A new spallation neutron source at the Paul Scherrer Institut (PSI) dedicated solely to the production of ultracold neutrons (UCN) has successfully started operation in August 2011. The UCN source shares the proton beam (2.2 mA @ 590 MeV) in a pulsed mode with SINQ and the meson production targets at a duty cycle of 1%. The UCN facility is now delivering UCNs to three experiments on a routine basis.
The concept of the new source is based on neutron production by spallation in a Zr-canned lead 'cannelloni' target, followed by moderation in a 3.6 m3 D2O tank and conversion to ultracold neutrons in a 30 liter solid ortho-deuterium crystal. Subsequently, the UCN are extracted by a vertical guide into a 2 m3 storage volume and finally distributed via NiMo coated neutron guides to the experiments.
An experiment searching for the neutron electric dipole moment (nEDM) is the first experiment being in operation at the UCN source. The nEDM experiment originally motivated the UCN source project and it will remain the flagship experiment for the next years. A permanent nEDM would violate time reversal symmetry which in fundamental physics is intimately connected to an asymmetry between matter and anti-matter. The latter two should have been produced in equal amounts in the big-bang. The very fact that we ourselves are made of matter and that the anti-matter seems to have vanished from our universe calls for such an asymmetry. Earlier searches could not yet find a finite nEDM, but this time may be special: the sensitivity for its detection will be much increased, initially by a factor of 5 and ultimately by more than 50 times. A discovery of a permanent electric dipole moment would be a major breakthrough for our understanding of the universe and of fundamental particle physics.
More information can be found at the homepage of the UCN source.
