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

Cross-section model for superfluid 4He at low temperatures down to 0.1 K is developed, which aims at evaluating high-density production of ultracold neutrons in a superthermal source. Our previous model which describes phonon–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 μeV and 10 eV. Typical results on double differential and total cross-sections are presented, especially for down scattering of 1 meV neutrons and up-scattering of ultracold neutrons due to phonon absorption. Hence, the cross-section model given here can serve for analysis of ultracold neutron processes in liquid 4He in terms of scattering, production, storage and transport.