Fission Energetics and Neutron Emission in 13-MeV Proton-Induced Fission ofRa226

Abstract

The energetics of the fission of $^{226}\mathrm{Ra}$ induced by 13-MeV protons have been studied by means of a threeparameter experiment in which the time of flight of one fragment was measured in coincidence with the pulse amplitudes produced by both fragments in silicon surface-barrier detectors. The average number of neutrons emitted from individual fragments and from both fragments together are obtained as functions of fragment mass and total kinetic energy. In addition, the pre- and post-neutron-emission fragment mass distributions are obtained, together with the fragment energy distributions and mass-versus-energy correlations. Fragment excitation energies are inferred from the neutron-emission data, and the total energy balance is investigated. The experimental results suggest the presence of two components in $^{226}\mathrm{Ra}+p$ fission, one a liquid-drop component describing events in the symmetric peak of the mass distribution, the other a fragment-structure component describing events in the asymmetric peaks. The various distributions and correlations obtained, including those involving neutron emission, have been analyzed from this point of view and are seen to be quantitatively consistent with the assumption of two such components. It remains unclear, however, whether one or two saddle points are involved.