The PSI ultra-cold neutron source

Abstract A new type of ultra-cold neutron (UCN) source based on the spallation process is under construction at PSI. The essential elements are a pulsed proton beam with highest intensity ( I p ≥ 2 mA ) and a low duty cycle (1%), a lead spallation target, a large D 2 O moderator and a solid deuterium ( sD 2 ) converter system. Spallation neutrons are thermalized in the D 2 O , further cooled and partially downscattered into the ultra-cold neutron range in the sD 2 . The expected UCN density is higher than 1000 UCN / cm 3 in typical experiments, an increase of almost two orders of magnitude over the best source currently available (at ILL). The new UCN source is expected to come into operation in 2009.