Zeng Jianrong, Bian Fenggang, Wang Jie, Li Xiuhong, Wang Yuzhu, Tian Feng, Zhou Ping
Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Zhangheng Road 239, Pudong District, Shanghai 201204, People's Republic of China.
J Synchrotron Radiat. 2017 Mar 1;24(Pt 2):509-520. doi: 10.1107/S1600577516019135. Epub 2017 Jan 24.
The optical system and end-station of bending-magnet beamline BL16B1, dedicated to small-angle X-ray scattering (SAXS) at the Shanghai Synchrotron Radiation Facility, is described. Constructed in 2009 and upgraded in 2013, this beamline has been open to users since May 2009 and supports methodologies including SAXS, wide-angle X-ray scattering (WAXS), simultaneous SAXS/WAXS, grazing-incidence small-angle X-ray scattering (GISAXS) and anomalous small-angle X-ray scattering (ASAXS). Considering that an increasing necessity for absolute calibration of SAXS intensity has been recognized in in-depth investigations, SAXS intensity is re-stated according to the extent of data processing, and the absolute intensity is suggested to be a unified presentation of SAXS data in this article. Theory with a practical procedure for absolute intensity calibration is established based on BL16B1, using glass carbon and water as primary and secondary standards, respectively. The calibration procedure can be completed in minutes and shows good reliability under different conditions. An empirical line of scale factor estimation is also established for any specific SAXS setup at the beamline. Beamline performance on molecular weight (MW) determination is provided as a straightforward application and verification of the absolute intensity calibration. Results show good accuracy with a deviation of less than 10% compared with the known value, which is also the best attainable accuracy in recent studies using SAXS to measure protein MW. Fast MW measurement following the demonstrated method also enables an instant check or pre-diagnosis of the SAXS performance to improve the data acquisition.
本文介绍了上海同步辐射装置上专门用于小角X射线散射（SAXS）的弯铁光束线BL16B1的光学系统和终端站。该光束线于2009年建成并于2013年升级，自2009年5月起对用户开放，支持包括SAXS、广角X射线散射（WAXS）、同步SAXS/WAXS、掠入射小角X射线散射（GISAXS）和反常小角X射线散射（ASAXS）等方法。考虑到在深入研究中已认识到对SAXS强度进行绝对校准的必要性日益增加，本文根据数据处理程度重新阐述了SAXS强度，并建议绝对强度作为SAXS数据的统一呈现方式。基于BL16B1，分别以玻璃碳和水作为一级和二级标准，建立了绝对强度校准的理论及实际程序。校准程序可在数分钟内完成，且在不同条件下具有良好的可靠性。还为光束线上的任何特定SAXS装置建立了比例因子估计的经验线。作为绝对强度校准的直接应用和验证，给出了光束线在分子量（MW）测定方面的性能。结果显示出良好的准确性，与已知值相比偏差小于10%，这也是近期使用SAXS测量蛋白质MW的研究中可达到的最佳准确性。按照所展示的方法进行快速MW测量还能够即时检查或预诊断SAXS性能，以改善数据采集。
