Monte Carlo approach to sequential neutron emission from fission fragments

Abstract

We have implemented a Monte Carlo simulation of fission fragment statistical decay by sequential neutron emission. Within this approach, we calculate the center-of-mass and laboratory prompt neutron energy spectra as a function of the mass of fission fragments and integrated over the whole mass distribution. We also assess the prompt neutron multiplicity distribution $P(\ensuremath{\nu})$, both the average number of emitted neutrons and the average neutron energy as a function of the mass of the fission fragments [respectively $\overline{\ensuremath{\nu}}(A)$ and $\ensuremath{\langle}\ensuremath{\varepsilon}\ensuremath{\rangle}(A)$]. We investigate the average total energy available for prompt \ensuremath{\gamma}-ray emission as a function of the mass of the fission fragments ${\overline{E}}_{\ensuremath{\gamma}}(A)$. We also calculate neutron-neutron correlations such as the full matrix $\overline{\ensuremath{\nu}}(A,\mathrm{TKE})$ as well as correlations between neutron energies. Two assumptions for partitioning the total available excitation energy among the light and heavy fragments are considered. Results are reported for the neutron-induced fission of $^{235}\mathrm{U}$ (at neutron energy of 0.53 MeV) and for the spontaneous fission of $^{252}\mathrm{Cf}$.