Fission Yield Fine Structure in the Mass Region 99-106

Fission yield measurements were carried out in the mass region 99 to 106 to investigate previously postulated fine structure related to nuclear closed shells. Radiochemical data were obtained in this mass region in the fission reactions ${\mathrm{U}}^{235}(n, f)$, ${\mathrm{U}}^{238}(\gamma , f)$, ${\mathrm{U}}^{235}(d, f)$, and ${\mathrm{U}}^{238}(d, f)$ for the yields of ${\mathrm{Mo}}^{99}$, ${\mathrm{Mo}}^{101}$, ${\mathrm{Mo}}^{102}$, ${\mathrm{Ru}}^{103}$, ${\mathrm{Ru}}^{105}$, and ${\mathrm{Ru}}^{106}$. Fine structure spikes were found in all reactions. It was found that the mass position of the spikes can be explained by the assumption that primary fission fragments with 82 neutrons or 50 protons and their complements have an enhanced yield as a result of selectivity in the fission process itself. Agreement was also found with two previously known reactions: ${\mathrm{U}}^{233}(n, f)$ and ${\mathrm{Cm}}^{242}$ spontaneous fission. Fine structure is also predicted for several other fission reactions.