CHARACERIZATION OF X-RAY WINDOW SCATTERING AND FLUORESCENCE FOR SAXS STUDIES

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 对于最具挑战性的SAXS研究，需要消除或最大限度地减少背景散射的所有来源，水散射是不可避免的例外。样品容器和真空路径分离的样品池X射线窗口是本底的主要来源。为了改进X射线散射设备，我们研究了多种窗口材料的X射线散射，包括氮化硅薄膜、白云母片、铍薄膜和三种类型的薄壁X射线毛细管，在很宽的Q范围内(0.01-1.2A-1)。水和空气的散射也被记录下来，以重新评估BL4-2真空毛细管电池的有效性。结果表明，与毛细管相比，Si3N4是目前表现最好的材料，在整个Q范围内给出的X射线散射最少，比毛细管少两个数量级，这可能是因为它的亚微米厚度。我们已经验证了厚度为200 nm、面积为1 mm×1 mm的Si(3)N(4)窗口可以承受1巴的压差，使其可用作真空窗口。与石英和玻璃毛细管相比，硼硅酸盐毛细管的X射线散射略弱，但所有毛细管，特别是石英，在较高角度下的散射相对较强。10微米厚的云母的X射线散射与极小角度下的毛细管相当，但在中到高散射角时弱4到20倍，因此使其成为高角度研究的良好选择。新解理的云母在小角度上的散布比未处理的云母小得多，而打磨的云母散布的强度更大，这表明在将云母片用作X射线窗口之前，应该解开云母片以暴露新鲜的表面。能量分辨涡旋探测器的使用使我们能够评估窗口内污染金属杂质所产生的X射线荧光的贡献。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. For the most challenging class of SAXS studies all sources of background scattering need to be eliminated or minimized, with the inevitable exception of water scattering. Sample cell x-ray windows for sample containment and vacuum path separation are primary sources of background. In order to improve the x-ray scattering facility, we have studied x-ray scattering from a variety of window materials, including silicon nitride foils, muscovite mica sheets, beryllium foils and three types of thin-wall x-ray capillaries on an absolute scale over a wide Q-range (0.01-1.2 A-1). Water and air scattering have also been recorded to re-evaluate the effectiveness of the BL4-2 in-vacuum capillary cell. The results indicate that Si3N4 is by far the best performer giving the least x-ray scattering in the entire Q range by two orders of magnitude compared to capillaries, likely due to its submicron thickness. We have verified that a 200-nm thick Si(3)N(4) window with 1 mm x1 mm area can withstand a 1 bar pressure difference, making it usable as a vacuum window. Borosilicate capillaries give slightly weaker x-ray scattering than quartz and glass capillaries, but all capillaries in particular quartz scatter relatively strongly at higher angles. X-ray scattering of 10 micron thick mica is comparable to capillaries at very small angles, but much weaker by a factor of 4 to 20 at intermediary to high scattering angles, thus making it a good choice for higher angle studies. Freshly cleaved mica scatters much less than untreated mica at small angles while sanded mica scatters orders of magnitude more strongly, indicating mica sheets should be cleaved to expose fresh surface prior to their use as an x-ray window. The use of energy-resolving Vortex detector allowed us to evaluate the contribution of x-ray fluorescence from contaminating metallic impurities within the window.