L.E. Glendenin

The mass distribution for spontaneous fission of 252Cf

Abstract The distribution of mass in the spontaneous fission of 252Cf has been investigated by the radiochemical determination of the fission yields for 35 mass chains. Absolute fission yields were measured for four nuclides, 99Mo, 111Ag, 132Te and 140Ba. Ratios of the yields of fission product isomers to total chain yields were determined for 115gCd, 125gSn, 127mTe and 129mTe. A comparison of this work with that of previous investigators has resulted in “recommended” yields for 51 mass chains.

Fission yields in spontaneous fission of Cf252

Abstract Spontaneous fission of Cf252 has been investigated by radiochemical determination of the yields of fifteen fission products ranging in mass number from 99 to 143. Fission is observed to be asymmetric with some indication of fine structure in the mass distribution associated with the 82-neutron shell. Both light- and heavy-fission product groups are shifted to higher masses relative to spontaneous fission of Cm242. The yield-mass curve indicates a value of 5 ± 1 for the average number of neutrons emitted per fission.

Half-lives of 90Sr and 137Cs☆

The half-lives of 90Sr and 137Cs have been measured both by specific activity and by direct decay over periods of 6–10 years. The results of the decay measurements are 28·0 ± 0·4 years for 90Sr and 29·9 ± 0·5 years for 137Cs; the values obtained by specific activity measurements are 28·5 ± 0·9 years for 90Sr and 30·9 ± 0·7 years for 137Cs. Recommended “best” values for these half-lives based on current literature values are 28·1 ± 0·3 years for 90Sr and 30·0 ± 0·2 years for 137Cs.

Mass distributions in monoenergetic-neutron-induced fission of /sup 239/Pu

Fission product yields for 24 masses were determined for the fission of /sup 239/Pu with essentially monoenergetic neutrons of 0.17, 1.0, 2.0, 3.4, 4.5, 6.1, and 7.9 MeV. Fission product activities were measured by Ge(Li) ..gamma..-ray spectrometry of irradiated /sup 239/Pu targets and by chemical separation of the fission product elements followed by ..beta.. counting. Yields of near symmetric (valley) fission products increase nearly monotonically with incident neutron energy and do not exhibit a break in the slope of the yield versus neutron energy curve in the energy region where second-chance fission begins. This is in contrast to the curves for /sup 232/Th, /sup 235/U, and /sup 238/U neutron-induced fission.

Formation of 111Pd isomers in neutron fission of several heavy nucleides

Abstract The cumulative yields of the 111Pd isomers have been measured in fission of 232Th, 233U, 235U, 238U and 239Pu by neutrons. The ratios of the 11 2 metastable state yield to the 5 2 ground state yield are 0·0043, 0·0209, 0·0096, 0·0048 and 0·0186 for the respective nucleides. The estimated error in each value is ±10%. Independent yield isomeric ratios have been calculated for various assumptions of charge distribution. The results of these calculations are discussed in terms of the parameters which describe the charge dispersion of mass-chain 111 and the angular momentum with which the fragments are formed. An upper limit of 0·43% has been placed on the β-decay branch of 111Rh111mPd.

Independent yields of 82Br, 86Rb, 136Cs and 150Pm in spontaneous fission of 252Cf

Independent fission yields in the spontaneous fission of 252Cf were determined by radiochemical techniques for the shielded nuclides 82Br, 86Rb, 136Cs and 150Pm. They were found to be < 3·7 × 10−6 per cent, 5·4 × 10−6 per cent, 2·2 × 10−2 per cent and 2·0 × 10−2 per cent, respectively. The corresponding fractional chain yields lead to empirical Zp (most probable charge) values which are in good agreement with Zp values determined by physical methods (K X-rays).

Mass distribution in the fission of 229Th

Abstract Yields for twenty-five mass chains in thermal-neutron-induced fission of 229 Th have been measured radiochemically. The mass-yield curve is asymmetric with the light peak centered at mass 88 and the heavy peak centered at mass 140. The peak-to-valley ratio is about 500. No significant increase in yield in the region of symmetric fission was observed.

Independent yields of 84Rb, 86Rb and 136Cs for thermal-neutron-induced fission of 233U, 235U and 239Pu

Abstract The independent fission yields of 84Rb (a positron emitter), 86Rb and 136Cs have been measured for thermal-neutron-induced fission of 233U, 235U and 239Pu. The yields of 84Rb are (6·6 ± 0·7) × 10−8% for 233U, (2·4 ± 0·3) × 10−9% for 235U, and (3·9 ± 0·4) × 10−8% for 239Pu. The yields of 86Rb are (9·2 ± 0·9) × 10−4% for 233U, (2·1 ± 0·2) × 10−5% for 235U, and (1·9 ± 0·2) × 10−4% for 239Pu. The yields of 136Cs are 0·105 ± 0·011% for 233U, 0·0074 ± 0·0007% for 235U, and 0·100 ± 0·010% for 239Pu. The half-life of 136Cs by least squares analysis of the decay of eleven independent samples is 13·16 ± 0·03 days.

Mass distributions for the spontaneous fission of 248Cm and 250Cf

Abstract The distribution of mass in spontaneous fission of 248Cm and 250Cf has been investigated radiochemically and with γ-ray spectrometry. Both distributions are asymmetric with peak-to-valley ratios of > 1000 for 248Cm and > 300 for 250Cf. The average light and heavy masses ( A L , A H ) are respectively 104.6, 139.9 and 105.2, 141.5. Values for the average number of neutrons emitted per fission obtained by subtracting A L + A H from the mass of the fissioning nucleus are respectively 3.5±0.5 and 3.3±0.5.

Mass distributions for the spontaneous fission of 253Es and the thermal-neutron-induced fission of 254Es☆

Abstract The distribution of mass in the spontaneous fission of 253Es and the thermal-neutron-induced fission of 254Es have been investigated radiochemically. Both mass distributions are asymmetric with peak-to-valley ratios of 326 and 6, respectively. The average light and heavy masses ( A L , A H ) for the respective systems are 105·9, 142·4 and 110·6, 140·2. The average numbers of neutrons emitted per fission determined by subtracting A L + A H from the mass of the fissioning nucleus are respectively 4·7 and 4·2.