ИСТИНА

Efficient neutron reflectors are mandatory for building neutron sources, such as nuclear reactors or spallation neutron sources, also in neutron investigations. For extremely slow, so-called ultracold neutrons (UCN) with the energy of <10-7 eV, neutron optical potential of matter plays a role of nearly ideal reflector. For UCN, the probability of specular elastic reflection from matter is close to unity at any temperature. In order to reflect neutrons with higher energy, <10-6 eV, one uses multi-layer coatings, so-called super-mirrors. The probability of specular elastic reflection of neutrons from good super-mirrors reaches 80-90 %. Until recently, efficient reflectors for neutrons of even higher energy, up to 10-2, had not been known. At even higher energy inelastic processes prevail; they are the basis for reflectors in nuclear reactors. Recently, the phenomena of efficient diffusive reflection of very cold neutrons (VCN) from nano-structured reflectors at any incidence angle, and quasi-specular reflection of cold neutrons (CN) at small incidence angles were observed for the first time. Nano-structured reflectors bridge nicely the energy gap between reflectors based on two mechanisms mentioned above. In both cases powder of diamond nano-particles was used as a nano-structured matter; in both cases reflection probabilities exceeded by far the characteristics of alternative neutron reflectors. Further, we assumed that substitution of hydrogen in nanoparticle shells by fluorine would increase the reflection efficiency due to the suppression of neutron losses associated with their travel in powder. In addition, a mean neutron-nuclei potential increases and gets sharper on surface due to the removal of amorphous sp2 carbon from nanoparticle shells; thus, the neutron scattering probability increases. The last results of model experiment to illustrate efficiency of such reflector for direct extraction of very cold neutrons will be presented.