Measurements of the neutron brightness from a phase II solid methane moderator at the LENS neutron source

Measurements of the neutron brightness from a solid methane moderator were performed at the Low Energy Neutron Source (LENS) at the Indiana University Cyclotron Facility (IUCF) to characterize the source and to test our new neutron scattering model of phase II solid methane [1]. A time-of-flight method was used to measure the neutron energy spectrum from the moderator in the energy range of 0.1 meV ∼ 1 eV . Neutrons were counted with a high efficiency 3He detector. The solid methane in the moderator occupied phase II and the energy spectra were measured at 20 K and 4 K. We tested our newly developed scattering kernels for phase II solid methane by calculating the neutron brightness expected from the methane moderator at the LENS neutron source using MCNP (Monte Carlo N-particle Transport Code). Within the accuracy of our approximate approach, our model correctly predicts the neutron brightness at both temperatures.