Fission Product Mass Yield Curves and Their Energy Dependence

Abstract

It has been found that the mass yield curves for 232Th, 233U, 235U, 238U and 239pU neutron fission can be fitted, with an accuracy of better than 20 %, by the superposition of two pairs of asymmetric gaussian curves and a single symmetric gaussian curve. The parameters of the fit have been investigated as a function of the nuclear temperature at the saddle point of the fissioning compound nucleus, and the widths and positions are found to vary linearly with this temperature. In addition, broad peaks are found in the weights of the gaussians, the weights being related to partial fission cross sections. This empirical analysis has been compared with the predictions of the Nix (1969) model of fission and deficiencies in the existing theory are discussed.