Operation of a superthermal ultra-cold neutron source and the storage of ultra-cold neutrons in superfluid Helium4

We report the first successful operation of a superthermal UCN source and the observation of the storage of Ultra-Cold Neutrons in superfluid Helium4 at Temperatures in the range 0.5–1.15K. From the observations we obtain the total cross section for UCN scattering by superfluid Helium. The temperature dependence of the total cross section is found to be consistent with calculations which include the effects of phonon absorption and phonon and roton scattering.