Understanding of ultra-cold–neutron production in solid deuterium

¹ Technische Universität München, Physik Department - James-Franck-Str.1 - D-85748 Garching, Germany, EU
² Institut Laue Langevin - 156X, F-38042 Grenoble Cedex, France, EU
³ Technische Universität München, Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II) - Lichtenbergstr. 1, D-85748 Garching, Germany, EU

^a egutsmie@e18.physik.tu-muenchen.de

Received: 16 June 2010
Accepted: 3 December 2010

Abstract

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 T_n = 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.