Cooling and Heating of Ultracold Neutrons during Storage

The rare processes of weak heating and cooling of ultracold neutrons reflected from the surface of fluorosubstituted oil are studied. The probability of these processes is estimated at 10^‑6 per single reflection at energy transfer commensurate with the primary neutron energy. Weak heating and cooling are shown to be a manifestation of a more general phenomenon—quasielastic neutron reflection whose probability is dependent on temperature.