Studies on Reflector Materials for Cold Neutrons

Granada, J.R.; Damián, José Ignacio Márquez; Helman, C.

doi:10.1051/epjconf/202023104002

Cited by 20 publications

(24 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Bands between 1090 and 1220 cm −1 correspond to CF 2 and CF 3 symmetric stretch, CF 2 asymmetric stretch, as well as CF=CF 2 , CF 3 -CF 2 and CF stretch vibrations [48]. This latter contribution dominates according to solid-state NMR characterization [12]; CF 2 and CF 3 are not evidenced neither by 19 F nor 13 C measurements. C-F bonds result from both conversion of C-H and COH into C-F in the diamond core and fluorination of sp 2 C in the shell (C exsp 2 -F).…”

Section: Chemical Composition By Naa and Ir Spectroscopymentioning

confidence: 91%

“…DNDs are particularly interesting for improving performance of VCN and CN sources as well as for the loss-limited extraction of slow neutrons from high-radiation zones. This argument motivates further measurements of DND neutron-scattering cross-sections [ 16 , 17 , 18 ] and the inclusion of neutron scattering on DNDs to neutron simulations [ 18 , 19 , 20 ]. These cross-section studies showed the smallness of inelastic scattering and the importance of accounting for clustering and agglomeration of DNDs in the interpretation of neutron-scattering experiments.…”

Section: Introductionmentioning

confidence: 87%

See 1 more Smart Citation

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

et al. 2021

View full text Add to dashboard Cite

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.

show abstract

Section: Chemical Composition By Naa and Ir Spectroscopymentioning

confidence: 91%

Section: Introductionmentioning

confidence: 87%

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

et al. 2021

View full text Add to dashboard Cite

show abstract

“…Not only can neutrons be reflected from DNDs, but they can also be lost due to the interaction with DNDs in the course of diffusive motion. As neutron losses in raw DNDs are dominated by a small admixture of hydrogen on the surface of DNDs, the removal of hydrogen by fluorination [21][22][23][24][25] is essential for reducing neutron losses.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

View full text Add to dashboard Cite

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.

show abstract

“…Scattering cross sections have been studied in detail in references [ 19 , 20 , 21 ], which in particular underlined the importance of clustering/agglomeration of DND powder samples to allow for a proper interpretation of neutron scattering experiments, and the virtual absence of inelastic scattering. Significant efforts have been devoted to including the diffusion of slow neutrons in the DND powders to neutron transport simulations [ 21 , 22 , 23 ].…”

Section: Introductionmentioning

confidence: 99%

Fluorination of Diamond Nanoparticles in Slow Neutron Reflectors Does Not Destroy Their Crystalline Cores and Clustering While Decreasing Neutron Losses

et al. 2020

View full text Add to dashboard Cite

If the wavelength of radiation and the size of inhomogeneities in the medium are approximately equal, the radiation might be intensively scattered in the medium and reflected from its surface. Such efficient nanomaterial reflectors are of great scientific and technological interest. In previous works, we demonstrated a significant improvement in the efficiency of reflection of slow neutrons from a powder of diamond nanoparticles by replacing hydrogen located on the surface of nanoparticles with fluorine and removing the residual sp2 amorphous shells of nanoparticles via the fluorination process. In this paper, we study the mechanism of this improvement using a set of complementary experimental techniques. To analyze the data on a small-angle scattering of neutrons and X-rays in powders of diamond nanoparticles, we have developed a model of discrete-size diamond nanospheres. Our results show that fluorination does not destroy either the crystalline cores of nanoparticles or their clustering in the scale range of 0.6–200 nm. This observation implies that it does not significantly affect the neutron scattering properties of the powder. We conclude that the overall increase in reflectivity from the fluorinated nanodiamond powder is primarily due to the large reduction of neutron losses in the powder caused by the removal of hydrogen contaminations.

show abstract

Studies on Reflector Materials for Cold Neutrons

Cited by 20 publications

References 19 publications

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

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

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

Fluorination of Diamond Nanoparticles in Slow Neutron Reflectors Does Not Destroy Their Crystalline Cores and Clustering While Decreasing Neutron Losses

Contact Info

Product

Resources

About