Energy and Spin Dependence of Fission:H1andHe4Emission fromHg194Compound Nuclei

Reactions of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ have been used to produce ${}_{}{}^{194}{}_{}{}^{}\mathrm{Hg}$ compound nuclei at excitation energies of 98 and 142 MeV. This combination of entrance channels permits the separation of energy and spin effects on the exit channels. Fission probability clearly increases with angular momentum at fixed energy. However, there is no increase in the cumulative fission fraction from 98 to 142 MeV for essentially constant spin domain. In contrast the probability of ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ evaporation increases rapidly with energy and seems to shield the system from fission.