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The sensitive surface of Geiger Muller counter tubes Makepeace, Ronald A. 1933

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U.B,G. LIBRARY 1 | CAT.  m.LMAj^MhjVzs^  J Ace. R o : « « ^ M ; i ^  THE SENSITIVE SURFACE OF GEIG-SR MULLER COUITLR TUBES.  by  ROHA1D A. MAKEPEACE  A T h e s i s submitted f o r the Degree  . c  of MASTER OF ARTS  May, 1953. at TEE UIIYERSITY OF BRITISH COLUMBIA.  s s  ^  B  f  THE SENS I f I Y E y s U R P A C E OP / GEIGEB WIIulRv GOTJHTER T U B E S .  IITROPUGTIOlsfc """  S i n c e G e i g e r l i i l l e r tubes 'are used as a  /.standard method l o r d e t e c t i n g cosmic rays i t i s important to a G e i g e r tube o f g i v e n  know' the ^ c o r r e c t " e ^ size.  The agreement between v a r i o u s observers on t h i s p o i n t  i s not v e r y good.  I t i s commonly accepted t h a t the number  o l c l i c k s p e r minute f o r a counter depends d i r e c t l y on the s u r f a c e area o f the metal, tube  forming the cathode  so that  the count o b t a i n e d "by v a r i o u s observers f o r Geiger tubes i s g i v e n here i n t h i s  form.  *J» A* Van den Akker Kniepkamp G e i g e r and M i i l l e r  1.4  p e r cm. p e r min.  7  per cm. p e r min.  '  .51 per cm! p e r min.  if.  1.1 * Present A r t i c l e  p e r cm! p e r min*  .S'Z. p e r cm I p e r min.  W r i t e r s marked w i t h a s t a r g i v e more data on c o n d i t i o n s which would a f f e c t the r e s u l t s . - t o : t h i s data the r e s u l t s s h o u l d have been s i m i l a r .  complete According A l l results  ; l i s t e d are f o r ; a •''bailer, count except 'perhaps t h a t o f Kniepkarnp ;  which i s f r o m q u i t e ah e a r l y a r t i c l e . :  Much- o f the d i s c r e p a n c y  may be a t t r i b u t e d t o d i f f e r e n t c o n d i t i o n s o f s h i e l d i n g due to the ^ s u r r o u n d i n g ^ b u i l d i n g and a l s o t o the unknown presence o f :  .Review 1  H  If 30  p<j. &  ' FVAyvs-I 'K;A r-j 5-.cfee-. ^ " . e . v . t " s G i ' H ^ f ; ..,3o- ;nvf :  :  '  Z e , f  5  c h r i f  t  fur Phys/K  J>f  : slightly z  3  7  -  &\n<f J% S<zbr-$> mi-  :  radioactive material.  However, the w r i t e r found t h a t two  G ei ge r tubes made from the same l e n g t h o f brass  tubing,  , p o l i s h e d and t h e n cut i n h a l f ...'and using, the :same h i n d o f wire  e l e c t r o d e g i v e n approximately  t h e same treatment showed  q u i t e a d i f f e r e n t p a l i e r count when f i l l e d with dry a i r t o the same p r e s s u r e .  With- these premises, i t was thought not  i n a d v i s a b l e t o attempt t o f i n d out what i n f l u e n c e s caused .the r a t e o f the counting  to vary. i  I . F. C u r t i s s h a s a l r e a d y g i v e n r e s u l t s on t h i s s u b j e c t s u g g e s t i n g -that- the tube w a l l s have a predominant e f f e c t on the count.  He a l s o g i v e s a p a r t i a l  o f the o p e r a t i o n o f the counter.  explanation  The e x p l a n a t i o n , however,  does not cover' t h e r e s u l t s o f Schulze  and others who s t a t e  t h a t the i n e r t gases when used pure i n the counter, a continuous  discharge.  maintain  T h i s a r t i c l e i s w r i t t e n i n an  attempt to show t h a t the presence o f adsorbed gases on the w a l l s o f the tube together, perhaps, with an o x i d i z e d l a y e r r  on t h i s : s u r f a c e c o n t r o l the o p e r a t i o n ' o f the tube t o a l a r g e extent.  A theory  s i m i l a r to that o f C u r t i s i s a l s o suggested  .on t h e f u n c t i o n of the gas l a y e r i n the Geiger on experimental  counter  based  r e s u l t s g i v e n here.and a l s o on r e s u l t s o f gas  a d s o r p t i o n experiments o f G-. I . F i n c h and J . C. Stimson. APPARATUS:' Geiger  F o r most o f the work, a demountable form o f .  counter  bureau  of  was used.  o f the u s u a l ground g l a s s  S t a n d a r d s •• Jo-ur.ndl  Pro c e e j i nc£S Vol- ne  Instead  o f J^ ^ 3 I S o c i e t y c  y ( . izo 0  mg.3  of Research oi London Vol-  Hav I^SO j?cj CO I S e r i e s f\ Vol- i n  3  j o i n t , a "brass head was threaded t o screw i n t o a b r a s s socket which was f i x e d on to t h e g l a s s tube with a Dekhotinsky The d e t a i l s are shown c l e a r l y i n F i g u r e I .  joint.  When the threads  were c o a t e d w i t h stopcock grease, a s e a l was formed q u i t e sufficient  f o r t h e purpose.  One end o f the wire f o r the  counter was fastened t o the c e n t r e o f the b r a s s head, the other was embedded i n a s m a l l g l a s s c y l i n d e r c o n t a i n i n g s u f f i c i e n t l e a d weight to h o l d t h e wire t a u t when the head was i n p l a c e and t h e tube was h e l d v e r t i c a l . aluminum tubes used  The b r a s s and  i n the counter f i t t e d the i n s i d e o f the  g l a s s t u b i n g c l o s e l y and r e s t e d on a narrow b r a s s r i n g which was i n t u r n supported by a b r a s s s p i r a l .  A g l a s s tube  outside was made with a tungsten s e a l . inside, t h e b r a s s s p i r a l prevented,any being produced.except counter.  A connection t o the fitting  e l e c t r i c a l disturbance  through the a i d o f t h e tube used as  The assembly was clamped"in  a vertical position  q u i t e r i g i d l y .so; t h a t the wire remained f a i r l y w e l l centred* The diagram o f the other form o f Geiger counter used i s s e l f e x p l a n a t o r y (see F i g u r e I I ) . During the e a r l y p a r t o f the work the source o f h i g h p o t e n t i a l was a transformer f e d by 110 v o l t s A . C . A vacuum tube r e c t i f i e r i n s e r i e s w i t h condensers  and a h i g h  r e s i s t a n c e was s u f f i c i e n t t o convert the h i g h A * C i v o l t a g e i n t o a reasonably constant D*G. supply, more convenient driven.  l a t e r i t was found  t o use a D . C . h i g h v o l t a g e generator, motor  The motor was operated by storage b a t t e r i e s .  A  v a r i a b l e r e s i s t a n c e i n s e r i e s with the b a t t e r i e s made i t  p o s s i b l e to r e g u l a t e the speed o f the motor and t h e r e f o r e the p o t e n t i a l a t the generator terminals.' The v o l t a g e r i p p l e was The III*  reduced by means o f a choke c o i l and  condensers.  e l e c t r i c a l G e i g e r tube c i r c u i t used i s shown i n F i g u r e The r e s i s t a n c e W was  1 0 ohms and was measured q u i t e  a c c u r a t e l y by determining the r a t e o f d i s c h a r g e o f a 1  condenser  through W.  I t was  made by marking an I n d i a i n k  line•.. on a p i e c e of cardboard which was p a r a f f i n and surrounded  by g l a s s .  then dipped i n  An e l e c t r o s t a t i c v o l t m e t e r  measured the p o t e n t i a l a c r o s s the G e i g e r tube.  I t was  c a l i b r a t e d a g a i n s t b a t t e r i e s ,'of known E.M.ff. EXPSRIMEET: av  Graphs I and I I g i v e the curves f o r two tubes •  . of apparently i d e n t i c a l construction.  I t w i l l ' be n o t i c e d  t h a t one tube g i v e s a p a l i e r count twice that o f the other ;  and t h a t the tube 'with' the lower curve has .a l o n g e r p a l i e r . . T h i s w i l l be found to agree w i t h l a t e r b.  experiments.  In.order t o t r y the e f f e c t o f v a r i o u s s u r f a c e s  .on.the count,, keeping e v e r y t h i n g .else; constant as f a r as p o s s i b l e , four b r a s s tubes were, prepared; the f i r s t had a p o l i s h e d b r a s s s u r f a c e which was the second was  given a l i g h t  gas flame, the t h i r d was gas flame, the f o u r t h was • t h i s experiment,  l e f t t o age  for several  days,  oxide coat by h e a t i n g with a  coated with a l a y e r o f soot from a coated w i t h mercury.  the; mercury coated tube was  Before use i n  aged by standing  , i n a i r f o r a few, days, s i n c e , as w i l l be e x p l a i n e d l a t e r , a ,. fresh, s u r f a c e behaves abnormally.  A l l , s u r f a c e s r e f e r t o the  i n s i d e o f the b r a s s tube only. Ihese prepared tuhes were p l a c e d s u c c e s s i v e l y  i n t h e demountable tube h o l d e r .  The counter was cleaned  with ether at d e s i r a b l e p o i n t s to prevent p o s s i b l e i n s u l a t i o n leaks.  Before each curve was taken.,the Geiger counter was  pumped but f o r t h r e e hours with an o i l pump a f t e r which dry ,, a i r was admitted t o a p r e s s u r e o f f i v e centimetres o f :  mercury.  As much p r e c a u t i o n was taken t o a v o i d  contamination  w i t h mercury vapor as was p o s s i b l e without the use o f l i q u i d air.  Graphs I I I , IV, V,,and VI i n d i c a t e the r e s u l t s o f  t h r e b minute r e a d i n g s taken at I n t e r v a l s o f t w e n t y - f i v e v o l t s which was as c l o s e a s c o u l d be reasonably estimated with the . :  e l e c t r o s t a t i c voltmeter*  Graphs ¥ 1 1 and V I I I are curves f o r  a .polished aluminum"tube which had been aged and f o r an aluminum tube coated w i t h soot.  :  Graphs IX and X i n d i c a t e  v the r e s u l t s - o f r e a d i n g s taken f o r the oxide and soot coated .brass t u b e s - f o u r days a f t e r the f i r s t these tubes*  s e t o f readings f o r  S o t h i n g had been changed between two s e t s o f  readings f o r the .same tube* V c* experiment*  F i g u r e IV sho^-fs the arrangement f o r t h i s  S l i m i n a t l o n o f a l l gases except mercury vapor  i n the G e i g e r tube was obtained "by keeping temperature  oven I a t a  o f 350°C. f o r three hours and at the same time  pumping out the.tube Iwith a mercury d i f f u s i o n pump.  The  lower h e a t e r was t h e n operated so t h a t the vapour p r e s s u r e o f merbury" i n c r e a s e d .  The Geiger tube was kept at a h i g h e r  leraperatiire than t h e mercury below so t h a t t h e r e would be no tendency  f o r merctify t o condense on the tube w a l l s .  The  h e a t e r s were then taken away and the mercury removed from  the  lo?;er tube.  The tube Yv-as now  f i v e centimetres pressure.  f i l l e d w i t h dry a i r at  On a p p l i c a t i o n of the necessary  p o t e n t i a l f o r normal o p e r a t i o n , i t was  found t h a t the tube  ;went. • i n t o a C o n t i n u a l c l i e k i n g ; d i s c h a r g e . heated t o 200°0. the  The tube was then  and evacuated f o r h a l f an hour.  After this  counter operated n o r m a l l y . A S i m i l a r .experiment, was performed i n which  only a brass tube i t s e l f was heated with mercury vapor f o r s e v e r a l hours.  The tube was then i n s e r t e d i n the demountable  Counter and showed i d e n t i c a l r e s u l t s w i t h the above tube immediately a f t e r i n s e r t i o n .  I n t h i s case the counter was  l e i t untouched and a f t e r s e v e r a l hours r e t u r n e d t o normal operation. ;thls::tim:e. the  :  The a i r i n the counter was not changed d u r i n g I f a:,tube:;is\':baked.,v'6ut-" and, evacuated without >  ,  ;  use o f m e r c u r y , n o i n t e r e s t i n g r e s u l t i s o b t a i n e d . .&»  A b r a s s tube was p o l i s h e d w i t h f i n e emery  ..paper td,:remove the., o l d s u r f a c e .  'When p l a c e d i n the demount-.-  Vabie;'-t.ub.:e.fhpld.e,r ,and used as the. .negative , e l e c t r o d e f o r a;  Geiger" counter,,a C l i c k i n g ^discharge took place, as i n the p r e v i o u s experiment,  Ho d i f f e r e n c e i n the e f f e c t could be  d e t e c t e d w i t h n i t r o g e n or oxygen used t o operate the counter although the n i t r o g e n i n the counter was not a b s o l u t e l y pure. ;;This ; was -'.because theeffect l a s t s r o n l y t h i r t y minutes 1  the  and;  u s u a l methods of baking out and evacuating a v e s s e l t o  d r i v e : o u t gases r e q u i r e f o u r hours.  Aluminum and magnesium  tubes act s i m i l a r l y but the, emery paper i n these, cases does not  remove the o l d s u r f a c e so w e l l .  7  '-  There was  i  was  a ' p o s s i b i l i t y t h a t the phenomenon  a photoeleetric elfeot  since, the oxide f i l m . h a d been  removed from the metal s u r f a c e * due t o l i g h t  I t was  found  that'clicks  f a l l i n g on the s u r f a c e d i d i n c r e a s e g r e a t l y i n  the case,; of- aluminum and magnesium ?/hen the s u r f a c e Was: :  p O l i s h e d but that:, i n complete per, minute was  darkness vthe number o f c l i c k s  s t i l l much too -great and t h a t w i t h .--a :fresh  ;  b r a s s ^ s u r f a c e , the change i n the d i s c h a r g e when the were switched . o f f  v  was  lights  not, n o t i c e a b l e .  A change i n the type of sandpaper the grade) made no d i f f e r e n c e -'to the r e s u l t . :was -noticed:;  used (not  A similar mercury was  but I n t h i s case t h e r e was  effect used  some p o s s i b i l i t y that water vapor  , ;on:;the:; surface was, causing,.;the phenomenon* ; ;  e. , experiments  As a r e s u l t o f c o n c l u s i o n s drawn from p r e v i o u s  i t was :thought p o s s i b l e : t h a i :pure n i t r o g e n used  \for:::a^&elger counter might not p r o v e - s a t i s f a c t o r y . was.obtained  Iltrogen  by h e a t i n g sodium azote, and alumina, and p a s s i n g  the gas produced  through/a phosphorus pentoxide: d r y i n g tube-.',  The u s u a l procedure o f baking out and evacuating the Geiger tube was  c a r r i e d out before a d m i t t i n g the n i t r o g e n . A f t e r one: f l u s h i n g out with n i t r o g e n , the  c l i c k s , appeared.rather, ^prolonged but- no: f u r t h e r -change .in the -quality of t h e c l i c k s c o u l d be o b t a i n e d . little  Gn a d m i t t i n g a  a i r i n t o the t u b e , immediately the same type of,,.  c l i c k i n g d i s c h a r g e was already described. morning.  I t was  obtained that; e x i s t e d i n experiments  The tube was  l e f t untouched  then working n o r m a l l y .  till  the next  8,  1  ^-;v^- >-;fv - I t was found by R. I* Smith that a Geiger ;  :  counter u s i n g a h e a v i l y o x i d i z e d b r a s s tube would  produce  only a;vdo;.scont.ihuous.vdischarge.-..-'-. 'This-..was not due t o a ;  mechanical d e f e c t i n t h e counter s i n c e a l i t t l e water washed ^oy.er the s u r f a c e o f the -tube and then removed, r e s t o r e d the counter t o normal o p e r a t i o n . -•g.. •''..•Using;-former• work 'as--a guide i t was decided to perform the f o l l o w i n g experiment.  Some powdered,  a c t i v a t e d c h a r c o a l was a t t a c h e d t o the i n s i d e w a l l o f a brass tube by '•"mean's o f a very t h l h . l a y e r o f lekhofinsky cement, :  f fie/tube ^was  then plae«d i n the tube holder,and the Geiger  counter 'thus/produced was Immersed, as f a r as p o s s i b l e , 'In'.' liquid air.  The p r e s s u r e was kept  fairly  constant at f i v e  c e n t i m e t r e s d.ue t o the r e l a t i v e l y l a r g e r e s e r v o i r o f dry a i r connected,to'the  tube.  The number o f c l i c k s per minute d i d  ,. n o t change/ hot ice a b l y while the temperature 'decreased but :  ;  '/after- •the. l i q u i d a i r was removed while; the temperature o f the tube was r i s i n g , a ' d i s c b n t i n u o u s discharge took p l a c e :  s i m i l a r t o those b e f o r e mentioned. r e p e a t e d twice*  T h i s procedure was  The t h i r d - t r i a l was not s u c c e s s f u l but on  r e p e a t i n g the experiment  some hours l a t e r , the.phenomenon was  "again evident;. A l s o , the first''-ahd- l a s t times t h e experiment was c a r r i e d out, when the tube had almost recovered room • temperature, due  the -counting s t o p p i n g completely.  (as thought  T h i s 'was not -  at f i r s t ) ' t o leakage o f t h e c u r r e n t along  E. I . 'Smith .- graduate -.student-'.in\PhysiesV U n i v e r s i t y of B r i t i s h Golumbia.  9.  the  o u t s i d e o f the tube owing to the f o r m a t i o n o f m o i s t u r e .  *. "7ThU "t*ube/will'-resUm'e- normal -.operation a f t e r approximately :  V; V f l v e fflihute-s.; In mentioned  a d d i t i o n t o these experiments may  be  two r e l a t e d f a c t s a l r e a d y known..,/. The f i r s t i s  t h a b a tube goes I n t o a discontinuous, d i s c h a r g e .when, heated; the  other that' a tube f i l l e d w i t h pure  C o n t i n u o u s l y a s Soon as the f i r s t •':-: v  :  :  argon  discharges. ,  c l i c k takes p l a c e  The p r e c i s i o n necessary I n c e r t a i n  : ::  m e e h a m o a ' l . d e t a i l s " o l c o n s t r u c t i o n ofVthe counter Should be :  /-.pointed";outvC'-VThe d e s i g n o f t h e demountable- tube makes i t •, ; ,y'ery^  from the centre of the tube...  ;  by t i l t i n g the  the counter s l i g h t l y .  I n v e s t i g a t i o n showed that  c e n t e r i n g o f the wire was not c r i t i c a l .  V-\. the  walls  Roughness o f  .  of/the* sJetal tube used as cathode d i d not have.  any- pronounced  effect.  P a r t i c l e s o f the s i z e o f phosphorus. .  yr::' vpentoxide :.dust• .-pr-.; sbb'tv'paroleles'---.:bn- the wire-*, however, cause :  sllentfcontinuous-  :  SISQUSSIDN OP THE RESULTS:  . A s be.for.'e ,st-ate.d',' tile: .resultfi ;  v  :  ' bear a r e l a t i o n t o those obtained by P i n c h and Stimson f o r the  a d s o r p t i o n o f gases on hot m e t a l l i c s u r f a c e s .  m e t a l l i c s u r f a c e i s heated i n vacuo  or In contact, with a gas  i t , becomes charged t o -a p o t e n t i a l dependent temperature and the metal.  When a  on. the gas, the  The p o t e n t i a l a t t a i n e d  i s always  n e g a t i v e except i n the case o f oxygen between 200° and 300° G i n which case i t i s p o s i t i v e . the  T h i s Is e x p l a i n e d by  assuming  a d s o r p t i o n o f both p o s i t i v e l y and n e g a t i v e l y charged moli*  10.  i n t h i s i n s t a n c e 'the  e c u l e s oh.the m e t a l l i c s u r f a c e *  p o s i t i v e l y c h a r g e d , p a r t i c l e s predominate. • Suppose t h a t due t o t h e n e g a t i v e p o t e n t i a l o f the tube with r e s p e c t t o the wire some, o f t h e - a d s o r b e d , molecules The  on, the s u r f a c e o f the tube, are charged n e g a t i v e l y .  o p e r a t i o n o f the counter i s t h e n explained.as f o l l o w s . .  E l e c t r o n s c r e a t e d by the i n i t i a l  i o n i z a t i o n i n the tube move  towards the wire, p r o d u c i n g a d d i t i o n a l i o n i z a t i o n i n the i n t e n s e f i e l d near the w i r e .  P o s i t i v e l y charged molecules  created  .'-'by.;'-'the o r i g i n a l f a s t p a r t i c l e i n the tube and by the r e s u l t a n t e l e c t r o n s move towards the tube w a l l s .  By e l e c t r o s t a t i c  a t t r a c t i o n e l e c t r o n s are r e l e a s e d from t h e n e g a t i v e l y charged m o l e c u l e s u n t i l over t h e s m a l l l o c a l area i n which the a c t i o n t a k e s p l a c e the .The discharge,, then, s t o p s .  supply- o f e l e c t r o n s i s exhausted. T h i s d e s c r i p t i o n may be a s l i g h t  Q l a r i f i c a t I o n over t h a t g i v e n by. G u r t i s s . . The .graphs f o r - d i f f e r e n t , s u r f a c e s were plotted"' in  an e f f o r t  t o .uh'de'r.st.aad' 'the-, w i d e l y , ' - . d i f f e r i n g -re"sult;s. o f  Curtisson various surfaces. 'bh, a brass tube ;  Curves  f o r four d i f f e r e n t s u r f a c e s  (Graphs 111, .'IY, Y and YI) are g i v e n i n which  gaseous and other c o n d i t i o n s were kept as constant as p o s s i b l e . . U s i n g the p a l i e r count  f o r t h e s u r f a c e s immediately  after  i n s t a l l a t i o n i n the counter, i t cannot be s a i d t h a t t h e number of  c l i c k s p e r minute v a r i e s more than 10$ except i n t h e case  of  t h e mercury surface, which a p p a r e n t l y has,only a v e r y  i n d i c a t i o n o f a p a l i e r at f i f t y  counts p e r minute.'  slight  iiv  The two  s u r f a c e s on the aluminum tube a l s o showed quite-  similar results  (Graphs ¥ 1 1 and. YTIT): although the count, per  Square,centimeter was h i g h e r because  o f the aluminum.  Graph I I I f o r the s o o t ' c o a t on the b r a s s tube has two The lower one i s assumed c o r r e c t  s i n c e i t occurs at the same  ;.p-Ot ehti.al' 'as..- th:ps:S';.r;epr e'S'eitting' -the.' other s u r f a c e s . r  s  s  e x p l a n a t i o n can'he o f f e r e d f o r the second low c o n s i d e r the two which have heeh untouched  paliers  lo  palier.  curves shown f o r counters  f o r a few days..  The count i s -  d i s t i n c t l y lower and the p a l i e r f l a t t e r than b e f o r e (Graphs 'iXv-.-ahd X) *  A l s o the percentage i n c r e a s e w i t h a sample o f at the same d i s t a n c e  '-'radI--OB.c'tl-v-e  S I I and X I I I ) . .'-:;,  '  a w a y  ' '  'is g r e a t e r :  (Graphs  -  . - : I t - . i $ .sugges-t'ed.:- t h a t - the-., concentration, of .  m o l e c u l e s on the s u r f a c e of: the tube i s g r e a t e r at atmospheric pressure' than at f i v e c e n t i m e t r e s .  To r e s t o r e e q u i l i b r i u m when  the p r e s s u r e : i s reduced, molecules' l e a v e .the surface..  If  thei.'molecule i s charged on l e a v i n g the s u r f a c e , i t w i l l , producea  click.  These e x t r a c l i c k s should d i m i n i s h i n ah  e x p o n e n t i a l manner.  The two lower curves approximate more,  closely, t o the c o r r B C t nomher o f e d i c t s per minute  as  determined by "a s e p a r a t e v e r y s a t i s f a c t o r y tube g i v i n g the curve shown i n Graph XI and a l s o a c c o r d i n g to r e s u l t s , o f Bi,Hamilton^Working 1  R.  i n the same room.  Hamilton - graduate student i n P h y s i c s , U n i v e r s i t y ....... o f B r i t i s h  Columbia.  12.  A theory  o f charged molecules l e a v i n g the  s u r f a c e could a l s o he adduced t o e x p l a i n r e s u l t s d e t a i l e d i n p a r t s (cl (e) and (g| .  In p a r t .(e), evaporating  molecules may be. assumed charged.  mercury  I n p a r t (e), the s m a l l  q u a n t i t y o f oxygen admitted d i s p l a c e s the n i t w g e h on the -surface o f the tube, the n i t r o g e n coming o f f charged* f h l s ^ a g r e e s w i t l i resuli;s on hot s u r f a c e s i n Vvhich i t i s found t h a t 2^ Oxygen w i l l cause the n i t r o g e n charge t o be d i s p l a c e d by the oxygen charge on the m e t a l l i c s u r f a c e . A f u r t h e r comparison w i t h t h e hot s u r f a c e suggested t h a t . n i t r o g e n might behave l i k e argon i n a Geiger  tube.  The  • r e s u l t o f t h i s ; experiment d e s c r i b e d in;(e) was not s a t i s f a c t o r y :  although i t d i d appear t h a t pure n i t r o g e n g i v e s prolonged c l i c k s * ; . .11 Is; p o s s i b l e t h a t the n i t r o g e n use e n t i r e l y pure*  - R e f e r r i n g t o p a r t (g),  not  i t i s known t h a t  charcoal  adsorbs gases when c o o l e d t o l i q u i d a i r temperatures and l i b e r a t e s them when the temperature i s r a i s e d . copper s u r f a c e .should.; give s i m i l a r r e s u l t s . The, f a c t t h a t a Geiger :very; pure .rare gas I s unstable  A spongy  ;  tube f i l l e d  with a  suggests t h a t the f i r s t ,  p o s i t i v e i o n s which approach the cathode a t t r a c t the charged ' g£a:iH"qleculesbthems-eiVeB'--;frpm the Surface, making i t p o s s i b l e ;  for  f u t u r e e l e c t r o n s t o be a t t r a c t e d from the s u r f a c e o f t h e  tube. I t s e l f and thus m a i n t a i n i n g  a discharge.  I f a small  q u a n t i t y o f oxygen i s admitted, i t w i l l at once d i s p l a c e the argon on the s u r f a c e and form a s t a b l e l a y e r .  /  The  13.  d i s c h a r g e s caused  by a f r e s h s u r f a c e  seemed t o have some r e l a t i o n to contact p o t e n t i a l s . A l l metals become mere e l e c t r o p o s i t i v e when the s u r f a c e f i l m i s removed.  E l e c t r o n s are more e a s i l y emitted from a f i l m  surface,.  T h i s film,may be an oxide coat or adsorbed  free  gas but  u n t i l i t i s formed a p p a r e n t l y a supply o f e l e c t r o n s from the .tube w a l l s keeps up a d i s c o n t i n u o u s d i s c h a r g e . A s i m i l a r e f f e c t due t o a heavy oxide coat on a brass: tube i s s t i l l without  adequate explanation*.  found i n hot s u r f a c e experiments :Coat .on; the s u r f a c e o f a copper ;  It was  a l s o t h a t a heavy oxide sheet prevented any "charge •  frbm/appearing. \ i n i c k e l sheet which had been o x i d i z e d ,  hbwever, p r e s e r v e d the s a m e . c h a r a c t e r i s t i c s as the pure nickel"surface.  I t would be i n t e r e s t i n g t h e r e f o r e t o  a s c e r t a i n the . r e s u l t o f u s i n g a n i c k e l oxide coat f o r a Geiger  tube. -Examination o f • the-'graphs  f o r a counter with  'a.--/clean; brass;^surface and also;:for the| c h e c k i n g  counter  which, had a p o l i s h e d b r a s s tube Shows that at" v o l t a g e s h i g h e r than the p a l i e r V o l t a g e , t h e curve i s f l a t t e r t h a n f o r other t u b e s . T h e aluminum tube which was p o l i s h e d and aged does not ;:sh.ow t h i s e f f e c t So markedly: due t o more complete o x i d a t i o n . /-For /curves;;;haying t h i s abnormal f l a t n e s s , / the / c l i c k s were prolonged  over that  o f the curve , and 4  sounded-'like t h r e e or f o u r c l i c k s i n quick s u c c e s s i o n .  . M: H e  . Ph  •  14  •'Ap^ar eht'lyva'"'thiii-'oxide f i l m non-metallic ;  serves the-ipurpose  surface  from; ^emerging f r o m t h e As  on a m e t a l l i c s u r f a c e o r  su  and. t h u s  a Geiger:counter  of preventing  electrons  extending  clicks. .  i s heated*  o f - t h e m o l e c u l e s on t h e t u b e s u r f a c e due begins;./v I f . a c c o r d i n g  to theory,  both  to  :  :  • " b e g a t i v e l y c h a r g e d i o n s " w i l l be frequency  charging  C w l t h t.emperat.nre and  t h a t an  up  of the  While the  explanation  of tbe  onsiirface  o f the hathode*  between the work a r e  operation  one; m i g h t g i v e a good c o u n t e r . free  from dust  tube, s h o u l d  used.  A  Also  One  counter  t u b e s and  other  to  i s very over  tbe  exist  fields  of  •'"'•' results  from a l l s o u r c e s  s h o u l d use  p a r t i c l e s . The  t o be  regarded  i n making  a smooth r a t h e r f i n e  f i n e r the wire  c e n t e r i n g o f the wire  have a t h i n  m e n t i o n e d above  oxide  coat  o t h e r gas  wire  used, the  i n the  less  tube.  i f a metal surface i s  s m a l l p e r c e n t a g e o f o x y g e n or h y d r o g e n s h o u l d  m i x e d v W i t h any  drawn  detailed  c e r t a i n r e l a t i o n s which  of Geiger  then  increases be  result  f i l m s w h i c h form a c o a t  certain precautions  c r i t i c a l w i l l .be t h e The  o f the Geiger  indicated. .' U s i n g  surface  a l t o g e t h e r c o r r e c t , I t i s safe  •«'oi£"eiMe>'that-,the '"operation  inside  surface  I n c r e a s i n g c u r r e n t may rises.  much d e p e n d e n t  and  T h i s . f o l l o w s from  temperature  t h i s paper/may •'•hot b e  activation .  temperature  on t h e  frbrh t h e * s u r f a c e as t h e  in  the  released with increasing  a s t h e t e m p e r a t u r e .Is r a i s e d .  the; f a  the  positively  • &egat iY0lytcharged,•• mbieeuies - a r e a d s o r b e d ;  a  t o be u s e d i n t h e  counter  due  be to  15.  the  high a f f i n i t y  vapor no  and m e r c u r y  l e a k a g e due  composing (l)that  the  has  no  to poor  gases  a r e t o be  conditions  not  gases which  The  affect  (S)that  found  f o r the s u r f a c e .  avoided.  insulation.  surface w i l l  adsorbed  t h e r e a r e no not  vapor  i t i s a conductor,  e m i t t e r under it  o f t h e s e two  There  actual  should  be  material  the count p r o v i d e d  i t i s not.an  electron  i n G e i g e r c o u n t e r s , (3) will  Water  be g i v e n o f f , (4)  sharp p o i n t s a l t h o u g h a f a i r l y rough  that that  surface i s  detrimental. I wish  Shrum f o r . many h e l p f u l work.  t o e x p r e s s my  i n d e b t e d n e s s t o D r . G.  s u g g e s t i o n s and  criticisms  in this  M.  .j  1 .  I  n  s Tul>g  .Soo'f Coe  1  )  1  _  ©  ( •  <  •go  Y --  ©  <  60 (  )  ©  - "" •  1  GO JV © <  • }  (  10  w00  II.  fo  /*  50  :  )0  W I ™T  OO  0>  j Tute  Soot COA1 I  /J.  /Si > 0  V  f—>,  ' , : 1,,-,,,.•„.  /¥ ^ 2 - - — -  5-0 —  visit  5  —  ©  Grdpk 0 1  m  :e/ii'*te ly ©  <1  J  in.  -v se r t W r v co0 1 yter.  10 /  >  /  «C  Qn T a ken.  cif  few  cf.'^y  s,  0 >  Lo 1/.  ...  >  >0  MO X  \  III SO  1300  '0  i3Z:  ffr-C>o  /yiro  Volts  I  .1  !  -  -7/5 :  •  Tub e.  Cod.fed  M e r c U r-\/  SO  '"/ -  C rA  p  K JT  HQ •  •  1  30  II  ro  iu  13*  so  /i/  OO  i  -  © ©  ,  3e  «  G i <  C Ke c k i r  1  . 1 -  to 10=>0  /OffO  ll'pO  l/ii'O  IZ P0 ]  12  . /3C3 0  / Jro .  Vo/ts  

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