Testing experimentally the dynamical-converter method for ultracold neutrons at a pulsed reactor BIGR

Previously, it was conjectured that a converter moving at a velocity of about 100 m/s can be used at high-flux pulsed reactors in order to obtain up to 105 ultracold neutrons (UCN) per cm3 in a volume of a few liters. With the aim of implementing this idea, an apparatus that features a moving polyethylene converter has been constructed and is currently being tested at the pulsed reactor BIGR installed at the All-Russian Institute of Experimental Physics (Sarov). The first results obtained with this apparatus - the UCN density of 26±5 neutron/cm3 at an energy deposition of 125 MJ during the reactor pulse has been achieved - are presented and possible means for increasing the UCN density - such as the optimization of the moderating block, the use of a polyethylene converter cooled to 80 K, and resort to reactor pulses of maximum intensity--are discussed. It is expected that these reserves would make it possible to increase the UCN density by a factor between 30 and 50