Aleksenskii Aleksander, Bleuel Marcus, Bosak Alexei, Chumakova Alexandra, Dideikin Artur, Dubois Marc, Korobkina Ekaterina, Lychagin Egor, Muzychka Alexei, Nekhaev Grigory, Nesvizhevsky Valery, Nezvanov Alexander, Schweins Ralf, Shvidchenko Alexander, Strelkov Alexander, Turlybekuly Kylyshbek, Vul' Alexander, Zhernenkov Kirill
Laboratory of Physics for Cluster Structures, Ioffe Institute, Polytechnicheskaya Str. 26, 194021 St. Petersburg, Russia.
National Institute of Standards and Technology Center for Neutron Research, Gaithersburg, MD 20899, USA.
Nanomaterials (Basel). 2021 Nov 14;11(11):3067. doi: 10.3390/nano11113067.
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.
十多年前，已证实爆轰纳米金刚石（DND）粉末在任何入射角下都能漫反射极冷中子（VCN），并且在小入射角下能准镜面反射冷中子。在本出版物中，我们报告了一项关于粒径对由DND制成的中子反射器整体效率影响的研究结果。为进行这项研究，我们通过离心从宽泛的初始尺寸分布中分离出较细的DND纳米颗粒部分（这里称为S-DND），并通过实验和理论比较了这种中子反射器与解团聚的氟化DND（DF-DND）的性能。典型的市售尺寸约为4.3 nm的DND对于典型速度约为50 m/s的VCN接近最佳，而较小和较大的DND分别对于更快和更慢的VCN速度更有效。模拟表明，对于实际的反射器几何形状，用S-DND（尺寸较小的DND）替代DF-DND（性能最佳的反射器）会在速度范围高于约60 m/s时提高中子反照率。这种反照率的增加导致这种反射器腔体内更快VCN的密度增加高达约25%，以及有效VCN反射速度的上限增加。
