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Experimental and calculated photopeak efficiencies for a coaxial Ge(Li) detector
NUCLEAR
INSTRUMENTS
EXPERIMENTAL
A N D M E T H O D S 93 ( ~ 9 7 t ) 3 8 9 - 3 9 0 ;
AND
CALCULATED COAXIAL
'~ NORTH-HOLLAND
PHOTOPEAK
EFFICIENCIES
PUBLISHING
FOR
CO.
A
Ge(Li) DETECTOR*
D. E. RAESIDE and M. A. L U D I N G T O N ¢
Physics Department, The University of Michigan, Ann Arbor, Michigan 48104, U.S.A. Received 29 December 1970 Experimental and calculated photopeak efficiencies have been obtained for a 32 cm 3 true coaxial Ge(Li) detector at four distances: 2 cm, 5 cm, 10 cm and 20 cm. A comparison of these results is presented. D u r i n g t h e p a s t few y e a r s s e v e r a l p a p e r s d i s c u s s i n g t h e e x p e r i m e n t a l efficiency c a l i b r a t i o n o f G e ( L i ) det e c t o r s h a v e a p p e a r e d L- v ) . R e c e n t l y a p a p e r by A u b i n et al. s) d e s c r i b i n g a M o n t e C a r l o c o m p u t e r p r o g r a m t o c a l c u l a t e t h e efficiency o f p l a n a r a n d t r u e c o a x i a l G e ( L i ) d e t e c t o r s h a s b e e n p u b l i s h e d . T h e p r e s e n t investigation was undertaken to provide a comprehensive comparison between the calculated results obtained with this program and experimental results obtained with t h e p a i r - p o i n t m e t h o d ~-4). Tell s o u r c e s were used t o
e
e 2cm
•
5cm
÷ +~. +. -+.. "''-.. __
10
20
i
i
io
3.0
, i
T~ E
3.0
e A
•.
loom
20cm
""*+..
'..,
i ..... +
10
2.0
3.0 0
1.0
2.0
3.0
.k
""--~_
Fig. 2. A comparison of experimental and calculated photopeak efficiencies (e) for a 32 cm a true coaxial Ge(ki) detector. The experimental values were overlapped with the calculated values visually to obtain the best fit. The scale of the ordinate is logarithmic; the scale of the abscissa is linear and the units are MeV. The dots represent calculated values and the crosses represent experimental values.
10cm 20crn
0.5
1.0
1.5
2.0
2.5
o b t a i n t h e d a t a f o r t h e e x p e r i m e n t a l officiency c u r v e s o f fig. 1: 22Na, 6 ° C o , 4 6 S c , loSmAg ' 8 8 y , 2,~Na ' 18°mHf, 137Cs, 139Ce a n d i ° ° T b . T h e p r o g r a m of
YO
Fig. I. The photopeak efficiency (e) of a 32 cm 3 true coaxial Ge(Li) detector (diameter 35.8 ram; length 39.2 mm; drift depth 11.8 ram; diffusion depth 0.9 ram) for a point source on the symmetry axis of the detector at distances 2, 5, l0 and 20 cm from the face of the detector. The scale of the ordinate is logarithmic; the scale of the abscissa is linear and the units are MeV. The absolute efficiencies at 2, 5, 10 and 20 cm are 2.15× l0 3, 9.40x 10 4, 3.17x 10-4, and 8.81 × l0 5, respectively, for the 1333 keV gamma ray of 6"Co. Here we understand absolute efficiency to mean the probability of the emission of a photon into an appropriate solid angle and its subsequent detection as a photoelectric event. 389
A u b i n et al. s) w a s r u n o n t h e P D P - 1 0 c o m p u t e r o f t h e University of Michigan physics department. Several hours of running time were required to obtain the data for each source-to-detector distance. Photon cross s e c t i o n s used in t h e c a l c u l a t i o n s w e r e t a k e n f r o m t h e w o r k o f S t o r m a n d l s r a e l g ) ; d e t e c t o r d i m e n s i o n s were * This work was supported in part by the U. S. Atomic Energy Commission. i Present address: Physics Department, Albion College, Albion, Michigan.
390
D. E. RAESIDE AND M. A. LUD1NGTON
t a k e n from the specifications of the m a n u f a c t u r e r (Ortec). A c o m p a r i s o n between experimental and calculated values is shown in fig. 2. Because of the fact that the c o m p u t e r p r o g r a m can n o t reproduce the h u m p [produced by a t t e n u a t i o n in the s u r r o u n d i n g s of the Ge(ki) crystal] at the low-energy end of each of the curves shown in fig. 1, the data of fig. 2 start at a n energy well beyond this h u m p (0.2 MeV). As fig. 2 shows, the agreement between experimental values and calculated values is excellent. The authors wish to t h a n k Prof. M. k. Wiedenbeck for his c o n t i n u i n g interest in this work and Prof. J. W. C h a p m a n for providing generous a m o u n t s of c o m p u t e r time.
References i)j. M. Freeman and J. G. Jenkin, Nucl. Instr. and Meth. 43 (1966) 269. z) W. R. Kane and M. A. Mariscotti, Nucl. Instr. and Meth. 56 (1967) 189. a) D. P. Donnelly, H. W. Baer, J. J. Reidy and M. L. Wiedenbeck, Nucl. Instr. and Meth. 57 (1967) 219. 4) D. P. Donnelly and M. L. Wiedenbeck, Nucl. Instr. and Meth. 64 (1968) 26. 5) R. S. Mowan, Nucl. Instr. and Meth. 70 (1969) 237. ~*)V. W. Slivinsky and P. J. Ebert, Nucl. Instr. and Meth. 71 (1969) 346. 7) T. Paradellis and S. Hontzeas, Nucl. Instr. and Meth. 73 (1969) 210. s) G. Aubin, J. Barrette, G. Lamoureux and S. Monaro, Nucl. Instr. and Meth. 76 (1969) 85. ~') E. Storm and H. 1. Israel, Los Alamos Scientific Laboratory Report LA-3753 (1967).
INSTRUMENTS
EXPERIMENTAL
A N D M E T H O D S 93 ( ~ 9 7 t ) 3 8 9 - 3 9 0 ;
AND
CALCULATED COAXIAL
'~ NORTH-HOLLAND
PHOTOPEAK
EFFICIENCIES
PUBLISHING
FOR
CO.
A
Ge(Li) DETECTOR*
D. E. RAESIDE and M. A. L U D I N G T O N ¢
Physics Department, The University of Michigan, Ann Arbor, Michigan 48104, U.S.A. Received 29 December 1970 Experimental and calculated photopeak efficiencies have been obtained for a 32 cm 3 true coaxial Ge(Li) detector at four distances: 2 cm, 5 cm, 10 cm and 20 cm. A comparison of these results is presented. D u r i n g t h e p a s t few y e a r s s e v e r a l p a p e r s d i s c u s s i n g t h e e x p e r i m e n t a l efficiency c a l i b r a t i o n o f G e ( L i ) det e c t o r s h a v e a p p e a r e d L- v ) . R e c e n t l y a p a p e r by A u b i n et al. s) d e s c r i b i n g a M o n t e C a r l o c o m p u t e r p r o g r a m t o c a l c u l a t e t h e efficiency o f p l a n a r a n d t r u e c o a x i a l G e ( L i ) d e t e c t o r s h a s b e e n p u b l i s h e d . T h e p r e s e n t investigation was undertaken to provide a comprehensive comparison between the calculated results obtained with this program and experimental results obtained with t h e p a i r - p o i n t m e t h o d ~-4). Tell s o u r c e s were used t o
e
e 2cm
•
5cm
÷ +~. +. -+.. "''-.. __
10
20
i
i
io
3.0
, i
T~ E
3.0
e A
•.
loom
20cm
""*+..
'..,
i ..... +
10
2.0
3.0 0
1.0
2.0
3.0
.k
""--~_
Fig. 2. A comparison of experimental and calculated photopeak efficiencies (e) for a 32 cm a true coaxial Ge(ki) detector. The experimental values were overlapped with the calculated values visually to obtain the best fit. The scale of the ordinate is logarithmic; the scale of the abscissa is linear and the units are MeV. The dots represent calculated values and the crosses represent experimental values.
10cm 20crn
0.5
1.0
1.5
2.0
2.5
o b t a i n t h e d a t a f o r t h e e x p e r i m e n t a l officiency c u r v e s o f fig. 1: 22Na, 6 ° C o , 4 6 S c , loSmAg ' 8 8 y , 2,~Na ' 18°mHf, 137Cs, 139Ce a n d i ° ° T b . T h e p r o g r a m of
YO
Fig. I. The photopeak efficiency (e) of a 32 cm 3 true coaxial Ge(Li) detector (diameter 35.8 ram; length 39.2 mm; drift depth 11.8 ram; diffusion depth 0.9 ram) for a point source on the symmetry axis of the detector at distances 2, 5, l0 and 20 cm from the face of the detector. The scale of the ordinate is logarithmic; the scale of the abscissa is linear and the units are MeV. The absolute efficiencies at 2, 5, 10 and 20 cm are 2.15× l0 3, 9.40x 10 4, 3.17x 10-4, and 8.81 × l0 5, respectively, for the 1333 keV gamma ray of 6"Co. Here we understand absolute efficiency to mean the probability of the emission of a photon into an appropriate solid angle and its subsequent detection as a photoelectric event. 389
A u b i n et al. s) w a s r u n o n t h e P D P - 1 0 c o m p u t e r o f t h e University of Michigan physics department. Several hours of running time were required to obtain the data for each source-to-detector distance. Photon cross s e c t i o n s used in t h e c a l c u l a t i o n s w e r e t a k e n f r o m t h e w o r k o f S t o r m a n d l s r a e l g ) ; d e t e c t o r d i m e n s i o n s were * This work was supported in part by the U. S. Atomic Energy Commission. i Present address: Physics Department, Albion College, Albion, Michigan.
390
D. E. RAESIDE AND M. A. LUD1NGTON
t a k e n from the specifications of the m a n u f a c t u r e r (Ortec). A c o m p a r i s o n between experimental and calculated values is shown in fig. 2. Because of the fact that the c o m p u t e r p r o g r a m can n o t reproduce the h u m p [produced by a t t e n u a t i o n in the s u r r o u n d i n g s of the Ge(ki) crystal] at the low-energy end of each of the curves shown in fig. 1, the data of fig. 2 start at a n energy well beyond this h u m p (0.2 MeV). As fig. 2 shows, the agreement between experimental values and calculated values is excellent. The authors wish to t h a n k Prof. M. k. Wiedenbeck for his c o n t i n u i n g interest in this work and Prof. J. W. C h a p m a n for providing generous a m o u n t s of c o m p u t e r time.
References i)j. M. Freeman and J. G. Jenkin, Nucl. Instr. and Meth. 43 (1966) 269. z) W. R. Kane and M. A. Mariscotti, Nucl. Instr. and Meth. 56 (1967) 189. a) D. P. Donnelly, H. W. Baer, J. J. Reidy and M. L. Wiedenbeck, Nucl. Instr. and Meth. 57 (1967) 219. 4) D. P. Donnelly and M. L. Wiedenbeck, Nucl. Instr. and Meth. 64 (1968) 26. 5) R. S. Mowan, Nucl. Instr. and Meth. 70 (1969) 237. ~*)V. W. Slivinsky and P. J. Ebert, Nucl. Instr. and Meth. 71 (1969) 346. 7) T. Paradellis and S. Hontzeas, Nucl. Instr. and Meth. 73 (1969) 210. s) G. Aubin, J. Barrette, G. Lamoureux and S. Monaro, Nucl. Instr. and Meth. 76 (1969) 85. ~') E. Storm and H. 1. Israel, Los Alamos Scientific Laboratory Report LA-3753 (1967).