Prompt Fission Neutron Spectra for Neutron-Induced Fission of 239Pu and 235U

M Devlin ,Denise Neudecker,C Y Wu ,S Mosby ,T.n Taddeucci ,K J Kelly ,J Henderson ,J A Gomez ,B Bucher ,Hye Young Lee ,J L Ullmann ,J M O’donnell ,Ν Fotiades ,R C Haight ,Matthew Buckner ,Morgan Curtis White ,R Henderson

doi:10.1051/epjconf/202023901003

Abstract

We report the current results of a large effort to accurately measure the Prompt Fission Neutron Spectra (PFNS) for neutron-induced fission of 235U and 239Pu for incident neutrons with energies from 1 to 20 MeV. The Chi-Nu experiment at the Los Alamos Neutron Science Center used an unmoderated, white spectrum of neutrons to induce fission in actinide samples that were placed inside a parallel plate avalanche counter to provide a fast fission signal. A double time-of-flight technique was used to determine the incoming and outgoing neutron energies. Two neutron detector arrays, one with 54 liquid scintillators and another with 22 lithium glass detectors, were used to detect the outgoing neutrons and measure the PFNS distributions over a wide range in outgoing neutron energy, from below 100 keV to 10 MeV. Extensive Monte Carlo modeling was used to understand the experiment response and extract the PFNS. Systematic errors and uncertainties in the method have been examined and quantified. A summary of these results for incoming energies from 1 to 5 MeV is presented here.

Highlights

Prompt Fission Neutron Spectra (PFNS) measurements for neutron-induced fission have been of interest since shortly after the discovery of fission [1]
Attempts at such measurements were necessarily primitive, but interest in these spectra was such that the first numbered report from the secret program at Los Alamos was titled A Discussion of the Fission Neutron Spectrum [2]; this document is no longer classified
In this paper we present measurements of the PFNS for multiple incident neutron energy ranges from 1 – 5 MeV following neutron-induced fission of 235U and 239Pu

Summary

Introduction

Prompt Fission Neutron Spectra (PFNS) measurements for neutron-induced fission have been of interest since shortly after the discovery of fission [1]. Improved data on PFNS are needed, for fast neutrons, to improve nuclear data libraries [15, 16] used in neutronics calculations for fast systems. These data needs were listed in the recent CIELO nuclear data program [17, 18] of high-priority measurements and evaluations. Preliminary results, for the lower-energy part of the PFNS for 235U, have been reported previously; the results

Experiments and Analysis

Uncertainty quantification and correlations

Summary