Event-by-event evaluation of the prompt fission neutron spectrum from 239Pu(n, f)

TL;DR

This paper extends the event-by-event fission model FREYA to simulate the prompt neutron spectrum from 239Pu(n, f) up to 20 MeV, incorporating multichance fission and pre-equilibrium emission, and fits model parameters to experimental data.

Contribution

It introduces an extended model with multichance fission and pre-equilibrium emission, providing a detailed analysis of the prompt neutron spectrum for 239Pu(n, f).

Findings

Extended model fits experimental neutron multiplicity data.

Incorporates energy-energy correlations in neutron spectrum.

Provides a new evaluation for prompt fission neutron spectrum.

Abstract

Earlier studies of 239Pu(n, f) have been extended to incident neutron energies up to 20 MeV within the framework of the event-by-event fission model FREYA, into which we have incorporated multichance fission and pre-equilibrium neutron emission. The main parameters controlling prompt fission neutron evaporation have been identified and the prompt fission neutron spectrum has been analyzed by fitting those parameters to the average neutron multiplicity nubar from ENDF-B/VII.0, including the energy-energy correlations in nubar(E) obtained by fitting to the experimental nubar data used in the ENDF-B/VII.0 evaluation. We present our results, discuss relevant tests of this new evaluation, and describe possible further improvements.