Ultracold and cold neutron cross-sections of liquid helium at low temperatures down to 0.1 K

Cross-section model for superfluid He-4 at low temperatures down to 0.1 K i s developed, which aims at evaluating high-density production of ultracold neutrons in a superthermal source. Our previous model which describes phono n-roton excitations and density ones at temperatures between 1 and 4.2 K is improved and generalized with wide applicability to liquid temperature and neutron incident energies from 0.1 mu eV and 10 eV. Typical results on dou ble differential and total cross-sections are presented, especially for dow n scattering of I meV neutrons and up-scattering of ultracold neutrons due to phonon absorption. Hence, the cross-section model given here can serve f or analysis of ultracold neutron processes in liquid He-4 in terms of scatt ering production, storage and transport. (C) 2001 Elsevier Science B.V. All rights reserved.