CHARACTERIZATION OF CCD DETECTOR ELECTRONICS FOR RECORDING WEAK X-RAY SCATTERING

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 如去年所述，我们解决了MarCCD 165探测器的探测器偏移（基线）波动问题。今年早些时候，探测器供应商通过我们的服务合同进行升级后，立即验证了基线稳定性提高到约0.2 ADU。同时，我们修改了我们的数据收集协议，以额外补偿基线波动，使该检测器在弱散射样品的X射线散射研究中非常有效。为补偿这种小水平的电子漂移，对数据采集方案进行了两项主要变更：1）每组一系列数据采集（通常为20张图像，每张图像曝光10 s）之前记录“暗图像”，该图像将在数据采集软件中从每个数据帧中自动减去。每个暗图像也被存储为文件序列号<$0 <$以供以后使用; 2）探测器接收到一个掩模，该掩模覆盖探测器有效区域上3点钟和9点钟位置的小区域，使得每个数据帧在所有四个探测器象限中具有真实基线水平的内部测量，由于独立的读出电路，这些象限可以具有不同的基线水平。SSRL开发的数据处理程序MarParse可以选择使用用户定义的全球基线值或在数据处理的第一步中为四个象限单独测量的实际偏移值。这些发展使我们能够为用户提供更可靠的解决方案散射数据结合更大的检测区域的方位平均，相比我们的线性探测器覆盖的面积小得多。MarCCD 165检测器最初购买用于单晶衍射研究和其他涉及强X射线散射体的研究，在整个2006年期间一直常规用于蛋白质溶液X射线散射。在这些改进过程中所获得的测试结果也为我们的新CCD探测器提供了一个基准点

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. We addressed the detector offset (baseline) fluctuation issue with our MarCCD165 detector as described last year. The improved baseline stability of ~0.2 ADU was verified earlier this year immediately following the upgrade by the detector vendor through our service contract. In parallel, we modified our data collection protocol for additional compensation of the baseline fluctuation, making this detector highly effective in x-ray scattering studies of weakly scattering samples. The two major changes to data collection protocol to compensate for this small level of electronic drift are 1) each set of a series of data collection (typically 20 images of 10s exposure each) is preceded by a recording of ¿dark image¿ which is subtracted automatically from each data frame in the data collection software. Each dark image is also stored as a file series number ¿zero¿ for later use; 2) the detector received a mask which covers small areas on the detector active area at 3 and 9 o¿clock positions so that each data frame has an internal measure of true baseline level in all four detector quadrants, which can have different baseline levels due to independent readout circuits. The SSRL-developed data processing program MarParse has an option of using either a user-defined global baseline value or the actual offset values measured individually for four quadrants in the first step of data processing. These developments allow us to provide users with much more reliable solution scattering data in combination with the larger detection area for azimuth averaging, compared to the much smaller area covered by our linear detector. The MarCCD165 detector, which was originally purchased for single crystal diffraction studies and other studies involving strong x-ray scatterers, has been in routine use in protein solution x-ray scattering for the entire duration of 2006. The test results we obtained in the process of these improvements have also provided a bench mark for specifying desired detector characteristics for our new CCD detector