Fractional independent yields of 104Tc and 105Tc from thermal-neutron-induced fission of 235U and of 239Pu

Abstract

The fractional independent yields of 104Tc and 105Tc were determined by measurement of the intensities of individual γ-rays with Ge(Li) detectors after rapid chemical separation of TcO 4 − from Mo(VI), following oxidation of lower oxidation states. The values determined for 104Tc and 105Tc, respectively, are: <0.01 (−0.016 ± 0.022 measured) and <0.03 (−0.002 ± 0.32 measured) from thermal-neutron-induced fission of 235U and 0.077 ± 0.012 and 0.264 ± 0.021 from thermal-neutron-induced fission of 239Pu. The small yields from 235U are consistent with most other values that have been reported, and the larger yields from 239Pu are consistent with the yields of antimony isotopes that are approximately complementary to 104Tc and 105Tc. The independent yields of 104Tc and 105Tc are much smaller (>25 and >50 times less, respectively) when formed by thermal-neutron-induced fission of 235U than when formed by thermal-neutron-induced fission of 239Pu. The large differences may be associated with the atomic numbers of the complementary elements ( 49In and 51Sb) being one less than and one greater than the “magic” atomic number of 50 for tin isotopes, and, therefore, these observations support the postulate that the presence of at least 50 protons in one fission fragment is a necessary condition, though not necessarily a sufficient one, for high yields from low-energy fission reactions.