Clustering of Diamond Nanoparticles, Fluorination and Efficiency of Slow Neutron Reflectors

Abstract

Neutrons can be an instrument or an object in many fields of research. Major efforts all over the world are devoted to improving the intensity of neutron sources and the efficiency of neutron delivery for experimental installations. In this context, neutron reflectors play a key role because they allow significant improvement of both economy and efficiency. For slow neutrons, Detonation NanoDiamond (DND) powders provide exceptionally good reflecting performance due to the combination of enhanced coherent scattering and low neutron absorption. The enhancement is at maximum when the nanoparticle diameter is close to the neutron wavelength. Therefore, the mean nanoparticle diameter and the diameter distribution are important. In addition, DNDs show clustering, which increases their effective diameters. Here, we report on how breaking agglomerates affects clustering of DNDs and the overall reflector performance. We characterize DNDs using small-angle neutron scattering, X-ray diffraction, scanning and transmission electron microscopy, neutron activation analysis, dynamical light scattering, infra-red light spectroscopy, and others. Based on the results of these tests, we discuss the calculated size distribution of DNDs, the absolute cross-section of neutron scattering, the neutron albedo, and the neutron intensity gain for neutron traps with DND walls.

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

“…For compatibility with previous results [22][23][24][25]46], we used raw DNDs produced at the Federal State Unitary Enterprise, "Russian Federal Nuclear Center-Academician E.I. Zababakhin All-Russian Research Institute of Technical Physics" (FSUE "RFNC-VNIIF"), Snezhinsk, Russia, Technical Regulations TY 2-037-677-94.…”

“…In relation to neutron reflectors, DNDs combine the large cross-section of coherent scattering and the low cross-section of neutron losses. As this paper shares the scientific motivations and some experimental methods with another article published in the same issue of this journal [46], we limit our description here to only the specific results related to the subject of our present research. We refer the reader to this previous publication for a detailed description of the principle of operation and the general properties of such neutron reflectors.…”

“…Figure 1 illustrates the calculated optimal particle sizes and the corresponding maximum VCN albedo for a range of neutron velocities from 20 to 200 m/s. This and all other calculations presented below were performed using Monte Carlo method and the model of discrete-sized diamond nanospheres (MDDNS) [17,46]. In the particular case shown in Figure 1, the powder layer thickness is 1 cm and the density is 0.56 g/cm 3 .…”

“…For comparison with the ideal case, we added a dashed curve corresponding to the albedo calculated for a model of the real powder of deagglomerated fluorinated DNDs (DF-DNDs) with the same density of 0.56 g/cm 3 described in ref. [46] (the sample with the best performance achieved). The difference between DF-DNDs and optimal diamond nanospheres is due to the deviation from the optimum size and the spread of sizes.…”

“…This approach allowed us to take into account all relevant properties of the interaction of neutrons with nanostructured media described in this work (diamond cores and This and all other calculations presented below were performed using Monte Carlo method and the model of discrete-sized diamond nanospheres (MDDNS) [17,46]. In the particular case shown in Figure 1, the powder layer thickness is 1 cm and the density is 0.56 g/cm 3 .…”