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Shape calibration and peak-to-total ratio measurements of a 5″ × 6″ NaI(Tl) scintillation detector
NUCLEAR
INSTRUMENTS
A N D M E T H O D S 93
(I97l) 381-383; © N O R T H - H O L L A N D
PUBLISHING
CO.
S H A P E CALIBRATION A N D PEAK-TO-TOTAL RATIO M E A S U R E M E N T S OF A 5 " × 6" NaI(Ti) SCINTILLATION D E T E C T O R N. A H M E D , M. A. R A H M A N , M. A. A W A L and S. K H A T U N
Atomic Energy Centre, Dacca, East Pakistan Received 18 January 1971 A number of (P,7) reactions have been used to obtain the single 7-ray spectra to obtain shape calibration curve and peak-to-total ratio for a 5"x 6" NaI(TI) scintillation detector from 0.662 to 8.92 MeV of 7-ray energy.
The Nal(T1) scintillation spectrometers are still in use for the detection of 7-ray spectra from nuclear reactions and to find the branching ratios of the emitted 7-ray transitions. G a m m a spectra of this kind are generally complex in nature and to know the detailed g a m m a ray distribution it is necessary to fold the detailed shape of the monoenergetic g a m m a rays of known energies into the unknown complex spectra for obtaining the contribution due to each of the g a m m a rays. With this point in view, the shape calibration along the peak-to-total ratio measurements for a 5 " x 6" NaI(TI) scintillation spectrometer was made. The energy region covered was from 0.662 to 8.920 MeV using the monoenergetic g a m m a rays from the various reactions and the radioactive source. A list of them are given in table 1. The scintillation spectrometer consisted of a 5" x 6" Nal(T1) crystal mounted on an E M I photomultiplier tube and is placed at a distance of 9 cm from the target. The detector was kept at an angle of 55" with the direc-
TABLE 1 G a m m a rays used for shape calibration. Sources
laTCs 2aNa(p,:dy)2"Ne 12C(p,v)laN 12C(p,?,)laN 30Si(p,y)alp ZaNa(p,7)~4Mg
Proton bombarding energy (MeV)
Calibration 7-ray energy (MeV)
1.161 0.457 1.698 0.620 1.415
0.661 1.63 2.37 3.51 7.89 8.92
31 Si ( P , ~ ) P R e a c t ion
¢-
at
v
E p = O. 6 2 0 MeV
~D
Z
0
6
~
~
/\v.
2000-
u. 0
6z
0
4.92
6119 GAMMA
7)45
RAY E N E R G Y
I1•11 8.7O
(MeV)
Fig. 1. Single 7-ray spectra of 7.89 MeV obtained from 3°Si(p,7)alP reaction at Ep
381
1 2 2 3,4 l
tion of the bombarding proton energy and was covered by a 10 cm thick lead shielding around the crystal with an aperture of 12.7 cm in diana. The pulse height distribution of 7.89 MeV 7-ray obtained from 3°Si(p,~)SlP reaction is shown in fig. 1. The multipeaked distribution observed in the corre-
4000 30
Ref.
=0.620 MeV.
O'250
0"500
0'750
1'00
1'25
12
7
1 2
GAMMA
RAY
ENERGYtMeV)
Fig. 2. Shape calibration curve for the 5" x 6" NaI(TI) scintillation detector.
3
2 t~ 10
4 5
13,14,Y
3
>-
z
GIO
SHAPE C A L I B R A T I O N OF A 5" X 6" 1.0
NaI(TI) D E T E C T O R
383
TABLE2 Peak-to-total ratios R.
-
Gamma-ray energy (MeV)
0 <
0.661 1.63 2.37 3.51 7.89 8.92
0 ~0.5 i
0pi
hJ IZ
10 0.5
1.0
5.0 GAMMA
10.0
RAY E N E R G Y ( M e V )
Fig. 3. Peak-to-total ratio (R) as a function of ?,-ray energy (in MeV). s p o n d i n g regions o f 7-rays is conserved by c h o o s i n g a n u m b e r o f p o i n t s at an interval o f 0.170 MeV starting a few intervals a b o v e full energy so t h a t the peak region is covered wellS). In the tail wider spacings were taken2). The n u m b e r o f counts at each o f the points (n), relative to the n u m b e r o f counts at full energy peak (he) has been plotted to preserve the feature o f the distribution. A set o f curves is p r e p a r e d for same experimental configuration o f counts, c o l l i m a t o r s and target system. The shape c a l i b r a t i o n thus obtained using the m o n o e n e r g e t i c y-rays is shown in fig. 2. This can be used to o b t a i n any s t a n d a r d lineshape for peeling off the complex y-ray spectra. The ratio of the n u m b e r of counts within the p h o t o p e a k area to the n u m b e r o f counts within the total
R
0.702 0.507 0.415 0.313 0.169 0.149
+ 0.018 + 0.015 + 0.015 + 0.010 _+ 0.010 + 0.014
a r e a (i.e. p e a k - t o - t o t a l ratio, R) is shown in fig. 3 and in table 2. While finding the total area, low tail o f the C o m p t o n d i s t r i b u t i o n was e x t r a p o l a t e d as a straight line to zero energy. These measurements, however, will be useful subsequently in the process of stripping the complex ,/-ray spectra and o b t a i n i n g the b r a n c h i n g ratios o f the 7-ray transitions in the nuclear reactions. The a u t h o r s wish to t h a n k Dr. S h a m s h e r Ali for his interest in the work. The valuable assistance o f Mr. E m d a d Hussain and the crews o f the Van de G r a a f f accelerator are gratefully a c k n o w l e d g e d .
References t)s. L. Andersen, O. Dorum, E. Gautvik and T. Holtebekk, Nu¢l. Phys. 22 (1961) 245. -') R. Nordhagen, Nucl. Instr. and Meth. 12 (1961) 291. :~) K. J. Van Oostrum and A. C. Meijer, Nucl. Instr. and Meth. 10 (1961) 37. 4) j. Kuperus, P. J. M. Smulders and P. M. Endt, Physica 25 (1959) 600. :') P. M. Endt and H. Heylingers, Physics 26 (1960) 230.
INSTRUMENTS
A N D M E T H O D S 93
(I97l) 381-383; © N O R T H - H O L L A N D
PUBLISHING
CO.
S H A P E CALIBRATION A N D PEAK-TO-TOTAL RATIO M E A S U R E M E N T S OF A 5 " × 6" NaI(Ti) SCINTILLATION D E T E C T O R N. A H M E D , M. A. R A H M A N , M. A. A W A L and S. K H A T U N
Atomic Energy Centre, Dacca, East Pakistan Received 18 January 1971 A number of (P,7) reactions have been used to obtain the single 7-ray spectra to obtain shape calibration curve and peak-to-total ratio for a 5"x 6" NaI(TI) scintillation detector from 0.662 to 8.92 MeV of 7-ray energy.
The Nal(T1) scintillation spectrometers are still in use for the detection of 7-ray spectra from nuclear reactions and to find the branching ratios of the emitted 7-ray transitions. G a m m a spectra of this kind are generally complex in nature and to know the detailed g a m m a ray distribution it is necessary to fold the detailed shape of the monoenergetic g a m m a rays of known energies into the unknown complex spectra for obtaining the contribution due to each of the g a m m a rays. With this point in view, the shape calibration along the peak-to-total ratio measurements for a 5 " x 6" NaI(TI) scintillation spectrometer was made. The energy region covered was from 0.662 to 8.920 MeV using the monoenergetic g a m m a rays from the various reactions and the radioactive source. A list of them are given in table 1. The scintillation spectrometer consisted of a 5" x 6" Nal(T1) crystal mounted on an E M I photomultiplier tube and is placed at a distance of 9 cm from the target. The detector was kept at an angle of 55" with the direc-
TABLE 1 G a m m a rays used for shape calibration. Sources
laTCs 2aNa(p,:dy)2"Ne 12C(p,v)laN 12C(p,?,)laN 30Si(p,y)alp ZaNa(p,7)~4Mg
Proton bombarding energy (MeV)
Calibration 7-ray energy (MeV)
1.161 0.457 1.698 0.620 1.415
0.661 1.63 2.37 3.51 7.89 8.92
31 Si ( P , ~ ) P R e a c t ion
¢-
at
v
E p = O. 6 2 0 MeV
~D
Z
0
6
~
~
/\v.
2000-
u. 0
6z
0
4.92
6119 GAMMA
7)45
RAY E N E R G Y
I1•11 8.7O
(MeV)
Fig. 1. Single 7-ray spectra of 7.89 MeV obtained from 3°Si(p,7)alP reaction at Ep
381
1 2 2 3,4 l
tion of the bombarding proton energy and was covered by a 10 cm thick lead shielding around the crystal with an aperture of 12.7 cm in diana. The pulse height distribution of 7.89 MeV 7-ray obtained from 3°Si(p,~)SlP reaction is shown in fig. 1. The multipeaked distribution observed in the corre-
4000 30
Ref.
=0.620 MeV.
O'250
0"500
0'750
1'00
1'25
12
7
1 2
GAMMA
RAY
ENERGYtMeV)
Fig. 2. Shape calibration curve for the 5" x 6" NaI(TI) scintillation detector.
3
2 t~ 10
4 5
13,14,Y
3
>-
z
GIO
SHAPE C A L I B R A T I O N OF A 5" X 6" 1.0
NaI(TI) D E T E C T O R
383
TABLE2 Peak-to-total ratios R.
-
Gamma-ray energy (MeV)
0 <
0.661 1.63 2.37 3.51 7.89 8.92
0 ~0.5 i
0pi
hJ IZ
10 0.5
1.0
5.0 GAMMA
10.0
RAY E N E R G Y ( M e V )
Fig. 3. Peak-to-total ratio (R) as a function of ?,-ray energy (in MeV). s p o n d i n g regions o f 7-rays is conserved by c h o o s i n g a n u m b e r o f p o i n t s at an interval o f 0.170 MeV starting a few intervals a b o v e full energy so t h a t the peak region is covered wellS). In the tail wider spacings were taken2). The n u m b e r o f counts at each o f the points (n), relative to the n u m b e r o f counts at full energy peak (he) has been plotted to preserve the feature o f the distribution. A set o f curves is p r e p a r e d for same experimental configuration o f counts, c o l l i m a t o r s and target system. The shape c a l i b r a t i o n thus obtained using the m o n o e n e r g e t i c y-rays is shown in fig. 2. This can be used to o b t a i n any s t a n d a r d lineshape for peeling off the complex y-ray spectra. The ratio of the n u m b e r of counts within the p h o t o p e a k area to the n u m b e r o f counts within the total
R
0.702 0.507 0.415 0.313 0.169 0.149
+ 0.018 + 0.015 + 0.015 + 0.010 _+ 0.010 + 0.014
a r e a (i.e. p e a k - t o - t o t a l ratio, R) is shown in fig. 3 and in table 2. While finding the total area, low tail o f the C o m p t o n d i s t r i b u t i o n was e x t r a p o l a t e d as a straight line to zero energy. These measurements, however, will be useful subsequently in the process of stripping the complex ,/-ray spectra and o b t a i n i n g the b r a n c h i n g ratios o f the 7-ray transitions in the nuclear reactions. The a u t h o r s wish to t h a n k Dr. S h a m s h e r Ali for his interest in the work. The valuable assistance o f Mr. E m d a d Hussain and the crews o f the Van de G r a a f f accelerator are gratefully a c k n o w l e d g e d .
References t)s. L. Andersen, O. Dorum, E. Gautvik and T. Holtebekk, Nu¢l. Phys. 22 (1961) 245. -') R. Nordhagen, Nucl. Instr. and Meth. 12 (1961) 291. :~) K. J. Van Oostrum and A. C. Meijer, Nucl. Instr. and Meth. 10 (1961) 37. 4) j. Kuperus, P. J. M. Smulders and P. M. Endt, Physica 25 (1959) 600. :') P. M. Endt and H. Heylingers, Physics 26 (1960) 230.