Ultracold neutrons (UCN) are low-energy neutrons that are used in a wide range of physics experiments. Unfortunately, many of these experiments, such as those involving high-precision measurements of the neutron lifetime, are limited by the rate or density of UCN production at current sources.
Leung et al. present the physics model for a next-generation spallation-driven high-current ultracold neutron source with a focus on increasing the UCN production rate.
“Our physics model is of a next-generation source of ultracold neutrons coupled closely to a spallation target that can produce several hundred times higher useful current than existing sources,” said author Kent Leung.
The authors employed what they called an “Inverse Geometry” design to maximize UCN production given a certain heat load and proton flux. The design involved nesting several cylindrical components in a radially inward fashion – first, the cylindrical heavy water pre-moderator, followed by the liquid deuterium moderator, and finally the He-II converter, which uses 40 L of superfluid He-II, cooled to ∼1.6 K for converting cold neutrons to UCNs. The tungsten spallation target, placed radially outside of these components, allow the proton beam to raster scan over a large volume and reduce cooling requirements to the point such that water edge-cooling is sufficient.
After optimizing their design, they were able to predict a production rate of almost two billion UCNs per second.
The authors think that the enormous ultracold neutron current offered by the new design will allow completely different thinking of possible experiments in nuclear and particle physics, astrophysics, cosmology, and condensed matter physics.
Source: “A next-generation inverse-geometry spallation-driven ultracold neutron source,” by K. K. H. Leung, G. Muhrer, T. Hügle, T. M. Ito, E. M. Lutz, M. Makela, C. L. Morris, R. W. Pattie, Jr., A. Saunders, and A. R. Young, Journal of Applied Physics (2019). The article can be accessed at https://doi.org/10.1063/1.5109879.
