A method to calculate fission-fragment yields Y(Z, N) versus proton and neutron number in the Brownian shape-motion model Application to calculations of U and Pu charge yields

We propose a method to calculate the two-dimensional (2D) fission-fragment yield Y (Z, N) versus both proton and neutron number, with inclusion of odd-even staggering effects in both variables. The approach is to use the Brownian shape-motion on a macroscopic-microscopic potential-energy surface which, for a particular compound system is calculated versus four shape variables: elongation (quadrupole moment Q(2)), neck d, left nascent fragment spheroidal deformation epsilon(f1), right nascent fragment deformation epsilon(f2) and two asymmetry variables, namely proton and neutron numbers in each of the two fragments. The extension of previous models 1) introduces a method to calculate this generalized potential-energy function and 2) allows the correlated transfer of nucleon pairs in one step, in addition to sequential transfer. In the previous version the potential energy was calculated as a function of Z and N of the compound system and its shape, including the asymmetry of the shape. We outline here how to generalize the model from the compound-system model to a model where the emerging fragment proton and neutron numbers also enter, over and above the compound system composition.