Improvement of Pulse Characteristics of Neutrons from a Decoupled Liquid-Hydrogen Moderator Using a Multi-Layer Decoupler System at a Pulsed Spallation Neutron Source

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Neutron pulse shapes are important in pulsed neutron sources, especially for high-resolution neutron scattering instruments. Around the region of thermal equilibrium energy, the moderator is the main factor in deciding the neutron pulse shapes from a decoupled moderator. However, in the slowing-down energy region, the reflector also affects the pulse shapes, and the neutrons in this energy region will be increasingly important for precise neutron-scattering experiments in the future. Lead has many preferable characteristics as a reflector from a neutronic point of view, but it has a disadvantage in that it creates a long pulse tail, since it takes a very long time for a neutron in lead to slow down. To shorten this pulse tail, we propose a multi-layer decoupler system and compare its performance with that of a traditional decoupler system. The multi-layer decoupler was found to shorten the pulse tail effectively without causing a large decrease in the pulse peak intensity, whereas the traditional decoupler caused a greater decrease in this intensity. This result indicates that the multi-layer decoupler is useful for improving pulse characteristics of neutrons from a decoupled moderator at the pulsed neutron source using a lead reflector.
一般社団法人日本原子力学会の論文
2004-01-25