Ultracold Neutron Production by the Phonon Excitation in Superfluid 4 He at Temperatures below 1 K

Abstract

Production of ultracold neutrons in superfluid ⁴He is discussed in terms of downscattering of an 1 meV neutron through phonon creation at temperatures below 1 K. By the use of a cross-section model developed for neutron scattering in liquid ⁴He, a set of scattering cross sections such as double-differential, angular-distributional and total ones is calculated. It is shown that the phonon–roton(quasipartic1e) excitation plays an essential role in marked production and storage of ultracold neutrons, especially for temperatures down to 0.1 K.