Understanding of ultra-cold neutron production in solid deuterium

Abstract

Our recent neutron scattering measurements of phonons and other quasi-particle excitations in solid deuterium (sD$_2$) and the extraction of the density of states for phonons and rotational transitions in sD2 have led us to a new understanding of the production of ultra-cold neutrons (UCN) in sD2. This new picture is somehow different to earlier published results for sD2. The cross section for UCN production in sD2 has been determined by using the density of states G1(E) in combination with the incoherent approximation and by a direct calibration of our measured neutron cross sections with the known cross section of the J=1 -> 0 rotational transition in deuterium. Both methods deliver new data on this cross section and agree quite well with direct measurements of this energy averaged UCN production cross section.