Production of ultracold neutrons from a cold neutron beam on a2H2target

Abstract

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 ${}^{2}{H}_{2}$ is used to calibrate the simulated target extraction and transport efficiencies of the experimental apparatus. The production cross section in solid ${}^{2}{H}_{2}$ at 8 K for UCN with energies between 0 and 250 neV is ${R}_{\mathrm{solid},8 K}={\ensuremath{\sigma}}_{\mathrm{solid},8 K}^{\mathrm{CN}\ensuremath{\rightarrow}\mathrm{UCN}} \ensuremath{\rho}=(1.11\ifmmode\pm\else\textpm\fi{}0.23)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. This value is consistent with other experiments in which UCN had been extracted from ${}^{2}{H}_{2}$. 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 ${}^{2}{H}_{2}$ down to 8 K can be explained within the same model when multiple-phonon excitation is included.