Experimental studies on neutronic performance of various cold-neutron moderators for the pulsed neutron sources

As a moderator material, solid methane is the best one from the neutronic point of view. However, solid methane has low-resisitivity to the radiation damage, and at some facilities it cannot be used due to the regulation to the explosive materials. We have been experimentally studied neutronic performances of various materials, explosive and non-explosive, to look for the materials having the good neutronic characteristics. Here, we present the experimental results on the neutronic performances of such materials. For the high-intensity type moderator and a coupled type moderator, we measured the neutronic performance of the mesitylene, methanol, benzene, etc. as inflammable materials, and also hydrogen and methane as flammable materials. It is concluded that, among inflammable materials mesitylene is the best, and that para-hydrogen would be the best in all materials studied. For the high-resolution-type moderator, a decoupled moderator, we also studied mesitylene, hydrogen, methane. The mesitylene moderator gives not so different spectral intensities compared with the hydrogen moderator but the pulse widths were wider than that of the hydrogen moderator at low energy. The use of the para-hydrogen improved the pulse characteristics very much, and it is expected that in some energy region the para-hydrogen moderator performance approaches to the methane moderator.