Production of ultracold neutrons from a cold neutron beam on a 2H2 target

The production rates of ultracold neutrons (UCN) from cold neutrons on gaseous, liquid, and solid deuterium targets have been measured. The comparison of the measured and calculated UCN production on gaseous 2H2 is used to calibrate the simulated target extraction and transport efficiencies of the experimental apparatus. The production cross section in solid 2H2 at 8 K for UCN with energies between 0 and 250 neV is Rsolid,8K=σsolid, 8KCN→UCNρ=(1.11±0.23)×10-8cm-1. This value is consistent with other experiments in which UCN had been extracted from 2H2. The value also agrees with calculations using the incoherent approximation and a simple Debye model and corroborates predictions for UCN densities expected at the high-intensity UCN source at the Paul Scherrer Institut. The temperature dependence of the UCN production in solid 2H2 down to 8 K can be explained within the same model when multiple-phonon excitation is included.