"Science, Faculty of"@en . "Physics and Astronomy, Department of"@en . "DSpace"@en . "UBCV"@en . "Kinnear, James Kerr"@en . "2012-03-09T00:48:49Z"@en . "1949"@en . "Master of Arts - MA"@en . "University of British Columbia"@en . "A radio frequency excited positive ion source has been designed and constructed. Hydrogen gas is excited in a discharge tube by a radio frequency oscillator operating at a frequency of 210 mc./sec. The hydrogen is disassociated and ionized. A voltage of the order of a 2 kV is used to accelerate the positive ions through the exit canal in the end of the discharge tube. The positive ions are then accelerated and focused into a bean by two cylindrical electrostatic lenses using voltages of the order of 10 kV and 50 kV. For purposes of analysing a one lens system is used, accelerating the beam to an energy of the order of 15 kV. A magnetic analyser resolves up to mass three ions, focussing them into a Faraday cup. The source delivers a beam containing 45% protons. A total current of 800 microamperes of positive ions has been measured."@en . "https://circle.library.ubc.ca/rest/handle/2429/41293?expand=metadata"@en . "ION SOURCE DEVELOPMENT by JAMES KERR KINNEAR A t h e s i s submitted i n p a r t i a l f u l f i l m e n t o f the requirements f o r the degree o f MASTER OP ARTS i n the Department of PHYSICS THE UNIVERSITY OP BRITISH COLUMBIA August, 1949 I ABSTRACT A r a d i o frequency e x c i t e d p o s i t i v e i o n source has been designed and c o n s t r u c t e d . Hydrogen gas i s e x c i t e d i n a d i s c h a r g e tube by a r a d i o frequenoy o s c i l l a t o r o p e r a t i n g a t a frequency o f 210 mc./sec. The hydrogen i s d i s a s s o c i a t e d and i o n i z e d . A v o l t a g e of the order of 2 kV i s used to a c c e l e r a t e the p o s i t i v e ions through the e x i t c a n a l In the end of the dis o h a r g e tube. The p o s i t i v e ions are then a c c e l e r a t e d and f o c u s -sed i n t o a beam by two c y l i n d r i c a l e l e c t r o s t a t i c l e n s e s U3lng v o l t a g e s of the or d e r o f 10 kV and 50 kV. F o r purposes of a n a l y s i n g a one l e n s system i s used, ac-c e l e r a t i n g the beam to an energy of the order o f 15 kV. A magnetic a n a l y s e r r e s o l v e s up to mass th r e e i o n s , f o c u s s i n g them i n t o a Faraday cup. The source d e l i v e r s a beam c o n t a i n i n g 45$ p r o t o n s . A t o t a l c u r r e n t o f 800 microamperes o f p o s i t i v e ions has been measured. I I ACKNOWLEDGEMENTS Th\u00C2\u00A9 author wiahea to express h i s thanks f o r the a s s i s t a n c e and guidance o f Dr. K.H. More, who super-v i s e d t h i s p r o j e c t . He would f u r t h e r l i k e to express a p p r e c i a t i o n to the N a t i o n a l Research C o u n c i l f o r awards and gr a n t s which were made In co n n e c t i o n w i t h t h i s r e s e a r c h . The author a l s o would l i k e t o acknowledge the a s s i s t a n c e of Mr. S.B. Woods who spent much time on t h i s p r o j e c t and s p e c i a l l y to thank him f o r the work he d i d i n g l a s s blowing. F i n a l l y , the author wishes to mention h i a a p p r e c i a t i o n to h i s c o l l e a g u e on t h i s p r o j e c t , Mr. R.H. Chow, f o r h i s c o o p e r a t i o n and earnest endeavour throughout a l l o f the work. ION SOURCE DEVELOPMENT Table of Contents Page Introduction 1 Design and Construction The Discharge Tube 3 The Lens Assembly 4 The Vacuum System 5 The Hydrogen Supply 6 The Radio Frequency O s c i l l a t o r 7 The Magnetic C o l l s 9 The Magnetic Analyser 11 The Power Supplies 13 Operation and Experimental Results 18 Discussion of Results 25 Conclusion and Recommendations 26 PLATES AND ILLUSTRATIONS Plat\u00C2\u00A9 I Plat\u00C2\u00A9 I I Plat\u00C2\u00A9 I I I Plat\u00C2\u00A9 IV P l a t e V P l a t e VI Plat\u00C2\u00A9 VII Diagram o f the Ion Source p Photograph of the Ap/aratus Diagram o f the Magnetic A n a l y s e r C i r c u i t o f th\u00C2\u00A9 50 kV Supply B l o c k W i r i n g Diagram o f the Power S u p p l i e s f a c i n g page 3 n II 4 5 6 13 14 P l a t e V I I I Graph of th\u00C2\u00A9 Analysed Beam n u n tt 16 22 1. ION SPURGE DEVELOPMENT INTRODUCTION Protons and o t h e r p o s i t i v e ions of v a r i o u s energies are used f o r n u c l e a r r e s e a r c h . The a c c e l e r a t i n g equipment i s dependent upon the i o n source f o r the k i n d of i o n beam i t oan f i n a l l y produce. An i o n source must t h e r e f o r e be a b l e to supply a l a r g e enough i o n c u r r e n t which i s as mono-energetic as p o s s i b l e . The e f f i c i e n c y of the source can be d e f i n e d as the number of ions p r o -duced per gas molecule used or as the number of d e s i r a b l e ions (say protons) compared w i t h the number of other ions i n the output beam. In these two r e s p e c t s the source must have h i g h e f f i c i e n c y . The beam must be w e l l f o c u s s e d w i t h a h i g h c u r r e n t d e n s i t y and s m a l l angular spread. I t l a d e s i r a b l e a l s o t h a t the source be of rugged c o n s t r u c t i o n and have a l o n g o p e r a t i n g l i f e . S e v e r a l d i f f e r e n t types of p o s i t i v e i o n sources have been d e s c r i b e d i n the l i t e r a t u r e . The f i r s t types^were c a n a l r a y sources. Other types f o l l o w e d i n -c l u d i n g c a p i l l a r y a r c , magnetic f i e l d r e f l e c t i o n and e l e c t r o d e l e s s or r a d i o frequency e x c i t e d sources. I t i s t h i s l a s t type which i s b e i n g d e s c r i b e d here. A paper by Rutherglen and C o l e 2 i n 1947 d e s c r i b e s auch a source u s i n g an o s c i l l a t o r o p e r a t i n g a t 180 mo./sec. to e x c i t e a hydrogen d i s c h a r g e . The output was 400 microamperes 2. w i t h 60% p r o t o n s . Th\u00C2\u00A9 source o f B a y l y and Ward 3 used an o s c i l l a t o r frequency o f 15 mc./sec. u s i n g hydrogen to get protons and deuterium to get deuterons. They r e p o r t a u s e f u l p o s i t i v e i o n c u r r e n t of 500 microamperes w i t h 60% atomic i o n s . H a l l 4 d e s c r i b e s In a paper h i s source w i t h o s c i l l a t o r o p e r a t i n g a t 450 mc./sec. A new f e a t u r e o f t h i s source was the e l i m i n a t i o n o f an e x t r a c t i o n v o l t a g e a c r o s s the d i s c h a r g e tube. The source d e l i v e r e d 400 microamperes w i t h 60% atomic i o n s . In a reoent p u b l i -c a t i o n , Thonemann 5 e t a l . t e l l o f t h e i r source d e l i v e r i n g a f o c u s a e d beam o f 500 jua w i t h 90% atomic i o n s . Previous l i t e r a t u r e i n d i c a t e d t h a t the l e s s metal exposed to the d i s c h a r g e th\u00C2\u00A9 h i g h e r percentage of protons f i n a l l y e m i t t e d s i n c e metal a c t s as a c a t a l y s t f o r the recombination o f atomic hydrogen. A magnetic f i e l d i s used i n the d i s c h a r g e tube as i t c o n c e n t r a t e s the d i s c h a r g e by r e s t r i c t i n g the l a t e r a l motion of e l e o t r o n s i n the d i s c h a r g e tube. I t i s f e l t by H a l l 4 t h a t the use o f an e x t r a c t i n g v o l t a g e g i v e s the f i n a l beam a s e r i o u s energy spread. T h i s o p i n i o n i s not h e l d by o t h e r w r i t e r s who r e p o r t s m a l l energy spreads. T h i s i s due to the f a c t t h at the e x t r a c t i o n v o l t a g e i s a c t u a l l y developed a c r o s s a very s m a l l space near the e x i t c a n a l of the disoharge tube where i o n f o r m a t i o n does not take p l a c e . Th\u00C2\u00A9 d e s i r a b l e f e a t u r e s o f the Radio PLATE I 3. Frequency Ion source are the combination of s u f f i c i e n t p o s i t i v e i o n c u r r e n t w i t h s m a l l energy spread, good per-centage Atomic ions and low consumption of hydrogen. I t a l s o has the advantage t h a t the d i s c h a r g e tube has l o n g l i f e , hence s a v i n g i n t e r r u p t i o n of o p e r a t i o n to renew cathodes e t c . DESIGN AND CONSTRUCTION P l a t e I i s a drawing of the i o n source which has been c o n s t r u c t e d d u r i n g the course o f t h i s r e s e a r c h . P l a t e s I I , I I I , and IV are photographs o f the i o n source and the a u x i l i a r y equipment, showing i t as I t appeared when the f i r s t s a t i s f a c t o r y beam c u r r e n t s were o b t a i n e d . The Discharge Tube The d i s c h a r g e tube i s made o f pyrex g l a s s t u b i n g 1-|- inches i n diameter and approximately 8 inches l o n g . A g l a s s cone i s r i n g s e a l e d i n t o one end of the d i s c h a r g e tube and has an opening about 3/16\" i n diameter i n i t s apex. T h i s i s the e x i t opening f o r p o s i t i v e ions from the d i s c h a r g e tube. The other end of the disoharge tube has a s h o r t c o n s t r i c t i o n to which i s s e a l e d a g l a s s b u l b w i t h a tungsten probe anode i n i t . The purpose of the c o n s t r i c t i o n i s to i s o l a t e the metal probe as much as p o s s i b l e f r o m the main disoharge thu3 d e c r e a s i n g somewhat the recombination of protons and e l e c t r o n s upon the metal s u r f a c e . An i n l e t tube f o r hydrogen e n t e r s the s i d e of PLATE I I View of Apparartus showing dischsrge tube at l e f t with magnetic c o i l mounted around i t , the o s c i l l a t o r at right of discharge tube, power supplies below and i s o l a t i n g transformer i n bottom l e f t hand corner. 4. th\u00C2\u00A9 d i s c h a r g e tube near the bulb end. The whole g l a s s s t r u c t u r e f i t s snugly over a s t e e l cone and Is f a s t e n e d w i t h v i n y l - s e a l and made vacuum t i g h t w i t h b l a c k wax. The metal cone a c t a as the cathode f o r the e x t r a c t i n g v o l t a g e . Through the centre of the cone al o n g i t s a x i s a h o l e i s d r i l l e d , i n t o which i a f i t t e d a d u r a l i n s e r t . The e x i t c a n a l i s made i n the i n s e r t . There are thr e e i n s e r t s w i t h d i f f e r e n t e x i t c a n a l diameters, 1/16\", 3/32 i n . , 1/8 i n . The l e n g t h o f the i n s e r t i s 3/4 In. The s t e e l cone shapes the magnetic f i e l d which then a s s i s t s i n f o o u s s i n g ions through the e x i t c a n a l . The g l a s s c o v e r i n g most of the s t e e l cone has a charge b u i l t upon i t d u r i n g o p e r a t i o n , f o r m i n g the e l e c t r i c f i e l d and a s s i s t i n g i n f o o u s s i n g ions through the e x i t c a n a l . Two f l a t copper r i n g s are f a s t e n e d around the middle o f the d i s c h a r g e tube t o a c t aa the r a d i o f r e q u e n c y e l e c t r o d e s . A magnetic c o l l i s mounted con-c e n t r i c w i t h the d i s c h a r g e tube a t the cone end. An a i r b l a s t i s needed to c o o l the d i s c h a r g e tube. The Lena Assembly The metal cone i n t u r n i s mounted to a l a r g e s t e e l f l a n g e by a clamping r i n g . T h i s f l a n g e i a b o l t e d t o a a t e e l \" T \" a e c t i o n . The stem of the \"T\" le a d s to the vacuum pumps. At the oth e r s i d e o f the \"T\" s e c t i o n two other l a r g e s t e e l f l a n g e s a r e mounted, separated by PLATE I I I View of the apparatus showing the exit flange and the Faraday cup assembly. 5 . p o r c e l a i n c y l i n d e r s and b o l t e d together w i t h t e x t o l i t e r o d s . These l a s t two f l a n g e s support the two br a s s c y l i n d r i c a l e l e c t r o d e s . The f i r s t c y l i n d e r has a diameter of 1 1/8 i n . whi l e the second has a diameter of 2jj|- i n c h e s . These two c y l i n d e r s together w i t h the base of the metal cone, which has a & i n c h diameter h o l e In i t , comprise the e l e c t r o s t a t i c f o c u s 3 i n g system. The f i r s t gap i s & in c h l o n g w h i l e the ends of the d i f f e r e n t diameter c y l i n d e r s a r e co - p l a n e r . The l a s t f l a n g e has a & in c h diameter e x i t h o l e I n i t . Rubber gaskets are used between a l l these s t e e l to s t e e l and s t e e l to p o r c e l a i n j o i n t s . The common a x i s of the di s c h a r g e tube and l e n s assembly l i e s h o r i z o n t a l l y . A Faraday cup was c o n s t r u c t e d by mounting a g l a s s c y l i n d e r between two brass f l a n g e s . The f i r s t f l a n g e has a hole of 3/8 i n c h diameter i n i t . S e a l e d through a hole i n the ce n t r e of the second f l a n g e i s a Kovar s e a l upon whioh i s mounted a d u r a l cup of % i n c h diameter. The Faraday cup assembly i s mounted a g a i n s t the e x i t h o l e i n the l a s t f l a n g e f o r measuring t o t a l p o s i t i v e i o n c u r r e n t . The magnetic a n a l y s e r can be p l a c e d between the l a s t f l a n g e and the Faraday cup when d e s i r e d . The Vacuum System The whole vacuum system i s made of metal w i t h the e x c e p t i o n of a 10 i n c h s e c t i o n o f g l a s s c y l i n d e r used t o i s o l a t e the \"T\" which may be a t 50 kV above ground. P l a t e IV To f a c e page 6. View o f apparatus showing o s c i l l a t o r and f l a n g e s a t l e f t , P i r a n i and I o n i z a t i o n gauge c i r c u i t s and 50 kV c o n t r o l p a n e l a t c e n t r e , hydrogen tank a t r e a r and 50 kV u n i t a t r e a r r i g h t hand bottom cor n e r . 6 An o i l d i f f u s i o n pump backed by two Welch mechanical pumps Is used f o r pumping down the vacuum system. A water c o o l e d b a f f l e i s mounted above the d i f f u s i o n pump to prevent o i l vapours from e n t e r i n g the main vacuum. A l l pump l i n e s a re bra s s p i p i n g o f i f i n c h diameter. Sylphon bellows a re used to damp the t r a n s m i s s i o n o f mechanical v i b r a t i o n s a l o n g the pumping l i n e s . Two vacuum Gauges are used\u00E2\u0080\u0094a P i r a n i on the f o r e pump and an I o n i z a t i o n gauge on the main vacuum system. A P i r a n i i s a l s o used when i t i s de-s i r e d to measure the p r e s s u r e i n the d i s c h a r g e tube. The Hydrogen Supply The hydrogen i s s u p p l i e d from a commercial hydrogen tank. I t i s s t o r e d a t atmospheric p r e s s u r e i n a g l a s s b o t t l e . A g l a s s tube l e a d s from the storage b o t t l e to the d i s c h a r g e tube. A needle v a l v e i n t h i s l i n e c o n t r o l s the r a t e o f f l o w o f hydrogen to the d i s c h a r g e tube and hence c o n t r o l s the d i s c h a r g e tube p r e s s u r e . The r a t e of f l o w o f hydrogen used i s measured by a type o f manometer. A g l a s s \"T n i s i n s e r t e d i n the f e e d l i n e j u s t b e f o r e the needle v a l v e . To the stem o f the \"T\" a l o n g g l a s s r o d i s j o i n e d whioh runs v e r t i c a l l y down i n t o a b o t t l e of pump o i l . The s u r f a c e of the o i l i s open to atmospheric p r e s s u r e . The r i s e o f o i l i n t o the v e r t i c a l tube i s d i r e c t l y p r o p o r t i o n a l t o the volume of hydrogen f l o w i n g a t atmospheric p r e s s u r e . 7. The Radio Frequency O s c i l l a t o r The tube used f o r the o s c i l l a t o r i s an Eimac 4-65 A. T h i s i s a s m a l l r a d i a t i o n - c o o l e d t r a n s m i t t i n g t e t r o d e . T h i s tube has been chosen because o f i t s low i n t e r e l e c t r o d e c a p a c i t i e s and s h o r t heavy l e a d s which are important f a c t o r s f o r s t a b l e and e f f i c i e n t o p e r a t i o n a t h i g h f r e q u e n c i e s . I t a l s o has rugged c o n s t r u c t i o n and the shape of the g l a s s envelope i s s u i t a b l e f o r s t r e n g t h , per-haps to with s t a n d h i g h enough p r e s s u r e to be used i n a Van de Gr a a f f Tank. I t can be operated w i t h p l a t e v o l t a g e s up to 3000 V w i t h p l a t e d i s s i p a t i o n of 65 watts. The o s c i l l a t o r c i r c u i t i s p u s h - p u l l w i t h tuned p l a t e , g r i d and heater l i n e s . The p l a t e and g r i d l i n e s are tuned w i t h s h o r t i n g b a r s while the heater l i n e s are tuned w i t h a v a r i a b l e condensor. The heater r e t u r n wire i s r u n i n s i d e the heater l i n e . A l l o f the l i n e s a r e made of 3/16 i n c h O.D. copper r o d orjbubing. The output i s taken from out-put l i n e s mounted near the p l a t e l i n e s . I t i s then f e d through a matching I I s e c t i o n to the r i n g s on the d i s -charge tube. The impedances o f the I I s e c t i o n a re made of 3 l i n e s which have s h o r t i n g b a r s on them i n p a i r s . The l i n e s are J- wave l e n g t h l o n g so t h a t any d e s i r e d Impedance may be o b t a i n e d w i t h any p a i r . Two of the p a i r s , however, have t h e i r s h o r t i n g bars coupled so t h a t they always present the same impedance as each o t h e r . To see 8. how t h i s f u n c t i o n s , c o n s i d e r a f o u r t e r m i n a l network con-s i s t i n g of three r e a c t a n c e s as shown\u00E2\u0080\u0094 When an impedance of Za u R Q 4 jX@ i s connected between one p a i r of t e r m i n a l s , the Impedance between the other p a i r i s g i v e n by the f o l l o w i n g r e l a t i o n \u00E2\u0080\u0094 T h i s e q u a t i o n shows t h a t you can tr a n s f o r m any impedance Z E i n t o any d e s i r e d impedance Z Q by s u i t a b l e choice o f X i and X\u00C2\u00A3. A r e p o r t on t h i s matching u n i t i s p u b l i s h e d i n P h i l i p s Research R e p o r t s 6 where i t i s c a l l e d \"A U n i v e r s a l A d j u s t a b l e Transformer f o r U.H.P.\" A matching d e v i c e can be c o n s t r u c t e d , working on t h i s p r i n c i p l e f o r use w i t h wave guides, c o a x i a l cable or open l i n e systems. 1500 V o l t s , 120 watts of power was d e l i v e r e d to a dummy l o a d . I t i s not known what power the o s c i l l a t o r a c t u a l l y d e l i v e r s to the d i s c h a r g e tube. ^ 0 = R o - t - j X 0 = i / l ( x , + x 2 ) z e - X.*\u00C2\u00AB) j X, j ( zX, +x 2 ) z e - x,x 2 - X,2 On a t e s t o p e r a t i o n o f the o s c i l l a t o r a t 9 . The Magnetic C o i l s A p a i r of Helmholtz c o i l s was designed f o r the magnetic f i e l d i n the d i s c h a r g e tube. Dimensions were chosen which would be s u i t a b l e f o r mounting around the d i s c h a r g e tube. These were; cross s e c t i o n of c o l l \u00E2\u0080\u0094 a 2 i n c h square; mean r a d i u s of c o i l \u00E2\u0080\u0094 7.54 cms.; d i s t a n c e between c o i l s \u00E2\u0080\u0094 2.46 cms. between near f a c e s . Using No. 12 B&S copper wire w i t h enamel i n s u l a t i o n we f i n d from the wire t a b l e s number o f turn3 a r e 544. The t o t a l l e n g t h of wire on the two c o l l s i s 168Q f e e t w i t h a r e s i s t a n c e of 2.72 ohms. Assuming a 24 v o l t s supply the c o i l s i n s e r i e s then draw 8.8 amps, c o r r e s -ponding to a c u r r e n t d e n s i t y of 750 c i r c u l a r mils/amp. The magnetic f i e l d on the a x i s midway between c o i l s w i l l then be H \u00C2\u00AB 0.9 ^ gauss = 570 gauss. T h i s f i e l d i s 10. expected to be a u f f i c l e n t . Now the s u r f a c e area of the c o l l s i s 274 i n . 2 Power d i s s i p a t e d a t 8.8 amps i s 212 watts. T h i s i s l e s s than one watt per square Inch so the c o i l s s h ould not overheat w i t h t h i s c u r r e n t . T h i s d e s i g n was then adopted and the c o i l s made. They were impregnated w i t h G9555 g l y p t a l baking v a r n i s h and baked a t 300\u00C2\u00B0P f o r two hours. The f i e l d i s c a l c u l a t e d f o r a c u r r e n t o f 5 amps, u s i n g the f o l l o w i n g formulae which takes Into account the f i n i t e dimensions o f the c o i l . i . e . \u00E2\u0080\u0094 H P = 2 i r r T * ( C x - H b ) I n - ^ t ^ i i ^ S ^ ^ ^ -p I c - d t ^ x + b ) 2 + ( a - d ) 2 _ *y W) L n a + d + :j_fe^blL\u00C2\u00B1J\u00C2\u00A3L\u00C2\u00B1d2l (pc o) In c _ d + ^ ^ b ) 2 + ( c L _ d ) 8 Where Hp i s the f i e l d a t p o i n t \"p\", u*$ n i s the c u r r e n t i n the c o i l and \"n\" i s the number of turns per u n i t c ross s e c t i o n . The r e s u l t s o f the c a l c u l a t i o n s are here shown; H (gauss)- 215 188 121 78 51 32 x(cms)- 0 2.54 5.08 7.62 10.16 12.70 We see the f i e l d on the a x i s a t the mid-p o i n t of one c o i l i s the 215 gauss. The c o l l a t the e x i t end of the di s c h a r g e tube has the s t e e l cone at i t s c e n t r e . The magnetic f i e l d then near the s t e e l cone w i l l be around 215 gauss f o r t h i s c u r r e n t . A c t u a l l y , o n l y t h i s one c o i l 11. has been used s i n c e no advantage has been experienced i n u s i n g the Helmholtz c o i l arrangement. The 110 v o l t D.C. mains are used to supply the r e q u i r e d c u r r e n t f o r t h i s c o i l . The r e q u i r e d r e s i s t o r s a re i n s e r i e s w i t h an am-meter and the c o i l . The Magnetic A n a l y s e r The magnetic a n a l y s e r has been des i g n e d w i t h the purpose i n mind t h a t i t co u l d r e s o l v e mass 3 and 4 ions of 50 kV energy. Using the formula; Hev s my2 e r (where H i s the magnetic f i e l d i n gauss, e i s the charge on the i o n i n e.s.u., v i s the v e l o c i t y o f the i o n In m i s c m . / s e c , / i t s mass i n grams, c i s the v e l o c i t y o f l i g h t In cm./sec., and r i s the r a d i u s of a r c i n cm.) together w i t h the other r e l a t i o n ; eV s $ mv2 300 (where here V i s the energy o f the i o n i n v o l t s ) we f i n d the magnetic f i e l d r e q u i r e d to bend the i o n of known energy through an a r c of g i v e n r a d i u s . The r e l a t i o n i s c / ~ m y H = r y 150e 12. Assuming the magnet w i l l produce a f i e l d of 10^ gauss i n a i r we f i n d by t h i s formula t h a t mass 4 ions of 50 kV energy w i l l be bent i n a c i r c l e o f r a d i u s 2.53 inches, mass 3, 2 and 1 ions i n t o c i r c l e s of r a d i i 2.23 inches, 1.79 inches, and 1.26 inches r e s p e c t i v e l y . With a p o l e p i e c e of 2 square inches c r o s s s e c t i o n , as shown, t h i s w i l l mean a s e p a r a t i o n of mass 3 and 4 i o n s by 1 cm. a t 3 inches from the magnet. The Ions w i l l have been bent through approximately 4 5 \u00C2\u00B0 . With these c a l c u l a t i o n s i n mind the magnet was designed u s i n g No. 18 Formel wire f o r the 2 c o i l s . A l a y e r of 3/16 i n c h copper t u b i n g was wound i n each c o i l . These tubes are used f o r water c o o l i n g o f the c o i l s . Thermo-couples were a l s o I n s e r t e d i n t o the c o i l s w h i l e winding* Test runs of temperature r i s e a t v a r i o u s c u r r e n t s P l a t \u00C2\u00A9 V To f a c \u00C2\u00A9 page 13 13. were made and the water c o o l i n g system was found to g i v e s a t i s f a c t o r y s e r v i c e . The p o l e p i e c e s o f the magnets were made from 2 i n c h diameter i r o n and shaped w i t h two f l a t s i d e s such that the I n c i d e n t beam of ions w i l l e nter the mag-n e t i c f i e l d normal to one s i d e and the e x i t beam which enters the Faraday cup w i l l l e a v e the magnetic f i e l d normal t o the other s i d e . S e c t i o n s o f r e c t a n g u l a r c e n t i -meter wave guide, which has one dimension equal t o ^ i n c h were s i l v e r s o l d e r e d t o g e t h e r making a bend of 45\u00C2\u00B0. Flanges were f i t t e d on each end f o r f a s t e n i n g to the e x i t f l a n g e o f the e l e c t r o d e system and f o r f a s t e n i n g to the Faraday cup. The magnet i s mounted a t the bend and the wave guide f i t s e x a c t l y i n t o the \u00C2\u00A3 i n c h gap between the p o l e p i e c e . P l a t e V shows a diagram of the a n a l y s e r The Power S u p p l i e s The power supply f o r the o s c i l l a t o r i s a standard f u l l wave c i r c u i t with choke condensor f i l t e r i n g . I t i s capable of d e l i v e r i n g up to 2000 v o l t s a t 400 m i l l i a m p e r e s . In the h i g h v o l t % g e n e g a t i v e l e a d an over-l o a d r e l a y c o i l i s connected which switches o f f the A.C. inp u t to the power supply when the c u r r e n t reaches 400 m i l l i a m p e r e s . An A.C. operated c o i l r e s e t s the r e l a y s w i t c h . T h i s r e l a y p r o t e c t s the o s c i l l a t o r tubes a g a i n s t damage due to sudden e x c e s s i v e c u r r e n t s . P l a t e VT To f a c e page 14 14. A f u r t h e r power supply waa c o n s t r u c t e d to supply 18 kV. I t uses 8013 r e c t i f i e r s i n a v o l t a g e t r i p l e r c i r c u i t . A b l e e d e r r e s i s t a n c e , c o n s i s t i n g o f one hundred 47 K ohm, 2 watt r e s i s t o r s , i s connected a c r o s s the output. The condensor p l a t e s and cases are a l l tapped to the c o r r e c t p o s i t i o n s on t h i s b l e e d e r . A 6 ma. meter i s I n s e r t e d i n s e r i e s w i t h the b l e e d e r f o r measuring b l e e d e r c u r r e n t and hence v o l t a g e s u p p l i e d by t h i s power supply. The r i p p l e was measured and found to be O.Q% o f the D.C. output. T h i s power supply was intended to supply probe v o l t a g e and f i r s t l e n s v o l t a g e . However a second power supply has been used to supply probe v o l t a g e Indep-endent of the f i r s t l e n s v o l t a g e . A 20 ma. meter Is i n s e r i e s w i t h the l e a d to the probe f o r measuring probe cur-r e n t s . A 50 kV power supply, the c i r c u i t o f which i s shown i n P l a t e VI, has a l s o been designed. The t r a n s -former and two r e c t i f i e r tubes are i n a case immersed i n o i l . A s w i t c h i n g arrangement Is used so t h a t e i t h e r p o s i t i v e or n e g a t i v e v o l t a g e as d e s i r e d i s d e l i v e r e d to the h i g h v o l t a g e output c a b l e . A b l e e d e r of 60 megohms i s connected across the output i n p a r a l l e l w i t h 0.5 micro-f a r a d s . A c u r r e n t meter i s i n s e r i e s w i t h the b l e e d e r f o r r e a d i n g v o l t a g e s u p p l i e d . A p r o t e c t i v e spark gap together w i t h a choke and neon tube are used. The c i r c u i t diagram i s shown from which the f u n c t i o n o f the s w i t c h i n g arrange-15 ment and p r o t e c t i v e c i r c u i t s can be seen. T h i s power supply-i s Intended f o r the f i n a l a c c e l e r a t i n g gap when i t i s r e -q u i r e d that the p o s i t i v e ions have 50 kV o f energy. In a l l o f these power s u p p l i e s the primary and secondary of a l l transformers are i n s u l a t e d from each o t h e r . One s i d e o f the D.C. output Is connected i n each case to the c h a s s i s of i t s own power supply. A common l i n e i s connected between a l l p o i n t s which are to be h e l d a t the same v o l t a g e . Only one e a r t h c o n n e c t i o n i s made to the water mains and t o the e a r t h s i d e of the A.C. mains s u p p l y . T h i s e a r t h p o i n t i s always made a t the output end of the l e n s system i n use so t h a t the output measuring equipment w i l l be a t e a r t h p o t e n t i a l . A l s o i n a l l power s u p p l i e s the h e a t e r supply f o r the r e c t i f i e r tubes i s c o n t r o l l e d independently from the Input t o the h i g h v o l t a g e t r a n s -former. The in p u t s u p p l y to the h i g h voltage transformer i n each case i s c o n t r o l l e d by a v a r l a c . A l l c o n t r o l knobs, which must be used when the h i g h v o l t a g e i s on, are mounted on lo n g i n s u l a t i n g r o d s . A l l c i r c u i t s are p r o -t e c t e d w i t h f u s e s . Since the output end of the l e n s system i s always maintained a t ground p o t e n t i a l , the other e l e c t r o d e s and the d i s c h a r g e tube core and probe w i l l be a t h i g h p o t e n t i a l s up to 50 kV above ground. Consequently the o s c i l l a t o r power supply, the probe v o l t a g e supply and the 18 kV supply must be i n s u l a t e d from e a r t h . T h i s was done to r.f. electrodes to probe t o cone t o f i r s t electrode r - to second electrode Isolating T r a n s f o r m e r f o m a i n s P l a t e V I I . Block W i r i n g Diagram o f the Power S u p p l i e s . 16 by c o n s t r u c t i n g a one to one transformer, w i t h 50 kV i n s u l -a t i o n from primary to secondary, to supply the 110 v o l t s A.C. to the power s u p p l i e s i n q u e s t i o n . The h i g h v o l t a g e windings were taken from a p o l e transformer l e a v i n g o n l y the 110 v o l t windings. I n s u l a t i n g m a t e r i a l was then mounted around these windings. Then u s i n g Formel wire a second winding was wound to d e l i v e r 110 v o l t s w i t h 110 v o l t i n p u t . The winding was wrapped w i t h empire c l o t h and v a r n i s h e d w i t h g l y p t a l . The whole was then Immersed i n a drum of transformer o i l . During o p e r a t i o n the t r a n s f o r m e r was found to g i v e s u f f i c i e n t c u r r e n t without breakdown o r o v e r h e a t i n g . A l l power s u p p l i e s f e d by the I s o l a t i o n transformer are mounted on an i n s u l a t e d deck. A b l o c k diagram of these power supply connections i s shown i n P l a t e VII. In measuring the p o s i t i v e i o n c u r r e n t w i t h a microammeter, u s i n g the Faraday cup, i t i s e s s e n t i a l t h a t the secondary e l e c t r o n s , due to p o s i t i v e i o n bomb-ardment of the cup and the cup mounting f l a n g e , are not measured. T h i s Is a s s u r e d by p u t t i n g s m a l l r e t a r d i n g p o t e n t i a l s i n such a d i r e c t i o n as to f o r c e the secondary e l e c t r o n s to r e t u r n to the s u r f a c e from which they a r e emitted. Dry c e l l b a t t e r i e s are used to s u p p l y these p o t e n t i a l s . See diagram on next page. 17. V P7\" / / \u00E2\u0080\u00A2 cup f l C inge Z. + 1 2 7 0 V llllllllll^ V - f l a n g e 1. 135 V WI$h the arrangement shown i n the diagram we see t h a t the cup i s 135V p o s i t i v e to entrance f l a n g e 1 and f l a n g e 2 i s 135 v o l t s p o s i t i v e to the cup. Secondary e l e c t r o n s e m i t t e d from the cup and f l a n g e 2 w i l l r e t u r n to the s u r f a c e from which they are emitt e d and w i l l not be measured i n t h e microammeter. With the a n a l y s e r f i t t e d the c u r r e n t s to be measured are s m a l l e r . A galvanometer was used w i t h shunts to g i v e f u l l s c a l e d e f l e c t i o n s of l j i a , 5p.a, and 50ua. A l l o f the equipment d e s c r i b e d , w i t h the ex c e p t i o n o f the P i r a n i tube and c i r c u i t , the i o n i z a t i o n gauge tube and the 50kV supply has been designed and cons-t r u c t e d by the author and c o l l e a g u e . 18 . OPERATION AND EXPERIMENTAL RESULTS On f i r s t s t r i k i n g , the d i s c h a r g e appears b l u i s h white. A f t e r a few minutes i t turns r e d and the Balmer l i n e s can be seen through a spectroscope. At about. 30 microns pressure i n the d i s c h a r g e tube the d i s c h a r g e i s b r i g h t r e d and spreads throughout the whole tube. In-c r e a s i n g the pre s s u r e i n c r e a s e s the redness but a t very-h i g h p r e s s u r e s the d i s c h a r g e f i l l s o n l y the space between the e l e c t r o d e s . As the pr e s s u r e decreases below 30 microns the d i s c h a r g e becomes p a l e r and appears to get t h i n n e r l o o k i n g u n t i l a t very low pr e s s u r e i t becomes b l u e r and at l a s t goes out . When the dis c h a r g e has gone out you can see the g l a s s i n the tube f l o u r e s c e . As the probe vol t a g e i s i n c r e a s e d the dis c h a r g e recedes from the cone l e a v i n g a s m a l l dark space. The s u r f a c e of the di s c h a r g e plasma surrounding t h i s dark space r e p r e s e n t s a source of p o s i t i v e i o n s . Most o f the e x t r a c t i o n v o l t a g e Is developed a c r o s s t h i s space. When the magnetic f i e l d i s turned on the d i s c h a r g e plasma shapes i t s e l f Into a l o n g cone a l o n g a t h i r d of the tube w i t h i t s apex a t the e x i t c a n a l . When the voltage was turned h i g h on the le n s e l e c t r o d e s , s e r i o u s a r c - o v e r was experienced, which was due to the pr e s s u r e being too h i g h . Because of t h i s runs were made to determine the b e s t heater c u r r e n t o f the d i f f u s i o n pump f o r lowest p r e s s u r e p o s s i b l e . A f t e r d etermining t h i s c o n d i t i o n the h i g h vacuum p r e s s u r e was 19. of the order of IO\"*5 mm. mercury while the forepump pressure was of the order o f 20 microns. F u r t h e r runs were made of r a t e s o f fl o w of hydrogen a t d i f f e r e n t d i s c h a r g e tube p r e s s u r e s w i t h d i f -f e r e n t e x i t c a n a l s . Note t h a t the r a t e o f flow through the e x i t c a n a l i s independent of the pr e s s u r e i n the main system but depends o n l y on the e x i t c a n a l dimensions and the p r e s s u r e i n the discharge tube. The r e s u l t s are here t a b u l a t e d . E x i t Canal P r e s s u r e i n Rate of Diameter Discharge tube H>> f l o w l / 8 i n c h 25 microns 8.8 c c . / h r . 15 5.3 10 3.5 3/32 i n c h 50 microns 9.6 cc . / h r . 25 4.4 15 2.6 1/16 i n c h 50 microns 3.7 c c . / h r 25 2.3 15 1.4 Runs were made of the p o s i t i v e i o n c u r r e n t w i t h probe v o l t a g e o n l y and v a r y i n g magnetic f i e l d . P l o t -t i n g p o s i t i v e i o n cu r r e n t a g a i n s t probe v o l t a g e shows a peak of c u r r e n t . I n c r e a s i n g the magnetic f i e l d i n o r e a s e s the value o f the cu r r e n t at the peak and moves the peak to highe r probe v o l t a g e s . T h i s seems to i n d i c a t e a f o c u s s i n g e f f e c t i n the di s c h a r g e tube but the a c t u a l mechanism i s 20 not c l e a r . The graph shows three t y p i c a l curves f o r magnetic f i e l d c u r r e n t s o f 0, 1 and 2 amps. A f t e r the peak the c u r r e n t appears to r i s e a g a i n hut t h i s i s due to secondaries which had not been suppressed d u r i n g these r e a d i n g s . 1 - n 1 1 \ i -C \u00E2\u0080\u00A2> --L _ / ... HV IV V. =2 i V 1 1 1 / 1 .1 i / it f > i I. / I I i o r l\u00C2\u00A3 a r-> i t a | / ^ t 1 1 i n i 1 1 n \ I i i \ SfSr C T l c J L * i Q~ / jy i - i r a y j i ren T i / \u00E2\u0080\u00A2 V i l -1 a \u00E2\u0080\u0094 z. 1 -r _ t> i i > i i i 1 i 2 i i 1 1 1 i I o I n o n T 3 0 0 0 a I i ii O I V TS 1 | 1 1 1 i j - - -- _-_ i - -, i 1 1 1 ~\" ' i i i When a r e t a r d i n g v o l t a g e i s put on to suppress the secondaries the peaks are a i m i l i a r and the p o s i t i v e i o n cur r e n t drops t o zero f o r h i g h e r probe vol t a g e ( i n d i c a t e d by d o t t e d l i n e s ) . When the v o l t a g e i s put on the f i r s t l e n s i t i s found that the p o s i t i v e i o n c u r r e n t i n c r e a s e s over that measured w i t h probe v o l t a g e above. T h i s i s due to the f i e l d i n the f i r s t l e n s gap p r e v e n t i n g so many ions from s t r i k i n g the w a l l s o f the e x i t c a n a l . The gap i n the f i r s t l e n s was v a r i e d and the vo l t a g e r a t i o between 21. the probe v o l t a g e and the f i r s t l e n s v o l t a g e ( V i and V&) was measured f o r each case when the l e n s f o c u s s e d a p a r a l l e l beam. An a p e r t u r e to a p e r t u r e l e n s was a l s o c o n s t r u c t e d w i t h a p e r t u r e diameters b o t h 3/8 i n c h and sp a c i n g between a p e r t u r e s 1 l / 8 i n c h and the v o l t a g e r a t i o compared w i t h other l e n s . The r e s u l t s are t a b u l a t e d here: Lens type c y l i n d e r to o y l i n d e r a p e r t u r e t o a p e r t u r e The a p e r t u r e to a p e r t u r e l e n s was much s t r o n g e r than the c y l i n d e r to c y l i n d e r types but i t was thought t h a t some of the i o n beam was b e i n g stopped by the f i r s t a p e r t u r e . The p o s i t i v e i o n c u r r e n t was measured w i t h the probe and f i r s t l e n s v o l t a g e on. The magnetic f i e l d was v a r i e d and a l s o the p r e s s u r e i n the d i s c h a r g e tube. The p o s i t i v e i o n c u r r e n t i n c r e a s e d w i t h i n c r e a s e d magnetic f i e l d u n t i l a f i e l d of around 250 gauss. Higher magnetic f i e l d d i d not i n c r e a s e the p o s i t i v e i o n c u r r e n t . V a r i a t i o n o f the pre s s u r e i n the d i s c h a r g e tube showed maximum i o n c u r r e n t f o r a range of p r e s s u r e s from 30 microns to about 80 microns i n d i c a t e d by the P i r a n i gauge. gap Vg (inches) Vj~ 1/8 9.5 1/2 7.5 1 3/8 7.5 1 1/8 5 Plat\u00C2\u00A9 V I I I To f a c e page g 2 P l o t o f ana l y s e d beam showing mass 1, mass 2 and mass-3 peaks l e f t to r i g h t . 22. A p o s i t i v e i o n c u r r e n t o f 800 ua was measured w i t h probe v o l t a g e , 2000 V.; probe c u r r e n t 7.6 ma.; f i r s t l e n s v o l t a g e 12.35kV; d i s c h a r g e tube p r e s s u r e , 38 microns and magnetic f i e l d , 240 gauss. The p o s i t i v e Ion c u r r e n t i n c r e a s e d w i t h i n c r e a s i n g R.F. power but there seemed to be a p a r t i c u l a r R.F. power which gave the peak p o s i t i v e i o n c u r r e n t . T h i s power v a r i e d w i t h o t h e r c o n d i t i o n s . I t appeared as i f the R.F. had an e f f e c t on the f o c u s s i n g i n the d i s c h a r g e tube. The 1/16 i n o h diameter e x i t c a n a l was f i r s t used. The 1/8 i n c h diameter c a n a l however gave a much h i g h e r p o s i t i v e Ion c u r r e n t . The a n a l y s e r runs were made with t h i s c a n a l . I t seems t h a t the l a r g e r the e x i t c a n a l the l a r g e r the p o s i t i v e i o n c u r r e n t . However there i s a l i m i t a t i o n to the s i z e of e x i t which may be used s i n c e w i t h a l a r g e c a n a l i t i s more d i f f i c u l t to pump the h i g h vacuum s i d e to a low enough p r e s s u r e to a v o i d c o l l i s i o n s of the p o s i t i v e ions w i t h gas m o l e c u l e s . The a n a l y s e r magnet was c a l i b r a t e d w i t h a f l u x m e t e r . The curve i s shown below. The h y s t e r e s i s loop was found to be very narrow so o n l y the f i e l d from zero c u r r e n t i s p l o t t e d . However b e f o r e every a n a l y s i s r u n the magnet was demagnetized. (See graph on next page.) P l a t e VIII i s a graph showing the r e s u l t s f o r a t y p i c a l a n a l y s e d beam. The mass 1 and mass 2 peaks 23. were found to be f a i r l y narrow and s l i g h t l y f l a t topped but the mass 3 peak was broader. The i n s t r u m e n t a l spread of the a n a l y s e r i s not known so the peroent protons i s estimated by comparison of the h e i g h t s of the peaks. An analyses was made w i t h ions o f energy o f 14kV w i t h d i f -f e r e n t magnetic f i e l d s . C a l i b r a t i o n of Ana l y s e r 1 1 s ft I \J -i i Q ' K . 1 i 1 / / ? \u00E2\u0080\u00A2/ / u. V. q / t n / / / / / i < f 1 / / / c i i 1 < i \u00E2\u0080\u00A2 fe \u00C2\u00BB d ~\ r \u00E2\u0080\u00A2if n T F ir \u00E2\u0080\u00A2 i rr f \"1 j R \u00E2\u0080\u00A2 i i 1 i 24. Analyses of Beam Magnetic F i e l d Current Mass 1 Mass 2 Mass 3 9 amps 21 % 38$ 46 42 39 40 33 41$ 24 20 15 13 38 7.8 6.9 6.08 5.58 4.6 25 38 46 46.5 28.5 From these r e s u l t s i t appears t h a t the mass 2 percentage i s not e f f e c t e d as much by the change o f magnetic f i e l d as t h a t o f the o t h e r i o n s . There seems to be an i n t e r -change o f mass 1 and mass 3 ions w i t h v a r i a t i o n i n magnetic f i e l d . T h i s i s thought to be caused by f o r m a t i o n of mass 3 Ions i n the e x i t c a n a l which i s prevented t o some extent by b e t t e r f o c u s s i n g through the e x i t c a n a l w i t h change of magnetic f i e l d . 25. DISCUSSION OF RESULTS T h i s i o n source can d e l i v e r 800 microamperes of p o s i t i v e ions 45$ of which are p r o t o n s . That i s i t can d e l i v e r 360 ^ ua of p r o t o n s . With the power s u p p l i e s already-i n s t a l l e d these protons can be a c c e l e r a t e d t o 50 kV of energy. T h i s source o f protons then can be used f o r some n u c l e a r experiments. I f deuterium i a used i n s t e a d of hydrogen i t i s expected t h a t the source w i l l then supply deuterons w i t h approximately the same performance. Again these deuterons oould be used i n a deuteron-deuteron r e a c t i o n c o n v e r t i n g the source to a ne u t r o n s o u r c e . The source can supply s u f f i c i e n t atomic ions and can be m o d i f i e d f o r I n s t a l l a t i o n i n a Van de Graaff generator. A s t r a i g h t through a n a l y s e r (crossed e l e c t r i c and magnetic f i e l d s ) c o u l d be i n c o r p o r a t e d i f d e s i r e d . I t i s f e l t t h a t the performance o f the aource can a t i l l be improved w i t h more time to apend a d j u s t i n g the many parametera i n v o l v e d . 26. CONCLUSION AND RECOMMENDATIONS I t i a f e l t t h a t there Is a much h i g h e r per-centage o f atomic ions i n the dis c h a r g e tube, j u d g i n g by the c o l o r o f the d i s c h a r g e , than i s b e i n g measured i n the a n a l y s e r . T h i s may be due to f o r m a t i o n o f t r i a t o m i c ions i n the e x i t c a n a l . I t i s recommended t h a t the e x i t c a n a l be made much s h o r t e r . T h i s may n e c e s s i t a t e an e x i t c a n a l of l e s s diameter due to pumping problems. The d e s i g n o f the metal cone then should be a l t e r e d so t h a t t h e r e i s the l a r g e s t p o s s i b l e hole i n i t a t the base end and that the e x i t c a n a l i n the cone be very 3hort. In d e s i g n i n g an e l e c t r o s t a t i c l e n s there i s a minimum o b j e c t d i s t a n c e . T h e r e f o r e i t i s d i f f i c u l t to f o c u s a p a r a l l e l beam w i t h o n l y one l e n s s i n c e we want the o b j e c t d i s t a n c e very s h o r t . That Is we wish the f i e l d o f the f i r s t a c c e l e r a t i n g gap to be e f f e c t i v e as c l o s e to the e x i t c a n a l as p o s s i b l e as t h i s prevents l o s s o f ions by c o l l i s i o n a g a i n s t the i n s i d e w a l l s o f the c o r e . F o r these two reasons then, i t i s suggested to use a s h o r t c y l i n d r i c a l e l e c t r o d e which reaches i n -s i d e the cone. The v o l t a g e on i t can be a d j u s t e d t o g i v e l e a s t l o s s o f ions i n the e x i t c a n a l . Then another c y l i n d r i c a l e l e c t r o d e can be mounted which w i l l do most of the f o c u s s i n g . I n t h i s way i t i s b e l i e v e d that a beam of s m a l l diameter may be produced. A r e t a r d i n g 27. l e n s may be uaed i f a s t r a i g h t through a n a l y s e r i s i n -corporated. A f i n a l a c c e l e r a t i n g e l e c t r o d e may then be used o f l a r g e r diameter than the others i n order t o g i v e a c c e l e r a t i o n to 50 kV without o v e r f o c u s s I n g . T h i s adjustment to the cone w i l l a l s o a s s i s t i n the pumping s i n c e t h e r e i s a l a r g e r diameter hole i n the cone. T h i s w i l l lengthen the mean f r e e path f o r the ions i n s i d e the e x i t c a n a l and cone and so s may prevent some c o l l i s i o n / which are ca u s i n g l o s s of ions or f o r m a t i o n o f u n d e s i r a b l e i o n s . I t may be worthy of c o n s i d e r a t i o n to b u i l d an o s o i l l a t o r o p e r a t i n g a t a much lower frequency, say 5 o r 6 mc./sec. s i n c e a t t h i s frequency much more power would be d e l i v e r e d by the same tubes. A l s o a t t h i s frequency matching and s h i e l d i n g problems are a l i t t l e l e s s d i f f i c u l t . S ince the whole e l e c t r o d e assembly i s enclo s e d i n p o r c e l a i n o r s t e e l i t i s imp o s s i b l e to see the beam. I t would be an advantage i f i t can be a r -ranged to see the beam a t as many p o i n t s i n the l e n s assembly as p o s s i b l e , e s p e c i a l l y where i t i s j u s t emerging from the cone. With these m o d i f i c a t i o n s suggested i t i s f e l t t h a t f u r t h e r improvement i n performance w i l l be r e a l i z e d . REFERENCES 1. Cragga, J.D. Proc. Phys. Soo. London 54:439. 1942. Lamar, E.S. Buechner, W.W., & Van de G r a a f f , R.J. J . A p p l i e d Phys. 12:132. 1941. Zi n n , W.H. Phys, Rev. 52:655. 1937. F i n k e l s t e i n , A.T. Rev. S c i . Instruments 11:94. 1940. 2. J.G. Rutherglen & J.F.T. Cole Nature, V o l . 1, #4068, Oct 18, 1947. 3. A . J . B a y l e y & A.3. Ward, Canadian J o u r n a l of Research, A,26:69-78 March/48. 4. R.N. H a l l Review of S c i e n t i f i c Instruments, 19:905; 1948. 5. P.C. Thonemann, J . M o f f a t t , D. Roaf, J.H. Sanders; Proceedings P h y s i c a l S o c i e t y , V o l . LXI, P483, 1948, 6. J.H. van Hofweegen & K.S. Knol P h i l i p s Research Reports, V o l . 3, No. 2, Apr. 1948, "@en . "Thesis/Dissertation"@en . "10.14288/1.0085838"@en . "eng"@en . "Physics"@en . 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