Ultra-cold neutrons (UCN) are produced in superfluid helium by single- and multi-phonon excitation. The UCN production rate density RII via multiphonons can be larger than that by one-phonon excitation RI being due to the dependence of the incident neutron spectral flux density dφ/dλ on the wavelength λ.
PACS. 78.70.Nx Neutron inelastic scattering – 67.20.+k Quantum effects on the structure and dynamics of nondegenerate fluids (e.g., normal phase liquid 4He) – 61.12.Ex Neutron scattering techniques (including small-angle scattering) – 29.25.Dz Neutron sources
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