Comparison between Pulsed Cold Neutron Intensities from Liquid Hydrogen Moderator and from Solid Methane Moderator in Decoupling Type Moderator Assembly

摘要

Although liquid hydrogen is at present a unique cold moderator applicable to high intensity neutron sources, the reported pulsed cold neutron intensity from a liquid hydrogen moderator is significantly lower than that from a solid methane moderator. In this report, a reflected assembly with a thick hydrogen moderator is used to enhance the pulsed cold neutron intensity and the intensity is compared with that from a solid methane moderator. For comparison, 5 and 15 cm thick moderators were used for liquid hydrogen moderators. The thicker one was used to obtain the saturated intensity of pulsed cold neutrons. The thickness of a solid methane was 5 cm. The cold neutron intensity from the 15 cm thick hydrogen moderator is about 1.6 times as high as that from the 5 cm one, in the case of the graphite reflected moderator assembly with a Cd decoupler. However, even in the case of the reflected assembly, the cold neutron intensities from the liquid hydrogen moderators are much less than that from the solid methane moderator ; intensity ratios of the cold neutrons emitted from the hydrogen moderator to the solid methane one are about 36% for the thin hydrogen moderator and about 56% for the thick one. These results show that although the thick hydrogen moderator should be used to increase the pulsed cold neutron intensity, the pulsed cold neutron intensity from the liquid hydrogen moderator cannot be increased up to that from the solid methane moderator regardless of the use of a reflector, only by thickening the moderator.