Directional reflection of cold neutrons using nanodiamond particles for compact neutron sources

Nanodiamond Particles (NDP) are new candidates for neutron reflection. They have a large scattering and low absorption cross-sections for low-energy neutrons. Very Cold Neutrons (VCN) are reflected from NDP with large scattering angles while Cold Neutrons (CN) have a quasi-specular reflection at small incident angles. A new scattering process has been added in Geant4 in order to examine the directional reflection of CN in an extraction beam made of NDP layer. Impurities in NDP are responsible for the up-scattered neutrons, especially hydrogen which has a large cross-section. Other impurities are also considered in Geant4 in order to produce a more accurate model for NDP scattering. The new scattering process is used to model a possible configuration of target-moderator-reflector in Compact Neutron Sources (CNS). A 13 MeV proton beam striking a beryllium target is chosen. Parahydrogen is placed as a cold moderator in order to produce CN. NDP are placed around the extraction beam for scattering the CN toward the exit of the beam. The results show that CN exiting the extraction beam can be increased thanks to the implemented NDP layer.

Rotational Effects of Nanoparticles for Cooling down Ultracold Neutrons

Due to quantum coherence, nanoparticles have very large cross sections when scattering with very cold or Ultracold Neutrons (UCN). By calculating the scattering cross section quantum mechanically at first, then treating the nanoparticles as classical objects when including the rotational effects, we can derive the associated energy transfer. We find that rotational effects could play an important role in slowing down UCN. In consequence, the slowing down efficiency can be improved by as much as ~40%. Since thermalization of neutrons with the moderator requires typically hundreds of collisions between them, a ~40% increase of the efficiency per collision could have a significant effect. Other possible applications, such as neutrons scattering with nano shells and magnetic particles,and reducing the systematics induced by the geometric phase effect using nanoparticles in the neutron Electric Dipole Moment (nEDM), are also discussed in this paper.

SIZE EFFECTS ON THE EFFICIENCY OF NEUTRON SHIELDING IN NANOCOMPOSITES — A FULL-RANGE ANALYSIS

Multiphase composites composed of a continuous hydrogenous (polymeric) phase and of neutron absorbing filler particles are attractive candidate materials for the design of light-weight neutron shields. While the characteristic size of the inclusions is traditionally in the micrometer range, we argue that the shielding performance of the composite is significantly enhanced for decreasing filler particle size. Within a semiclassical approximation scheme we analytically determine the corresponding scaling law valid for inclusions from the nanometer scale up to macroscopic sizes and recover meaningful limiting cases. We find that amongst polymer composites, the physical benchmark for optimized shielding at minimal weight penalty is essentially reached, as soon as the size of the filler particles drops within the nanometer range. We demonstrate that our results are in agreement with recent experimental findings and comment on the emerging potential for aeronautic and aerospace applications.

Application of Diamond Nanoparticles in Low-Energy Neutron Physics

Diamond, with its exceptionally high optical nuclear potential and low absorption cross-section, is a unique material for a series of applications in VCN (very cold neutron) physics and techniques. In particular, powder of diamond nanoparticles provides the best reflector for neutrons in the complete VCN energy range. It allowed also the first observation of quasi-specular reflection of cold neutrons (CN) from disordered medium. Effective critical velocity for such a quasi-specular reflection is higher than that for the best super-mirror. Nano-diamonds survive in high radiation fluxes; therefore they could be used, under certain conditions, in the vicinity of intense neutron sources.