Effect of Particle Sizes on the Efficiency of Fluorinated Nanodiamond Neutron Reflectors.

Aleksander Aleksenskii,Alexander Nezvanov,Artur Dideikin,Alexander Vul’,Alexei Muzychka,Ekaterina Korobkina,Marc Dubois,Alexei Bosak,Egor Lychagin,Grigory Nekhaev,Alexander Strelkov,Marcus Bleuel,Ralf Schweins,Valery Nesvizhevsky,Alexandra Chumakova,Alexander Shvidchenko,Kirill Zhernenkov,Kylyshbek Turlybekuly

doi:10.3390/nano11113067

Abstract

Over a decade ago, it was confirmed that detonation nanodiamond (DND) powders reflect very cold neutrons (VCNs) diffusively at any incidence angle and that they reflect cold neutrons quasi-specularly at small incidence angles. In the present publication, we report the results of a study on the effect of particle sizes on the overall efficiency of neutron reflectors made of DNDs. To perform this study, we separated, by centrifugation, the fraction of finer DND nanoparticles (which are referred to as S-DNDs here) from a broad initial size distribution and experimentally and theoretically compared the performance of such a neutron reflector with that from deagglomerated fluorinated DNDs (DF-DNDs). Typical commercially available DNDs with the size of ~4.3 nm are close to the optimum for VCNs with a typical velocity of ~50 m/s, while smaller and larger DNDs are more efficient for faster and slower VCN velocities, respectively. Simulations show that, for a realistic reflector geometry, the replacement of DF-DNDs (a reflector with the best achieved performance) by S-DNDs (with smaller size DNDs) increases the neutron albedo in the velocity range above ~60 m/s. This increase in the albedo results in an increase in the density of faster VCNs in such a reflector cavity of up to ~25% as well as an increase in the upper boundary of the velocities of efficient VCN reflection.

Highlights

Slow neutrons are usually subdivided into three ranges: ultracold neutrons (UCNs) [1,2,3,4,5], very cold neutrons (VCNs), and cold neutrons (CNs)
We investigated the effect of particle sizes on the efficiency of detonation nanodiamond (DND) neutron reflectors
If typical DNDs with a size of ~4.3 nm are efficient for the reflection of typical VCNs with a velocity of ~50 m/s, other mean sizes are more efficient for other VCN velocities

Summary

Introduction

Slow neutrons are usually subdivided into three ranges: ultracold neutrons (UCNs) [1,2,3,4,5], very cold neutrons (VCNs), and cold neutrons (CNs). The characteristic feature of UCNs is their (nearly) total reflection from a material surface provided the neutron velocity is smaller than the critical velocity of the surface material; a typical value of the critical velocity of materials used to build UCN traps is ~5 m/s. The available UCN fluxes are extremely low; this property of total reflection makes them an invaluable tool in fundamental neutron physics. Most of the neutrons are thermalized in cryogenic CN sources [6] in research nuclear reactors and spallation neutron sources to this energy range

Methods

Results

Discussion

Conclusion