Online monitoring the detector calibration process at a synchrotron X-ray source

This paper describes an online noble gas monitor used for the detector calibration process with a cryogenic radiometer. The process is implemented under a high-flux synchrotron radiation X-ray source in the energy range from 2100 to 6000 eV at the Beijing Synchrotron Radiation Facility (BSRF). This online monitoring system aims to lower the uncertainty of the calibration results caused by electron beam decay in the storage ring during the detector calibration process. Because the calibration process is performed under the high vacuum condition, an ionization chamber with adjustable Kr gas pressure is chosen as the monitoring device. To decrease the electronic noise, a method for obtaining the signal by collecting the counts within a specified time has been applied. Under the properly controlled conditions, the uncertainty of the calibration results introduced by the online monitoring system is estimated to be better than 0.15%, which can meet the demands of various high-precision calibration processes.