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

甲烷水合物被认为是一种冷中子减速剂，在较宽的能量范围内具有较高的强度。我们主要进行了实验研究。我们在英国的ISIS测量了中子的非弹性散射，以了解中子的截面特性。甲烷水合物中甲烷分子的旋转能级为1.1meV，与甲烷的自由旋转能级基本一致，似乎是自由旋转的。我们可以推导出大小冰架的平移模态。甲烷水合物中冰的振动模态和振动模态与冰的振动模态基本相似，但存在较小的畸变。这些数据表明，甲烷水合物的横截面可以模拟成两种材料横截面的线性组合。甲烷作为慢化剂的作用很重要，但甲烷水合物中甲烷的含量并不高。因此，我们通过慢化剂实验来观察甲烷水合物的中子性能。我们研究了一个耦合的和一个解耦的缓和器。通过比较，还得到了甲烷和氢的慢化剂数据。在耦合慢化剂的情况下，甲烷水合物的能谱形状与冰相似，甲烷水合物慢化剂的峰值能量略高于其他甲烷和氢材料的峰值能量。冷中子区周围的光谱强度远低于其他材料。但在热中子区附近，强度较高。解耦慢化剂的光谱强度接近氢慢化剂，但远低于甲烷。发射时间的脉冲宽度比其他缓冲剂宽得多。因此，甲烷水合物减速剂没有冷减速剂那么好的特性，在高能区可以给出更高的强度。

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.