The ultracold neutron source at PSI

A new type of ultracold neutron source based on the spallation process is under construction at PSI. The essential elements of this source are a pulsed proton beam with a highest intensity of (Ip > 2mA) and a low duty cycle (~1%), a lead spallation target, a large D2O moderator and a solid D2 (sD2) converter system. Spallation neutrons are thermalized in the D2O, further cooled in the sD2 and, finally, some of them are down-scattered into the ultra-cold neutron range (Tkin < 250 neV). The expected UCN density in the new source is 3000 UCN/cm-3, almost two orders of magnitude higher than with the best source currently available (at ILL).