Taking a look at the calibration of a CCD detector with a fiber-optic taper

Abstract

At the Structural Biology Center beamline 19BM, located at the Advanced Photon Source, the operational characteristics of the equipment are routinely checked to ensure they are in proper working order. After performing a partial flat-field calibration for the ADSC Quantum 210r CCD detector, it was confirmed that the detector operates within specifications. However, as a secondary check it was decided to scan a single reflection across one-half of a detector module to validate the accuracy of the calibration. The intensities from this single reflection varied by more than 30% from the module center to the corner of the module. Redistribution of light within bent fibers of the fiber-optic taper was identified to be a source of this variation. The degree to which the diffraction intensities are corrected to account for characteristics of the fiber-optic tapers depends primarily upon the experimental strategy of data collection, approximations made by the data processing software during scaling, and crystal symmetry.

Real-space analysis of radiation-induced specific changes with independent component analysis

“…The mosaicity of crystals varied between 0.2 and 0.4 , indicating a good microscopic order of the crystal lattice. To include recent advances in data scaling (Alkire et al, 2016;Otwinowski et al, 2012) and to assure the consistency of the reciprocal lattice definition, the previous GI data sets (Borek et al, 2007) were rescaled using HKL2000 (Otwinowski & Minor, 1997) with the 15 K data set used as a reference point. The aim of this operation was to assure that the grids used to calculate the electron density maps in real space, which are the input to the ICA procedure described in x2.3, have the same dimensions.…”