The neutron performance of a pre-moderated beryllium reflector-filter hydrogen moderator system for the Manuel Jr. Lujan Neutron Science Center

The Manuel Lujan Jr. Neutron Scattering Center (Lujan Center) at the Los Alamos National Laboratory produces currently the highest time-averaged cold source brightness of any pulsed neutron scattering facility in the world, and efforts are underway to increase this even further. Part of these efforts is to boost the long-wavelength (>5 Å) source brightness of the lower-tier hydrogen moderator by a factor of two. Of the many concepts that were evaluated for boosting cold source brightness, three proved to be sufficiently beneficial to recommend they be implemented in the next target system. These are: a light water flux-trap premoderator, a light water perimeter premoderator, and a cold (77 K) Be reflector-filter. A detailed study of the Monte Carlo simulations for these concepts is presented in this paper.