Remote Online Performance Evaluation of Photomultiplier Tube and Electronics of DPCAM

Continuous monitoring of the ambient air for the presence of radioactivity is a mandatory requirement in nuclear facilities to be able to initiate prompt actions for the protection of workers from internal exposures. The dual-phosphor scintillator-based continuous air monitor (DPCAM) is an instrument to measure airborne of alpha and beta radioactivities. The functionality of the detector, photomultiplier tube (PMT) along with electronics of DPCAM, is to be tested at periodic intervals to ensure reliability. This paper describes the development of a technique for remote online performance evaluation of PMT along with its electronics, using an LED light source activated from the central monitoring station. A detailed study was made on the response of DPCAM subjected to a pulsed light source of different wavelengths using LEDs. The most suitable LED was selected based on alpha-beta pulse discrimination with zero crosstalk and minimum relative intrinsic error for the full range. The selected LED was fixed on PMT. The DPCAM test circuit was designed and developed for the generation of test frequency to drive this LED. A dedicated radiation data acquisition system was configured using ZigBee wireless network. The remote online performance evaluation of the prototype DPCAM was carried out using loaded filter paper in the field and alpha-beta radioactive sources along with the pulsed light source. The realtime trend graphs generated during the evaluation provides five-point calibration, verification of relative intrinsic error, and verification of crosstalk between alpha-beta channels.