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Isomeric cross-section ratios in the (n, γ) reactions on 130Te and 110Pd
J. Inorg. Nucl. Chem., 1966, Vol. 28, pp. 1 to 4. Pergamon Pre~ Ltd. Printed in Northern Ireland
ISOMERIC CROSS-SECTION RATIOS IN THE (n, y) REACTIONS ON 18°Te AND 11°Pd M. N. NAMBOODIRI, M. RMAGOPALAN, N. RAVn,a)RAN, K. RENGAN and M. V. RAMANIAH Radiochemistry and Isotope Division, Atomic Energy Establishment, Trombay, Bombay (Received 15 January 1965)
Abstract--Isomeric cross-section ratios, am/(om + ag), in the (n, ~,) reactions on 13°Te and l'°pd have been determined using radiochemical techniques and have been found to be 0.059 and 0.045 respectively. These results have been compared with those of others and those calculated on the basis of Huizenga-Vandenbosch model. Tim relative yields of pairs of isomers produced in (n, y) reactions on a large number of nuclides have been investigated, cl-6) HtnZENGA and VAh~m~mOSCH developed a model (v) to calculate the relative yields of isomers using the spins of the c o m p o u n d nucleus and of the isomers, the number of ~,-rays, Ny, emitted in the process of de-excitation of the compound nucleus and the spin fall-off parameter, a, which determines the dependence of the nuclear level density on the spin. Comparison of calculated and experimental'cross-section ratios has been used to deduce the values of the parameters Ny and a, although this method does not always lead to unique values of the parameters for a given system. (1-~ The model has been extended to other
nuclear reactions like (~, n) etc.cs-m Recently SEHOAL is)measured the cross-sectionratio in the thermal neutron activation of ~ r e by directlycounting the ~,-radiationsof the tStTe isomers. DZANTIEV et al.(14) determined the isomeric cross-sectionratio for the (n, ~,) reaction on 11°pd using a radiochemical method, in the course of a study of the decay characteristics of the 111pd isomers and SBHGAL et al. (I~ reported a limit for this ratio, obtained by direct counting of the isomers. The modes of formation and decay of 13tTe and luPd isomers are given in Figs. I and 2.(13) In thiscommunication are reported the measurements of the cross-sectionratios of the isomers produced in (n, 7,)reactions on 1~q'e it) M. L. SEHOAL,H: S. HANSand P. S. GILL,Nucl. Phys. 12, 261 (1959). (~ M. L. SF~IOAL,Phys. Rev. 128, 761 (1962). ,s~ B. K~CH, Phys. Rev. 129, 769 (1962). ~4~C. T. BISHOV,Report ANL-6405 (1961). ,5~ C. T. BISHOP,J. R. HUIZENGAand J. P. HUMMEL,Phys. Rev. 135B, 401 (1964). ,6~ S. K. MA~OALand P. S. GILL,Nucl. Phys. 36, 542 (1962). '~) J. R. HUIZENOAand R. VANDENBOSCH,Phys. Rev. 120, 1305 (1960). ,s) R. VANDENBOSCHand J. R. HUIZmNOA,Phys. Rev. 120, 1313 (1960). is) j. L. NEEDand B. LINDER,Phys. Rev. 129, 1298 (1963). ,lo~ j. L. NEED,Phys. Rev. 129, 1302 (1963). m~ C. R_mEx"and B. LINDER,Phys. Rev. 134, 559 (1964). ,1~ C. RILEy, K. V ~ o and B. LINDEn,Phys. Rev. 135 B, 1340 (1964). ,m Nuclear Data Sheets, National Academy of Sciences, National Research Council, Washington, D.C. ,1,~ B. G. DzAwrmv et al., Soy. Phys. (Doklady), 2, 154 (1957). 1 1
2
M.N.
N ~ m o o ~ w a et aL
Spin H/~ 30 hi"131rnTe
Spin 3/2 FIG. 1.--l~lation betweenthe isomers of ~S~Te. Spin 11/2 5.5 hr ="mPd. . . . ,,opd(n~x)J
\\
I=.-74 seclilmAg --
\~
22rnin gPd_--~7. 6 doy.l~Aq ~S~ob[e Spin 5/2 Cd FIe. 2.--Relation betweenthe isomers of z=tPd.
a n d zl°pd b y r a d i o c h e m i c a l m e t h o d s t a k i n g a d v a n t a g e o f the difference in the halflives o f the isomers. EXPERIMENTAL 1. (n, 7) reaction on 18°Te About 500 mg of telluric acid were irradiated for an hour in the Canada-India Reactor and dissolved in water in the presence of iodide carrier. The solution was divided into three fractions. Fraction I was used for the estimation of tellurium in the solution by precipitation of the metal. This value is needed for calculating the chemical yield of telluriulm in Fraction III below. Fraction II was set aside and after the complete decay of 13~"Te and ~8~'~Te, iodine was separated, purified, precipitated as PdI2 and ~3~Iassayed using a beta proportional counter (sample A). Fraction rff was treated as follows to determine lslI formed by the decay of ~81'~Tealone. After complete decay of the independently formed 25 rain ~8~gTe,tellurium was purified from iodine by repeated precipitations of the metal. The purified tellurium was weighed and dissolved immediately, iodide carrier was added (as otherwise carrier-free iodine is likely to be lost) and set aside for the complete decay of the 1.2 day ~s~'~Te. Iodine was separated, purified and ~8~Iassayed (sample B). The activity of sample B was due to ~8~Iformed by the decay of a fraction of the initial amount of ~al'~Te alone. The ~s~I activity corresponding to the initially formed ~8~'~Tewas calculated by correcting the count rate for the decay of ~3~=Tefrom the end of the irradiation to the last tellurium precipitation, for the chemical yields of tellurium and iodine and for the growth and decay of ~3~I. From the count rate of sample A, the iodine activity due to ~31gTe and ~sl'~Te together was calculated by applying corrections for the chemical yield of iodine and for the growth and decay of ~s~I. Since the chemical yields of iodine were different in the two fractions, self absorption-scattering corrections were applied to the ~81I activities. The cross-section ratio was calculated from ~s~Iactivities in the two fractions. 2. (n, 7) reaction on n°Pd About 100 mg of PdCl= were irradiated in "Apsara" for 30 rains and dissolved in 1 : 1 HCI and divided into two fractions. Fraction I was kept aside after adding 20 mg of silver carrier. Silver was purified after the complete decay of l~lPd isomers and l~Ag assayed (sample A). To fraction IL 20 mg of silver were added and after about 6 hours during which the 22 rain Zl~epd completely decayed to ~l~Ag, silver activity was removed by eight more AgCI scavengings. The time of the last scavenging was noted. Again, 20 mg of silver were added and after the complete decay of
Isomeric cross-section ratios in the (n, ?) reactions
3
5'5 hr m=Pd, silver was purified and m A g assayed (sample ]3). From the activities of the samples A and B, the value of am/(ag + o'm) was calculated. Any possible errors due to the solubility of silver chloride and the loss of m=Pd tracer by adsorption on silver chloride precipitates were found to be negligible,c16~ RESULTS
AND OBSERVATIONS
The values of ~m/(~g + o'm) for the isomers of X3XTeand m P d are given in Table 1. The value 0.059 for the cross-section ratio for X3XTe isomers differs considerably from S~IGAL'S value ~2) of 0"13 obtained by direct measurement of the two cross-sections Cg = 270 ± 60 rob, and oTn = 40 ± I0 rob. The reason for this TABLE 1. (a)
ISOMERIC CROSS-SECTIONRATIO FOR (n, y) REACTIONON XS°Te
Experiment oxn/(ag + am)
1
2
3
4
5
0.057
0.054
0.063
0.063
0.058
(b)
Isor, m m c
6
7
0.061 0.059 mean = 0.059 4- 0-003
CROSS-SECTION RATIO FOR
(n, 7) R~ACrloN ON u°Pd Experiment
crm/(ag + am)
1
2
0"044 0"045
3
4
0"046 0"047 mean 0.045 + 0.001
TABLE 2.---COMPARISON OF CALCULATED AND EXPERIMENTAL VALUES
Values of oTn/(~g + ore) Calculated Target nucleus
Spins of the cr = 3 a = 4 o = 5 isomers N? = 4 N)' = 5 N ~ / = 4 Ny = 5 N? = 4 N7 = 5
~3°Te
3/2, 11/2
0.04
0.085
0.061
0.15
0.062
0-13
xl°pd
5/2, 11/2
0
0.023
0
0.052
0
0.044
Experimental 0.059 (present work) 0.13 (Ref. 2) 0.046 (present work)
0.044 0tel. 14)
disagreement is not known. In our experiments, the irradiations have been carried out in the Canada-India Reactor in a position where the fast flux is about 3 per cent of the thermal flux. A separate experiment carried out with a target wrapped in cadmium also yielded the same value indicating that the values are not very sensitive to the energy spectra of the neutrons. The cross-section ratio for m P d isomers 0.046, reported here is in agreement with the value 0.044 obtained by Dzxrrrmv et al. ( m who also used a radiochemical procedure involving periodic milking of mAg. ~xs~M. V. RAMAI,aAI-I,K. RENOAN and N. RAVlNDRAr~,J. Inorg. NucL Chem. 25, 725 (1963).
4
M . N . NAMBOODIRIet al.
In Table 2 the values of the cross-section ratios predicted by the HUIZENGAVANDENBOSCH model are given for various values of Ny and a. The cross-section ratio for 1SiTe isomers does not indicate any definite choice of the parameters, while that for lUpd isomers comes close to the value predicted for Ny = 5 and tr ---- 5. It has also been observed by others ~2's'7} that in this mass region the cross-section ratios correspond to values of both Ny and ~ in the range 3-5. Acknowledgement--The authors are grateful to Dr. BaAHM P ~ S H , Director, Metallurgy Group for his interest in this work. They are also thankful to Dr. C. L. RAO for his help during the preparation of the manuscript.
ISOMERIC CROSS-SECTION RATIOS IN THE (n, y) REACTIONS ON 18°Te AND 11°Pd M. N. NAMBOODIRI, M. RMAGOPALAN, N. RAVn,a)RAN, K. RENGAN and M. V. RAMANIAH Radiochemistry and Isotope Division, Atomic Energy Establishment, Trombay, Bombay (Received 15 January 1965)
Abstract--Isomeric cross-section ratios, am/(om + ag), in the (n, ~,) reactions on 13°Te and l'°pd have been determined using radiochemical techniques and have been found to be 0.059 and 0.045 respectively. These results have been compared with those of others and those calculated on the basis of Huizenga-Vandenbosch model. Tim relative yields of pairs of isomers produced in (n, y) reactions on a large number of nuclides have been investigated, cl-6) HtnZENGA and VAh~m~mOSCH developed a model (v) to calculate the relative yields of isomers using the spins of the c o m p o u n d nucleus and of the isomers, the number of ~,-rays, Ny, emitted in the process of de-excitation of the compound nucleus and the spin fall-off parameter, a, which determines the dependence of the nuclear level density on the spin. Comparison of calculated and experimental'cross-section ratios has been used to deduce the values of the parameters Ny and a, although this method does not always lead to unique values of the parameters for a given system. (1-~ The model has been extended to other
nuclear reactions like (~, n) etc.cs-m Recently SEHOAL is)measured the cross-sectionratio in the thermal neutron activation of ~ r e by directlycounting the ~,-radiationsof the tStTe isomers. DZANTIEV et al.(14) determined the isomeric cross-sectionratio for the (n, ~,) reaction on 11°pd using a radiochemical method, in the course of a study of the decay characteristics of the 111pd isomers and SBHGAL et al. (I~ reported a limit for this ratio, obtained by direct counting of the isomers. The modes of formation and decay of 13tTe and luPd isomers are given in Figs. I and 2.(13) In thiscommunication are reported the measurements of the cross-sectionratios of the isomers produced in (n, 7,)reactions on 1~q'e it) M. L. SEHOAL,H: S. HANSand P. S. GILL,Nucl. Phys. 12, 261 (1959). (~ M. L. SF~IOAL,Phys. Rev. 128, 761 (1962). ,s~ B. K~CH, Phys. Rev. 129, 769 (1962). ~4~C. T. BISHOV,Report ANL-6405 (1961). ,5~ C. T. BISHOP,J. R. HUIZENGAand J. P. HUMMEL,Phys. Rev. 135B, 401 (1964). ,6~ S. K. MA~OALand P. S. GILL,Nucl. Phys. 36, 542 (1962). '~) J. R. HUIZENOAand R. VANDENBOSCH,Phys. Rev. 120, 1305 (1960). ,s) R. VANDENBOSCHand J. R. HUIZmNOA,Phys. Rev. 120, 1313 (1960). is) j. L. NEEDand B. LINDER,Phys. Rev. 129, 1298 (1963). ,lo~ j. L. NEED,Phys. Rev. 129, 1302 (1963). m~ C. R_mEx"and B. LINDER,Phys. Rev. 134, 559 (1964). ,1~ C. RILEy, K. V ~ o and B. LINDEn,Phys. Rev. 135 B, 1340 (1964). ,m Nuclear Data Sheets, National Academy of Sciences, National Research Council, Washington, D.C. ,1,~ B. G. DzAwrmv et al., Soy. Phys. (Doklady), 2, 154 (1957). 1 1
2
M.N.
N ~ m o o ~ w a et aL
Spin H/~ 30 hi"131rnTe
Spin 3/2 FIG. 1.--l~lation betweenthe isomers of ~S~Te. Spin 11/2 5.5 hr ="mPd. . . . ,,opd(n~x)J
\\
I=.-74 seclilmAg --
\~
22rnin gPd_--~7. 6 doy.l~Aq ~S~ob[e Spin 5/2 Cd FIe. 2.--Relation betweenthe isomers of z=tPd.
a n d zl°pd b y r a d i o c h e m i c a l m e t h o d s t a k i n g a d v a n t a g e o f the difference in the halflives o f the isomers. EXPERIMENTAL 1. (n, 7) reaction on 18°Te About 500 mg of telluric acid were irradiated for an hour in the Canada-India Reactor and dissolved in water in the presence of iodide carrier. The solution was divided into three fractions. Fraction I was used for the estimation of tellurium in the solution by precipitation of the metal. This value is needed for calculating the chemical yield of telluriulm in Fraction III below. Fraction II was set aside and after the complete decay of 13~"Te and ~8~'~Te, iodine was separated, purified, precipitated as PdI2 and ~3~Iassayed using a beta proportional counter (sample A). Fraction rff was treated as follows to determine lslI formed by the decay of ~81'~Tealone. After complete decay of the independently formed 25 rain ~8~gTe,tellurium was purified from iodine by repeated precipitations of the metal. The purified tellurium was weighed and dissolved immediately, iodide carrier was added (as otherwise carrier-free iodine is likely to be lost) and set aside for the complete decay of the 1.2 day ~s~'~Te. Iodine was separated, purified and ~8~Iassayed (sample B). The activity of sample B was due to ~8~Iformed by the decay of a fraction of the initial amount of ~al'~Te alone. The ~s~I activity corresponding to the initially formed ~8~'~Tewas calculated by correcting the count rate for the decay of ~3~=Tefrom the end of the irradiation to the last tellurium precipitation, for the chemical yields of tellurium and iodine and for the growth and decay of ~3~I. From the count rate of sample A, the iodine activity due to ~31gTe and ~sl'~Te together was calculated by applying corrections for the chemical yield of iodine and for the growth and decay of ~s~I. Since the chemical yields of iodine were different in the two fractions, self absorption-scattering corrections were applied to the ~81I activities. The cross-section ratio was calculated from ~s~Iactivities in the two fractions. 2. (n, 7) reaction on n°Pd About 100 mg of PdCl= were irradiated in "Apsara" for 30 rains and dissolved in 1 : 1 HCI and divided into two fractions. Fraction I was kept aside after adding 20 mg of silver carrier. Silver was purified after the complete decay of l~lPd isomers and l~Ag assayed (sample A). To fraction IL 20 mg of silver were added and after about 6 hours during which the 22 rain Zl~epd completely decayed to ~l~Ag, silver activity was removed by eight more AgCI scavengings. The time of the last scavenging was noted. Again, 20 mg of silver were added and after the complete decay of
Isomeric cross-section ratios in the (n, ?) reactions
3
5'5 hr m=Pd, silver was purified and m A g assayed (sample ]3). From the activities of the samples A and B, the value of am/(ag + o'm) was calculated. Any possible errors due to the solubility of silver chloride and the loss of m=Pd tracer by adsorption on silver chloride precipitates were found to be negligible,c16~ RESULTS
AND OBSERVATIONS
The values of ~m/(~g + o'm) for the isomers of X3XTeand m P d are given in Table 1. The value 0.059 for the cross-section ratio for X3XTe isomers differs considerably from S~IGAL'S value ~2) of 0"13 obtained by direct measurement of the two cross-sections Cg = 270 ± 60 rob, and oTn = 40 ± I0 rob. The reason for this TABLE 1. (a)
ISOMERIC CROSS-SECTIONRATIO FOR (n, y) REACTIONON XS°Te
Experiment oxn/(ag + am)
1
2
3
4
5
0.057
0.054
0.063
0.063
0.058
(b)
Isor, m m c
6
7
0.061 0.059 mean = 0.059 4- 0-003
CROSS-SECTION RATIO FOR
(n, 7) R~ACrloN ON u°Pd Experiment
crm/(ag + am)
1
2
0"044 0"045
3
4
0"046 0"047 mean 0.045 + 0.001
TABLE 2.---COMPARISON OF CALCULATED AND EXPERIMENTAL VALUES
Values of oTn/(~g + ore) Calculated Target nucleus
Spins of the cr = 3 a = 4 o = 5 isomers N? = 4 N)' = 5 N ~ / = 4 Ny = 5 N? = 4 N7 = 5
~3°Te
3/2, 11/2
0.04
0.085
0.061
0.15
0.062
0-13
xl°pd
5/2, 11/2
0
0.023
0
0.052
0
0.044
Experimental 0.059 (present work) 0.13 (Ref. 2) 0.046 (present work)
0.044 0tel. 14)
disagreement is not known. In our experiments, the irradiations have been carried out in the Canada-India Reactor in a position where the fast flux is about 3 per cent of the thermal flux. A separate experiment carried out with a target wrapped in cadmium also yielded the same value indicating that the values are not very sensitive to the energy spectra of the neutrons. The cross-section ratio for m P d isomers 0.046, reported here is in agreement with the value 0.044 obtained by Dzxrrrmv et al. ( m who also used a radiochemical procedure involving periodic milking of mAg. ~xs~M. V. RAMAI,aAI-I,K. RENOAN and N. RAVlNDRAr~,J. Inorg. NucL Chem. 25, 725 (1963).
4
M . N . NAMBOODIRIet al.
In Table 2 the values of the cross-section ratios predicted by the HUIZENGAVANDENBOSCH model are given for various values of Ny and a. The cross-section ratio for 1SiTe isomers does not indicate any definite choice of the parameters, while that for lUpd isomers comes close to the value predicted for Ny = 5 and tr ---- 5. It has also been observed by others ~2's'7} that in this mass region the cross-section ratios correspond to values of both Ny and ~ in the range 3-5. Acknowledgement--The authors are grateful to Dr. BaAHM P ~ S H , Director, Metallurgy Group for his interest in this work. They are also thankful to Dr. C. L. RAO for his help during the preparation of the manuscript.