Yields and genetic histories of 128Sb, 129Sb and 130Sb from thermal-neutron induced fission of 235U

Abstract

The following fractional independent yields have been determined: 10-min 128Sb, ≤0·037; 9·1-hr 128Sb, 0·031 ± 0·005; 129Sb, 0·114 ± 0·046; 6·3-min 130Sb, 0·202 ± 0·030; 40-min 130Sb, 0·138 ± 0·034. The cumulative yield of 130Sn has been determined to be 0·89 ± 0·10%, and the following chain yields have been derived from this, the fractional independent yields and literature values: A = 128, 0·344 ± 0·018%; A = 129, 0·61 ± 0·03%; A = 130, 1·43 ± 0·18%. It has also been determined that 3·1 ± 0·2% of 128Sn decays to the 9·1-hr 128Sb isomer and that 52·9 ± 3·4% of 129Sb is formed by decay of 2·5-min 129Sn and 35·7 ± 3·0% is formed by decay of 7·4-min 129Sn. Rapid chemical separation procedures are described, and a method is discussed of correcting gamma-ray peak areas determined with a Ge(Li) detector for decay of activities and for changing analyzer dead-time during each counting period. The yields of the antimony isotopes are all somewhat smaller than estimated “normal” yields, as has usually been observed for odd Z nuclides. The data help to show that most of the large initial increase in yield with mass number above A = 125 is due to the increasing cumulative yields of tin isotopes, an indication that closure of the 50-proton shell is an important cause for the high probability of asymmetric mass division in low energy fission.