Correlation studies of fission fragment neutron multiplicities

TL;DR

This study models neutron multiplicities from fission fragments by simulating shape evolution and energy partitioning, achieving good agreement with experimental data and revealing a superlong fission mode at higher neutron energies.

Contribution

It introduces a detailed five-dimensional potential-energy landscape model with microscopic level densities to predict neutron multiplicities and their correlations with fission fragment properties.

Findings

Good agreement with experimental neutron multiplicity data from $^{235}$U(n$_{ m th}$,f)

Identification of a superlong fission mode at higher neutron energies

Shape-dependent microscopic level densities improve excitation energy partitioning

Abstract

We calculate neutron multiplicities from fission fragments with specified mass numbers for events having a specified total fragment kinetic energy. The shape evolution from the initial compound nucleus to the scission configurations is obtained with the Metropolis walk method on the five-dimensional potential-energy landscape, calculated with the macroscopic-microscopic method for the three-quadratic-surface shape family. Shape-dependent microscopic level densities are used to guide the random walk, to partition the intrinsic excitation energy between the two proto-fragments at scission, and to determine the spectrum of the neutrons evaporated from the fragments. The contributions to the total excitation energy of the resulting fragments from statistical excitation and shape distortion at scission is studied. Good agreement is obtained with available experimental data on neutron multiplicities in correlation with fission fragments from $^{235}$U(n$_{\rm th}$,f). At higher neutron energies a superlong fission mode appears which affects the dependence of the observables on the total fragment kinetic energy.