Understanding of ultra-cold–neutron production in solid deuterium

Our recent neutron scattering measurements of phonons and other quasi-particle excitations in solid deuterium (sD2) 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. The UCN production rate reaches a maximum at an equivalent neutron temperature of Tn = 40 K for a neutron flux with Maxwellian energy distribution. 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 as well as by a direct calibration of our measured neutron cross-sections with the known cross-section of the J = 1↦0 rotational transition in deuterium. Using this cross-section we deduced the production rate of UCN in sD2 which agrees quite well with direct measurements of this energy averaged UCN production cross-section.