y e r s added f o r t h e s t u d y . The t h i c k n e s s e s o f the i n i t i a l c a r b o n l a y e r s on both s i d e s o f the p o l y e t h y l e n e f i l m were d e t e r m i n e d by the w e i g h i n g t e c h n i q u e d e s c r i b e d i n s e c t i o n 2.2.2. The e r r o r i n the t o t a l number o f c a r b o n l a y e r s on e i t h e r f r o n t o r back i s thus made up o f the e r r o r i n the i n i t i a l c a r b o n l a y e r p l u s the e r r o r i n the subsequent e v a p o r a t e d l a y e r s o f c a r b o n as measured by t h e T m o n i t o r . The " f i n a l • a l p h a y i e l d " v a l u e ( a f t e r 300 yc) i s d e t e r m i n e d by f i t t i n g a s t r a i g h t l i n e t o t h o s e v a l u e s o c c u r r i n g a f t e r t h e a l p h a y i e l d d e c r e a s e had s t a b i l i z e d ( u s u a l l y by 150 yc) and become l i n e a r on t h e p l o t . In a l l c a s e s the s t r a i g h t l i n e passed t h r o u g h the e r r o r f l a g s o f t h e s e v a l u e s . The e r r o r s in t h e a l p h a y i e l d s a r e t a k e n as t h e s t a t i s t i c a l u n c e r t a i n t y i n the number o f c o u n t s a t 300 y c . I t may be noted h e r e , t h a t t h e p r e s e t i n t e g r a t e d c u r r e n t o f 0.9 yc f o r w h i c h t h e a l p h a c o u n t s were t a k e n , was chosen f o r c o n v e n i e n c e . The second l a s t column o f T a b l e 3 g i v e s the f a c t o r i n c r e a s e i n the f i n a l y i e l d when a d d i t i o n a l l a y e r s o f c a r b o n have been added t o t h e t a r g e t . The e r r o r f o r each f a c t o r i n c r e a s e i s t a k e n as the sum o f the r e -l a t i v e e r r o r s o f t h e f i n a l y i e l d s f o r t a r g e t s w i t h and w i t h o u t t h e added c a r b o n l a y e r s . For t a r g e t s I I I B S ( l ) and I I IBS (2)R, no y i e l d c u r v e was measured f o r the t a r g e t sandwiches w i t h o u t c a r b o n l a y e r s added. The a c t u a l a l p h a y i e l d c u r v e s a r e d i s p l a y e d i n F i g u r e s 18, 19, 20 and 21. For each g r a p h , t h e legend at the top i n d i c a t e s the p a r t i c u l a r t a r g e t by i t s numbered c u r v e . B e s i d e each t a r g e t d e s i g n a t i o n a r e b r a c k e t e d symbols w h i c h 10' 9 -8 -7 -6-5 4-\ — 3 H O o 3 O o o u < I 0-z4 I 0 5 -9 -8 -7 -6 -5 -o 4-^ 10' A A A I I I a o (1) = T a r g e t I IAS (2) - (3CB) (2) = T a r g e t I I AS (1) I 1 I I 0 10 2 0 5 0 100 150 2 0 0 2 5 0 3 0 0 (I) I H CO I 1 1 I I 1 I I II 1 3 5 0 TOTAL INTEGRATED BEAM CURRENT (^C) FIGURE 18: ALPHA YIELD AS A FUNCTION OF THE TOTAL INTEGRATED BEAM CURRENT ON TARGET FOR THE TARGETS I I AS (1) AND I IAS (2) 10 —I 1 1 (1) = T a r g e t I IBS(3) - (4CB) (2) = T a r g e t I IBS(2) - (2CB) (3) = T a r g e t I I B S ( l ) 9 8 — 7 — 6 I 5 -i A- — o o cn t— z o i o 3 _ | 8 • O 7-1 J 6 - 1 % T T 0 i o e U o a A A o e o 6> O 0 • • o I I I I I 1 I I I 1 * I A A A A A ! I I I (I) (2) I I I I I U J < . - I Q. 3 5 IO' o o o © i I ( 3 ) • 1 1 I I I I 1 I I J__L 0 10 2 0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 TOTAL INTEGRATED BEAM CURRENT (yuC) FIGURE 19: ALPHA YIELD AS A FUNCTION OF THE TOTAL INTEGRATED BEAM CURRENT ON TARGET FOR THE TARGETS I I B S ( l ) , I IBS (2) AND I IBS (3) 10* 9 — 8 — 7 — 6 - 1 1 1-^ - 5-O CD 6 cn • »-z O s IO:-H 9 -Q 8 " _l 7 -6 -5-4-UJ < I QL 3 -Z — 10' T T ^ 6 O o 6 . A A A A I I 1 1 1 (1) = T a r g e t I 1 CS (3) - (4CB) (2) = T a r g e t I ICS (2 )R - (4CF) (3) = T a r g e t I I C S ( l ) (I) * I I I * I I I * » I' I I I I I (2) e o (3) © o ' i n ' i i i i H i i i _ L _ L 0 10 2 0 5 0 100 150 2 0 0 2 5 0 3 0 0 3 5 0 T O T A L I N T E G R A T E D B E A M C U R R E N T {jxC) -F- l GURE 20:- A L P H A Y I E L D A S A F U N C T I O N OF THE TOTAL INTEGRATED. BEAM. CURRENT ON TARGET FOR THE TARGETS M C S ( l ) , I ICS (2 )R AND I I CS (3) 10' i 6 — 5 -4 -3 ^ O co r-Z Zi o o L U < X O L 2-^ 9 - # 8 -7 -8 -io* A A • * O O © & ^ A *A A A A _L_L T T (1) = T a r g e t I I IBS (1) - (3CB) (2) = T a r g e t I I IBS(2)R - (3CF) i i i 1 I I T I I I I I I (|) 1 I I I T i i (2) _L 0 10 20 50 100 150 200 250 300 350 TOTAL INTEGRATED BEAM CURRENT (yuC) F I G U R E 2 1 : A L P H A Y I E L D AS A F U N C T I O N OF THE TOTAL INTEGRATED BEAM CURRENT ON T A R G E T FOR THE T A R G E T S I I I B S ( 1 ) AND II IBS (2)R - 72 -i n d i c a t e the number o f 10 yg/cm 2 c a r b o n l a y e r s on the back o r the f r o n t eg 3CB i n d i c a t e s 3 c a r b o n l a y e r s on t h e back, 4CF i n d i c a t e s k c a r b o n l a y e r s on the f r o n t e t c . Absence of t h e s e symbols i n d i c a t e s a " b a s i c s a n d w i c h " t a r g e t w i t h one c a r b o n l a y e r on both back and f r o n t . I m p l i c i t i n t h e s e symbols (as i n a l l t h i s d i s c u s s i o n ) i s the f a c t t h a t a t a r g e t , h a v i n g s e v e r a l c a r b o n l a y e r s on e i t h e r s i d e o f the t a r g e t always has one ca r b o n l a y e r on the o p p o s i t e s i d e . Comments r e g a r d i n g t h e s e c u r v e s a r e as f o l l o w s : ( i ) The " b a s i c s a n d w i c h " t a r g e t y i e l d c u r v e s I I A S ( l ) , I I B S ( l ) and 1ICS(1) show a l l the t a r g e t d e t e r i o r a t i o n and c u r v e c h a r a c t e r -i s t i c s as d i s c u s s e d i n 3 - 3 -1 -( i i ) The y i e l d c u r v e s f o r t a r g e t s w i t h m u l t i c a r b o n l a y e r s do not d e c r e a s e as r a p i d l y o v e r the f i r s t 60 t o 100 y c . The ^ t a r g e t d e t e r i o r a t i o n appears t o be more u n i f o r m and does not e x p e r i e n c e the l a r g e e a r l y r e l a t i v e f l u c t u a t i o n s such as seen f o r t h e " b a s i c " t a r g e t I I B S ( l ) . The a l p h a y i e l d d e c r e a s e s t a b i l i z e s and e x h i b i t s a s l o w d e c r e a s e ( l i n e a r on t h e graph) sooner than f o r t h e b a s i c t a r g e t s . Moreover the y i e l d appears t o s t a b i l i z e sooner f o r an i n c r e a s i n g number o f c a r b o n l a y e r s . An i n c r e a s e d number o f car b o n l a y e r s on t h e back i s more e f f e c t i v e i n i n c r e a s i n g t h e f i n a l y i e l d t han the same number o f c a r b o n l a y e r s on the f r o n t . The f i n a l r a t e o f a l p h a y i e l d d e c r e a s e appears t o be the same f o r both " b a s i c " and m u l t i c a r b o n l a y e r e d t a r g e t s ( i e t h e f i n a l s l o p e s a r e p a r a l l e l ) . An a n a l y s i s o f t h e change i n " f i n a l a l p h a y i e l d s " w i t h d i f f e r e n t c a r b o n l a y e r t h i c k n e s s e s i s p r e s e n t e d i n F i g u r e s 22 and 23, where the d a t a has been - 73 -2000 1800 6 in >— z 3 o o 1600 1400 1200 d 10001 < £ 800| 600 400 200 100 1 0 1 2 3 4 5 6 7 8 No. OF 10^ugm/cm* CARBON LAYERS ON TARGET BACK FIGURE 22: FINAL ALPHA YIELD AS A FUNCTION OF THE NUMBER OF 10 yg/cm2 CARBON LAYERS ON THE "BACK" OF THE TARGET - Ik -No. OF 10/igm/cm* CARBON LAYERS ON TARGET BACK F I G U R E 23: THE R A T I O OF THE " F I N A L A L P H A Y I E L D " FOR A G I V E N NUMBER OF CARBON L A Y E R S ON THE " B A C K " TO THE " F I N A L A L P H A Y I E L D " FOR THE SAME TARGET IN ITS O R I G I N A L " B A S I C " SANDWICH FORM, AS A F U N C T I O N OF THE NUMBER OF CARBON L A Y E R S - 75 -t a k e n from T a b l e 3- F i g u r e 22 i s a graph o f the " f i n a l a l p h a y i e l d " ( counts / 0 . 9 yc a t 300 yc) as a f u n c t i o n o f the number o f 10 yg/cm 2 c a r b o n l a y e r s on the "back" o f the t a r g e t . For one c a r b o n l a y e r , the t h r e e o b s e r v e d p o i n t s a r e the a l p h a y i e l d s f o r t h e " b a s i c s a n d w i c h " t a r g e t s com-posed o f one 10 yg/cm 2 c a r b o n l a y e r on the back and on the f r o n t . The c l o s e g r o u p i n g o f the p o i n t s ( t h e y a g r e e w i t h i n the s t a t i s t i c a l e r r o r s ) i n d i c a t e s t h e c o n s i s t e n c y o f the t h r e e t a r g e t samples. The r e l a t i o n s h i p appears t o be r o u g h l y l i n e a r and i n f a c t a s t r a i g h t l i n e can be drawn t h r o u g h the e r r o r f l a g s o f a l l the p o i n t s . A c o r r e s p o n d i n g graph f o r a v a r i a t i o n o f car b o n l a y e r s on the " f r o n t " c o u l d not be drawn because o n l y one p o i n t was a v a i l a b l e and t h e r e s u l t would have been i n c o n c l u s i v e . To t a k e i n t o a c c o u n t p o s s i b l e v a r i a t i o n s between t a r g e t s , the r e s u l t s o f T a b l e 3 a r e p r e s e n t e d i n F i g u r e 23 as the r a t i o o f the " f i n a l a l p h a y i e l d " f o r a g i v e n number o f car b o n l a y e r s on t h e "back" t o the " f i n a l a l p h a y i e l d " f o r t h e same t a r g e t i n i t s o r i g i n a l " b a s i c " sandwich form, as a f u n c t i o n o f t h e number o f c a r b o n l a y e r s . F i g u r e 23 i s t h e r e f o r e a p l o t o f the f a c t o r i n c r e a s e i n t h e f i n a l y i e l d as a f u n c t i o n o f the number o f car b o n l a y e r s on the "back" o f the t a r g e t . A s t r a i g h t l i n e may be drawn t h r o u g h the e r r o r 1 f l a g s o f the p o i n t s . I t may be noted t h a t the e r r o r s i n t h e number o f carbon l a y e r s i n F i g u r e s 22 and 23 have been l i s t e d i n T a b l e 3 and d i s c u s s e d a t t h e b e g i n n i n g o f t h i s s e c t i o n . The o b s e r v e d l i n e a r dependence c o r r e s p o n d s t o an average f a c t o r i n c r e a s e i n the " f i n a l 4He y i e l d " o f 1.83 t 0.35 per carb o n l a y e r on the back of the t a r g e t . The c o r r e s p o n d i n g f a c t o r i n c r e a s e i n f i n a l y i e l d per 10 yg/cm 2 c a r b o n l a y e r on the " f r o n t " o f t h e t a r g e t was based on o n l y one p o i n t (at k c a r b o n l a y e r s ) and y i e l d e d t h e v a l u e 1.38 t 0.26. - 76 In a d d i t i o n two t a r g e t s , IIC and 1MB, were each compared d i r e c t l y f o r the " f i n a l a l p h a y i e l d " w i t h a g i v e n number o f car b o n l a y e r s e i t h e r on the back o r on the f r o n t o f the t a r g e t . T h i s was a c c o m p l i s h e d by r o t a t i n g the same t a r g e t 180° w i t h r e s p e c t t o t h e i n c i d e n t beam d i r e c t i o n and i n v e s t i g a t i n g a new " s p o t " . The r a t i o o f the " f i n a l a l p h a y i e l d " f o r a number o f c a r b o n l a y e r s on the "back" t o the f i n a l a l p h a y i e l d f o r t h e same number o f car b o n l a y e r s on t h e " f r o n t " was 1.29 t 0.07k f o r t a r g e t IIC and 1.28 ± 0.05 f o r t a r g e t 1MB. A l t h o u g h t h e s e r e s u l t s a r e not c o n c l u s i v e , they do s u g g e s t t h a t e x t e n d i n g the c a r b o n t h i c k n e s s on t h e back o f the t a r g e t i s more e f f e c t i v e i n i n c r e a s i n g the " f i n a l a l p h a y i e l d " than e x t e n d i n g the c a r b o n t h i c k n e s s on the f r o n t o f t h e t a r g e t . I t may be noted t h a t t a r g e t 1MB has a poured ^ D i j n t h i c k n e s s o f 125 pg/cm 2, i n d i c a t i n g t h a t t h e phenomenon o c c u r s i n the same manner f o r t a r g e t s w i t h t h i c k e r as w e l l as t h i n n e r p o l y -e t h y l e n e l a y e r s . 3.4 P r o t o n Beam P r o f i l e 2.4.1 O p t i m i z a t i o n o f Measurement Parameters As e x p l a i n e d i n s e c t i o n 2.5.2, i n o r d e r t o l o c a t e the a l p h a and p r o t o n d e t e c t o r s a t t h e i r k i n e m a t i c a 1 1 y c o r r e s p o n d i n g a n g l e s , i t was n e c e s s a r y t o f i n d the c o r r e c t l o c a t i o n f o r t h e s o l i d s t a t e d e t e c t o r a ssembly. The r e s u l t s o f the o p t i m i z a t i o n p r o c e d u r e s a r e p r e s e n t e d i n F i g u r e s 24, 25, 26 and 27. In a l l c a s e s the e r r o r s i n the AC/C q u a n t i t i e s a r e d e t e r m i n e d from the sum o f t h e r e l a t i v e e r r o r s i n the AC and C s c a l e r c o u n t s . F i g u r e 24 i s a graph o f the r a t i o o f a n t i c o i n c i d e n c e t o c o i n c i d e n c e c o u n t s as a f u n c t i o n o f t h e s o l i d s t a t e d e t e c t o r assembly a n g l e . I t may be noted - 77 -2 3 4 2 3 5 2 3 B 2 3 7 2 3 8 2 3 9 2 4 0 241 SOLID STATE DETECTOR A S S E M B L Y A N G L E ( 0 ) F I G U R E 2k: THE RATIO OF A N T I C O I N C I D E N C E TO C O I N C I D E N C E COUNTS AS A F U N C T I O N OF THE S O L I D STATE DETECTOR A S S E M B L Y A N G L E - 78 -F I G U R E 25: 7 5 7.6 7 7 7.8 7.9 8.0 SOLID STATE DETECTOR HEIGHT(cm.) THE R A T I O OF A N T I C O I N C I D E N C E TO C O I N C I D E N C E COUNTS AS A F U N C T I O N OF THE S O L I D STATE DETECTOR HE IGHT - 79 -2 0 0 2 2 0 2 4 0 2 6 0 2 8 0 3 0 0 3 2 0 3 4 0 TIME D E L A Y I nanosec. ) F IGURE 26: THE RAT IO OF A N T I C O I N C I D E N C E TO CO INC IDENCE COUNTS AS A FUNCT ION OF THE T IME DELAY FOR THE PROTON PULSES i r 8 0 -I T " t.o 0.9 o.a-0.7 0.6 O \ o < 0.5 0-4 0.3 0.2 0.1 i r i r S o l i d S t a t e D e t e c t o r A s s e m b l y A n g l e = 2 4 0 . 5 ° \ \ \ \ I \ \ \ \ 1 0 0 k e V W i n d o w C e n t e r e d o n A l p h a P e a k f o r t h i s B a s e L i n e S e t t i n g J L _L J L J L J L 0.4 0.8 1.2 1.6 2.0 2 .4 2.8 B A S E LINE S E T T I N G 3.2 3.6 F I G U R E 2 7 : THE R A T I O OF A N T I C O I N C I D E N C E TO C O I N C I D E N C E COUNTS A S A FUNCTION OF THE BASE L I N E S E T T I N G FOR THE 1 0 0 keV WINDOW - 81 -t h a t t h e a n g u l a r numbers used a r e not k i n e m a t i c a 1 1 y c o r r e c t but a r e a n g l e s p e c u l i a r t o the chamber used and s e r v e o n l y t o a c c u r a t e l y d e f i n e the a n g u l a r s t e p s t a k e n . The minimum p o i n t on t h e c u r v e o c c u r r e d a t 2 3 7 - 5 ° and t h e c u r v e was symmetric about a v e r t i c a l l i n e drawn t h r o u g h t h i s p o i n t . T h i s i s t h e k i n e m a t i c a 1 1 y c o r r e c t a n g l e (i£. a c t u a l l y 9 6 . 2 ° ) and the d e t e c t o r assembly was t e m p o r a r i l y l o c a t e d a t 2 3 7 - 5 ° - 0 . 2 ° . F i g u r e 25 i s a graph o f the AC/C r a t i o as a f u n c t i o n o f the s o l i d s t a t e d e t e c t o r h e i g h t where t h i s h e i g h t i s d e f i n e d as the v e r t i c a l p o s i t i o n r e l a t i v e t o the p l a n e d e f i n e d by t h e 3He beam and t h e a x i s o f the p r o t o n d e t e c t o r . The minimum p o i n t on the c u r v e o c c u r r e d a t 7-7 cm and the c u r v e was s y m m e t r i c about a v e r t i c a l l i n e drawn t h r o u g h t h i s p o i n t . The a l p h a d e t e c t o r was p o s i t i o n e d a t 7 . 7 - 0 . 5 cm t h e r e b y l o c a t i n g i t i n the p l a n e d e f i n e d . F i g u r e 26 i s a graph o f t h e AC/C r a t i o as a f u n c t i o n o f the t i m e d e l a y ( i n nanoseconds) where t h i s d e l a y i s a d j u s t e d a t t h e p r o t o n channel T i m i n g SCA'. As e x p l a i n e d i n s e c t i o n 2 . 5 - 2 , i t was n e c e s s a r y t o d e l a y t h e " c o i n c i d e n t " p r o t o n p u l s e s t o l o c a t e t h e i r " z e r o - c r o s s o v e r " p o i n t s a t t h e same time as t h o s e o f the " c o i n c i d e n t " a l p h a p u l s e s . The minimum o f the graph was a f l a t r e g i o n 70 nanoseconds w i d e . T h i s wide v a l l e y i s due t o the r e s o l u t i o n o f the " c o i n c i d e n c e " e l e c t r o n i c s . T h i s l i m i t e d r e s o l u t i o n r e s u l t s p a r t i a l l y f r om the w i d t h o f the " f a s t " p u l s e s used i n t h e " f a s t c o i n c i d e n c e " e l e c t r o n i c s . The t i m e d e l a y was chosen as 265 i 0 . 5 nanoseconds c o r r e s p o n d i n g t o the c e n t r e o f the f l a t r e g i o n . - 82 -F i g u r e 27 i s a graph o f the AC/C r a t i o as a f u n c t i o n o f the base l i n e s e t t i n g on the a l p h a channel T i m i n g SCA f o r a g i v e n a n g l e o f t h e s o l i d s t a t e d e t e c t o r (S.S.D.) as s e m b l y . T h i s measurement was performed f o r s e v e r a l a n g u l a r p o s i t i o n s o f the S.S.D. assembly where the AC/C r a t i o was measured w h i l e sweeping t h e 100 keV window a c r o s s the a l p h a peak. T h i s s e r v e s as a f u r t h e r check o f the a n g u l a r p o s i t i o n o f the S.S.D. asse m b l y . For F i g u r e 27 t h e AC/C r a t i o minimum o c c u r r e d a t a base l i n e s e t t i n g o f 2.0 t 0.5 w h i c h c o r r e s p o n d e d t o the 100 keV window c e n t e r e d on the a l p h a peak. S i n c e t h i s was the opimum c o r r e l a t i o n , t h i s a n g l e o f the S.S.D. assembly (240.5° - 0.2°) was a c c e p t e d as the c o r r e c t one k i n e m a t i c a l l y . 3.4.2 H o r i z o n t a l P r o f i l e F i g u r e 28 p r e s e n t s t h r e e s e p a r a t e h o r i z o n t a l p r o f i l e s o f the p r o t o n beam. The " o b s e r v e " p r o f i l e i s the one measured u s i n g t h e c o l l i m a t o r d e v i c e and method d e s c r i b e d i n s e c t i o n 2.5. F o r t h i s p r o f i l e the r e l a t i v e i n t e n s i t i e s were d e t e r m i n e d by m e a s u r i n g t h e r a t i o C/(C + AC) f o r each p o s i t i o n o f t h e c o l l i m a t o r d e v i c e and n o r m a l i z i n g t h e s e i n t e n s i t y r a t i o s t o a peak i n t e n s i t y o f one. The e r r o r s i n the i n t e n s i t i e s were d e t e r m i n e d from t h e sum o f the r e l a t i v e e r r o r s o f the C and (C + AC) c o u n t s . In t h i s case the a b s o l u t e e r r o r o f the (C + AC) count v/as equated t o the s q u a r e r o o t o f t h e sum o f the squ a r e s o f the a b s o l u t e e r r o r s i n t h e C and AC count v a l u e s . The r e l a t i v e i n t e n s i t i e s were p l o t t e d as a f u n c t i o n o f the a n g l e from the c e n t r e o f the p r o t o n beam i n the h o r i z o n t a l d i r e c t i o n . These a n g l e s were d e t e r m i n e d f r o m t h e p o s i t i o n o f the c o l l i m a t o r o p e n i n g and the c o l l i m a t o r t o t a r g e t s p o t d i s -t a n c e . However t h e s e measurements were i n e f f e c t , d e t e r m i n i n g an i n t e g r a t e d - 83 -T T i-oh 0-9 OQl 07 t 0-G\ (ft Z UI I-z 0-5I" > £ o-4 03r 0-2 Ol P r o f i 1 e f r o m P r e v i o u s Work (Ho 68) O b s e r v e d P r o f i l e " T r u e " P r o f i l e ±4* - 8 ° FIGURE? 2 8 : ' 1 JZ> ' •6° -5° -4* . 3° _ 2° _j° 0 ° +.1° +2° +3° +4° +5° +6° +7° +8° ANGLE FROM BEAM CENTER HORIZONTAL P R O F I L E S OF PROTON BEAM - 84 -p r o f i l e s i n c e t h e c o l l i m a t o r o p e n i n g i s not o f a t o m i c s i z e but has a f i n i t e d i a m e t e r o f 0.125". Hence t h e o b s e r v e d i n t e n s i t y a t a p o i n t ( the p o i n t b e i n g chosen as t h e c e n t r e o f t h e c o l l i m a t o r o p e n i n g ) i s a c t u a l l y the i n t e g r a t e d i n t e n s i t y o v e r t h e c o m p l e t e s u r f a c e o f the c i r c u l a r c o l l i m a t o r o p e n i n g . S i n c e t h e p r o f i l e i s r e l a t i v e l y s h a r p , such an i n t e g r a t i n g p r o c e s s w i l l tend t o widen t h e " t r u e " p r o f i l e . To t e s t t h i s e f f e c t , an " i n t e g r a t i n g p r o c e s s " was c a r r i e d out on the " o b s e r v e d " p r o f i l e by f i r s t assuming t h a t i t was the " t r u e " p r o f i l e ( t h e r e s u l t s o f the t e s t a r e not p r e s e n t e d here i n g r a p h i c a l f o r m ) . For each o b s e r v e d p o i n t , a measurement o f the a r e a bounded by the p r o f i l e c u r v e and v e r t i c a l l i n e s 1.85° on e i t h e r s i d e o f the a n g u l a r p o s i t i o n o f t h e p o i n t was t a k e n as t h e i n t e g r a t e d i n t e n s i t y f o r the p o i n t . The f i g u r e 1.85° was chosen because the c o l l i m a t o r o p e n i n g subtends a h a l f a n g l e o f 1.85° a t the t a r g e t . These new " i n t e g r a t e d i n t e n s i t i e s " were n o r m a l i z e d t o a peak i n t e n s i t y o f one and p l o t t e d on a d i a g r a m w i t h the " o b s e r v e d " p r o f i l e . The c o n s t r u c t e d p r o f i l e was w i d e r than the o b s e r v e d p r o f i l e . To a l l o w f o r t h i s i n t e g r a t i n g e f f e c t , th e " o b s e r v e d " p r o f i l e o f F i g u r e 28 was narrowed by an amount equal t o the measured s p r e a d i n g e f f e c t o f t h e " c o n s t r u c t e d " p r o f i l e . T h i s new p r o f i l e was d e s i g n a t e d t h e " t r u e " p r o f i l e on the g r a p h . As a c r o s s check o f t h i s method, t h e " t r u e " p r o f i l e i n t h e f i g u r e was s u b j e c t e d t o the same i n t e g r a t i n g p r o c e s s j u s t d e s c r i b e d (i.e. c a l c u l a t i n g t h e a r e a s e t c . ) , and the r e s u l t a n t " c o n s t r u c t e d " p r o f i l e c o i n c i d e d w i t h the " o b s e r v e d " p r o f i l e t h e r e b y con-f i r m i n g the p r o c e d u r e . The p r o f i l e from p r e v i o u s work (Ho 68) r e p r e s e n t s the r e s u l t s u s i n g a s o l i d i c e D20 copper backed t a r g e t as e x p l a i n e d i n s e c t i o n 1.1. As e x p l a i n e d i n - 85 -s e c t i o n 2.5.2 (and i n t h e r e s u l t s i n 3-4.1), measurements o f t h e a t t e n u a t i o n ( v i a t h e r a t i o A C / C ) as a f u n c t i o n o f t h e a n g u l a r and v e r t i c a l p o s i t i o n s o f t h e s o l i d s t a t e d e t e c t o r a s s e m b l y were used t o p o s i t i o n i t . In t h i s c a s e H o j v a t (68) a l s o used t h e s e measurements to o b t a i n t h e a n g u l a r p r o f i l e o f t h e p r o t o n beam. U s i n g t h e 2 H ( 3 H e , p ) ^ H e r e a c t i o n ' s k i n e m a t i c a l r e l a t i o n s ( e . g . s e e F i g u r e s 1, 2 and 3) he was a b l e t o t r a n s l a t e a c h a n g e i n t h e a n g u l a r p o s i t i o n o f t h e 4 H e d e t e c t o r i n t o t h e c o r r e s p o n d i n g s h i f t i n t h e a n g u l a r p o s i t i o n o f t h e p r o t o n beam [ n o t e t h a t " t h e a s s y m e t r y o b s e r v e d i n t h e f i g u r e f o r t h e h o r i z o n t a l p r o f i l e was p r o d u c e d by a c h a n g e o f heavy i c e t a r g e t t h i c k n e s s d u r i n g t h a t p a r t i c u l a r r u n " (Ho 68)]. A com-p a r i s o n o f t h e " f u l l w i d t h a t h a l f maximum" o f t h e " t r u e " p r o f i l e and t h e " p r e v i o u s w o r k " p r o f i l e was an i n d i c a t i o n o f t h e r e d u c e d e l a s t i c s c a t t e r i n g a c c o m p l i s h e d by use o f t h e s e l f - s u p p o r t e d t a r g e t r a t h e r t h a n t h e c o p p e r b a c k e d t a r g e t . T h e f u l l w i d t h , a t a r e l a t i v e i n t e n s i t y o f 0.5, was 8.5° f o r t h e " p r e v i o u s " p r o f i l e and 3-5° F o r t h e " t r u e " p r o f i l e . T h i s i m p l i e s t h a t t h e s p r e a d i n g o f t h e h o r i z o n t a l p a r t o f t h e p r o t o n beam was r e d u c e d by 59% ( i . e . by a f a c t o r o f 2.43), t h r o u g h t h e use o f t h e s e l f - s u p p o r t i n g c a r b o n b a c k e d t a r g e t . T h e r e f o r e , t h i s i m p l i e s t h a t f o r f u t u r e p r o t o n r e a c t i o n c r o s s s e c t i o n m e a s u r e m e n t s , t h e s o l i d a n g l e s u b t e n d e d by t h e p r o t o n d e t e c t o r c o u l d a l s o be r e d u c e d by a f a c t o r o f 2.43- The r e s u l t i n g a t t e n u a t i o n , due t o p r o t o n s s c a t t e r e d i n t h e c a r b o n b a c k i n g i n t o a n g l e s l a r g e r t h a n t h o s e . s u b t e n d e d by t h e d e t e c t o r , s h o u l d s t i l l be <5 x 10~5 as d e s i r e d (see s e c t i o n 1.1). 3.4.3 V e r t i c a l P r o f i l e F i g u r e 29 p r e s e n t s t h r e e s e p a r a t e v e r t i c a l p r o f i l e s o f t h e p r o t o n beam. The measurements a r e f r o m t h e same s o u r c e s as d e s c r i b e d f o r t h e h o r i z o n t a l - 86 -l O h ANGLE FROM BEAM CENTER F I G U R E 29: V E R T I C A L P R O F I L E S OF PROTON BEAM - 87 -p r o f i l e s ( s e c t i o n 3.4.2). In t h i s c a s e t h e r e s u l t s a r e i n c o n c l u s i v e s i n c e the i n i t i a l " s t e p s " t a k e n about t h e p r o t o n beam c e n t r e i n t h e v e r t i c a l d i r e c t i o n were too l a r g e t o d e f i n e the p r o f i l e a c c u r a c t e l y . That i s , the v e r t i c a l p r o f i l e was so narrow t h a t the r e l a t i v e i n t e n s i t y was reduced t o z e r o when t h e c o l l i m a t o r o p e n i n g was moved one " s t e p " ( i . e . the o p e n i n g was c e n t e r e d on a p o i n t 3-70° from the beam c u r r e n t ) on e i t h e r s i d e o f t h e beam c e n t r e . An " i n t e g r a t i n g p r o c e s s " (as d e s c r i b e d f o r the h o r i z o n t a l p r o f i l e ) was c a r r i e d o u t on t h e " o b s e r v e d " p r o f i l e y i e l d i n g the " t r u e " p r o f i l e . The o n l y c o n c l u s i v e remark t o be made i s t h a t the a c t u a l v e r t i c a l p r o t o n beam p r o f i l e i s a t l e a s t as narrow as t h e " t r u e " p r o f i l e and may be n a r r o w e r . The v a l u e o f t h e " f u l l w i d t h a t h a l f maximum" was 6.7° f o r the " p r e v i o u s " p r o f i l e as compared w i t h 3.2° f o r t h e " t r u e " p r o f i l e . T h i s i m p l i e s a r e d u c t i o n i n t h e s p r e a d i n g o f the v e r t i c a l p a r t o f t h e p r o t o n beam by " a t l e a s t " 52% t h r o u g h use o f the s e l f - s u p p o r t i n g t a r g e t s . - 88 -CHAPTER IV CONCLUSIONS AND SUGGESTIONS h. 1 G e n e r a l C o n c l u s i o n s The (C 2 D t f)n " s a n d w i c h " t a r g e t d e s i g n , d e v e l o p e d by p o u r i n g the p o l y e t h y l e n e w h i l e i n s o l u t i o n , r e s u l t s i n m e c h a n i c a l l y s t r o n g e r t a r g e t s than t h o s e t a r g e t s produced by e v a p o r a t i n g the p o l y e t h y l e n e . In a d d i t i o n , the p o u r i n g t e c h n i q u e d e s c r i b e d i n t h i s t h e s i s ( s e c t i o n 2.2.2) i s 83% more e c o n o m i c a l than the e v a p o r a t i n g t e c h n i q u e . T h i s i s p r i m a r i l y due t o the l a r g e r number o f "poured" t a r g e t s produced f o r a g i v e n q u a n t i t y o f ( C 2 D i + ) n as w e l l as the 65% h i g h e r s u c c e s s r a t e f o r s t r i p p i n g and mounting. The poured and e v a p o r a t e d ( C 2 D i + ) n t a r g e t s a r e e s s e n t i a l l y o f equal d i f f i c u l t y t o produce as re g a r d s t o tim e and e f f o r t . They both appear t o be e q u a l l y e f f e c t i v e i n t h e i r p e r f o r -mance when s u b j e c t e d t o a 3He beam as measured by t h e i r a l p h a y i e l d c u r v e s , t o t a l t h i c k n e s s l o s s e s and d e u t e r i u m l o s s e s . The use o f a q u a r t z r e s o n a t o r t h i c k n e s s m o n i t o r produced the most a c c u r a t e t h i c k n e s s d e t e r m i n a t i o n s f o r the carb o n l a y e r s o f both d e s i g n s . The c o n c l u s i o n i s t h a t the " s a n d w i c h " t a r g e t d e s i g n i n v o l v i n g p o u r i n g o f the p o l y e t h y l e n e i s a b e t t e r p r o c e s s than t h e d e s i g n i n v o l v i n g e v a p o r a t e d p o l y e t h y l e n e , a l t h o u g h the l a t t e r p r o c e s s e n a b l e s 6% more a c c u r a t e measurements o f the ( C 2 D t | ) n t h i c k n e s s . T h i s a c c u r a c y d i f -f e r e n c e would be reduced t o 1% through a b e t t e r w e i g h i n g t e c h n i q u e and c a r b o n e v a p o r a t i o n geometry as e x p l a i n e d i n s e c t i o n 3-2. The l i m i t e d t e s t i n g on "cross-1 i n k i n g " o f the ( C 2 D i + ) n polymer c h a i n s t h r o u g h gamma r a d i a t i o n i n d i c a t e s t h a t t h i s p r o c e s s may be e f f e c t i v e i n s t r e n g t h e n i n g the t a r g e t s . - 89 -Carbon l a y e r s e v a p o r a t e d o n t o both s i d e s o f the ( C 2 D i t ) n f i l m o f f e r m e c h a n i c a l r i g i d i t y t o the t a r g e t s , as w e l l as e l e c t r i c a l and thermal c o n d u c t i v i t y . T h e i r main importance i s t h a t they i n h i b i t the e v a p o r a t i o n o f the C 2 D 4 m o l e c u l e s as a whole from the p o l y e t h y l e n e f i l m t h e r e b y p r o v i d i n g t a r g e t s t a b i l i t y . The s t r e n g t h e n i n g e f f e c t o f t h e carbon l a y e r s i s such t h a t the t a r g e t s were a b l e t o w i t h s t a n d beam c u r r e n t d e n s i t i e s o f 5 t o 10 yA/cm 2 f o r s e v e r a l hours ( d u r i n g the measurements) w i t h o u t d e s t r u c t i o n o r w i t h o u t a marked change i n the t y p i c a l s l o w a l p h a y i e l d d e c r e a s e . Moreover, d u r i n g i s o l a t e d t e s t s , the t a r g e t s d i d w i t h s t a n d beam c u r r e n t d e n s i t i e s o f 50 yA/cm 2 f o r one hour and the r e s u l t i n g r e l a t i v e l y undamaged appearance o f t h e t a r g e t s i n d i c a t e d t h e y c o u l d have w i t h s t o o d even g r e a t e r beam d e n s i t i e s . A l l the b a s i c "sandwich", t a r g e t s o f both 45 yg/cm 2 and 135 yg/cm 2 t h i c k p o l y e t h y l e n e (poured and e v a p o r a t e d ) , e x h i b i t the same t a r g e t d e t e r i o r a t i o n c h a r a c t e r i s t i c s as f o l l o w s : ( i ) An i n i t i a l r a p i d d e c r e a s e i n the a l p h a y i e l d o v e r the f i r s t 150 yc o f t o t a l i n t e g r a t e d 3He beam c u r r e n t on t a r g e t , r e f l e c t i n g an i n i t i a l l a r g e d e u t e r i u m l o s s o f up t o 93%. ( i i ) S t a b i l i z a t i o n o f the d e t e r i o r a t i o n between 150 t o 200 yc w i t h t h e a l p h a y i e l d e x h i b i t i n g a s l o w d e c r e a s e o f l e s s than 0.05% per yc d u r i n g subsequent beam bombardment, ( i i i ) A l o s s i n the t o t a l t a r g e t t h i c k n e s s o f 30 t o 40% o v e r t h e f i r s t 300 yc w i t h a l m o s t 100% o f t h i s l o s s o c c u r r i n g i n the f i r s t 150 y c . The l a r g e d i s c r e p a n c y between the l o s s o f t o t a l t a r g e t m a t e r i a l and the l o s s o f d e u t e r i u m i m p l i e s t h a t a l a r g e f r a c t i o n o f the CgD^ m o l e c u l e s i n t h e t a r g e t were f i r s t broken i n t o t h e i r c arbon and d e u t e r i u m components by - 90 -i n t e r a c t i o n s w i t h the 3He beam. T h i s p r o c e s s then r e s u l t e d i n a l a r g e f r a c t i o n o f d e u t e r i u m atoms d i f f u s i n g out o f the t a r g e t s whereas most o f the c a r b o n atoms from the p o l y e t h y l e n e remained i n the t a r g e t . A f t e r the i n i t i a l t a r g e t d e t e r i o r a t i o n , the d e u t e r i u m atoms s t i l l r e m a i n i n g i n t h e t a r g e t c o u l d be p a r t l y i n the o r i g i n a l C^D^form and p a r t l y i n the form o f d e u t e r i u m atoms (or m o l e c u l e s ) t r a p p e d i n the carbon i n the t a r g e t . The o b s e r v a t i o n s o f the i n c r e a s e d " f i n a l a l p h a y i e l d s " w i t h i n c r e a s i n g t h i c k n e s s o f the ca r b o n l a y e r s on e i t h e r the "back" o r the " f r o n t " o f the t a r g e t i n d i c a t e t h a t indeed a l a r g e f r a c t i o n o f the d e u t e r i u m from the C 2 n i 4 m o l e c u l e s seems t o be t r a p p e d i n t h e c a r b o n . I t i s s u g g e s t e d (from the co m p a r i s o n o f the t e s t s on " t h i n " and " t h i c k " t a r g e t s i n s e c t i o n 3-3.1) t h a t the d e u t e r i u m m i g r a t e s t h r o u g h o u t the t a r g e t and i s t r a p p e d by the ca r b o n t o a c o n c e n t r a t i o n o f 0.11 d e u t e r i u m atoms per ca r b o n atom. I f the d e u t e r i u m atoms m i g r a t e by an a p p r o x i m a t e l y i s o t r o p i c d i f f u s i o n o n l y , the i n c r e a s e i n " f i n a l a l p h a y i e l d " s h o u l d be independent o f the l o c a t i o n o f the c a r b o n i n the t a r g e t s a n d w i c h . The o b s e r v e d l i n e a r dependenceof F i g u r e 23 (the r a t i o o f the " f i n a l a l p h a y i e l d s " as a f u n c t i o n o f the number o f 10 yg/cm 2 c a r b o n l a y e r s on the back o f the t a r g e t ) c o r r e s p o n d e d t o an a v e r -age f a c t o r i n c r e a s e i n the " f i n a l a l p h a y i e l d " o f 1.83 - 0.35 per ca r b o n l a y e r o n the back o f the t a r g e t . S i m i l a r t e s t i n g f o r ca r b o n l a y e r v a r i a t i o n on the f r o n t r e s u l t e d i n a f a c t o r i n c r e a s e i n the " f i n a l a l p h a y i e l d " o f 1.38 t 0.26 per ca r b o n l a y e r on t h e f r o n t . In a d d i t i o n t a r g e t s were t e s t e d i n d i v i d u a l l y f o r comparison of the " f i n a l a l p h a y i e l d " i n c r e a s e s f o r both back and f r o n t c a r b o n t h i c k n e s s v a r i a t i o n . The " f i n a l a l p h a y i e l d " per ca r b o n - 91 -l a y e r was c o n s i s t e n t l y lower f o r the l a y e r s on the f r o n t o f the t a r g e t s as compared w i t h t h o s e on the back. A l t h o u g h t h e s e r e s u l t s a r e not c o n c l u s i v e , they s u g g e s t an a d d i t i o n a l p r o c e s s o t h e r than merely i s o t r o p i c d i f f u s i o n o f the d e u t e r i u m atoms w i t h i n t h e t a r g e t . A c a l c u l a t i o n o f t h e k i n e m a t i c p arameters f o r the e l a s t i c s c a t t e r i n g o f 3He on d e u t e r i u m and a c o n s i d e r a t i o n o f the ranges o f the s c a t t e r e d 2 H i n t h e t a r g e t m a t e r i a l , y i e l d e d the f o l l o w i n g r e s u l t : based on the l a r g e s t t a r g e t t h i c k n e s s used and the d e u t e r i u m atom s c a t t e r e d a t an a n g l e o f 2k.2° w i t h an energy o f 552 keV ( t h e s c a t t e r e d d e u t e r i u m atoms were k i n e m a t i c a 1 1 y r e s t r i c t e d t o a " f o r w a r d cone" o f h a l f - a n g l e 24.2°), the range of t h i s atom was a p p r o x i m a t e l y f i v e t i m e s g r e a t e r than t h e amount o f t a r g e t s t o p p i n g m a t e r i a l " p r e s e n t e d " t o i t . Hence d e u t e r i u m atoms t h a t have a s i g n i f i c a n t amount o f momentum t r a n s f e r r e d t o them would be s c a t t e r e d c o m p e t e l y out o f the t a r g e t and t h e r e f o r e would not c o n t r i b u t e t o the m i g r a t i o n o f t h e deu-t e r i u m atoms w i t h i n t h e t a r g e t . The r e s u l t s o f the carbon l a y e r v a r i a t i o n s t u d y s u g g e s t t h a t a t a r g e t w i t h the d e s i r e d h i g h " f i n a l a l p h a y i e l d " c o u l d be o b t a i n e d t h r o u g h the use o f v e r y t h i c k c a r b o n l a y e r s i n t h e " s a n d w i c h " t a r g e t . However f o r the purposes o f t h i s e x p e r i m e n t (and f u t u r e t o t a l p r o t o n r e a c t i o n c r o s s s e c t i o n e x p e r i -m e n t s ) , the t a r g e t t h i c k n e s s i s l i m i t e d by the r e q u i r e m e n t o f a 100 keV energy l o s s f o r a 690 keV He beam, as e x p l a i n e d i n s e c t i o n 1.1 f o r good p r o t o n beam c o l l i m a t i o n . P r e v i o u s measurements (Ho 68) i n t o t a l p r o t o n r e a c t i o n c r o s s s e c t i o n s t u d i e s , u s i n g a copper backed heavy i c e t a r g e t , r e q u i r e d the p r o t o n d e t e c t o r t o sub-- 92 -tend a. ha.l.f. ang.le of. rl fl °. a t . the t a r g e t . The angle-was chosen s o - t h a t the a t t e n u a t i o n -S o f the. p r o t o n beam, due t o the p r o t o n s s c a t t e r e d i n the copper i n t o a n g l e s l a r g e r than 1 1 ° , was < 5 x 1 0 ~ 5 as d e s i r e d (see s e c t i o n 1 . 1 ) . The use o f a s e l f - s u p p o r t i n g c a r b o n backed (C 2D t +)n t a r g e t s h o u l d reduce t h i s r e q u i r e d a n g l e o f the p r o t o n d e t e c t o r . By i n t e g r a t i n g t he d i f f e r e n t i a l s c a t t e r i n g c r o s s s e c t i o n f o r 1 2 C ( p , p ) 1 2 C [where E (p) = 1 5 . 2 MeV] and u s i n g a c a r b o n backing layer, thickness o f 2 0 yg/cm2,- the a t t e n u a t i o n , 6, due,.to. scattering of, the. protons by this .carbon -layer, was c a l c u l a t e d .for d i f f e r e n t v a l u e s o f t h e ha 1 f - a n g 1 e 6 subtended by the p r o t o n d e t e c t o r . The r e s u l t s a r e p r e s e n t e d i n T a b l e 4 . TABLE 4 : A t t e n u a t i o n 6 o f the P r o t o n Beam (due t o S c a t t e r i n g ) f o r D i f f e r e n t H a l f A n g l e s 6 , , , Subtended by the P r o t o n D e t e c t o r . / . ' - T r H l o i f : : „ a . ,Ha\ft-Arjg.1 e_t e . . ( . . . . , • A t t e n u a t i o n :<5; ; . • ••• . . • • " 4 ° ' 6° 7 ° i 8 ° • ; . • }..• ; • . • .• 2 0 ° ' R ; •-I t i s i l l u s t r a t e d i n the t a b l e t h a t t o a c h i e v e t h e re q u i r e m e n t o f 6 < 5 x 1 0 5 , t h e h a l f a n g l e subtended by the p r o t o n d e t e c t o r c o u l d be r e -duced from 1 1 ° t o 7 ° - C o n s e q u e n t l y the s o l i d a n g l e subtended by the p r o t o n d e t e c t o r would be reduced by a f a c t o r o f 2 . 4 7 . T h i s r e s u l t a g r ees f a v o u r a b l y 5 . 5 0 x 10 5 5.12 x 10"5 4.95 x 10"5 4.80 x 10"5 '4.48 x IO"5 3.15 x'10~5 - 93 -w i t h the r e s u l t s o f t h e p r o t o n h o r i z o n t a l p r o f i l e measurements (see s e c t i o n 3.4.2). The o b s e r v e d r e d u c t i o n i n the s p r e a d i n g o f t h e p r o t o n beam, compared w i t h the h o r i z o n t a l p r o f i l e o b t a i n e d u s i n g a c opper backed t a r g e t ( H 0 6 8 ) , i m p l i e d t h a t the s o l i d a n g l e subtended by the p r o t o n de-t e c t o r c o u l d be reduced by a f a c t o r o f 2.43 and the c o n d i t i o n 6 < 5 x 10 5 would s t i l l be r e t a i n e d . A r e d u c t i o n o f t h e s o l i d a n g l e by a f a c t o r o f 2.47 (as c a l c u l a t e d above) would a l s o reduce t h e n o n - c o i n c i d e n t background p r o t o n f l u x i n c i d e n t on t h e d e t e c t o r by a f a c t o r o f 2.47. T h i s would reduce an i n c i d e n t p r o t o n f l u x o f 70 x 103 S 1 t o 28.3 x 103 S 1 . A c c o r d -i n g l y , t h e f r a c t i o n o f c o u n t s t r a n s m i t t e d by the " p a r a l y z a b l e dead t i m e " g a t e would be i n c r e a s e d from 0.35 t o 0.63 [see (Ho 68) f o r t h i s f u n c t i o n a l , r e l a t i o n s h i p ] . T h i s r e p r e s e n t s a f a c t o r i n c r e a s e i n t h e c o i n c i d e n t count r a t e o f 1.80. A f t e r 8 t o 10 hours o f 3He bombardment a t beam c u r r e n t d e n s i t i e s o f 10 uA/cm 2, t h e c o i n c i d e n t count r a t e u s i n g the ( C ^ D i J n " s a n d w i c h " t a r g e t [where the ( C 2 D i + ) n t h i c k n e s s was 45 yg/cm 2] was 1.7 x I03 yA 1 S 1 as compared w i t h 1.0 x 103 yA 1 S 1 f o r the copper-^backed heavy i c e t a r g e t under s i m i l a r c o n d i t i o n s . T h i s r e p r e s e n t s a f a c t o r i n c r e a s e o f 1.7 i n t h e c o i n c i d e n t count r a t e due t o t h e g r e a t e r number o f d e u t e r i u m atoms a v a i l -a b l e i n t h e ( C 2 D i t ) n t a r g e t as compared w i t h the heavy i c e t a r g e t . Hence, use o f the s e l f - s u p p o r t i n g ( C 2D t t)n " s a n d w i c h " t a r g e t and t h e s u b s e -quent a l l o w a b l e r e d u c t i o n of the a n g l e subtended by the p r o t o n d e t e c t o r would p r o v i d e an i n c r e a s e by a f a c t o r o f 3.5 (as compared w i t h t h e heavy i c e c o p p e r - b a c k e d t a r g e t usage) i n the c o i n c i d e n t count r a t e t r a n s m i t t e d - 3k -t h r o u g h the "dead time g a t e " . For t o t a l p r o t o n r e a c t i o n c r o s s s e c t i o n measurements, t h i s i n c r e a s e i n the c o u n t i n g would r e s u l t i n a r e d u c t i o n o f the e r r o r s t o 57% o f t h e p r e v i o u s e x p e r i m e n t a l e r r o r s (Ho 68) o f the a t t e n u a t i o n d i f f e r e n c e measurements f o r the same " r u n n i n g t i m e " . The un-c e r t a i n l y i n t h e c r o s s s e c t i o n v a l u e s would thus be reduced by 43% f o r the same " r u n n i n g t i m e " . 4.2 S u g g e s t i o n s f o r F u r t h e r Study The r e s u l t s o f t h i s t h e s i s w a r r a n t f u r t h e r t o t a l p r o t o n r e a c t i o n c r o s s s e c t i o n measurements u s i n g the a s s o c i a t e d p a r t i c l e t e c h n i q u e and " c o i n c i -dence e l e c t r o i c s " [as d e v e l o p e d by C. H o j v a t (Ho 68)]. For t h e s e measure-ments the use o f a s e l f - s u p p o r t i n g d e u t e r a t e d p o l y e t h y l e n e " s a n d w i c h " t a r g e t [ o f a (C 2 ni+)n t h i c k n e s s e q u a l t o 45 yg/cm 2] would reduce the un-c e r t a i n t y i n t h e c r o s s s e c t i o n v a l u e s by 43% f o r the same " r u n n i n g t i m e " . I t i s s u g g e s t e d t h a t t h e p o l y e t h y l e n e l a y e r be e n c l o s e d i n a 20 yg/cm 2 t h i c k c a r b o n l a y e r on both s i d e s t o i n c r e a s e the " f i n a l a l p h a y i e l d " (based on t h e e x p e r i m e n t a l r e s u l t s of t h i s t h e s i s , i t can be shown t h a t a f t e r 300 yc o f 3He bombardment, t h i s " s a n d w i c h " t a r g e t m a t e r i a l w i l l r e p r e s e n t a 100 keV energy l o s s t o a 690 keV 3He beam as d e s i r e d ) . An extended i n v e s t i g a t i o n o f the phenomena, r e f l e c t e d by the i n c r e a s e d " f i n a l a l p h a y i e l d s " w i t h t h i c k e r c a r b o n l a y e r s ( i n t h e t a r g e t " s a n d w i c h " ) , i s needed. There a r e s e v e r a l i n t e r e s t i n g q u e s t i o n s i m p l i e d by the r e s u l t s w h i c h s h o u l d be p u r s u e d . A few o f t h e s e a r e as f o l l o w s : ( i ) Is t h e r e an upper l i m i t t o the g a i n t h a t can be a c h i e v e d by a d d i n g e x t r a c a r b o n l a y e r s , and i f so a t what c a r b o n t h i c k n e s s ? ( i f ) How would the " f i n a l a l p h a y i e l d " be a f f e c t e d , i f v e r y t h i n - 95 -(0 .1 t o 2 yg/cm 2) i n i t i a l c a r b o n l a y e r s were i n c o r p o r a t e d i n th e " s a n d w i c h " t a r g e t ? ) What a r e the mechanisms by w h i c h the d e u t e r i u m appears t o m i g r a t e and i s t r a p p e d by the carbon? ) Would a t a r g e t composed o f a l t e r n a t i n g l a y e r s o f ( C 2 D i t ) n and c a r b o n produce the optimum r e s u l t s , as r e g a r d s t o t a r g e t p e r -formance, i n v i e w o f the o b s e r v e d phenomenon? - 96 -BIBLIOGRAPHY Ar 66 G.T. A r n i s o n , N u c l . I n s t r . and Meth. 40_ (1966) 359. Ca 69 C a n b e r r a I n d u s t r i e s , 50 S i l v e r S t . , Midd1etown, C o n n e c t i c u t . De 69 D e u t e r a t e d p o l y e t h y l e n e (>S8% D) o b t a i n e d from Merck, Sharp and Dohme o f Canada L t d . , M o n t r e a l , Quebec. E l 69 E l d o r a d o E l e c t r o n i c s , B e r k e l e y , C a l i f o r n i a . Ho 68 C F . H o j v a t , N u c l . I n s t r . and Meth. 66_ ( l 968) 13 C F . H o j v a t , Ph.D. T h e s i s , U n i v e r s i t y o f B r i t i s h C olumbia (1967) -Ko 66 E.H. K o b i s k , N u c l e o n i c s 24 (1966) 122. Ku 55 W.E. Kunz, Phys. Rev. 97 (1955) 456. Ma 67 S.H. Maxman, N u c l . I n s t r . and Meth. 50. (1967) 53-Ma 69 R.D. M a t h i s Co., 2840 Gundry Ave., Long Beach, C a l i f o r n i a 90806. Nu 60 N u c l e a r Data T a b l e s , P a r t 3 (i960), ed. J.B. M a r i o n ( N a t i o n a l Academcy o f S c i e n c e s , N a t i o n a l Research C o u n c i l I960). Nu 69 N u c l e a r Data I n c . , P.O. Box 451, P a l o t i n e , I l l i n o i s 6OO67. 01 67 M.A. O l i v o and C M . B a i l e y , N u c l . I n s t r . and Meth. 57. (1967) 353-Or 69 Oak Rid g e T e c h n i c a l E n t e r p r i s e s C o r p o r a t i o n , Oak R i d g e , Tennessee. Pr 67 P r o g r e s s i n Polymer S c i e n c e Vol 1, ed. A.D. J e n k i n s (Pergamon P r e s s 1967). SI 69 S l o a n I n s t r u m e n t s Co., Santa B a r b a r a , C a l i f o r n i a . T r 67 G.E. T r i p a r d and B.L. W h i t e , Rev. S c i . I n s t r . 38. (1967) 435. Wh 58 W. W h a l i n g , Handbuch. d e r P h y s i k ( S p r i n g e r - V e r l a g , 1958, rev 1962). Wh 65 M. Wh i t e , Vacuum ]5_ (1965) 449. Ya 62 L. Y a f f e , Annual Rev. o f N u c l . Sc. 12 (1962) 153-- 97 -APPENDIX A ( C 2 D i J n THICKNESS REQUIREMENT The t h i c k n e s s o f the (C 2D [ +)n f i l m i s r e q u i r e d t o r e p r e s e n t a 100 keV energy l o s s t o an i n c i d e n t 690 keV 3He beam. The r e q u i r e d t h i c k n e s s yg/cm 2 i s c a l c u l a t e d from a c o n s i d e r a t i o n o f t h e a t o m i c (or m o l e c u l a r s t o p p i n g c r o s s s e c t i o n s e f o r 3He i n ( C 2 D [ + ) n . To d e t e r m i n e the e f o r 3He, we use t h e r e l a t i o n from (Nu 60) ( 3He) z 2 e ( p r o t o n ) E/3 where z 2 from (Nu 60) f o r an E o f 690 keV i s z 2 = 3.11 The v a l u e s f o r e from (Wh 58) a r e s For c a r b o n : e( 3He) 690 keV = 3.11 x E ( p r o t o n ) 230 keV = 3.1 1 x 12 x I O " 1 5 — cm-" atom For hydrogen: e ( 3 H e ) 690 keV = 3.11 x e ( p r o t o n ) 230 keV = 3.H x 3.4 x 10 • 15 £ V _ c m 2 atom In g e n e r a l , f o r t h e m o l e c u l a r s t o p p i n g c r o s s s e c t i o n o f compounds, Emol ( X n Y m ) n e(X) , + m e(Y) ^ atom atom .'. f o r a C 2 DL. m o l e c u l e : £(0201,) = 2 x E(C ) + 4 x e ( H ) - 98 -and f o r an i n c i d e n t 3He beam o f 69O keV, e(C2Uk) = 2 x 3.11 x 12 x 1 0 " 1 5 + 4 x 3.11 x 3 . 4 x 1 0 " 1 5 - 116.936 x 1 0 - 1 5 « V c f m o l e c u l e For a polymer c h a i n o f (C 2Di+)n whose degree o f p o l y m e r i z a t i o n i s d e t e r -mined by the s u b s c r i p t n, the m o l e c u l a r s t o p p i n g c r o s s s e c t i o n i s e [ ( C 2 D i t ) n ] = n x e ( C 9 . D 4 ) = n x 116.936 x I O " 1 5 e V ~ C ? moiecu 1e R e c a l c u l a t e e i n terms o f ev - cm 2 per gm o f s t o p p i n g m a t e r i a l ev - cm z c ? i ev - crrr no. o f m o l e c u l e s gm J — £ moiecu 1e x gm For ( C 2 D 4 ) n t h i s becomes = n x E (C 2 D I + ) x n x ^ ^ 2 ' ^ = Avagadro's number e ( C 2 D u ) x A 32 D i v i d i n g t h e energy l o s s AE = 100 keV = 1 0 5 ev by eQ r e s u l t s i n t h e r e q u i r e d t h i c k n e s s o f ( C 2 D [ + ) n i n gm/cm2 AE (ev) = 1 0 5 x 32 e 0 (ev - cm2/gm) e ( C 2 D T T ) x A 1 0 5 x 32 ' I 16.936 x 1 0 " 1 3 x 6 . 0 2 5 x 1023 = 4 5 . 5 x 1 0 " 6 gm/cm2 .'.the r e q u i r e d t h i c k n e s s o f ( C 2 D L,)n i s 4 5 - 5 yg/cm 2. - 99 -APPENDIX B ENERGY LOSS OF THE 3 H E BEAM IN A CARBON FILM The e n e r g y l o s s o f a 690 keV 3 H e beam i n a c a r b o n f i l m o f a g i v e n t h i c k -n e s s i n y g / c m 2 i s d e t e r m i n e d by c o n s i d e r i n g t h e a t o m i c s t o p p i n g c r o s s s e c t i o n e f o r 3 H e i n c a r b o n . To d e t e r m i n e t h e e f o r 3 H e we use t h e r e l a t i o n from (Nu 60) z 2 e ( p r o t o n ) e(3He) E/3 where z 2 f r o m (Nu 60) f o r an E = 690 keV i s z 2 = 3 - H F o r c a r b o n : e ( 3 H e ) f r o m (Wh 58), 690 keV 3.11 x e ( p r o t o n ) 230 keV = 3.11 x 12 x 1 0 " 1 5 37.32 x 10-15 e y - c m atom R e c a l c u l a t e e i n terms o f ev - c m 2 p e r gm o f s t o p p i n g m a t e r i a l ev - cm 21 ( 9\ !ev - cm^ gm F o r c a r b o n t h i s becomes atom n o . o f atoms gm A E X T2 = 3 7 . 3 2 X 1 0 " 1 5 X y 2 , A = A v o g a d r o ' s number M u l t i p l y i n g e 0 t i m e s t h e t h i c k n e s s o f c a r b o n i n g m / c m 2 y i e l d s t h e e n e r g y l o s s o f t h e 3 H e beam i n ev - 100 -.". t h e e n e r g y l o s s AE i n keV o f ,a 6.90 i.keV 3 H e beam as a f u n c t i o n o f t h e c a r b o n f i l m t h i c k n e s s do ( y g / c m 2 ) t h r o u g h w h i c h i t i s p a s s i n g i s : A E ( k e V ) J 3 7 . 3 2 x 1 0 ~ 1 5 x 6 . 0 2 5 x 1 0 2 3 . 103 x 12 c M9 —"rt" cm-To^ A E ( k e V ) = 1 . 8 8 x d 0 ( y g / c m 2 ) efl.. : f o r a c a r b o n f i l m t h i c k n e s s o f 10 y g / c m 2 , t h e e n e r g y l o s s s u f f e r e d by the- 3 He, .beam i,.s.,Uin 1 . 8 8 ;x 10 = 1 8 . 8 , k e V . . . j | , ; v - 101 -APPENDIX C THE "EQUIVALENT POLYETHYLENE THICKNESS" AS A FUNCTION OF THE ALPHA YIELD (COUNTS/yc) The a l p h a y i e l d , as r e c e i v e d by the Si s u r f a c e b a r r i e r d e t e c t o r , i s a measure o f t h e c o n c e n t r a t i o n o f d e u t e r i u m atoms i n t h e t a r g e t m a t e r i a l f o r a . g i v e n amount o f 3He beam char g e i n c i d e n t on the t a r g e t . I f the t a r g e t m a t e r i a l was i n t h e form ( C ^ i j n , then t h i s c o n c e n t r a t i o n o f d e u t e r i u m atoms would y i e l d a c o r r e s p o n d i n g ( C 2 D t t ) n t h i c k n e s s . S i n c e i t i s not c l e a r i n what form t h e t a r g e t m a t e r i a l e x i s t s a f t e r e x p o s u r e t o the 3He beam (see s e c t i o n 3-3.1), th e ( C 2 D i t ) n t h i c k n e s s c a l c u l a t e d from the o b s e r v e d c o n c e n t r a t i o n o f d e u t e r i u m atoms i s g i v e n as an " e q u i v a l e n t p o l y e t h y l e n e t h i c k n e s s " [ o r an " e q u i v a l e n t (C 2D i +)n t h i c k n e s s " ] . C o n s i d e r t h e f o r m u l a ^— = aM (A) M where AM = t o t a l no. o f **He p a r t i c l e s e m i t t e d a t t h e t a r g e t f o r a g i v e n number o f i n c i d e n t 3He M = no. o f 3He p a r t i c l e s i n c i d e n t on the t a r g e t c h a r g e Q, i n coulombs Of i n c i d e n t 3He ; 1.6 x 10 -19 = Q/1.6 x 1 0 " 1 9 a = r e a c t i o n c r o s s s e c t i o n ( i n cm 2) f o r t h e r e a c t i o n 2H ( 3He,p) l +He and i s d e t e r m i n e d by the energy of t h e i n c i d e n t N = c o n c e n t r a t i o n o f the d e u t e r i u m atoms i n the t a r g e t m a t e r i a l ( i n no. o f d e u t e r i u m atoms/cm 2) - 102 -The ^He detector subtends a given sol id angle at the target which is equal to 5.16 x l b _ l 4 of the t o t a l s o l i d angle of 4ir steradians. Hence assuming the number of alpha p a r t i c l e s produced at the target is i s o t r o p i c , no. of 4He counts at the detector AM = 5.16 x 10 _ I » 5.16 x 10 H Rearranging (A)' we have C D x 1.6 x I O " 1 9 fl = 5 . 1 6 x 10" 1 * x Q x a (B) For an incident 3He energy of 690 keV, we assume an average energy loss in the target of 50 keV. The reaction cross section a has a peak at a 3He energy of 640 keV and we use t h i s value of a = 695 mb = 695 x 1 0 _ 2 7 c m 2 (Ku 5 5 ) . The concentration N of deuterium atoms is related to the thickness P (in g/cm2) of (C 2 D i +)n as follows: N = P (g/cm2) x (no. of (C 2Di 4)n/gm) x (no. of deuterium atoms per ( C ^ D i J n ) : = P x A x 4n , A = Avogadro's number n x 32 Rearranging, we have P = 32 x N 4 x A • Substituting (B), we have P - f x H 8 1.6 x 1 0 ~ 1 9 C D 6.025 x 1 0 2 3 5-16 x 1 0 - 4 x 695 x 10" 2 7 Q 6.02 x I O " 1 5 x Si W Q - 103 -M u l t i p l y i n g t h e R.H.S. o f (C) by 1 0 1 2 y i e l d s the " e q u i v a l e n t p o l y -e t h y l e n e t h i c k n e s s " Po in yg/cm 2 as a f u n c t i o n o f the number o f ^He c o u n t s a t t h e d e t e c t o r per yc o f i n c i d e n t 3He on t h e t a r g e t . ije. Po(yg/cm 2) = 1 0 1 2 x 6 . 0 2 x 1 0 " 1 5 x ( C D / 0 0 ) = 6 . 0 2 x 10~ 3 x Cn/Qo (number o f 4He c o u n t s / y c ) The r a t i o CD/O.o i s o b t a i n e d by i n t e g r a t i n g the 3He beam c u r r e n t up t o a p r e d e c i d e d q u a n t i t y o f yc and measuring the t o t a l number o f ^He c o u n t s d u r i n g t h i s i n t e g r a t i o n . - 10*1 -APPENDIX D "EQUIVALENT CARBON THICKNESS" OF TARGET MATERIAL CALCULATED FROM THE 1 9 F RESONANCE SHIFT As e x p l a i n e d i n s e c t i o n 2.4.1, a c a l c i u m f l u o r i d e t a r g e t was placed b e h i n d the (C 2D( +)n " s a n d w i c h " t a r g e t and u s i n g a proton beam, the energy s h i f t i n the 873 . 5 keV resonance o f t h e 1 g F ( p , a ) 1 6 0 * reaction was measured. T h i s energy s h i f t r e p r e s e n t s the energy l o s s o f the protons in the target m a t e r i a l . T h i s energy l o s s f o r t h e p r o t o n s of a given energy can be r e a d i l y c o n v e r t e d t o a t a r g e t t h i c k n e s s for a given target stopping m a t e r i a l . As e x p l a i n e d i n 2.4.1, due to the large deuterium losses o f tine " s a n d w i c h " t a r g e t s when exposed t o the 3He beam, i t was decided t o assume the t a r g e t m a t e r i a l was composed completely of carbon atoms f o r t h e s e c a l -c u l a t i o n s . C o n s e q u e n t l y the energy loss suffered by the p r o t o n s i n t h e t a r g e t m a t e r i a l i s c o n v e r t e d i n t o an "equivalent carbon t h i c k n e s s " 1 . T h i i s " e q u i v a l e n t c a r b o n t h i c k n e s s " i s then the thickness o f a comipletelly c a r t o n f i l m w h i c h would g i v e t h e same energy loss (for the p r o t o n foeaw iuise«0 a s the a c t u a l t a r g e t m a t e r i a l . The a t o m i c s t o p p i n g cross section s for protons in carbon may be ffowmdl iiirn (Wh 58) i n u n i t s of ev - cm2/atom. R e c a l c u l a t e e i n terms of ev - cm2 per gm of stopping m a t e r i a l ! no. of atoms) ( 9^  ev - crrr f 91 ev - ctrr f V I J atom A gm For c a r b o n t h i s becomes c x .» A « Avoga d r o ' s niuinfeeir - 105 -D i v i d i n g the energy l o s s AE(ev) o f t h e p r o t o n beam by e 0 and m u l t i -p l y i n g by 1 0 5 ( t o change from g t o yg) y i e l d s the " e q u i v a l e n t c a r b o n t h i c k -n e s s " E c i n yg/cm 2-E c = x 106 e o(ev - cm2/gm) AE x 1 0 6 x 12 yg/cm 2 e x 6 . 0 2 5 x 1 0 2 3 The a t o m i c s t o p p i n g c r o s s s e c t i o n e depends on the i n c i d e n t energy o f the p r o t o n beam. The i n c i d e n t energy o f the p r o t o n beam, r e q u i r e d t o a c t u a t e the 873 keV resonance, changes w i t h the t h i c k n e s s o f the t a r g e t m a t e r i a l . T h e r e-f o r e t h e e v a l u e must be d e t e r m i n e d f o r each c a s e s e p a r a t e l y . F o r example, i f a p r o t o n beam o f energy 8 8 3 . 5 keV a c t u a t e d t h e " 8 7 3 . 5 keV r e s o n a n c e " , t h i s would c o r r e s p o n d t o a 10 keV energy l o s s f o r the p r o t o n s and the z v a l u e f o r an i n c i d e n t p r o t o n energy o f 8 8 3 . 5 keV i s 5 . 0 x 1 0 ~ 1 5 ev - cm2 atom .'. the " e q u i v a l e n t c a r b o n t h i c k n e s s " would be 10 x 1 0 3 x 12 x 1 0 6 Ec 5 . 0 x 1 0 " 1 5 x 6 . 0 2 5 x 1 0 2 3 = 3 9 . 8 = kO yg/cm 2 

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