Cumulative yields in the 14 MeV neutron fission of 232Th and 238U in the symmetric region

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Abstract
The radiochemical yields of molybdenum-99, ruthenium-103 and -105, palladium-109 and -112, silver-111 and -113, cadmium-115, and tin-121 and -125 formed in the 14 MeV fission of thorium-232 and uranium-238 have been determined using a low background Geiger–Muller counter, NaI(Tl) crystal, and Ge(Li) detector. The absolute mass yield for molybdenum-99 has been obtained using a copper monitor for neutron flux and for the other nuclides using molybdenum-99 as an internal standard. The mass distribution curves derived from the chain yields, in the symmetric region show the presence of a third peak in thorium-232, and only the familiar two peaks for uranium-238 in the asymmetric region. By comparison of normalized cumulative mass yields from this study with prompt fission yield data, the average number of prompt neutrons emitted from fission fragments has been obtained as a function of mass in 238U + n fission. It appears that there are two regions of enhanced neutron emission in the mass range 103–128, and that the heavy fragments emit more neutrons than the light ones.
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