低能中子源（LENS）靶慢化剂反射器组件的中子学设计和测量性能
Neutronic Design and Measured Performance of the Low Energy Neutron Source (LENS) Target Moderator Reflector Assembly
摘要：
低能中子源（英语：Low Energy Neutron Source，缩写LENS）是美国印第安纳大学回旋加速器实验室（英语：Indiana University Cyclotron Facility，缩写IUCF）正在建造的一个基于加速器的脉冲冷中子设施。LENS背后的想法是产生脉冲冷中子束，从Be中的（p，n）反应开始，其被缓和到meV能量，并从小立体角提取，用于中子仪器，其可以以相对宽（~1 msec）的中子脉冲宽度有效地操作。虽然这个源的功能和操作参数的组合是独一无二的，目前，中子设计具有几个功能类似于那些设想为未来的中子设施，如长脉冲中子源（LPSS）和非常冷的中子（VCN）源。我们描述的基本思想和设计细节的目标/减速器/反射器系统（TMR）和比较测量的亮度，能谱，和发射时间分布在不同的减速器配置与MCNP模拟。亮度测量使用环境温度水慢化剂同意MCNP模拟的测量精度在20%以内。从固体甲烷慢化剂测量的中子发射时间分布与模拟一致，冷中子通量是足够的材料的中子散射研究。我们描述了一些可能的修改现有的设计，这将增加冷中子的亮度，发射时间分布的影响可以忽略不计。
英文摘要：
The Low Energy Neutron Source (LENS) is an accelerator-based pulsed cold neutron facility under construction at the Indiana University Cyclotron Facility (IUCF). The idea behind LENS is to produce pulsed cold neutron beams starting with ~MeV neutrons from (p,n) reactions in Be which are moderated to meV energies and extracted from a small solid angle for use in neutron instruments which can operate efficiently with relatively broad (~1 msec) neutron pulse widths. Although the combination of the features and operating parameters of this source is unique at present, the neutronic design possesses several features similar to those envisioned for future neutron facilities such as long-pulsed spallation sources (LPSS) and very cold neutron (VCN) sources. We describe the underlying ideas and design details of the target/moderator/reflector system (TMR) and compare measurements of its brightness, energy spectrum, and emission time distribution under different moderator configurations with MCNP simulations. Brightness measurements using an ambient temperature water moderator agree with MCNP simulations within the 20% accuracy of the measurement. The measured neutron emission time distribution from a solid methane moderator is in agreement with simulation and the cold neutron flux is sufficient for neutron scattering studies of materials. We describe some possible modifications to the existing design which would increase the cold neutron brightness with negligible effect on the emission time distribution.
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