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Nuclear lifetime measurements of some excited states in 75As, 131Cs, 133Cs, 170Yb, 187Re and 197Au
Nuclear Physics A182 (1912) 669-612; Not to be reproduced
by photoprint
NUCLEAR IN “As
,
131Cs ,
North-Holland
Publishing Co., Amsterdam
or microfilm without written permission
LIFETIME
OF SOME
@
MEASUREMENTS
EXCITED
133CS
D. K. GUPTA
from the publisher
170M,
,
,
and
STATES 187&
and
197Au
G. N. RAO
Department of Physics, Indian Institute of Technology, Kanpur, India 7 Received
27 September
(Revised
16 November
1971 1971)
Abstract: The half-lives of some short-lived nuclear excited states in “As, 13rCs, r3%s, I’OYb, “‘Re and 19’Au are measured using the delayed-coincidence technique. A new value of T* = 8.110.1 nsec is reported for the 134 keV level in 13rCs. The present values are compared with the previous measurements. E
RADIOACTIVITY
&J-, K X-rayy-delay.
75Se “As,
, 13rBa,
133Ba, “OTrn, l*‘W and lg7Hg; measured yy-, and 19’Au deduced levels, T+. 131Cs, lJ3Cs, r70Yb, “‘Re
1. Introduction
There have been considerable discrepancies in the values of the nuclear lifetimes reported by different workers for the excited states in 75A~, 131Cs, 133Cs, “‘Yb, “‘Re and 19’Au. We have remeasured the nuclear lifetimes of some of the excited states in the above nuclei using the delayed-coincidence method. In each of the measurements reported in this paper, we have either reduced the statistical errors or removed the existing discrepancies. Our measurements on the nuclear lifetimes of the 134 keV state in 13rCs falls under the second category and therefore will be discussed in detail. The results of all the other nuclear lifetime measurements are presented in the form of a table and no detailed discussion of these measurements is given in the text. 2. Experimental
details
Depending on the particular radiation to be detected, Ge(Li) detectors (OILCC), NaI(T1) crystals or plastic scintillators coupled to 56AVP photomultipliers have been used. The fast pulses from the germanium detectors were amplified using EG and G 1 nsec DC amplifiers and then fed into Ortec fast discriminators. The outputs were fed into a model 437A Ortec time-to-pulse-height converter. The linearity of the system was found to be better than 0.1 %. The system was calibrated with an Ortec model 427 + Work supported funds under project BRNS/Phys./31/70.
by the National Bureau of Standards, Washington, DC out of its PL-480 NBS(G)-127 and the Department of Atomic Energy, India, under project 669
670
D. K. GUPTA
AND
G. N. RAO
~1sdelay amplifier and an Ortec model 425 nsec delay unit, which were in turn calibrated with known lengths of RG 58A/U cables. The details and the performance of the spectrometer are given elsewhere ‘). The prompt time spectrum of 22Na obtained with the NaI(TI) scintillator on the stop side (gated at 128 keV with a window of hy 30 keV) and the Ge(Li) detector gated at 483 keV with a window of 6 keV on the start side is given in fig. I (with hollow circles).
104L ‘1
I 1
/
I I
I
: 134 : 486
Stop Start
10’
a
20 I I 10
40 I 20
60 I 30 Time
I
I
I
Channel 80 I I 40 50 in nsec
no. 100 60 (Arbitrary
keV
(NaI
keV(Ge
120 I 70 zero
tT1)) (Li))
140
160 I 90
I 60
I 100
1 180 ’
1
Fig. 1. Delayed-coincidence spectrum of 134 keV level in t3’Cs (solid circles) obtained with the NaI(II) scintillator on the stop side (gated at 128 keV with a window of NN30 keV) and the Ge(Li) detector on the start side (gated at 483 keV with a window of 6 keV). This is raw data uncorrected for the prompt spectrum. The prompt spectrum with hollow circles was obtained with the *‘Na source under the same gating conditions.
3. Results and discussion Many measurements already exist for the lifetime of the 134 keV state in 13iCs. The reported values vary from 9.3 nsec to as much as 13.5 nsec. Some 2, “) of the groups used NaI(T1) detectors on both sides and allowed the combined photopeaks of the 123 and 134 keV y-rays in the stop channel. Other groups 4, ‘) have used a plastic scintillator in the start channel and a P-ray spectrometer in the stop channel. These workers have used the K-capture X-rays of i31Ba which do not directly feed the 134 keV level in i3iCs and hence the measurement assumes that there exist no other lifetimes in r3iCs which would interfere with the lifetime measurement of the 134 keV state. Beside this, the statistical uncertainties in these measurements seem to be large.
NUCLEAR
LIFETIME
MEASUREMENTS
671
TABLE 1 Comparison
of the present half-life measurement of 134 keV in r3iCs with available values Nucleus
Level (keV)
T+ (nsec)
Ref.
134
12.7 41.0 13.5 10.5 9.3 10.3 9.75f0.3 8.1 fO.l
4, 5, present meas.
131Cs
published
TABLE2 Comparison
of the present lifetime measurements
with available published values T+
Nucleus
Level (keV)
Radiation energy (keV) in stop channel (detector used)
Radiation energy (keV) in start channel (detector used)
‘sAs
280
280 (NaI(T1))
121 (plastic)
0.277rtO.031
0.298&0.055 “) 0.28 kO.02 b)
i3lCs
124
124 (NaIW))
496 (Ge(Li))
3.80 20.01
3.7 50.1 3.48 10.07
“) d,
133CS
81
81 (plastic)
356 (NaIW))
6.36 10.03
6.27 50.04 6.30 10.07
“) ‘)
r’“Yb
84
84 (plastic)
886 @-) (plastic)
1.62 10.02
1.56 f0.08 1.58 10.03
g) h)
i*‘Re
206
72 (plastic)
480 (NaIOn))
’ a’ Au
77
77 (plastic)
K X-ray 68 (plastic)
“) Ref. 6). *) Ref. lo).
a) Ref. ?). “) Ref. lx).
‘) Ref. 4). *) Ref. r2).
(nsec) present measurements
555.3
&I.7
T*(nsec) previous measurements
570 557
1.84 10.02
d, Ref. ‘). 1) Ref. r”).
“) Ref. g). k, Ref. r4).
15 fl2
1.95 io.05 1.95 iO.06
‘) 1) h) “)
‘f Ref. g).
Our measurement is a direct one, in which the 486 keV y-ray in the start channel was precisely selected with the help of a Ge(Li) (FWHM M 3 keV) detector. A NaI(T1) detector was used for the detection of the 134 keV y-ray. The time spectrum thus obtained is given in fig. 1 (with solid circles). The value obtained for the half-life of the 134 keV state in j31Cs is 8.110.1 nsec. This value was obtained after the subtraction of the slope due to electronics, obtained with the prompt spectrum of 22Na having the same statistical accuracy and under the same energy settings. A comparison of the present value with the values reported earlier is given in table 1. The lifetime measurements performed on other nuclei and the comparison with the earlier measure-
672
D. K. GUPTA
AND G. N. RAO
ments are given in table 2. Each of the reported measurements is a statistically computed result of at least two independent runs. The data were least-squares fitted using an IBM 7044 computer. It is a pleasure to thank Dr. C. V. IL Baba (TIFR, Bombay), Dr. B. V. N. Rao, Dr. D. N. Sanwal and Prof. T. M. Srinivasan for some useful discussions and Mr. B. K. Jain for his help during the course of these measurements. One of us (D.K.G.) is grateful to Prof. Rais Ahmed (M.U. Aligarh) for his interest in this work. References 1) D. K. Gupta and G. N. Rao, IIT technical report no. 5/71, March, 1971 2) W. H. Kelley and D. J. Horen, Nucl. Phys. 47 (1963) 454 3) G. A. Vartapetyan, T. A. Garibyan, N. A. Demekhina and E. G. Muradyan, Izv. Akad. Nauk SSSR (ser. fiz.) 28 (1964) 1657; Bull. Acad. Sci. USSR (phys. ser.) 28 (1964) 1550 4) D. J. Horen, J. M. Hollander and R. L. Graham, Phys. Rev. 135 (1964) B301 5) J. Fechner, A. Hammesfahr, A. Kluge, S. K. Sen, H. Toschinski, J. Voss, P. Weigt and B. Martin, Nucl. Phys. 130A (1969) 545 6) E. N. Shipley, R. E. Holland and F. J. Lynch, Phys. Rev. 182 (1969) 1165 7) M. Hojeberg and S. G. Malmskog, Nucl. Phys. 133 (1969) 691 8) K. G. Valivaara, A. Mereluis and J. Kozyczkowski, Physica Scripta 2 (1970) 19 9) F. S. Akilov, E. E. Beriovich, V. V. Lukashevich and V. M. Romanov, Izv. Akad. Nauk SSSR (ser. fiz.) 32 (1968) 808; Bull. Acad. Sci. USSR Ephys. ser.) 32 (1968) ‘744 10) E. G. Funk, H. J. Prask and J. W. Mihelich, Phys. Rev. 141 (1966) 1200 11) A. Bticklin, S. G. Malmskog and H. Solhod, Ark. Fys. 34 (1967) 495 12) H. K. Walter, A. Weitsch and P. Kienle, Z. Phys. 175 (1963) 520 13) S. KoiCki, A. KoiCki and G. T. Wood, Nucl. Phys. 49 (1963) 161 14) M. T. Rama Rao, V. V. Ramamurthy and V. Lakshminarayana, Ind. J. Phys. 42 (1968) 709
by photoprint
NUCLEAR IN “As
,
131Cs ,
North-Holland
Publishing Co., Amsterdam
or microfilm without written permission
LIFETIME
OF SOME
@
MEASUREMENTS
EXCITED
133CS
D. K. GUPTA
from the publisher
170M,
,
,
and
STATES 187&
and
197Au
G. N. RAO
Department of Physics, Indian Institute of Technology, Kanpur, India 7 Received
27 September
(Revised
16 November
1971 1971)
Abstract: The half-lives of some short-lived nuclear excited states in “As, 13rCs, r3%s, I’OYb, “‘Re and 19’Au are measured using the delayed-coincidence technique. A new value of T* = 8.110.1 nsec is reported for the 134 keV level in 13rCs. The present values are compared with the previous measurements. E
RADIOACTIVITY
&J-, K X-rayy-delay.
75Se “As,
, 13rBa,
133Ba, “OTrn, l*‘W and lg7Hg; measured yy-, and 19’Au deduced levels, T+. 131Cs, lJ3Cs, r70Yb, “‘Re
1. Introduction
There have been considerable discrepancies in the values of the nuclear lifetimes reported by different workers for the excited states in 75A~, 131Cs, 133Cs, “‘Yb, “‘Re and 19’Au. We have remeasured the nuclear lifetimes of some of the excited states in the above nuclei using the delayed-coincidence method. In each of the measurements reported in this paper, we have either reduced the statistical errors or removed the existing discrepancies. Our measurements on the nuclear lifetimes of the 134 keV state in 13rCs falls under the second category and therefore will be discussed in detail. The results of all the other nuclear lifetime measurements are presented in the form of a table and no detailed discussion of these measurements is given in the text. 2. Experimental
details
Depending on the particular radiation to be detected, Ge(Li) detectors (OILCC), NaI(T1) crystals or plastic scintillators coupled to 56AVP photomultipliers have been used. The fast pulses from the germanium detectors were amplified using EG and G 1 nsec DC amplifiers and then fed into Ortec fast discriminators. The outputs were fed into a model 437A Ortec time-to-pulse-height converter. The linearity of the system was found to be better than 0.1 %. The system was calibrated with an Ortec model 427 + Work supported funds under project BRNS/Phys./31/70.
by the National Bureau of Standards, Washington, DC out of its PL-480 NBS(G)-127 and the Department of Atomic Energy, India, under project 669
670
D. K. GUPTA
AND
G. N. RAO
~1sdelay amplifier and an Ortec model 425 nsec delay unit, which were in turn calibrated with known lengths of RG 58A/U cables. The details and the performance of the spectrometer are given elsewhere ‘). The prompt time spectrum of 22Na obtained with the NaI(TI) scintillator on the stop side (gated at 128 keV with a window of hy 30 keV) and the Ge(Li) detector gated at 483 keV with a window of 6 keV on the start side is given in fig. I (with hollow circles).
104L ‘1
I 1
/
I I
I
: 134 : 486
Stop Start
10’
a
20 I I 10
40 I 20
60 I 30 Time
I
I
I
Channel 80 I I 40 50 in nsec
no. 100 60 (Arbitrary
keV
(NaI
keV(Ge
120 I 70 zero
tT1)) (Li))
140
160 I 90
I 60
I 100
1 180 ’
1
Fig. 1. Delayed-coincidence spectrum of 134 keV level in t3’Cs (solid circles) obtained with the NaI(II) scintillator on the stop side (gated at 128 keV with a window of NN30 keV) and the Ge(Li) detector on the start side (gated at 483 keV with a window of 6 keV). This is raw data uncorrected for the prompt spectrum. The prompt spectrum with hollow circles was obtained with the *‘Na source under the same gating conditions.
3. Results and discussion Many measurements already exist for the lifetime of the 134 keV state in 13iCs. The reported values vary from 9.3 nsec to as much as 13.5 nsec. Some 2, “) of the groups used NaI(T1) detectors on both sides and allowed the combined photopeaks of the 123 and 134 keV y-rays in the stop channel. Other groups 4, ‘) have used a plastic scintillator in the start channel and a P-ray spectrometer in the stop channel. These workers have used the K-capture X-rays of i31Ba which do not directly feed the 134 keV level in i3iCs and hence the measurement assumes that there exist no other lifetimes in r3iCs which would interfere with the lifetime measurement of the 134 keV state. Beside this, the statistical uncertainties in these measurements seem to be large.
NUCLEAR
LIFETIME
MEASUREMENTS
671
TABLE 1 Comparison
of the present half-life measurement of 134 keV in r3iCs with available values Nucleus
Level (keV)
T+ (nsec)
Ref.
134
12.7 41.0 13.5 10.5 9.3 10.3 9.75f0.3 8.1 fO.l
4, 5, present meas.
131Cs
published
TABLE2 Comparison
of the present lifetime measurements
with available published values T+
Nucleus
Level (keV)
Radiation energy (keV) in stop channel (detector used)
Radiation energy (keV) in start channel (detector used)
‘sAs
280
280 (NaI(T1))
121 (plastic)
0.277rtO.031
0.298&0.055 “) 0.28 kO.02 b)
i3lCs
124
124 (NaIW))
496 (Ge(Li))
3.80 20.01
3.7 50.1 3.48 10.07
“) d,
133CS
81
81 (plastic)
356 (NaIW))
6.36 10.03
6.27 50.04 6.30 10.07
“) ‘)
r’“Yb
84
84 (plastic)
886 @-) (plastic)
1.62 10.02
1.56 f0.08 1.58 10.03
g) h)
i*‘Re
206
72 (plastic)
480 (NaIOn))
’ a’ Au
77
77 (plastic)
K X-ray 68 (plastic)
“) Ref. 6). *) Ref. lo).
a) Ref. ?). “) Ref. lx).
‘) Ref. 4). *) Ref. r2).
(nsec) present measurements
555.3
&I.7
T*(nsec) previous measurements
570 557
1.84 10.02
d, Ref. ‘). 1) Ref. r”).
“) Ref. g). k, Ref. r4).
15 fl2
1.95 io.05 1.95 iO.06
‘) 1) h) “)
‘f Ref. g).
Our measurement is a direct one, in which the 486 keV y-ray in the start channel was precisely selected with the help of a Ge(Li) (FWHM M 3 keV) detector. A NaI(T1) detector was used for the detection of the 134 keV y-ray. The time spectrum thus obtained is given in fig. 1 (with solid circles). The value obtained for the half-life of the 134 keV state in j31Cs is 8.110.1 nsec. This value was obtained after the subtraction of the slope due to electronics, obtained with the prompt spectrum of 22Na having the same statistical accuracy and under the same energy settings. A comparison of the present value with the values reported earlier is given in table 1. The lifetime measurements performed on other nuclei and the comparison with the earlier measure-
672
D. K. GUPTA
AND G. N. RAO
ments are given in table 2. Each of the reported measurements is a statistically computed result of at least two independent runs. The data were least-squares fitted using an IBM 7044 computer. It is a pleasure to thank Dr. C. V. IL Baba (TIFR, Bombay), Dr. B. V. N. Rao, Dr. D. N. Sanwal and Prof. T. M. Srinivasan for some useful discussions and Mr. B. K. Jain for his help during the course of these measurements. One of us (D.K.G.) is grateful to Prof. Rais Ahmed (M.U. Aligarh) for his interest in this work. References 1) D. K. Gupta and G. N. Rao, IIT technical report no. 5/71, March, 1971 2) W. H. Kelley and D. J. Horen, Nucl. Phys. 47 (1963) 454 3) G. A. Vartapetyan, T. A. Garibyan, N. A. Demekhina and E. G. Muradyan, Izv. Akad. Nauk SSSR (ser. fiz.) 28 (1964) 1657; Bull. Acad. Sci. USSR (phys. ser.) 28 (1964) 1550 4) D. J. Horen, J. M. Hollander and R. L. Graham, Phys. Rev. 135 (1964) B301 5) J. Fechner, A. Hammesfahr, A. Kluge, S. K. Sen, H. Toschinski, J. Voss, P. Weigt and B. Martin, Nucl. Phys. 130A (1969) 545 6) E. N. Shipley, R. E. Holland and F. J. Lynch, Phys. Rev. 182 (1969) 1165 7) M. Hojeberg and S. G. Malmskog, Nucl. Phys. 133 (1969) 691 8) K. G. Valivaara, A. Mereluis and J. Kozyczkowski, Physica Scripta 2 (1970) 19 9) F. S. Akilov, E. E. Beriovich, V. V. Lukashevich and V. M. Romanov, Izv. Akad. Nauk SSSR (ser. fiz.) 32 (1968) 808; Bull. Acad. Sci. USSR Ephys. ser.) 32 (1968) ‘744 10) E. G. Funk, H. J. Prask and J. W. Mihelich, Phys. Rev. 141 (1966) 1200 11) A. Bticklin, S. G. Malmskog and H. Solhod, Ark. Fys. 34 (1967) 495 12) H. K. Walter, A. Weitsch and P. Kienle, Z. Phys. 175 (1963) 520 13) S. KoiCki, A. KoiCki and G. T. Wood, Nucl. Phys. 49 (1963) 161 14) M. T. Rama Rao, V. V. Ramamurthy and V. Lakshminarayana, Ind. J. Phys. 42 (1968) 709