Experimental studies of neutronic characteristics of hydrogen moderators at para rich concentrations and comparison with calculations

Hydrogen is the most important material as a cold neutron moderator for the future high power spallation neutron sources. However, experimental data for the moderators of hydrogen with high para concentration are very scares and not suitable for design of the future moderator system. We made equipments to convert ortho to para-hydrogen and to measure the ortho/para ratio. After then, we measured the neutronic performance of the hydrogen moderators with 5 cm thickness and compared with simulation. The results indicated that overall characteristics of the experimental result agreed with the calculated results but there exist difference in the absolute values. Therefore, the simulation is useful for the basic design but experiments are necessary to evaluate the precise neutronic performance. (orig.)