Enhancement of superthermal ultracold neutron production by trapping cold neutrons

In the production of ultracold neutrons (UCN) by scattering cold neutrons in superfluid 4He or cold solid D2 (“superthermal” processes), the UCN production rate is proportional to the spatial density of cold neutrons in the material. For a superthermal source fed from a cold neutron guide, we show that the rate of UCN production can be increased by up to a factor of about 2.3 for realistic substances by enclosing the source in a cavity made of a material with a high cold neutron albedo.