ABSTRACT
In India, approximately 58,000 radiation workers are monitored using locally made CaSO4:Dy teflon embedded thermoluminescence dosemeter (TLD) badge system. The automatic hot gas readers developed locally are also used in TL measurements. The hot gas reader system has many advantages over the manual readers used previously and has completely replaced the manual reader system in all TLD personnel monitoring units in India. In the present study, the new reader system is studied and a theoretical attempt has been made to interpret the experimentally obtained results. The glow curves are generated theoretically and are also plotted experimentally. It has been found that the heat capacity of the heating gas, which is responsible for the transfer of heat, has a role in deciding the position of peak and is verified experimentally using different gas flow rates of nitrogen and argon as heating gases in the reader. The theoretical study may also be helpful in fitting the experimentally obtained glow curves and, therefore, the elimination of unwanted non-radiation-induced contributions, such as dark current, electronic spikes, light leakage and triboluminescence that generally distort the glow curve shape, can be achieved.
Subject(s)
Radiation Monitoring/methods , Thermoluminescent Dosimetry/methods , Automation , Gases , Hot Temperature , Humans , Lithium Compounds , Models, Theoretical , Occupational Exposure , Radiation Monitoring/instrumentation , Temperature , Thermoluminescent Dosimetry/instrumentation , Thermoluminescent Dosimetry/standards , Time FactorsABSTRACT
The TL sensitivity of CaCO4 : Dy Teflon TLD discs was found not to change after isothermal annealing for 1 h in the temperature range 220--400 degrees C. The reusability of these TLD discs after two separate annealing treatments (240 degrees C and 400 degrees C, each 1 h) were studied for 20 cycles of use. The former annealing treatment resulted in a 12% loss in TL sensitivity after 20 cycles, mainly due to the increase in optical density of these discs. A decrease in the maximum temperature from 300 to 250 degrees C while clamped for read-out in the TLD reader has prevented any change in the optical density of these discs, and their TL sensitivity did not show any change after 20 cycles. The darkening of PTFE-based TL dosemeters was attributed to the reorientation of molecules in PTFE when the temperature during readout exceeds 250 degrees C; isothermal annealing at 400 degrees C restored their original colour. Their TL sensitivity decreased gradually with the number of cycles (over 15% in 20 cycles) after the 400 degrees C anneal, mainly because of the loss in TL sensitivity of the CaSO4 : Dy phosphor itself. This study has demonstrated that under controlled conditions, the Teflon TL dosemeters can be reused a number of times without any change in TL sensitivity.