Fission yields in the symmetric region: Yields of the stable isotopes of tin and cadmium in the thermal neutron fission ofU235andPu239

Abstract

The relative isotopic abundances of five isotopes of cadmium (111, 112, 113, 114, and 116) and eight isotopes of tin (117, 118, 119, 120, 21, 122, 124, and 126) have been measured in the thermal neutron fission of $^{235}\mathrm{U}$ and $^{239}\mathrm{Pu}$. Samples of $^{235}\mathrm{U}$ and $^{239}\mathrm{Pu}$ were irradiated in a reactor; the elements were chemically separated and the isotopic abundances were mass spectrometrically determined. By suitably normalizing these relative yields, it has been possible to obtain the cumulative chain yields at 12 masses in the symmetric region of the mass distribution. These results indicate that there is a fine structure in the 113-115 mass region, especially in the fission of $^{235}\mathrm{U}$. However, the mass distribution appears to be smooth between masses 116 and 126. The depression in the mass-yield curve around mass 115 may be related to the break around this mass number in the prompt neutron distribution as a function of mass.NUCLEAR REACTIONS, FISSION $^{235}\mathrm{U}(n, f)$ and $^{239}\mathrm{Pu}(n, f)$ measured abundances of tin and cadmium isotopes.