Development of a Low Energy Neutron Scattering Facility

该项目涉及在印第安纳州大学回旋加速器设施（IUCF）建造一个低能中子散射（透镜）设施。 透镜将使用IUCF现有的线性加速器产生11 MeV的质子，通过Be靶上的（p，n）反应产生脉冲中子束。 透镜不仅是一种新颖的和相对便宜的脉冲冷中子源，而且-在2005年完成时-透镜将能够设计用于小角散射的新型中子仪器，材料科学和生物学研究的广泛计划，新型中子源和减速器的开发，以及美国下一代中子科学家的教育和培训。 透镜还将作为一个区域用户设施，特别适合高风险实验和可行性研究。 通过该项目正在完成的透镜的具体方面是（1）中子导管的建造和（2）用于自旋回波小角中子散射（SESANS）实验的新型拉莫尔旋进散射仪（PSI）的开发。 PSI将使用极化中子，并将对10 nm至1000 nm尺寸范围内的结构敏感。 它既可以作为反射计，也可以作为高分辨率折射计。 此外，使用来自针孔源的相干中子波、编码孔径掩模和新开发的相衬成像将允许对尺寸从1微米到1厘米的结构进行成像。 与传统的小角中子散射（SANS），SESANS PSI和相衬成像，透镜将使定性新类型的中子散射测量，导致新的科学。 将在透镜进行的初步实验包括研究玻璃和陶瓷中的不均匀性、磁性半导体中的“自旋电子学”、合金和纯金属中的氢化物形成、聚合物网络和混合物、纳米结构聚合物、RNA解旋酶和蛋白质：小角中子散射（SANS），使用相对低能量的中子（所谓的“冷”中子），使科学家能够研究使用其他类型的辐射（如X射线）无法获得的材料和生物物质的各个方面。 特别是，中子是原子和分子的结构和动力学的灵敏探针。 因此，它们现在不仅在物理学、化学和材料科学中，而且在生物学、地球科学和工程学中得到了广泛的应用。 随着2006年橡树岭国家实验室的Sputterus中子源（SNS）的建成，中子有望越来越多地用作灵敏和多功能的科学探测器。 然而，到目前为止，美国的中子源相对缺乏，这导致了美国中子源的消耗。S.中子科学家 印第安纳州大学的低能中子散射（透镜）设施将有助于纠正这种情况，通过在大学环境中为下一代中子科学家提供教育和培训的机会，包括那些来自生物学等领域的中子散射技术传统上没有充分发挥其作用。 此外，透镜将作为一个区域用户设施，使其他机构-包括工业界-的研究人员能够利用中子散射方法。 透镜还将用于潜在的高回报实验，这些实验风险太大，无法证明在更大的脉冲中子源上花费时间是合理的。

This project involves the construction of a Low Energy Neutron Scattering (LENS) facility at the Indiana University Cyclotron Facility (IUCF). LENS will use the existing linear accelerator at IUCF to produce 11 MeV protons, generating a pulsed neutron beam through (p, n) reactions on a Be target. Not only is LENS a novel and relatively inexpensive pulsed cold neutron source, but also - when completed in 2005 - LENS will enable the design of novel neutron instrumentation for small angle scattering, a broad program of research in materials science and biology, the development of novel neutron sources and moderators, and the education and training of the next generation of neutron scientists in the United States. LENS will also serve as a regional user facility that will be particularly well-suited for high-risk experiments and feasibility studies. The particular aspects of LENS that are being completed through this project are (1) the construction of neutron guides and (2) the development of a novel Larmor Precession Scattering Instrument (PSI) for spin-echo small-angle neutron scattering (SESANS) experiments. PSI will use polarized neutrons and will be sensitive to structures in the size range from 10 nm to 1000 nm. It can be operated either as a relectometer or as a high-resolution difractometer. In addition, use of coherent neutron waves from pinhole sources, a coded aperture mask, and newly developed phase-contrast imaging will allow imaging of structures from 1 micron to 1cm in size. With conventional small-angle neutron scattering (SANS), the SESANS PSI, and phase-contrast imaging, LENS will enable qualitatively new types of neutron scattering measurements, leading to new science. Among the initial experiments that will be conducted at LENS are studies of heterogeneities in glasses and ceramics, "spintronics" in magnetic semiconductors, hydride formation in alloys and pure metals, polymer networks and blends, nanostructured polymers, RNA helicases and protein:protein complexes, and chlorophyll aggregates.Small-angle neutron scattering (SANS), using neutrons with relatively low energies (so-called "cold" neutrons), allows scientists to study aspects of materials and biological substances that are not accessible using other types of radiation, such as X-rays. In particular, neutrons are sensitive probes of the structure and dynamics of atoms and molecules. For this reason, they have now become widely used, not only in physics, chemistry, and materials science, but also in biology, earth science, and engineering. With the completion of the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory in 2006, neutrons promise to be used increasingly as sensitive and versatile scientific probes. However, the relative dearth of neutron sources in the United States up to this time has contributed to the depletion of the ranks of U. S. neutron scientists. The Low Energy Neutron Scattering (LENS) facility at Indiana University will help to correct this situation by providing in a university setting the opportunity for the education and training of the next generation of neutron scientists, including those from fields such as biology that have not traditionally employed neutron scattering techniques to the full extent of their usefulness. In addition, LENS will serve as a regional user facility, enabling investigators from other institutions - including industry - to make use of neutron-scattering methods. LENS will also be used for potentially high-payoff experiments that are too risky to justify time on larger pulsed-neutron sources.