Symmetric and Asymmetric Fission of U238 Induced by Helium Ions

Abstract

The energetics of helium-ion-induced fission of U 238 has been investigated, a back-to-back solid state detector system being used. The measurements have been made at two center-of-mass angles 90° and 160° and at bombarding energies of 27.8, 30.4, 32.6, 34.2 and 35.6 Mev. It Is found that the position of the asymmetric fission peak in the kinetic energy contour diagram and the most probable values of E L , E H and E K are nearly independent of the excitation energy of compound nucleus. From the comparison with results obtained so far at lower energies, it is probably concluded that the average total kinetic energy in symmetric Fission increases with the excitation energy of fissioning nucleus but the one at the peak in the mass yield distribution is approximately independent of the excitation energy. Some systematics are derived for the average total kinetic energies. The average excitation energy of fragments remains nearly constant in symmetric fission but not in asymmetric fission as the excitation energy of fissioning nucleus increases. The anisotropies for symmetric and asymmetric fission are probably consistent with a theoretical prediction.