Further Radiochemical Studies of Fission of theU236*Compound Nucleus

Fission-product yields relative to the fission yield of ${\mathrm{Mo}}^{99}$ were measured for the fission of ${\mathrm{Th}}^{232}$ with ${\mathrm{He}}^4$ ions of energies ranging from threshold to 45 MeV and for the fission of ${\mathrm{U}}^{235}$ with 14-MeV neutrons. The linear relationships between fission yields predicted by the two-mode fission hypothesis and previously observed for fission of ${\mathrm{U}}^{236*}$ at low excitation energies break down at the higher energies in many cases. The fission yield of ${\mathrm{Mo}}^{99}$ and the total fission cross section were evaluated as a function of ${\mathrm{He}}^4$ ion energy.