Event-by-event study of prompt neutrons from 239Pu(n,f)

TL;DR

This paper uses a Monte Carlo model to analyze prompt neutron emission from 239Pu fission, providing precise constraints on microscopic calculations and improving neutron spectrum estimates crucial for reactor physics.

Contribution

The study introduces a novel Monte Carlo approach combined with statistical analysis to refine predictions of prompt neutron characteristics from 239Pu fission.

Findings

Total excitation energy must be within 1 MeV for accurate neutron multiplicity predictions.

The method reduces uncertainties in the fission neutron spectrum by several times.

The approach enhances the evaluation of fission neutron data for reactor applications.

Abstract

Employing a recently developed Monte Carlo model, we study the fission of 240Pu induced by neutrons with energies from thermal to just below the threshold for second chance fission. Current measurements of the mean number of prompt neutrons emitted in fission, together with less accurate measurements of the neutron energy spectra, place remarkably fine constraints on predictions of microscopic calculations. In particular, the total excitation energy of the nascent fragments must be specified to within 1 MeV to avoid disagreement with measurements of the mean neutron multiplicity. The combination of the Monte Carlo fission model with a statistical likelihood analysis also presents a powerful tool for the evaluation of fission neutron data. Of particular importance is the fission spectrum, which plays a key role in determining reactor criticality. We show that our approach can be used to develop an estimate of the fission spectrum with uncertainties several times smaller than current experimental uncertainties for outgoing neutron energies up to 2 MeV.