Calculation of the ultracold neutron yield from a superfluid helium source in the WWR-M reactor

Abstract

A new high-intensity source of ultracold neutrons (UCNs) is being developed on the WWR-M reactor at the Petersburg Nuclear Physics Institute. In this source, superfluid helium will be used, which will make it possible to attain the UCN density 2 to 3 orders of magnitude higher than in available sources in the world. With the most intense UCN source, the WWR-M reactor will become an international center of fundamental studies with UCNs. As a result of optimization of parameters of this source, the UCN density in the main trap is estimated as ρ_{35 L} = 1.3 × 10⁴ neutrons/cm³ (for a trap with a volume of 35 L) and ρ_{350 L} = 8.4 × 10³ neutrons/cm³ (for a trap with a volume of 350 L). For an auxiliary trap located on the platform, the calculated UCN densities are ρ_{35 L} = 150 neutrons/cm³ and ρ_{350 L} = 120 neutrons/cm₃. The ratio of UCN densities amounts to 2 orders of magnitude and indicates the effectiveness of the method of UCN extraction in the case of accumulation in superfluid helium.