Correlation of Fission-Fragment Kinetic-Energy Fine Structure with a Semiempirical Mass Surface

Abstract

A correlation has been established between fine structure in primary fragment yields for thermal-neutron-induced fission of several targets and structure in the energy release calculated from semiempirical mass equations. The origin of the structure in the calculated energy release has been elucidated and can be attributed to two general properties of the mass surface: (1) The energy release for even-even products is greater than for odd-mass products, so that the structure is determined by the mass surface for even-even products. (2) The structure for even-even products has a periodicity of about 5 mass units because the mass number of the most stable nuclide for a given $Z$ changes about 2.5 units for a unit change in $Z$. The existence of structure in the fission fragment yields suggests that there is a preference for forming even-even primary fragments in the fission of an even-even compound nucleus.