Calibration of spiral-readout image-plate detectors

An improved method for intensity-uniformity calibration of diffraction data collected on spiral-readout image-plate (IP) systems is described. This te chnique is applicable to all types of spiral-readout IP detectors. The proc edure utilizes an attenuated direct-beam scan of the IP to generate a radia l-sensitivity calibration table. Exposure and scanning of the calibration f rame are done on the same time scale as typical data collections, and requi re no additional equipment. Specific examples are presented for use with Ma c Science DIP2000 systems. The new radial calibration is shown to reduce si gnificantly structure-based R factors. The improved radial calibration is a lso shown to lower R-merge when the IP is offset from the beam center. In a ddition to improving data quality and statistics, this method provides a qu ick and simple diagnostic tool to monitor changes in the sensitivity of the IP detector as a function of age.