Optimization of decoupled hydrogen moderator

摘要

A decoupled hydrogen moderator (H_2 moderator) with a H_2O premoderator is the primary candidate as a high-resolution moderator in Japanese spallation neutron source (JSNS). However, it has already pointed out that a premoderator for a decoupled H_2 moderator has no merit (or attenuation) in both neutron time-integrated and pulse peak intensities in a Be reflector. On the other hand, for a Pb reflector system. We found that a premoderator can provide a higher time-integrated and peak intensities than those in the Be reflected case. It should be noted that the Pb reflector gave longer pulse tails (loner decay times)than the Be one due to a long slowing-down time of Pb.