Development of high efficiency pursed neutron source by using a new material of methane hydrate

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Methane hydrate has been expected as a cold neutron moderator material giving higher intensity over wide energy range. We have performed experimental studies mainly. We measured neutron inelastic scattering at ISIS in UK to know the neutron cross-section characteristics. The methane molecule in methane hydrate seemed to rotate freely since the rotational energy level was 1.1meV which is almost same as the energy level of free rotation of methane. We could deduce the translational modes in the small and large ice cages. The ice vibrational mode and librational mode in methane hydrate were almost similar to those of ice In although there existed small distortion. These data suggested that methane hydrate cross section can be simulated linear combination of cross sections of both materials. As a moderator the effect of methane is important but the content of methane is not so high in methane hydrate.So, we performed moderator experiments to observe the neutronic performance of methane hydrate. We studied a coupled and a decoupled moderators. Methane and hydrogen moderator data were also obtained fro the comparison. In the case of the coupled moderator, the shape of the energy spectrum of methane hydrate was similar to that of ice, the peak energy of methane hydrate moderator was little bit higher than those of other materials of methane and hydrogen. Spectral intensity around the cold neutron region was much lower than other materials. However, around the thermal neutron region the intensity was higher. In the case of the decoupled moderator the spectral intensity was approaching that of hydrogen moderator but much lower than methane. The pulse width of emission time was much wider than other moderators. Therefore, it will be concluded that the methane hydrate moderator does not have so good characteristics as a cold moderator and can give higher intensity at higher energy region.