Superthermal Ultra-Cold Neutron Sources—a current overview and future prospects

Chen-Yu Liu

Ultra-cold neutrons (UCN) are neutrons with small kinetic energy—so small that UCN cannot penetrate the material wall and are trapped by the effective Fermi's material potential (~300neV). Experiments with bottled UCN can offer orders-of-magnitude improvement for various precise measurements of neutron properties that are sensitive to physics beyond the standard model. At LANL, there are currently two such experiments which are being pursued vigorously. One is a measurement of the angular correlation between the neutron spin and the decayed electron momentum; the result of which can put stringent test on the unitarity of the CKM matrix. The other is a search for the neutron electric dipole moment, which serves to test the time reversal symmetry of fundamental particle theories. However, these experiments are limited by presently available UCN densities.

UCN can be produced at rates higher than expected from the conventional neutron moderation process by using the superthermal mechanism. In this talk, I will describe our recent efforts to understand and characterize the performance of cryogenic solids (solid deuterium and solid oxygen) as superthermal UCN sources. We have experimentally demonstrated with a prototype solid deuterium UCN source that we can produce UCN densities much higher than what other facilities can provide. I will also discuss the prospect of solid oxygen as a promising candidate for the next generation superthermal UCN source. Our preliminary calculations indicate that this new material might offer 250-times greater UCN flux output than what we have achieved with solid deuterium.

The P/T Colloquium is
typically held each
Thursday, 3:45–5:00 PM.
Refreshments are served
at 3:15 PM.