Pair breaking and even-odd structure in fission-fragment yields

The probabilities of single-particle excitations that preserve completely p aired configurations of the nuclear proton and neutron subsystems are formu lated as a function of excitation energy in the framework of the superfluid nuclear model. These calculations are used to analyse measured data on eve n-odd structure in fission-fragment yields. Excitation energies acquired at scission are deduced. The strongly differing even-odd structures in proton and neutron numbers are explained within the assumption of thermal equilib rium of intrinsic excitations at scission. (C) 2000 Elsevier Science B.V. A ll rights reserved.