Noble gas activity monitor with gamma compensation
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Noble gas monitoring system is used to measure the volumetric activity of beta particles due to radioactive noble gases—41Ar, 85Kr and 133Xe. Background compensation in these monitors is necessary as ambient radiation field, mainly due to gamma field, influences the measurement of noble gas activity. Algorithm based on two gamma compensation methods have been developed and implemented on two channel gross counting data acquisition system having embedded controller. Modified floating mean algorithm has been incorporated and implemented in firmware to estimate the count rate with better accuracy (Dharmapurikar et al., in: National symposium on radiation physics (NSRP-17), November 14–16, 2007 organized by Indian Society on Radiation Physics (ISRP), 2007). The algorithm has been developed to reject spurious counts generated due to electronic noise and transients. Experiments have been carried out using 90Sr + 90Yr (Beta source) and 137Cs (Gamma source) to compare the above two gamma compensation methods and beta shielding effectiveness of different shielding materials. The results have been validated in presence of gamma field of 100 mR/h and beta source of 200 µCi. The system was calibrated using 90Sr + 90Yr and 137Cs sources of known strength.
KeywordsGamma compensation Shielding method Gamma sensitive detector method Modified floating mean algorithm Shield materials Bremsstrahlung effect Dead time
The authors are thankful to Smt. Anita Behere, Head, Electronics Division, BARC for allowing us to undertake this research work. We are also thankful to Shri Sunil Sawant, Smt. Shalaka Phadke and Electronics Division workshop for their help and support.
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