Premoderator studies for a coupled liquid-hydrogen moderator in pulsed spallation neutron sources

A coupled liquid-hydrogen moderator with a premoderator is one of the most promising candidates for a cold neutron source at an intense pulsed spallation neutron source. The choice of the premoderator material is especially important since the neutronic performance strongly depends on the material. We experimentally studied premoderators of polyethylene, water and zirconium hydride. The cold neutron intensity from a coupled liquid-hydrogen moderator with a ZrH2 premoderator is unexpectedly low: about 75% of that with a polyethylene premoderator. However, the pulse widths (FWHM) of the former are narrower than those of the latter, and the peak intensities are almost unchanged. We also discuss the function of the premoderator. (orig.)