MICRODIFFRACTION ON BEAMLINE X25

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。 目的在最近的更新提案中提出的目标是：我们将启用新的微衍射仪，开发微晶体自动安装器的常规使用，安装Bilderback聚焦毛细管以提供尽可能干净的光束，计划使用266 nm的前照灯进行晶体可视化，开发将微晶体输送到X射线束的新方法。 我们放弃了266 nm照明方案，因为它非常昂贵，而开发这种方法的ESRF发现它不值得麻烦。我们增加了一个新的目标，这就是描述和利用狭缝来提供微光束。 结果新研制的显微衍射仪调试成功，达到了常规使用要求。在工作过程中，我们做了一些机械上的小改动。主要的改进是我们安装了一台视野更大的数码相机，从而提高了样品的可视化程度。这对用户来说是一个巨大的成功。 自动挂载器的常规使用：请参阅自动挂载器部分；我们正在制造一台仪器。 安装Bilderback聚焦毛细管：Don Bilderback的团队为我们创造了一种与我们现有聚焦系统的特性相匹配的聚焦毛细管。它的目的是产生一束25米的光束，会聚2mrad，与这种尺寸的狭缝光束相比，强度将增加约2.5倍。我们获得了一种适合当前限束缝位置的聚焦机构，并煞费苦心地对毛细管进行了表征。事实上，我们可以在样品位置得到非常明亮的光束，而且它似乎可能比预测的要小。由于很难获得这种大小的光束的绝对强度，我们没有得到一个确切的增益数字。 我们还失望地发现，现实中有一束2mrad会聚的光束。为了分辨大的单胞，人们希望光束发散小于最紧密间隔的倒格点所遮盖的角度的四分之一。也就是说，要很好地使用这个系统，最大的单元格间距需要是1/a&0.004？-1或a&gt；250？我们遇到的样本中，有太多至少有一个轴那么大。(这对摇摆曲线宽度和探测器上反射的大小都有影响。)也许我们不会进一步追踪聚焦的毛细血管。然而，这激发了我们的新目标 描述并利用狭缝来提供微束：X25衍射仪上的x射线束水平会聚约1mrad，垂直方向约平行。我们使用毛细管的经验表明，为了保留小晶体的尖峰，我们希望探测器上的光束不超过样品宽度的大约两倍。Q315使用的典型样品到检测器距离为300 mm。这在辐射为1？的边缘提供了约2？的分辨率。在这300毫米的距离内，光束从20米增加到40米，发散角将为0.07mrad。一组狭缝位于x射线槽上游17米处。实验发现，当水平缝隙为0.7 mm时，发散角将被削减到0.07mrad左右。来自波荡器的整个光束在4 mm处通过；0.7 mm的设置将总光束强度降低到大约最大值。我们认为，为了从微小的晶体中获得高信噪比，这是一个合适的价格。 操作问题：以前报告的聚焦X射线束低频波动的间歇性问题是通过重建单色仪的第二个晶体组件来解决的，其方式是允许进行单色仪的全部对准和调谐能力。为了隔离我们继续间歇注意到的其他低频噪声源，并解决它们，我们继续密切监测X射线束的稳定性，并与光源控制室协调，分析数据中看到的任何波动。事实上，这种波动在另一个PXRR间歇性地观察到 光束线也是如此，这让我们怀疑它们来自全球。通过更换一些电机控制模块，解决了光束线电机控制系统中遇到的一些困难。 在X25上继续开发处理微晶体的能力的计划是我们更新提案的重要部分，该提案于2007年9月提交，并于2008年3月进行了审查。明年将通过探索我们新的微晶衍射仪的使用来平衡常规数据收集。目标是在潜望镜上安装数字视频，并将狭缝小波束的使用带入正常操作。我们设想，X25将继续作为非常困难甚至可能是冒险的项目的地点，补充X29的高吞吐量重点。 意义光学和显微衍射仪的新升级将使我们能够进一步推动微小晶体的使用。X25的亮度在某些光子能量范围内超过了X29，这也将为我们提供宝贵的经验，因为我们正在努力规划NSLS-II光束线的发展。 出版物T.Shaftan、S.Hulbert和L.Berman，“长周期摇摆器和短周期波动器计算的辐射亮度和通量的比较”，J.Synch。拉德。15,335-340(2008)。

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. Objectives The objectives stated in the recent renewal proposal are these: We will commission the new microdiffractometer, develop routine use of the automounters for microcrystals, install a Bilderback focusing capillary to provide the cleanest possible beam, make plans to employ 266nm front-lighting for crystal visualization, develop novel methods to deliver microcrystals to an x-ray beam. We have dropped the 266nm-illumination project because it is very expensive, and the ESRF, who had developed the method, found it to be not worth the trouble. We have added a new objective, and this is to characterize and exploit the use of slits to provide a micro beam. Results  Commissioning the new microdiffractometer: The instrument is in routine use. We've made minor mechanical modifications during the course of the work. The major improvement has been to improve the visualization of the sample by our installation of a digital camera with a larger field of view. This is a great success with the users. Routine use of automounters: See the automounter section; we are building an instrument. Install a Bilderback focusing capillary: Don Bilderback's group created a focusing capillary for us that matched the characteristics of our existing focusing system. It was intended to produce a 25¿m beam, with a convergence of 2mrad, that would have an increased intensity of about 2.5X over a slitted beam that size. We acquired a focusing mechanism that fit in the position of the current beam-limiting slits and took some pains to characterize the capillary. Indeed, we could get a very bright beam at the specimen position, and it seemed to be possibly smaller than predicted. Because of difficulties in getting an absolute intensity for a beam this size, we didn't get a firm number for the gain. We also were dismayed to discover the reality of having a 2mrad-converging beam. To resolve large unit cells, one would like the beam divergence to be less than maybe one quarter of the angle subtended by the most closely spaced reciprocal lattice points. That is, to use this system well the largest unit-cell spacing would need to be 1/a > 0.004¿-1 or a > 250¿. Too many of the specimens we encounter have at least one axis that large. (This has implications for both the rocking curve width and the size of reflections on the detector.) Probably we won't pursue the focusing capillaries further. However this stimulated our new objective Characterize and exploit the use of slits to provide a micro beam: The x-ray beam at the X25 diffractometer converges by about 1mrad horizontally and is about parallel vertically. Our experience with the capillary suggested that, in order to preserve the sharp peak from a small crystal, we'd like the beam at the detector to be no wider than about twice its width at the specimen. A typical specimen-to-detector distance used with the Q315 is 300mm. This gives a resolution of about 2¿ at the edge with 1¿ radiation. For the beam to increase from about 20 to 40¿m over this 300mm distance, the divergence would be 0.07mrad. A set of slits lies 17m upstream from the x-ray hutch. We discovered empirically that the divergence will be cut to about 0.07mrad when the horizontal slit is 0.7mm. The whole beam from the undulator gets through at 4mm; a 0.7mm setting reduces the total beam intensity to about ¿ the maximum value. We feel this is an appropriate price to pay to get high signal-to-noise from a tiny crystal. Operational issues: The previously-reported intermittent problem of low frequency fluctuations of the focused x-ray beam was addressed through re-construction of the second crystal assembly of the monochromator, done in a way to permit the full capabilities of aligning and tuning the monochromator to be undertaken. Hoping to isolate other sources of low-frequency noise that we continue to notice intermittently, and resolve them, we continue to monitor the stability of the x-ray beam closely, and to coordinate with the Light Source Control Room, analyzing any fluctuations seen in the data. In fact, such fluctuations are observed intermittently at the other PXRR beamlines too, which leads us to suspect that they are of global origin. Some difficulties encountered in the beamline motor control system were resolved through replacement of some of the motor controls modules. Plans  Continued development of the capability to handle microcrystals at X25 was an important part of our renewal proposal, submitted in Sep 07 and reviewed in Mar 08. This next year will be filled with balancing routine data collection with exploring the use of our new micro-crystal diffractometer. Objectives will be to install a digital video on the periscope and to bring use of the slitted small beam into normal operations. We imagine that X25 will continue to be the site for very difficult and perhaps adventuresome projects, complementing the high-throughput emphasis at X29. Significance  The new upgrades to the optics and micro-diffractometer will allow us to push further into the use of tiny crystals. The brightness of X25, which surpasses that of X29 in certain photon energy ranges, also will provide us with experience that will be valuable as we work to plan development of beamlines for NSLS-II. Publication  T. Shaftan, S. Hulbert, and L. Berman, "Comparison of calculated brightness and flux of radiation from a long-period wiggler and a short-period undulator", J. Synch. Rad. 15, 335-340 (2008).