Production of ultra-cold neutrons in solid alpha-oxygen

Our recent neutron scattering measurements of phonons and magnons in solid alpha-oxygen have led us to a new understanding of the production mechanism of ultra-cold neutrons (UCN) in this super-thermal converter. The UCN production in solid alpha-oxygen is dominated by the excitation of phonons. The contribution of magnons to UCN production becomes only slightly important above E > 10meV and at E similar to 4meV. Solid alpha-oxygen is in comparison to solid deuterium less efficient in the down-scattering of thermal or cold neutrons into the UCN energy regime. Nevertheless, the lower efficiency might be compensated by the larger mean free-path of UCN in oxygen with respect to deuterium. Copyright (C) EPLA, 2011