Measurements of cold neutron intensity distribution of coupled hydrogen moderators

Kai, Tetsuya   ; Kamiyama, Takashi*; Hiraga, Fujio*; Ikeda, Yujiro; Kiyanagi, Yoshiaki*

The spatial distributions of low-energy neutron intensity from a normal- and a para-hydrogen moderator were measured. Position sensitive helium-3 detectors were used to observe neutrons through a cadmium plate with pin-hole,which was located at the middle of the flight-path. The distribution on the para-hydrogen moderator surface exhibited a intensity increase toward the edge near premoderator,while a decrease at the edge part was found in the normal-hydrogen one. Neutron energy spectra were also measured for both moderator sat various positions on the moderator surfaces, finding that the position dependence on the energy spectrum was quite different. In the para-hydrogen case, the intensity increased toward the edge below 100 meV. In the normal-hydrogen case, the intensity also increased toward the edgebetween 10 to 100 meV, while below 10 meV an almost flat distribution was found except the lower intensity at the edge.