  Two hypothesizes concerning interaction of neutrons with nanoparticles and
having applications in the physics of ultracold neutron (UCN) were recently
considered in ref. [Physics of Atomic Nuclei 65(3): 400 (2002)]; they were
motivated by the experimental observation of small changes in energy of UCN
upon their collisions with surface. The first hypothesis explaines the nature
of the observed phenomenon by inelastic coherent scattering of UCN on
nanoparticles weakly attached at surface, in a state of permanent thermal
motion. It got experimental confirmed in ref. [Physics of Atomic Nuclei 65(11):
1996 (2002)]. The second hypothesis inverts the problem of neutron interaction
with nanoparticles in the following sence. In all experiments with UCN, the
trap-wall temperature was much higher than a temperature of about 1 mK, which
corresponds to the UCN energy. Therefore, UCN preferentially increased their
energy. The surface density of weakly attached nanoparticles was low. If,
however, the nanoparticles temperature is lower than the neutron temperature
and if the nanoparticles density is high, the problem of interaction of
neutrons with nanoparticles is inverted. In this case, the neutrons can cool
down, under certain conditions, owing tot heir scattering on
ultracold-heavy-water, deuterium, and oxigen nanoparticles to their temperature
of about 1 mK, with result that the UCN density increases by many orders of
magnitude. In the present article we repeat the argumentation given in the
first mentioned article and formulate in a very general way the research
program in order to verify validity of this hypothesis. Both the theoretical
and the experimental investigation of the problem are going to intensify in the
near future.
