The Neutron Energy Spectrum Study from the Phase II Solid Methane Moderator at the LENS Neutron Source

TL;DR

This study measures the neutron energy spectrum from a solid methane moderator at LENS, compares it with predictions from a new scattering model, and finds good agreement validating the model's accuracy.

Contribution

The paper introduces and validates a new scattering kernel model for phase II solid methane, verified through experimental measurements and Monte Carlo simulations.

Findings

Measured neutron spectra at 20K and 4K match model predictions.

Validated the optimal moderator thickness for different temperatures.

Confirmed the accuracy of the new scattering kernels for solid methane.

Abstract

Neutron energy spectrum measurements from a solid methane moderator were performed at the Low Energy Neutron Source (LENS) at Indiana University Cyclotron Facility (IUCF) to verify our neutron scattering model of solid methane. The time-of-flight method was used to measure the energy spectrum of the moderator in the energy range of 0.1$meV\sim$ 1$eV$. Neutrons were counted with a high efficiency $^{3}{He}$ detector. The solid methane moderator was operated in phase II temperature and the energy spectra were measured at the temperatures of 20K and 4K. We have also tested our newly-developed scattering kernels for phase II solid methane by calculating the neutron spectral intensity expected from the methane moderator at the LENS neutron source using MCNP (Monte Carlo N-particle Transport Code). Within the expected accuracy of our approximate approach, our model predicts both the neutron spectral intensity and the optimal thickness of the moderator at both temperatures. The predictions are compared to the measured energy spectra. The simulations agree with the measurement data at both temperatures.