Experiments with neutron induced neutron emission from U-235, Pu-239, and graphite

Yaron Danon,Keegan J.Kelly,Kumar Mohindroo,Matt Devlin,Jaime Gomez,John O'Donnell,Ezekiel Blain,Z Ge,H Zhang,Y Chen,N Shu,W Wang

doi:10.1051/epjconf/202023901004

Abstract

A neutron induced neutron emission experiment was conducted as the Los Alamos Neutron Science Center (LANSCE) facility at Los Alamos National Laboratory (LANL). In this experiment, a sample was placed in a well collimated neutron beam and was surrounded by an array of 28 fast neutron detectors (EJ-309). The experiment was performed with a neutron flight path of 21.5 m from the source to the sample, and 1 m from the sample to the detectors. The neutron emission from the sample was measured as a function of neutron time of flight covering an incident energy range from 0.7- 20 MeV. The samples included U-235, Pu-239, carbon (graphite), and blanks that matched the encapsulation of the sample. The measured samples were constantly cycled in and out of the neutron beam. This type of experiment measures neutron emission from all reactions occurring in the sample such as fission and elastic and inelastic scattering. Similar to the methodology previously developed at RPI [1], the measurements were compared with detailed simulations of the experiment using different cross section evaluations for the sample. The observed differences can be attributed to the evaluated neutron cross section and angular distributions. The carbon sample was used as a reference to validate both the experiment and simulation methodology and showed good agreement between experiments and simulations. A review of the experimental setup, analysis methods, and some of the results will be presented.

Highlights

The uncertainty in evaluations of neutron induced reactions propagates to quantities calculated using these data such as the multiplication factor for a critical system, or leakage rates for critical or other nuclear systems
A neutron beam from the Rensselaer Polytechnic Institute (RPI) LINAC hit the sample and scattered neutrons are detected using the time of flight (TOF) method
The experiment was performed using the Chi-Nu liquid scintillation detector array [11] at Los Alamos National Laboratory (LANL), the detector array was conFigured with 28 EJ-309 liquid scintillation detectors positioned at 9 different angles covering the range from 30 deg, to 150 deg. configured with 2 to 4 detectors measuring at the same angle

Summary

Introduction

The uncertainty in evaluations of neutron induced reactions propagates to quantities calculated using these data such as the multiplication factor for a critical system, or leakage rates for critical or other nuclear systems. In order to test the performance of nuclear data evaluation, different benchmark experiments are usually used; they include measurements of the multiplication factor, integral neutron flux (activation), neutron leakage, and transmission. We discuss a neutron induced neutron emission quasi-differential measurements that can be used to test the nuclear data of neutron scattering angular distributions and cross sections. A quasi-differential experiment with high sensitivity to neutron scattering was previously developed at Rensselaer Polytechnic Institute (RPI) [1]. In this experiment, an array of 8 liquid scintillation detectors (EJ-301) was positioned at different angles around a sample of the material being measured.

Methods

Results

Conclusion