Canada's National Laboratory for Particle and Nuclear Physics Laboratoire national canadien pour la recherche en physique nucléaire et en physique des particules

Workshop on Ultra Cold Neutrons Attracts International Experts

21 September 2007

Many years after the last neutrons from the TRIUMF 4C neutron beam passed down the collimator, scientists are considering bringing back neutrons to the Proton Hall, albeit some fifteen orders of magnitude lower in energy. To that end, experts from around the world met at TRIUMF on September 13th and 14th, 2007 for the International Workshop on UCN Sources and Experiments.

UCN stands for ultracold neutrons, which are very cold indeed! UCN's are produced by downscattering cold neutrons in very, very cold materials, resulting in a phonon carrying away much of the kinetic energy. They become “ultracold” by definition when they are slow enough — below 8 m/s — to be confined by the Fermi potential. Fermi originally proposed that the strong force that holds nuclei together could conceivably result, for a bulk assemblage of certain materials, in a very small residual repulsive potential for neutrons: of the order of 300 neV! Thus, it is literally possible to confine neutrons in a bottle. Confined neutrons can be observed for much longer times, allowing experimentalists to make higher precision measurements of neutron properties – the neutron being important for understanding the laws of physics.

UCN's were first produced years ago by sending neutrons from reactors onto turbine blades such that some few of these neutrons would scatter off and become UCN's. Several talks dealt with the relatively new development of superthe