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SENSITIVE AREA OF A BACK-SCATER-TYPE GAS FLOW DETECTOR FOR CONVERSION ELECTRON
MÖSSBAUER SPECTROMETRY
M. Inaba, K. Nomura, Y. Ujihira
To cite this version:
M. Inaba, K. Nomura, Y. Ujihira. SENSITIVE AREA OF A BACK-SCATER-TYPE GAS FLOW
DETECTOR FOR CONVERSION ELECTRON MÖSSBAUER SPECTROMETRY. Journal de
Physique Colloques, 1980, 41 (C1), pp.C1-115-C1-116. �10.1051/jphyscol:1980122�. �jpa-00219690�
JOURNAL DE PHYSIQUE Colloque
Cl,
suppl6ment au n O 1 , Tome41,
janvier1980,
pageC1-115
SENSITIVE AREA OF A BACK-SCATTER-PIPE GAS FLCW DETECTOR FOR CONVERSION ELECTRON M&SBAUER SPECTRMTRY
M. Inaba, K. Nomura and Y. U j i h i r a
F a c u l t y o f Engineering, t h e U n i v e r s i t y o f Tokyo, 7-3-1 Hongo, Tokyo, Japan.
Abstract.- Counting c h a r a c t e r i s t i c s of a back-scatter-type d e t e c t o r f o r CEMS were studied i n terms of a sample p o s i t i o n , a distance from a sample t o a source, a window diameter of a de- t e c t o r e t c . ; Useful information on a p o s i t i o n s e n s i t i v i t y was obtained f o r t h e b e t t e r sample s e t t i n g i n a d e t e c t o r .
1. Introduction.- !he gas flow d e t e c t o r f o r CEMS was devised by Swanson and Spijkerman/l/. Since then many s c i e n t i s t s have s u c c e s s f u l l y used detec- t o r s of t h i s type f o r q u a l i t a t i v e analyses 12-41 and o t h e r s made new d e t e c t o r s f o r obtaining a good counting e f f i c i e n c y 151. However counting charac- t e r i s t i c s of resonantly s c a t t e r e d e l e c t r o n i n t h e s e d e t e c t o r s i n terms of t h e sample p o s i t i o n and o t h e r f a c t o r s have not been evaluated i n d e t a i l . It i s important t o c l a r i f y s e v e r a l f a c t o r s t h a t influence t h e s e n s i t i v i t y of a d e t e c t o r , not only f o r t h e de- s i g n of an e f f e c t i v e d e t e c t o r , b u t a l s o f o r t h e establishment of a q u a n t i t a t i v e s u r f a c e a n a l y s i s by CEMS
.
2. Experimental.- We chose a model BSD-2400 made by Austin Science Associates Inc. a s a t e s t d e t e c t o r and t h e counting performance was i n v e s t i g a t e d by changing s e v e r a l f a c t o r s . A high voltage applied t o an anode of t h e d e t e c t o r was 1800V and Q - g a s ( ~ e 9 8 . 7 % + i s o - ~ ~ ~ ~ ~ 1.3%) was flowed during a measure- ment. A 5 7 ~ e 90.6% enriched s t a i n l e s s s t e e l f o i l of 6mm i n diameter, purchased from New England Nu- c l e a r Co., was adopted a s a probe. A y-ray source was 3mCi 5 7 ~ o d i f f u s e d i n Rh. Counting character- i s t i c s were assessed by comparing r e l a t i v e i n t e n s i - t i e s , peak a r e a s and FWHMs obtained by CEM s p e c t r a . These t h r e e parameters were computed by employing a computer f i t t i n g method assuming Lorentzian l i n e shape 161.
A t f i r s t , t h e probe was placed a t t h e c e n t e r of t h e sample-mounting p l a t e of t h e d e t e c t o r and e l e c t r o n energy s p e c t r a and CEM s p e c t r a were mea- sured by changing some f a c t o r s - t h e d i s t a n c e from t h e y-ray source t o t h e probe, t h e window diameter of t h e d e t e c t o r and t h e flow r a t e of Q-gas.
Next, t h e p o s i t i o n of t h e enriched probe was s h i f t e d from piace t o place t o e s t a b l i s h t h e sensi-
t i v i t y change i n terms of t h e probe p o s i t i o n . The flow r a t e of Q-gas was controled t o lOml/min t o avoid t h e v i b r a t i o n of an anode and t h e gradient of Q-gas concentration i n t h e d e t e c t o r . The d i s t a n c e from the.-probe t o t h e y-ray source was s e t t o 5cm and t h e window diameter of t h e d e t e c t o r was 2.5cm so t h a t any p o s i t i o n s were exposed t o y-ray evenly.
3.Results.-l.-We t e s t e d t h r e e tungsten anodes of 10 pm, 3QIm and 6mm i n diameter. Though a 1mm tung-
s t e n anode was somewhat weak i n mechanical s t r e n g t h
,
it was used i n throughout experiments. It gave a high counting r a t e - e l e c t r o n s p e c t r a with r e l a t i v e - l y low applied voltage. An applied voltage t o an anode was one of t h e f a c t o r s t o change t h e shape df an e l e c t r o n spectrum. We observed one peak a t 1600 V and two peaks above 1700V. The p o s i t i o n s o f two peaks were independent of applied voltage range 1700~-lgoov.2.- Peaks i n an e l e c t r o n sgectrum s h i f t e d when t h e distance from t h e probe t o t h e y-ray source o r t h e window diameter of t h e d e t e c t o r f o r i n c i d e n t y-ray
x a S varied. The decrease of t h e window diameter o r t h e i n c r e a s e of t h e d i s t a n c e improved t h e energy r e s o l u t i o n of t h e e l e c t r o n spectrum and increased t h e r e l a t i v e i n t e n s i t y of t h e CEM spectrum. The adoption of an absorber f o r s c a t t e r e d X-ray(acry- l i t e , lcm i n t h i c k n e s s ) i n f r o n t of t h e d e t e c t o r window a l s o improved t h e energy r e s o l u t i o n of t h e e l e c t r o n spectrum, b u t decreased t h e r e l a t i v e in- t e n s i t y of t h e CEM spectrum. When an ~ n e n r i c h e d
s t a i n l e s s s t e e l p l a t e of 50mm i n diameter was mounted i n s t e a d of t h e 6 d probe, t h e r e l a t i v e in- t e n s i t y was not vasied by changing t h e window d i - ameter. These r e s u l t s a r e summarized i n Table 1.
To o b t a i n r e l a t i v e l y high i n t e n s i t y of a CEM spec- trum, a sample must be e f f e c t i v e l y exposed t o y-
ray. The window diameter of a d e t e c t o r and t h e
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980122
c1-116 JOURNAL DE PHYSIQUE
d i s t a n c e from a sample t o a s o u r c e should b e d e t e r - mined c o n c i d e r i n g t h e sample s i z e .
Table.1 Peak i n t e n s i t i e s a s a f u n c t i o n o f t h e d i s - t a n c e o r t h e window diameter
SAMPLE DISTANCE WINDOW ABSORBER REL.IN.PEAK AREA (em) (cm) ( a c r y l i t e )
($1
( counts/min)A 5 2.5 NO 126 1027
A 8 2.5 NO 135 505
A 8 0.6 NO 223 489
A 8 2 . 5 YES 1 1 3 129
A 8 0.6 YES 138 83
B 8 2.5 NO 1 1 3 332
B 8 0.6 NO 1 1 3 83
A; e n r i c h e d s t a i n l e s s s t e e l ( 6 m m d B; unenriched s t a i n l e s s s t e e l ( 5 O d ) RFL. I N . ; r e l a t i v e i n t e n s i t y
3.- It t o o k about an hour till t h e d e t e c t o r showed s t a b l e working c h a r a c t e r i s t i c s . The w a t t i n & t i m e r e q u i r e d b e f o r e t h e r e p r o d u c i b l e counting of t h e d e t e c t o r was c o n s i d e r e d t o b e caused by t h e contam- i n a t i o n with r e s i d u a l a i r itl t h e d e t e c t o r . When t h e d e t e c t o r was evacuated b e f o r e t h e f l o w of Q-gas i n t o t h e d e t e c t o r , t h e s t a b l e counting achieved i n s h o r t e r p e r i o d of i d l i n g . The f l u c t u a t i o n o f Q-gas flow r a t e t o t h e d e t e c t o r a l s o changed t h e shape.of an e l e c t r o n spectrum and t h e peak a r e a o f a CEM spectrum. There appeared one peak i n t h e e l e c t r o n spectrum i n t h e c a s e o f a low f l o w r a t e of Q-gas.
The i n c r e a s e of a flow x a t e of Q-gas gave a n o t h e r peak and t h e energy r e s o l u t i o n of t h e e l e c t r o n spectrum was seemingly improved. Two =ode wires which were z t r e t c h e d i n p a r a l l e l 2.5cm a p a r t had been s u s p e c t e d t o b e t h e o r i g n of two peaks a t a high flow r a t e o f Q-gas. But t h i s p o s i b i l i t y was denied when t h e measurement were performed w i t h a s i n g l e w i r e and t h e two peaks were s t i l l observed.
A s t h e two peaks were observed on removing t h e probe, Whey were not peaks o f conversion e l e c t r o n s . We could g e t CEM s p e c t r a by s e t t i n g t h e d i s c r i m i n a - t i o n range a t any energy range i n an e l e c t r o n spec- trum though peak a r e a and r e l a t i v e i n t e n s i t y o f a CEM spectrum v a r i e d . Therefore t h e two peaks were n o t n o i s e peaks. While t h e peak a r e a of a CEM spectrum was i n c r e a s e d , t h e r e l a t i v e i n t e n s i t y of t h a t was n o t v a r i e d b y t h e i n c r e a s e of t h e f l o w r a t e o f Q-gas.
4.-
S i g n i f i c a n t d i f f e r e n c e s were observed i n peak a r e a s , r e l a t i v e i n t e n s i t i e s and FWHMs when t h e po- s i t i o n o f t h e probe was m ~ v e d . Th"e r e s u l t s a r e shown i n Fig.1, i n which ( x , y ) denotes t h e Carte- s i a n c o o r d i n a t e s o f t h e c e n t e r of t h e probe. V a l - ues o f peak a r e a s o f CEM s p e c t r a were expressed b y n o r m a l i z i n g it t o t h e peak a r e a o b t a i n e d a t t h ec e n t e r o f t h e d e t e c t o r - t h e p o s i t i o n o f ( 0 ~ 0 ) . No peak appeared a t t h e p o s i t i o n of ( + 2 , 0 ) . There ap- peared s m a l l peaks a t t h e p o s i t i o n of (O,t2). The movement of t h e probe from t h e c e n t e r of t h e coor- d i n a t e a l o n g y-axis caused g r a d u a l change i n v a l u e s o f t h e s e t h r e e parameters. However t h e movement o f t h e probe a l o n g x-axis r e s u l t e d i n t h e d r a s t i c de- c r e a s e o f t h r e e parameters. The d i f f e r e n c e o f t h e o o l ~ t i w , e f f i c i e n c y i n t e r m s o f t h e sample p o s i t i o n
might be r e l a t e d t o t h e g e o m e t r i c a l c o n f i g u r a t i o n o f anodes i n t h e d e t e c t o r o r t h e end e f f e c t s o f a n o d e s . / 7 / . Our r e s u l t s r e v e a l e d t h a t t h e v a r i a - t i o n of t h r e e parameters was independent of t h e in- c i d e n t a n g l e o f y-ray. It was c l e a r t h a t t h e sen- s i t i v e a r e a o f d e t e c t o r s o f t h i s t y p e was s u r p r i s - i n g l y l i m i t e d t o s m a l l a r e a . When t h e probe was moved along t h e x - a x i s , t h e counting r a t e was seem- i n g l y i n c r e a s e d by t h e increment of t h e p r o p o r t i o n of e l e c t r o n s s c a t t e r e d through t h e nonresonant- p r o c e s s and peak i n t e n s i t i e s were consequently de- c r e a s e d .
-1.0-
PosmON
OF A PROBE(cm) PEAK AREA-TIE
INT~SrrV(eIe) FWHM (mmlsec)
Fig.1. P o s i t i o n s e n s i t i v i t y References
/1/ K.R.Swanson and J.J.Spijkerman,J.Appl.Phys.
&
(1970)3155
/2/ Y.Ujihira and K.Nomura,Japan Analyst a ( 1 9 7 8 ) 782
.
- -Y.Ujihira,A.Handa,Y.Abe and I.Okabe,J.Chem.Soc.
Japan
,=
,234Y.Ujihira and K.Nomura,Bunseki 1978,555 Y.Isozumi,D.I.Lee and I . K a d a r , N u c l . I n s t r . and Meth. ~ ( 1 9 7 4 123
B.L.Christman and T.A.Wmolillo,Comput.Phys.
Comm
.
2(1971)322/7/ B.B.ROS;~ and H.H.Staub,Ionization Chambers and Counters,chap
