Cold neutron production in solid and liquid CH4 moderators. II: on the reentrant-hole configuration

It has been shown in our previous paper (Part I) that a solid CH4 moderator produces higher density of cold neutrons inside and greater cold-neutron leakage flux from the surface, in comparison with those for liquid H2 and CH4. To take such advantages of the moderator, a porous configuration with many thin holes for emerging cold-neutron beam is being studied. In the present preliminary report, neutronic characteristics of the hole are described together with the results of Monte Carlo calculation.