Fragment Kinetic Energy Release in Heavy-Ion-Induced Fission Reactions

The most probable kinetic-energy release in fission reactions induced by 125-MeV C¹² ions and 166-MeV O¹⁶ ions has been measured for the target nuclei Pr¹⁴¹, Tb¹⁵⁹, Ho¹⁶⁵, Tm¹⁶⁹, Lu¹⁷⁵, Au¹⁹⁷, Bi²⁰⁹, Th²³², U²³⁸, and Pu²⁴⁰. Silicon diode surface-barrier detectors were used in these measurements, and a Cf²⁵² spontaneous-fission source served as the absolute energy standard. A least-squares analysis of our data and those obtained by others gives ĒK(MeV)=0.1065 Z²A1/3+20.1. The dependence of the most probable kinetic energy on the scission shape of the fissioning nucleus has been examined by comparison with recent calculations based on the work of Cohen and Swiatecki. The data are consistent with scission shapes corresponding to spheroids whose shapes minimize the total energy of the system.The most probable kinetic-energy release has been found to be essentially independent of the excitation energy of the compound nucleus. It is also observed that the full width at half-maximum of the kinetic-energy distribution is relatively constant for values of the fissionability parameter x less than 0.7, but increases rapidly above this value. The halfwidth also exhibits an increased spread as the excitation energy of the compound nucleus increases.