Modelling of the total excitation energy partition including fragment deformation and excitation energies at scission

Abstract

In the frame of refined prompt neutron emission models used for evaluation purposes, the partition of the total excitation energy (TXE) between fully accelerated fission fragments plays an important role. In this work the TXE partition between complementary fission fragments is obtained by taking into account the energy components at scission. The method consists of two steps: the calculation of additional deformation energies of nascent fragments (which are relaxed into excitation energy at full acceleration) and the partition of the available excitation energy at scission (obtained by subtracting the calculated deformation energies from TXE) assuming statistical equilibrium. The obtained fragment excitation energies, as the sum of deformation and excitation energy components at scission, are then used in the frame of the Point-by-Point model to describe experimental data of prompt fission quantities. This TXE partition method was applied to the following fissioning systems: 233,235U(nth,f), 239Pu(nth,f), 237Np(n,f) at 0.8 and 5.5 MeV incident energies and 252Cf(SF). The presented procedure of TXE partition is based exclusively on models and straightforward assumptions practically without the need for adjustable parameters (the parameters have been adjusted a priori and to global systematics). It allows the prediction of prompt neutron emission data and, therefore, may be successfully used for evaluation purposes.