HIGH PERFORMANCE NEUTRON DETECTOR FOR PROTEIN CRYSTALLOGRAPHY

描述(申请人提供)：最近，随着固定和便携式的新中子源数量的增加，以类似的方式对中子的利用也在增加。与X射线和？射线相反，中子与物质相互作用的概率不取决于原子序数，而是在元素周期表中相当不规则，并取决于吸收体的核结构。与X射线不同，中子可以很容易地穿透许多重元素，但也很容易被各种轻同位素吸收或散射，如氢、氢或锂。因此，中子可以提供常规射线照相术无法检测到的信息。在生物医学和制药研究中，中子被用在大分子结晶学中来研究分子和蛋白质的结构，这些分子和蛋白质主要由轻元素组成。中子散射实验不仅可以确定原子的位置(弹性散射)，还可以确定原子的动力学(非弹性散射)。由于氢和氢的散射截面的巨大差异，中子使解决远远超出X射线能力的氢交换过程成为可能。虽然中子研究在生物医学科学中的好处是显而易见的，但目前此类研究的范围受到现有中子探测器的限制。拟议项目的目标是探索一种新的探测器，用于基于一种明亮的Gd化合物的中子成像研究。Gd基探测器的优点是具有最高的热中子吸收截面。这意味着这种材料只需要非常薄的一层(200微米或更少)就可以几乎100%地吸收热中子。这一点很重要，有三个原因。首先，它提高了中子束的利用率。其次，它将提供更好的空间分辨率(小于1 mm)，从而提高仪器的分辨率。由于生物样品的尺寸通常在毫米量级，因此这是一个重要的参数。第三，薄层具有较小的伽马吸收截面，减少了伽马背景，提高了信噪比。大分子(如蛋白质)的结构与其功能和性质密切相关。中子结晶学可以精确定位氢原子的位置，并有助于确定分子结构。中子探测器仪器的进步将提供更好的能力来定义这些结构，并有助于识别分子的目的。

DESCRIPTION (provided by applicant): Recently, with the increase in number of new neutron sources, stationary as well as portable, there has been growing utilization of neutrons in a similar manner. Contrary to X- and ?-rays, the probability of interaction of neutrons with matter does not depend on the atomic number but is rather irregular across the periodic table and depends on the nuclear structure of the absorber. Unlike X-rays, neutrons can easily penetrate many heavy elements, but are readily absorbed or scattered by various light isotopes, like hydrogen, deuterium, or lithium. Consequently, neutrons can provide information that would otherwise escape detection by conventional radiography. In biomedical and pharmaceutical research, neutrons are used in macromolecular crystallography to investigate the structure of molecules and proteins, which consist mostly of light elements. Neutron scattering experiments can resolve not only the atomic positions (elastic scattering) but also their dynamics (inelastic scattering). Due to the huge difference in scattering cross-section of hydrogen and deuterium, neutrons make it possible to resolve hydrogen exchange processes that are well beyond the capabilities of X-rays. While the benefits of neutron studies in biomedical sciences are obvious, the scope of such studies is limited at present by the available neutron detectors. The goal of the proposed project is to explore a new detector for neutron imaging studies based on a bright Gadolinium (Gd) compound. Advantage of Gd-based detectors is that this element has the highest cross-section for absorption of thermal neutrons. It means that only very thin layers of this material (200 microns or less) are required for nearly 100% absorption of thermal neutrons. This is important for three reasons. First, it improves utilization of the neutron beam. Second, it will provide better spatial resolution (less 1 mm) thus it will improve the resolving power of the instrumentation. Since the biological samples are usually on the order of millimeter in size it is important parameter. Third, thin layers will have small cross-section for gamma absorption, reducing gamma background and improving signal to noise ratio. The macromolecular (e.g. protein) structure strongly relates to its function and properties. Neutron crystallography can precisely pinpoint location of hydrogen atoms and help to define molecule's structure. Advancements in neutron detector instrumentation will provide better capabilities define these structures and help to recognize the molecule's purpose.