Liebschner Dorothee, Dauter Miroslawa, Rosenbaum Gerold, Dauter Zbigniew
Synchrotron Radiation Research Section, MCL, National Cancer Institute, Argonne National Laboratory, Argonne, IL 60439, USA.
Acta Crystallogr D Biol Crystallogr. 2012 Oct;68(Pt 10):1430-6. doi: 10.1107/S0907444912034658. Epub 2012 Sep 18.
The accuracy of X-ray diffraction data depends on the properties of the crystalline sample and on the performance of the data-collection facility (synchrotron beamline elements, goniostat, detector etc.). However, it is difficult to evaluate the level of performance of the experimental setup from the quality of data sets collected in rotation mode, as various crystal properties such as mosaicity, non-uniformity and radiation damage affect the measured intensities. A multiple-image experiment, in which several analogous diffraction frames are recorded consecutively at the same crystal orientation, allows minimization of the influence of the sample properties. A series of 100 diffraction images of a thaumatin crystal were measured on the SBC beamline 19BM at the APS (Argonne National Laboratory). The obtained data were analyzed in the context of the performance of the data-collection facility. An objective way to estimate the uncertainties of individual reflections was achieved by analyzing the behavior of reflection intensities in the series of analogous diffraction images. The multiple-image experiment is found to be a simple and adequate method to decompose the random errors from the systematic errors in the data, which helps in judging the performance of a data-collection facility. In particular, displaying the intensity as a function of the frame number allows evaluation of the stability of the beam, the beamline elements and the detector with minimal influence of the crystal properties. Such an experiment permits evaluation of the highest possible data quality potentially achievable at the particular beamline.
X射线衍射数据的准确性取决于晶体样品的性质以及数据收集设备（同步辐射光束线元件、测角仪、探测器等）的性能。然而，从旋转模式下收集的数据集质量很难评估实验装置的性能水平，因为诸如镶嵌性、不均匀性和辐射损伤等各种晶体性质会影响测量强度。在多图像实验中，在相同晶体取向连续记录几个类似的衍射帧，可以将样品性质的影响降至最低。在阿贡国家实验室的先进光子源（APS）的SBC光束线19BM上测量了一系列100张奇异果甜蛋白晶体的衍射图像。根据数据收集设备的性能对获得的数据进行了分析。通过分析一系列类似衍射图像中反射强度的行为，实现了一种估计单个反射不确定性的客观方法。发现多图像实验是一种简单且合适的方法，可将数据中的随机误差与系统误差分解开，这有助于判断数据收集设备的性能。特别是，将强度显示为帧数的函数，可以在晶体性质影响最小的情况下评估光束、光束线元件和探测器的稳定性。这样的实验可以评估在特定光束线上可能达到的最高数据质量。
