Performance characteristics of newly modified CaSO₄. Dy based indigenous thermoluminescent dosimeters for environmental radiation monitoring

Environmental gamma radiation monitoring around the nuclear installations in India is being carried out for over three decades. This programme was essentially based on powder based Thermoluminescent Dosimeters (TLDs) using naturally occurring calcium fluoride (Fluorite) powder. Being powder based, it was labor intensive and to cater to the increasing demand for monitoring new stations, it was necessary to go for automatic TLD reader system. This was achieved by modifying the TLD cards suitably and using the automated PC based TLD badge TLD reader system indigenously developed and being used for personal dosimetry in India. This paper discusses the modifications that were carried out to make the TLDs suitable for environmental gamma monitoring using TLDs. Performance characterisation of the TLDs like accuracy, precision and energy dependence etc were carried out to see the efficacy of the system for use in the environmental gamma radiation monitoring. In addition, inter-comparison with the existing TLD system, both deployed simultaneously in the field was also carried out. It was found that the new TLD exhibit the accuracy of 89-96% of the various delivered doses in the laboratory while the precision was observed to be within 4% for all the doses delivered. The gamma radiation levels as measured using two TLD systems were found to match very well with each other. The paper also discusses the results. (author)