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

甲烷水合物作为一种冷中子慢化材料，在较宽的能量范围内具有较高的中子强度。我们主要进行了实验研究。我们在英国的ISIS测量了中子非弹性散射，了解了中子截面特性。甲烷水合物中甲烷分子的转动能级为1.1meV，与甲烷分子的自由转动能级基本一致，因此甲烷分子似乎是自由转动的。我们可以推导出大小冰笼中的平动模态。甲烷水合物中冰的振动模和自由振动模与冰的振动模和自由振动模基本相似，但存在微小的畸变。这些数据表明，甲烷水合物截面可以模拟的两种材料的截面的线性组合。甲烷作为慢化剂的作用是重要的，但甲烷水合物中甲烷的含量并不高，因此我们进行了慢化实验来观察甲烷水合物的中子学性能。我们研究了一个耦合和解耦的主持人。甲烷和氢慢化剂的数据也得到了比较。在耦合慢化剂的情况下，甲烷水合物的能谱形状与冰的能谱形状相似，甲烷水合物慢化剂的峰值能量略高于其他甲烷和氢的物质。冷中子区附近的光谱强度比其他材料低得多。然而，在热中子区附近的强度较高。在退耦慢化剂的情况下，光谱强度接近氢慢化剂的光谱强度，但远低于甲烷。发射时间的脉宽比其他慢化剂宽得多。因此，甲烷水合物慢化剂不具有冷慢化剂那样好的特性，并且可以在更高的能量区域提供更高的强度。

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.