Design of a low enriched uranium fission plate for boosting the UCN density at the LANL UCN source*

The unique properties of ultracold neutrons (UCN) make them ideal for precision measurements of neutron properties. With high enough UCN densities, precision measurements can access Beyond the Standard Model (BSM) physics that rivals or surpasses capabilities of high energy physics and other areas of nuclear physics. One can also consider new applications in measurements of surface science using a high density of UCN. Densities of the current generation of UCN sources are limited by radiation heating of the cryogenic UCN conversion material as well as by the cumulative impacts from the primary beam intensity. These include radiation damage to cold moderator materials and potentially hazardous nuclide production in the materials surrounding the source. Here we will present progress on the design of a low enriched uranium fission plate that could provide a gain of UCN production up to a factor of 3 to 10. When coupled to the tungsten target, this will provide a more optimal source of primary neutrons while managing those limitations that tend to come with an increased neutron density.