Development of a Low Energy Neutron Scattering Facility

该项目涉及在印第安纳大学回旋加速器设施（IUCF）建设一个低能中子散射（LENS）设施。LENS将利用IUCF现有的直线加速器产生11mev的质子，在Be靶上通过（p, n）反应产生脉冲中子束。LENS不仅是一种新型且相对便宜的脉冲冷中子源，而且-当2005年完成时- LENS将能够设计用于小角度散射的新型中子仪器，材料科学和生物学的广泛研究计划，新型中子源和减速剂的开发，以及美国下一代中子科学家的教育和培训。LENS还将作为特别适合高风险实验和可行性研究的区域用户设施。通过本项目完成的LENS的特殊方面是(1)中子波导的构建和(2)用于自旋回波小角中子散射（SESANS）实验的新型Larmor进动散射仪（PSI）的开发。PSI将使用极化中子，对10纳米到1000纳米的结构非常敏感。它既可以用作反射计，也可以用作高分辨率衍射计。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1微米到1厘米大小的结构进行成像。通过传统的小角度中子散射（SANS）、SESANS PSI和相衬成像，LENS将实现定性的新型中子散射测量，从而引领新科学。将在LENS进行的初步实验包括研究玻璃和陶瓷的异质性、磁性半导体的“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：蛋白质复合物以及叶绿素聚集体。小角度中子散射（SANS），利用能量相对较低的中子（所谓的“冷”中子），使科学家能够研究材料和生物物质的各个方面，这些方面是使用其他类型的辐射（如x射线）无法获得的。特别是，中子是原子和分子结构和动力学的敏感探针。由于这个原因，它们现在不仅在物理、化学和材料科学中得到广泛应用，而且在生物、地球科学和工程中也得到广泛应用。随着2006年在橡树岭国家实验室完成散裂中子源（SNS），中子有望越来越多地被用作敏感和多功能的科学探测器。然而，到目前为止，美国中子源的相对匮乏导致了美国中子科学家队伍的枯竭。印第安纳大学的低能中子散射（LENS）设施将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来帮助纠正这种情况，包括那些传统上没有充分利用中子散射技术的领域，如生物学。此外，LENS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。LENS还将用于潜在的高回报实验，这些实验风险太大，不值得在更大的脉冲中子源上花费时间。

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.