UBC Theses and Dissertations

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UBC Theses and Dissertations

A portable device for detecting radio-active ores Smith, Ronald 1933

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U . B . C . LIBRARY OAT.  m . ^ A i ^ i m . d & ^ g i  A PORTABLE DEVICE FOR DETECTING  by Ronald Smith.  A T h e s i s s u b m i t t e d f o r t h e Degree o f MASTER in  OF  ARTS  t h e Department of PHYSICS.  THE UNIVERSITY OF BRITISH COLUMBIA APRIL  1933.  l%hm6r>mTXm»JMmJMiL  A PORTABLE DEVICE FOR DETECTING RADIO-ACTIVE ORES*  -  Page 1 o  TRIBQ-ELEGTRIG EFFECT BETWEEN GLASS AND MERCDRT. Page 1 3 <  A SIMPLE APPARATUS FOR SPUTTERING METALLIC FILMS, Page 17,  A SENSITIVE PHOTO-ELECTRIC QUANTUM COUNTER FOR ULTRA-VIOLET LIGHT. Page 19*  (1)  A PORTABLE DEVICE FOR DETEGTING RADIO*ACTIVE ORES.  Introduction: Tremendous i n t e r e s t has been aroused i n Canada over the r e c e n t d i s c o v e r y of r i c h r a d i u m ore d e p o s i t s i n the G r e a t Bear Lake d i s t r i c t . of t h e l o c a t i o n o f s t i l l  The  probability  f u r t h e r d e p o s i t s I n t h e neighborhood  makes t h i s an opportune time f o r the development  of a  p r a c t i c a l Instrument c a p a b l e o f i n d i c a t i n g the presence o f radium o r e *  P r o s p e c t i n g f o r r a d i o - a c t i v e ore d e p o s i t s  d i r e c t l y by the d e t e c t i o n o f t h e gamma r a d i a t i o n s from them has i n the p a s t been c o n f i n e d t o the use o f the electroscope« S a t i s f a c t o r y o p e r a t i o n o f t h i s i n s t r u m e n t i n the open i s handicapped by s e v e r a l p r a c t i c a l d i f f i c u l t i e s ,  such as the  f r a g i l i t y of i t s w o r k i n g p a r t s and the n e c e s s i t y o f k e e p i n g i t absolutely dry.  (1)  H. G e i g e r and W, M u l l e r , P h y s . Z e l t s . 29, 839, (1928) Some subsequent work on t h e G e i g e r - M u l l e r tube i s d e s c r i b e d i n the f o l l o w i n g l i t e r a t u r e ,  (2)  H. G e i g e r and W. M u l l e r , P h y s . Z e i t s .  (3)  H. Knlepkamp, P h y s . Z e i t s .  (4)  J.A. Van den A k k e r , Rev. S c i . I n s t . 1, 672,  (5)  L.F. G u r t i s s , B u r . of S t a n d . J o u r , o f Res. 5, 115,  30, 237,  30, 4-89,  (1929)  (1929) (1930) (1930)  (2)  An i n s t r u m e n t i s here d e s c r i b e d t h a t a t t a i n s a l l the s e n s i t i v i t y o f t h e e l e c t r o s c o p e t o gamma r a y s and i s moreover c o n v e n i e n t l y p o r t a b l e and f o o l - p r o o f i n u s e , r e q u i r i n g no t e c h n i c i a n t o o p e r a t e * The G-eiger-MuIler Gounting Tube; Advantage was taken o f the E l e c t r o n (1) C o u n t i n g tube d e v e l o p e d by G e i g e r and M u l l e r the purpose was  i n 1928 f o r  of d e t e c t i n g gamma and s i m i l a r r a d i a t i o n s . I t  n e c e s s a r y t o modify these tubes so t h a t t h e y c o u l d be  o p e r a t e d on a v o l t a g e low enough t o be p r a c t i c a l f o r a portable  outfits R  V A W —  16  G-M. —-  'w  B L.S. 10'Q  TL.  Fig.  I.'  tube ;  G.H.- Geiger-nailer  A-Amp/i/i'er  ;  flattery  - B ;  L.J.-Loud-  sp ea.ker.  Such a tube c o n s i s t s o f a h o l l o w m e t a l c y l i n d e r and a w i r e arranged' c o n c e n t r i c a l l y , t h e space between t h e s e two e l e c t r o d e s b e i n g f i l l e d w i t h a gas a t a p r e s s u r e o f 7 cm. o f mercury o r l e s s .  A high potential i s  a p p l i e d a c r o s s t h e two e l e c t r o d e s t h r o u g h a r e s i s t a n c e o f t h e o r d e r o f 1C-9 ohms.  A two o r t h r e e stage r a d i o  amplifier  (3)  e n a b l e s c u r r e n t surges I n t h e . c i r c u i t t o be d e t e c t e d . ( F i g . 1 ) . When t h e p o t e n t i a l a c r o s s t h e Geiger-M t i l l e r tube I s r a i s e d s u f f i c i e n t l y c l i c k s a r e heard i n t h e l o u d speaker a t i r r e g u l a r I n t e r v a l s .  The f r e q u e n c y o f these  c l i c k s w i l l be g r e a t l y i n c r e a s e d i f a s m a l l q u a n t i t y o f radium I s p l a c e d c l o s e t o t h e t u b e .  The r e s i d u a l c o u n t ,  when a l l r a d i o - a c t i v e m a t e r i a l s a r e removed from t h e n e i g h borhood,  i s due t o cosmic r a y s and s t r a y gamma r a y s from t h e  e a r t h , a c l i c k b e i n g heard when one o f these passes  through  the tube. There I s a d e f i n i t e minimum o p e r a t i n g p o t e n t i a l w h i c h depends on t h e dimensions o f t h e w i r e and s u r r o u n d i n g m e t a l c y l i n d e r , and on t h e gas between t h e two. Above t h i s t h r e s h o l d t h e r e i s a v o l t a g e range, t h e b r e a d t h of w h i c h depends on v a r i o u s v a r i a b l e c o n d i t i o n s i n t h e gas or  on the i n n e r m e t a l s u r f a c e s , i n w h i c h t h e count p e r  minute i s f a i r l y c o n s t a n t ; t h i s count b e i n g assumed t o c o r r e s p o n d t o t h e number o f cosmic and gamma r a y s p a s s i n g through the tube.  Above t h i s range, s p u r i o u s c l i c k s a r e  produced, t h e number I n c r e a s i n g w i t h t h e a p p l i e d p o t e n t i a l . A Low Operating; P o t e n t i a l ; The m a j o r i t y o f G e i g e r - M u l l e r tubes used f o r l a b o r a t o r y purposes c o n t a i n a i r a t from 3 t o 7 cm. p r e s s u r e , r e q u i r i n g from 1000 t o 1500 v o l t s t o o p e r a t e them. As t h i s i s n e a r l y p r o h i b i t i v e f o r f i e l d work, i t was n e c e s s a r y t o develop a tube w o r k i n g on a much lower v o l t a g e .  (4)  There are t h r e e main f a c t o r s determine  which  the t h r e s h o l d p o t e n t i a l . 1.  Diameter o f o u t s i d e m e t a l  cylinder.  2.  P r e s s u r e of the gas i n the tube,.  3«  Nature o f the  gas.  The v a r i a t i o n o f t h e t h r e s h o l d V w i t h the d i a m e t e r b of the m e t a l c y l i n d e r i s g i v e n by (6) formula  the  & l o g b/a where X, the e l e c t r i c f i e l d a t the s u r f a c e of the w i r e remains c o n s t a n t f o r a c o n s t a n t w i r e d i a m e t e r the l e s s b i s , the lower w i l l be V.  a; t h a t i s ,  However the l o w e r i n g  of b I s accompanied by a c o r r e s p o n d i n g decrease  of the  e f f e c t i v e a r e a of t h e tube, t h e r e b y d e c r e a s i n g the sensitivity. i n c h e s was  On t h i s account  a d i a m e t e r o f 1/2  to  chosen as the most s a t i s f a c t o r y s i z e .  5/8 The  v o l t a g e v a r i e d v e r y l i t t l e w i t h the r a d i u s of the w i r e , f i n e tungsten  or manganin w i r e b e i n g used (6) I t has been shown  throughout.  t h a t the t h r e s h o l d  p o t e n t i a l of a G-eiger-Muller tube changes w i t h gas i n the same way used..  as does the s p a r k i n g p o t e n t i a l of the  Consequently  a c o n s i d e r a b l e decrease  the v o l t a g e was r e d u c e d a i r a t one t o t e n  gas  s h o u l d be  o b t a i n e d by l o w e r i n g the p r e s s u r e of t h e g a s .  (6)  pressure  In t h i s  way  t o s i x or seven hundred v o l t s f o r  m i l l i m e t r e s p r e s s u r e ; but s p u r i o u s c l i c k s  D. Cooksey and MoC.  Henderson, B u l l . Am. Phy. June 9 1932. S  Soc,  (5)  produced a t v o l t a g e s l i t t l e above t h e t h r e s h o l d i n t h i s r e g i o n made the t u b e u n r e l i a b l e f o r measurement p u r p o s e s . I n a d d i t i o n the s e n s i t i v i t y  (count p e r minute) was  very  a p p r e c i a b l y d e c r e a s e d a t these p r e s s u r e s , as G e i g e r (2) . M u l l e r have a l r e a d y p o i n t e d o u t .  and  The t h i r d v a r i a b l e , the n a t u r e o f the gas h e l d the g r e a t e s t promise  of g i v i n g r e s u l t s .  A number  of workers have used gases o t h e r than a i r i n t h e s e  tubes  s u c c e s s f u l l y , I t b e i n g f o u n d t h a t e a c h gas r e q u i r e s I n general a d i f f e r e n t operating voltage.  The l o w e s t p o t e n t i a l  r e p o r t e d bv G e i g e r and M u l l e r f o r any gas I n v e s t i g a t e d by them (2) (7) (8) was t h a t f o r argon. B o s c h and Klumb and S c h u l z e have shown however t h a t i n e r t gases have c e r t a i n d i s t i n g u i s h i n g p r o p e r t i e s when used i n t h e s e tubes»  U s i n g pure neon and  h e l i u m they o b t a i n e d a c o n t i n u o u s d i s c h a r g e on r a i s i n g the v o l t a g e above t h e t h r e s h o l d , as a g a i n s t the r a p i d l y e x t i n g u i s h e d d i s c h a r g e c h a r a c t e r i s t i c of base g a s e s . t r a c e of a i r o r o t h e r base gas was added, a normal was  When a  click  produced. In view o f t h e s e r e s u l t s a tube  baked out i n a good vacuum and pure argon a d m i t t e d .  was This  gas e x h i b i t e d t h e same p r o p e r t i e s as r e p o r t e d f o r pure neon and h e l i u m . it,  i t was  Upon h e a t i n g the tube a g a i n w i t h the argon i n found t h a t , p r o v i d e d the b r a s s had not been  t h o r o u g h l y baked out, enough o c c l u d e d gas c o u l d be d r i v e n o f f (7) C. B o s c h and H. Klumb, D i e N a t u r w l s s . 18, 1098. (8) W. S c h u l z e , Z e i t . f u r P h y s i k 89, 92, (1932)  (1930)  (6)  to  cause the t u b e t o c l i c k n o r m a l l y . The t h r e s h o l d p o t e n t i a l  was now about 360 v o l t s a t one c e n t i m e t r e p r e s s u r e and moreover t h e r e l i a b l e v o l t a g e range compared f a v o r a b l y w i t h t h a t f o r a i r a t 5 cm,, p r e s s u r e . I t was.found t h a t i f one of these argon tubes was s e a l e d o f f , i t s c h a r a c t e r i s t i c s sometimes over a p e r i o d of t i m e .  changed  I f the b r a s s had been w e l l baked out  b e f o r e a d m i t t i n g the pure g a s , the t r a c e of gas d r i v e n o f f by r e - h e a t i n g as above seemed t o be r e - a b s o r b e d by the m e t a l , the  tube d e v e l o p i n g a tendency t o d i s c h a r g e c o n t i n u o u s l y .  the  o t h e r hand i f no d e - g a s s i n g was done the t h r e s h o l d  On  v o l t a g e would sometimes r i s e a f t e r a month o r so, a p p a r e n t l y owing t o g a s e s d i f f u s i n g out o f the b r a s s i n t o the a r g o n .  To  o b t a i n a c o n d i t i o n under w h i c h the gas m i x t u r e would remain c o n s t a n t I n d e f i n i t e l y , a p a r t i a l d e - g a s s i n g was f i r s t g i v e n the  assembled t u b e , w h i c h was then f i l l e d to the p r o p e r  p r e s s u r e w i t h argon c o n t a i n i n g a s m a l l p e r c e n t a g e of a i r .  Frc  seven to t e n m i l l i m e t r e s p r e s s u r e was found most s a t i s f a c t o r y , an o p e r a t i n g p o t e n t i a l of from 350 t o 450 v o l t s b e i n g then required.  Neon gas, when t r i e d i n the same way,  showed  s i m i l a r p r o p e r t i e s , r e q u i r i n g about 50 v o l t s l e s s than argon under the same c o n d i t i o n s . The Oomplete P o r t a b l e  Outfit? Having d e v e l o p e d a G e i g e r - M u l l e r  Counting tube w h i c h would o p e r a t e on a r e a s o n a b l y low v o l t a g e , i t was now n e c e s s a r y t o c o n s t r u c t a complete  (7)  portable o u t f i t comprising  a tube and a l l i t s a u x i l i a r y  equipment. A  s u i t a b l e d e s i g n o f the tube i s shown  i n F i g . 2.  Fi . 9  H.  The o u t e r e l e c t r o d e B, a l e n g t h o f b r a s s t u b i n g 5/8 i n c h e s i n d i a m e t e r and f r o m one t o s i x i n c h e s l o n g , i s h e l d i n p l a c e by a copper w i r e W s o l d e r e d t o i t and clamped onto the t u n g s t e n w i r e T s e a l e d i n t o one end o f t h e p y r e x g l a s s c o v e r i n g D. c e n t r a l e l e c t r o d e M, a f i n e t u n g s t e n  The  o r manganin w i r e , i s  suspended a t one end from a g l a s s hook G-, f u s e d onto t h e g l a s s w a l l , and a t t h e o t h e r by a second t u n g s t e n w i r e s e a l e d i n t o the outer case.  The f i n a l s e a l o f f , a t S, I s made a t one end.  I n t h i s way a l l s i d e p r o j e c t i o n s are e l i m i n a t e d , a l l o w i n g t h e tube t o be c o n v e n i e n t l y h a n d l e d or p a c k e d . One end ( T  1  i n F i g . 2) i s then immersed  i n p a r a f f i n i n s i d e a g l a s s c o n t a i n e r j u s t w i d e r t h a n the d i a m e t e r of the tube i t s e l f , going i n w i t h i t .  the s e r i e s r e s i s t a n c e (R, F i g . 1)  T h i s o u t e r c o v e r i n g a c t s n o t o n l y as a  (8)  p r o t e c t i o n but a l s o p r e v e n t s any e l e c t r i c a l l e a k a g e a t the terminal T ,  an i m p o r t a n t f a c t o r because of the h i g h r e s i s t a n c e  1  (lO^ohms) of R.  V;  The whole i s now  Wood  case j  I:  inclosed i n a hollow  Insulated  wires.  c y l i n d r i c a l wooden c a s e , a l e n g t h of i n s u l a t e d w i r e c o n n e c t i n g t h i s u n i t t o t h e r e s t of the a p p a r a t u s * The a u x i l i a r y equipment c o n s i s t s of a set  of t e n 45 v o l t b a t t e r i e s , a two-stage audio a m p l i f i e r and  a p a i r of ear-phones. F i g . 4,  The e l e c t r i c a l arrangement i s shown i n  the p l a t e v o l t a g e f o r the a m p l i f i e r b e i n g tapped  the 450 ¥olts s u p p l y i n g the G-eiger-Muller t u b e .  from  Small radio  " B " b a t t e r i e s were o b t a i n e d and they t o g e t h e r w i t h the a m p l i f i e r were mounted i n a w a t e r - p r o o f case on a s t a n d a r d Pack-board, the whole w e i g h i n g about 55 pounds. The ear-phones  are p l u g g e d i n , the two  l e a d s from the tube connected t o t h e i r c o r r e s p o n d i n g t e r m i n a l s and the complete a p p a r a t u s c a r r i e d as shown i n F i g . 5»  The  tube i s mounted on the end of a l i g h t handle so t h a t i t can  (9)  be kept c l o s e t o the g r o u n d .  Fig. V Sensitivity  Tests. As w i t h a l l s m a l l G e i g e r - M u l l e r t u b e s ,  the  number o f c l i c k s p e r minute when a l l r a d i o - a c t i v e m a t e r i a l  i s removed from the neighborhood v a r i e s c o n s i d e r a b l y from minute t o m i n u t e .  One tube gave t h e f o l l o w i n g r e a d i n g s f o r  twenty c o n s e c u t i v e m i n u t e s : 10, 12,  1 1 ,  8 ,  13,  1 0 , 7,  1 3 , 1 0 ,  1 3 , 1 0 ,  1 0 ,  9,  13, 6 ,  11,  14,  9 ,  9 ,  1 0  e a c h f i g u r e b e i n g t h e number o f cosmic and s t r a y gamma r a y s p a s s i n g t h r o u g h the tube d u r i n g t h a t m i n u t e .  For five  minute  c o u n t s , however, t h e p e r c e n t a g e v a r i a t i o n s a r e much s m a l l e r , as t h e f o l l o w i n g r e a d i n g s o b t a i n e d from t h e same tube show: 51,  5 8 ,  4 9 ,  5 0  Thus i t may be seen t h a t by t a k i n g f i v e minute r e a d i n g s o n l y , an I n c r e a s e o f t h r e e gamma r a y s p e r minute t h r o u g h the tube c o u l d be d e f i n i t e l y d e t e c t e d .  I n case o f doubt as t o whether  a h i g h count i s due t o a d d i t i o n a l r a d i o - a c t i v e m a t e r i a l i n  (10)  the neighborhood o r t o s t a t i s t i c a l f l u c t u a t i o n o f the normal c o u n t , a l o n g e r - r e a d i n g w i l l s e t t l e the q u e s t i o n . T e s t s were made w i t h radium and radium ore,  A 53 gram p i e c e of p i t c h b l e n d e from G r e a t Bear Lake  c o n t a i n i n g 60% uranium oxide and about 9 thousandths of a m i l l i g r a m o f r a d i u m gave a count o f 62 f o r f i v e minutes when s i x f e e t from t h e d e t e c t i n g tube and 88 when t h r e e f e e t away. The z e r o count (no r a d i u m i n the neighborhood) was  51»  E i g h t y m i l l i g r a m s of radium, k i n d l y l o a n e d by Dr. G.W.  Prowd o f S t , P a u l ' s H o s p i t a l , Vancouver,  c o u l d be d e t e c t e d a t a d i s t a n c e of 350 f e e t t a k i n g o n l y minute r e a d i n g s .  five  R e s u l t s of a t e s t w i t h t h i s s t a n d a r d are  shown i n T a b l e 1 and t h e g r a p h i n F i g , 6 .  T a b l e 1.  Distance  (feet)  Count (5 m i n u t e s ) •  Zero Count;  100  150  200  265  139  99  45  250.  300  350  82  64  55  (11)  d  .. .  .  = d i s t a n c e  Fig.  •  • l. • •. • • -  i n  ft.  Ii i  E L :  j  I t may be seen from t h e g r a p h t h a t t h e i n v e r s e square l a w i s obeyed w i t h i n t h e l i m i t s o f s t a t i s t i c a l error. I t i s o f i n t e r e s t t o note t h a t o n l y about f i v e out o f e v e r y t e n thousand gamma r a y s p a s s i n g t h r o u g h t h e - t u b e are"'detected. T h i s r a t i o was a r r i v e d a t from t h e a v a i l a b l e d a t a on gamma r a y s from radium i n c o n j u n c t i o n w i t h the  r e s u l t s of t h e a f o r e - m e n t i o n e d t e s t w i t h 80 m i l l i g r a m s  of r a d i u r n .  Other uses f o r t h i s i n s t r u m e n t , b e s i d e s t h a t of p r o s p e c t i n g f o r radium ore may suggest themselves; f o r exaraple  a  t h e l o c a t i n g o f radium n e e d l e s m i s l a i d i n h o s p i t a l s . •Dr. G.M. Shrum o f t h e U n i v e r s i t y o f  B r i t i s h Columbia i s r e s p o n s i b l e f o r t h e o r i g i n a l i d e a o f a d a p t i n g a G e i g e r - M u l l e r tube t o t h e purpose o u t l i n e d I n t h i s  (12)  paper and has a l s o taken an a c t i v e p a r t I n the development o f the complete  instrument.  (13)  TRIBO-EXEGTRIG EFFECT BETWEEN GLASS AND MERCURY. Introduction; When a p a r t i a l l y evacuated g l a s s tube, c o n t a i n i n g s e v e r a l grams o f mercury, i s v i o l e n t l y a g i t a t e d , l i g h t i s g i v e n o f f w h i c h i s e a s i l y observ/ed I n a dark room* The  e x p l a n a t i o n o f t h e p r o d u c t i o n o f t h i s l i g h t was t h e p u r -  pose o f t h i s  investigation. Two p o s s i b l e a l t e r n a t i v e s were c o n s i d e r e d ;  1.  t r i b o - l u m l n e s o e n c e between t h e mercury and g l a s s ;  2.  d i s c h a r g e s i n t h e g a s c o n t a i n e d i n t h e tube between  o p p o s i t e t r i b o - e l e c t r l c charges g e n e r a t e d  on t h e mercury and  g l a s s s u r f a c e s .• Trlbo-luminesoenee.. Most s o l i d s e x h i b i t  tribo-luminescenee  to some d e g r e e , t h e e f f e c t b e i n g produced by r u b b i n g o r r u p t u r i n g the s u r f a c e .  L i g h t w i t h a continuous  spectrum i s  e m i t t e d , the i n t e n s i t y d i s t r i b u t i o n v a r y i n g f o r d i f f e r e n t ' (2) .; materials.  No l i q u i d s have been r e p o r t e d as showing t h i s  phenomenon o r as b e i n g s u c c e s s f u l l y used as '• e x c i t e r s - .  1.  Karl: Comptes Rendu 146, P. 1104; 1907 W. K l u g e : Ann. d e r P h y s i k 1, 1 P. 1, J a n . 2, 1929.  2.  D.M. N e l s o n . J.O.S.A. and R . S . c l . , 12, P. 207 March 1926. CoS. B e a l s : Roy. S o c . Canada T r a n s . 17, S e c t . 3, P. 125 1923• & others.  (14)  Trlbo-electrlclty. The t r i b o - e l e c t r i c  e f f e c t i s the  d u c t i o n o f o p p o s i t e e l e c t r i c a l charges on two  pro-  s u r f a c e s of  d i f f e r e n t m a t e r i a l when they "break c o n t a c t or are r u b b e d (3) together.  Daws on  has  i n v e s t i g a t e d the case f o r mercury  and q u a r t z , o b t a i n i n g a charge of 1 e.s.u./cm. p l a t e w h i c h had been q u i c k l y s e p a r a t e d surface.  2  on a q u a r t z  from a c l e a n mercury .  A p o t e n t i a l d i f f e r e n c e of 3 5 0 v o l t s e x i s t e d between  the two when 1 » 5 m i l l i m e t r e s a p a r t . ,  Thus a s p e c t r o s c o p i c a n a l y s i s of the  i n q u e s t i o n s h o u l d d e c i d e whether a tribo«luminescent o r e l e c t r i c effect i s taking place. continuous  light trib6-  I f the former i s c o r r e c t , a  spectrum s h o u l d be observed; i f the l a t t e r ,  c h a r a c t e r i s t i c spectrum o f the gas p r e s e n t  the  i n the g l a s s tube  s h o u l d appear. Experimental  Procedure. P r e l i m i n a r y experiments w i t h v a r i o u s  g a s e s and gas p r e s s u r e s r e s u l t e d i n argon a t about .4 m i l l i metres p r e s s u r e b e i n g used f o r the f i r s t t r i a l s , g i v i n g the g r e a t e s t luminescence of any t r i e d .  this The  gas  k i n d of  g l a s s or p u r i t y of the mercury used, w i t h i n c e r t a i n l i m i t s , had no a p p r e c i a b l e e f f e c t on  this.  A s m a l l spectroscope c o l l i m a t o r and 3»  w i t h a long  s h o r t f o c u s camera l e n s f o r good  light  l i . H . Dawson. J.6.S.A, and R.S.- I . , 18, P. 344, A p r i l  1929  (15)  g a t h e r i n g power was u s e d . the  A mechanical device f o r shaking  t u b e s w i t h a n e a r l y v e r t i c a l motion e n a b l e d the s l i t t o  be c o n t i n u o u s l y i l l u m i n a t e d .  Even so t h e f e e b l e n e s s of the  l i g h t made exposures of from 12 hours t o 3 or 4 days necessary. Experimental Results; A p l a t e t a k e n w i t h argon a t .4 m i l l i metres p r e s s u r e I n a p y r e x tube showed 2 6 l i n e s on i t , 6 o f w h i c h v/ere i d e n t i f i e d as s t r o n g l i n e s of the mercury spectrum from 4048 t o 5769 R*, 7 as l i n e s In the argon r e d spectrum, 12 from the argon b l u e spectrum and one as the  l i n e of water  vapouro A p y r e x tube c o n t a i n i n g a i r a t .5 m i l l i metres p r e s s u r e gave two s t r o n g l i n e s w h i c h c o r r e s p o n d e d t o two o f t h e f i r s t n e g a t i v e bands of nitrogen*.  3914 and 4278.  Three v e r y weak l i n e s were a l s o p r e s e n t . A f a i n t l i n e spectrum was  o b t a i n e d from a  q u a r t z tube c o n t a i n i n g an unknown gas and p r o d u c i n g a r e l a t i v e l y f e e b l e luminescence« Gonclusion; These r e s u l t s i n d i c a t e d e f i n i t e l y the  that  l i g h t e m i t t e d by t h e s e tubes i s coming from t h e gases  p r e s e n t i n them, t h a t I s , from s m a l l d i s c h a r g e s between o p p o s i t e c h a r g e s produced on t h e mercury and g l a s s w a l l s •> No e v i d e n c e of a c o n t i n u o u s spectrum b e i n g observed a t any  time, i t l a concluded electric  t h a t t h i s phenomenon i s p u r e l y a t r i b e -  effect. The presence o f o n l y t h e f i r s t  negative  bands o f n i t r o g e n on t h e p l a t e from t h e a i r tube was explained, when p r a c t i c a l l y t h e same d i s t r i b u t i o n o f i n t e n s i t i e s was f o u n d i n t h e spectrum o f a weak r i n g d i s c h a r g e t h r o u g h t h i s tube; t h a t i s w i t h t h e low p o t e n t i a l  gradients obtained i n  b o t h c a s e s t h e f i r s t n e g a t i v e bands p r e d o m i n a t e .  The  e x i s t e n c e of o n l y s m a l l v o l t a g e d i f f e r e n c e s a l s o e x p l a i n s the g r e a t e r l u m i n o s i t y o f t h e argon t u b e s , a lower  sparking p o t e n t i a l  than a i r .  s i n c e argon has  (17)  A_SfflPLE APPARATUS FOR  SPUTTERING METALLIC FILMS.  A c o n v e n i e n t form of apparatus f o r cathode s p u t t e r i n g of t h i n m e t a l f i l m s has been c o n s t r u c t e d , A l a r g e h e l l j a r 10 cm. ground opening  i n d i a m e t e r and 20 cm. t a l l , w i t h a  (G., F i g . 1) a t the top and a ground l i p a t  the bottom r e s t s f l a t on a p l a t e g l a s s base ( B ) , the b e i n g made a i r - t i g h t w i t h s t o p - c o c k g r e a s e .  joint  The t o p s e c t i o n ,  T, w h i c h i s ground t o f i t the opening G a c t s as a support f o r the demountable cathode, C, and a l s o as a c o n n e c t i o n t o the pumping system.  An aluminium anode (L, F i g • 2) i s b o l t e d t o  the base B t h r o u g h a h o l e d r i l l e d i n i t , the g a s k e t s S w i t h t h i n l a y e r s o f s t o p - c o c k grease s e r v i n g t o make the c o n n e c t i o n l e a k - p r o o f and t o ease any s t r a i n s on the g l a s s p l a t e .  V:  Water  to  cool  anode, A.  As i t i s e s s e n t i a l t h a t no m e t a l be exposed i n the d i s c h a r g e chamber other than t h a t a c t u a l l y b e i n g s p u t t e r e d , (the aluminium anode excepted s i n c e i t does  (18)  not s p u t t e r a p p r e c i a b l y ) t h e t u n g s t e n  hook s u p p o r t i n g t h e  cathode i s c o a t e d w i t h g l a s s , a s m a l l p o i n t b e i n g l e f t exposed t o make e l e c t r i c a l c o n t a c t w i t h the cathode hook*  For the  same r e a s o n t h e r e i s o n l y a s m a l l opening ( J , F i g . 1) from the. chamber t o t h e pumping system, The cathode i s c o n s t r u c t e d t o s u i t t h e r e q u i r e m e n t s o f t h e work t o be done.  I t must have a f l a t  s u r f a c e of d i a m e t e r g r e a t e r than t h e w i d t h o f t h e o b j e c t t o r e c e i v e t h e m e t a l l i c f i l m and h e l d from two t o f o u r above i t .  centimetres  Copper cathodes c a n be e l e c t r o - p l a t e d w i t h many  metals w i t h which I t i s inconvenient complete c a t h o d e .  o r expensive  t o make a  I n any case only t h e one m e t a l b e i n g  s p u t t e r e d s h o u l d be exposed d u r i n g t h e d i s c h a r g e . From 500 t o 1000 v o l t s D.C. a r e r e q u i r e d to  operate t h e d i s c h a r g e , a l t h o u g h s a t i s f a c t o r y work has been  done u s i n g A,G. v o l t a g e . s u r f a c e t o be c o a t e d  The p r e s s u r e  i s a d j u s t e d so t h a t t h e  i s t a n g e n t t o the edge o f t h e cathode  d a r k space, i . e . about .04 m i l l i m e t r e s of m e r c u r y . G-ood r e s u l t s have been o b t a i n e d w i t h t h i s a p p a r a t u s i n s i l v e r i n g , a h a l f - s i l v e r e d s u r f a c e on a M i c n e l s o n i n t e r f e r o m e t e r m i r r o r p r o v i n g s u p e r i o r t o those p r e v i o u s l y p r e p a r e d by c h e m i c a l means.  B e s t o p t i c a l g l a s s may be  s p u t t e r e d i n t h i s way, t h e r e b e i n g no a p p r e c i a b l e e f f e c t i f the discharge  heating  i s run s u f f i c i e n t l y slowly.  (19)  A SENSITIVE PHOTO-ELECTRIC QUANTUM COUNTER FOR ULTRA-VIOLET . , ;..  . -.,  . •.  •  LIGHT*  , ;  ;  .  \  . v  .  ;  A G e l g e r - M t i l l e r quantum c o u n t i n g tube has been developed  that i s notable f o r i t s great  to u l t r a - v i o l e t l i g h t .  sensitivity  I t s c o n s t r u c t i o n d i f f e r s i n no way  from t h e s t a n d a r d d e s i g n of G-elger-Miiller tube, of a p o l i s h e d t u n g s t e n w i r e  consisting  ,07 m i l l i m e t r e s i n diameter  suspended i n t h e c e n t r e of a l e n g t h of 5 / 8 i n c h b r a s s t u b i n g 9 cms. l o n g , t h e whole e n c l o s e d i n p y r e x g l a s s as shown i n Fig.  le  Fi . I. : T-B rass tube; ; Soldered C o n n e c t i o n at 9  u/ire  W-Tunqsteri S.  A s e n s i t i v e cathode s u r f a c e was p r e p a r e d by h e a t i n g t h e whole tube I n vacuum t i l l z i n c i n t h e lump of s o l d e r a t S evaporated;  some of t h e  t h e n when the  b r a s s was a l l o w e d t o c o o l , t h e z i n c d e p o s i t e d i n a t h i n l a y e r over t h e I n s i d e w a l l a t one end.  The tube was now  fill-  ed w i t h neon a t 9 m i l l i m e t r e s p r e s s u r e and s e a l e d o f f , o p e r a t i n g i n the dark s i m i l a r l y t o o t h e r G e i g e r - M u l l e r t u b e s .  (20)  The s p e c i a l l y t r e a t e d end was to u l t r a - v i o l e t  sensitive  l i g h t of w a v e - l e n g t h n o t more than 3100  and a l t h o u g h p y r e x g l a s s t r a n s m i t s v e r y l i t t l e  1*  radiation  below 2900 A., t h e s e n s i t i v i t y seems t o be g r e a t e r than t h a t of the b e s t s u r f a c e s I n v e s t i g a t e d by G.L. L o c h e r r e c e n t l y , u s i n g a q u a r t z window. Counts from two d i f f e r e n t l i g h t s o u r c e s are  shown:  Source  Distance  Cathode A r e a Count/min Exposed  Non-luminous 7 metres Bunsen Flame  .04 s q . cm.  50 Watt Lamp 7  .015  "  11  18  Count/min/sq.cm. cathode a t 1 metre d i s t a n c e *  48 45  60^000 150,000  liocher g i v e s a v a l u e of 188 i n t h e l a s t column f o r a Bunsen f l a m e , u s i n g a t i n cathode, a l t h o u g h a r e c a l c u l a t i o n from h i s r e a d i n g s i n d i c a t e s t h a t t h i s s h o u l d have been 1880 i n s t e a d o f 188. surface to u l t r a - v i o l e t the  H i s most s e n s i t i v e  l i g h t was 15 t i m e s as s e n s i t i v e as  t i n cathode, b u t even t h i s I s l e s s e f f i c i e n t t h a n the  cathode s u r f a c e here d e s c r i b e d .  #  figure  G.L.  L o c h e r , P h y s . Rev. 42, 525, ( 1 9 3 2 ) .  

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