Improved beam extraction at compact neutron sources using diamonds nanoparticles and supermirrors

Aimed to investigate potential benefits from mounting reflecting layers of diamond nanoparticles or supermirrors in neutron extraction channels, a conceptual compact neutron source was designed using Geant4 and MCNP. The scattering of low-energy neutrons with nanodiamonds was implemented in Geant4 and validated with existing experimental data. The source design was based on a 13 MeV proton beam hitting a beryllium target, with neutron moderation facilitated by a water premoderator, supplemented by a quasi 1-dimensional parahydrogen moderator, before emission towards a few (2–5) beamlines. In an attempt to increase the neutron flux available for experiments, reflecting layers of diamond nanoparticles or supermirrors were placed in the neutron extraction channel, and results for different implementations were assessed and compared.

The results show that the cold neutron flux is increased by using the nanodiamond powder, in particular for large divergence neutrons (greater than 2°), but a significant effect is observed also for low-divergence neutrons, which are of particular interest to neutron scattering experiments. The effect is dependent on the neutron wavelength and the size of nanodiamonds, with larger effects in general obtained for longer wavelengths, and particles of larger size. The same configuration was studied, where instead of nanodiamonds, supermirrors were used. The use of supermirrors at the beam extraction predicts even higher potential gains. These results are very promising to increase the efficiency of compact sources and can be applied to various configurations of such sources.