A study on CaSO4:Dy TLDs was undertaken to confirm the validity of the annealing treatment (400 degrees C, 1 h) for its re-use. The temperature range of the study was from 230 degrees C to 700 degrees C. The effect of thermal treatments on the TL sensitivity and glow curve structure showed that the lattice of CaSO4:Dy is sensitive to thermal treatment in the temperature range from 350 degrees C to 425 degrees C. It is also seen that both TL sensitivity and peak height ratio (dosimetric peak at 240 degrees C to low temperature satellite peak at 140 degrees C) reduces with an increasing number of annealing cycles in the temperature range from 350 degrees C to 425 degrees C. No significant change was observed in TL emission and ESR spectrum of the phosphor. The study shows that the annealing treatment in the temperature range from 600 degrees C to 650 degrees C could be the best alternative for annealing and re-use of CaSO4:Dy phosphor or a temperature below 350 degrees C for Teflon embedded dosemeters.

In view of the introduction of International Commission on Radiation Units and Measurements operational quantities Hp(10) and Hp(0.07), defined for individual monitoring, it became necessary to develop an algorithm that gives direct response of the dosemeter in terms of the operational quantities. Hence, for this purpose and also to improve the accuracy in dose estimation especially in the mixed fields of X ray and gamma, an algorithm was developed based on higher-order polynomial fit of the data points generated from the dose-response of discs under different filter regions of the present TL dosemeter system for known delivered doses. Study on the response of the BARC TL dosemeter system based on CaSO(4):Dy Teflon thermoluminescence dosemeter discs in the mixed fields of X and gamma radiation was carried out to ensure that the accuracies are within the prescribed limits recommended by the international organisations. The prevalent algorithm, based on the ratios of the disc response under various filters regions of the dosemeter to pure photons, was tested for different proportion of two radiations in case of mixed field dosimetry. It was found that the accuracy for few fields is beyond the acceptable limit in case of prevalent algorithm. The new proposed algorithm was also tested in mixed fields of photon fields and to pure photon fields of varied angles. It was found that the response of the dosemeter in mixed fields of photons and its angular response are satisfactory. The new algorithm can be used to record and report the personal dose in terms of Hp(10) as per the international recommendation for the present TL dosemeter.

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The effective implementation of a comprehensive quality assurance (QA) programme in any individual monitoring service plays a key role in attaining and sustaining the level of performance at par with international standards. In India, individual monitoring of more than 120 000 radiation workers is provided through 16 laboratories using a CaSO4:Dy based thermoluminescence dosimetry (TLD) badge system. In such a wide-spread programme, the harmonization of procedures and regular QA check on the dosimetry system are utmost important to ensure the uniform standard of accuracy and reliability of the service. This paper discusses some aspects of the QA programme implemented at different stages of the TLD monitoring system and provides the results of the performance test of monitoring laboratories.

The objective of this paper is to estimate the combined uncertainty in the measurement of dose equivalent at laboratory level using CaSO4:Dy-based thermoluminescent dosemeter badge system by including variations in the components of the system. The variability of performance of the system is analysed using random effects one way analysis of variance model. The model enables estimation of the overall variance of the performance of the sampled population. The population in the study comprises all possible indicated dose equivalents on irradiation of dosemeters to a specific dose equivalent and radiation quality. Coefficient of variation and combined uncertainty at 95% level of confidence in the measurement of Hp(10) due to S-Cs radiation quality are found to be 6.6 and 14.3%, respectively, at the dose level of 5.31 mSv. The above parameters in the measurement of in-use quantity, i.e. whole body dose or photon dose equivalent are found to be 7.4 and 16.4%, respectively. The performance of the monitoring system on relative response has been observed to be satisfactory. Various factors affecting the variability of performance of the system are identified for further improvement in coefficient of variation.