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 technique is applicable to all types of spiral-readout IP detectors. The procedure utilizes an attenuated direct-beam scan of the IP to generate a radial-sensitivity calibration table. Exposure and scanning of the calibration frame are done on the same time scale as typical data collections, and require no additional equipment. Specific examples are presented for use with Mac Science DIP2000 systems. The new radial calibration is shown to reduce significantly structure-based R factors. The improved radial calibration is also shown to lower R_merge when the IP is offset from the beam center. In addition to improving data quality and statistics, this method provides a quick and simple diagnostic tool to monitor changes in the sensitivity of the IP detector as a function of age.