Comprehensive applications of the gas flow proportional counters for Radiological Surveillance

Gas Flow Proportional Counters (GFPC) have been developed indigenously for various radiation protection applications. These detectors can be fabricated for 2” diameter filter paper sample counting applications to large area (~1500 cm) detectors for surface contamination applications. Thin entrance windows allow nonpenetrating type of radiations like alpha and low energy beta particles. Efficiencies (for alpha and beta radiations) are comparable to conventional detectors used to measure these radiations. Poor gamma efficiency (<1%) compared to ~30% beta efficiency provides a large ß/γ ratio, a high figure of merit and enables efficient gamma background rejection. These detectors are quite suitable for Indian environmental conditions. Three systems have been developed and successfully incorporated in to the radiation surveillance program at various nuclear facilities. The systems based on GFPC detectors include (a) Multiple sample gross alpha counting system, (b) Laundry monitoring system and (c) Alpha hand contamination monitoring system. The first of these enables simultaneous gross alpha counting of five air activity filter paper samples. The area of the detector surface is optimized to cover the 2′′ sized filter paper samples routinely used for the purpose. Five numbers of GFPC’s are arranged sequentially coupled to five individual amplifiers microcontroller modules to process the signal from the five counters. The laundry monitor which is microcontroller based system consists of four large area multiwire GFPC detectors (700 cm sensitive area) used to monitor alpha contamination of decontaminated laundry. Each detector uses a charge sensitive preamplifier coupled to IC counter. The alpha hand monitoring system consists of four large area multiwire gas flow proportional detectors (330 cm sensitive area each). A microcontroller-based module is employed to initiate the counting process automatically when the hands are inserted in to the suitably designed window slots and provides audio and visual alarm.