A study of the performance of the gas transmission monitor of the PHENIX Hadron Blind Detector

For the successful operation of the Hadron Blind Detector (HBD) of the PHENIX Experiment at RHIC, it is essential that the radiator gas quality be continuously monitored. This is accomplished through the use of a gas transmission monitor, which is based on a customized McPherson 234/302 VUV spectrometer. After studying the performance characteristics of the spectrometer at the completion of RHIC Run9, a number of improvements were implemented to greatly improve its performance during Run10, including the replacement of all of the system optics. Following this upgrade, the transmission monitor was successfully used to monitor the gas quality of the HBD for the most recent Au+Au run at RHIC. With the aid of the transmission monitor, the absolute integrated transmittance of the detector was used to determine an absolute measure of the HBD detector efficiency throughout the run.