Storage of ultracold neutrons in vessels whose walls are made from graphite,fluorine polymer oil,or heavy-water ice

The possibility of attaining the calculated probabilities of the losses of ultracold neutrons (UCN) stored in vessels whose walls are made from graphite, fluorine polymer oil, or heavy-water ice is tested experimentally. It is found that UCN hitting the walls of a graphite vessel undergo additional inelastic scattering not predicted by the theory. It is shown that this scattering may be due to the presence of surface hydrogen that provides a channel of UCN leakage slightly varying with temperature. For vessels whose walls are coated with fluorine polymer oil, additional inelastic UCN scattering is also observed and is found to be efficiently suppressed with decreasing temperature. The experimentally observed and calculated values of the probabilities of UCN losses are shown to be in good agreement for vessels whose walls are made from heavy-water ice.