[en] In India, more than 100,000 TLD cards are currently in use for routine monitoring of about 30,000 radiation workers. Stringent quality assurance parameters are introduced at three levels during the production of TLD cards. (1) CaSO₄:Dy TLD phosphor of grain size <75 μm having a sensitivity in the production batches (each of 600 g) within ± 5%; (2) CaSO₄:Dy Teflon TLD discs showing a sensitivity within ± 8%; and (3) TLD cards having a sensitivity within ± 12%. Significant batch to batch variations were observed for the same preparation procedure and starting materials. The glow peak height ratio of the main glow peak and lower temperature satellite peaks was found to vary by more than a factor of 4 while the TL sensitivity was found to seldom vary by more than 20%. The variation of glow peak height ratio with grain size was more pronounced in some batches while no significant change was observed in some other batches. This was attributed to the variation in the extent of diffusion of impurities into the lattice during preparation of the phosphor. Testing of each batch of phosphor in the range of grain sizes that were as close as possible to those actually used was found to be crucial and a necessary parameter. Important parameters for keeping the sensitivity of different batches of TLDs the same are the availability of bulk CaSO₄.2H₂O powder having trace impurities within specified limits, constant vigil on the method of phosphor preparation, detailed testing for the selection of phosphor batches, and sample testing of TLD discs and cards. (author)

[en] The response of the CaSO₄:Dy, Teflon based TLD badges was studied on the semi Automatic TLD Badge reader using clamped heating in the dose range of 0.06 mSv to 10 Sv of ¹³⁷Cs -⁶⁰Co γ-rays. It was found that the response was within ± 10% up to the dose of 5 Sv. The changes in the glow curve were observed at the doses in excess of 3 Sv. The flattening of the glow curve was pronounced at 5 Sv onwards. Above 5 Sv dose, the response was found to be sub-linear in the range of study. Thus, the upper limit of measurable dose is estimated to be 5 Sv, much higher than the normal range of individual monitoring. Methodology for measurement of low dose of the order of few tens of microsivert is also discussed. (author)

[en] Performance of CaSO₄: Dy teflon TLD discs based personnel monitoring badge was evaluated for estimation of personal dose equivalents Hp (10) and Hp (0.07) in photon fields as per the recommended criteria of testing set by international bodies. Mixed fields of low energy and high energy photons were accordingly included for testing. Response of discs under metal filter in the badge (D1) without any correction factor for energy dependence was found satisfactory to measure the Hp(10) for photons of effective energy above 40 keV and specially for mixed fields of photons of low and high energy. Readout of disc D1 under metal filter is sufficient for recording and reporting Hp(10) even in diagnostic x-ray departments where TLD badge is worn under lead apron, as the effective energy of x-ray after passing through the lead apron is always more than 40 keV for the tube potentials as low as 60 KVp. In situations where the badge is worn over lead apron or lead apron is not used during exposures from low energy x-rays, response of discs under plastic filter and open window could be used for the estimation of Hp(0.07). This situation will remain unambiguous for ratios of D1/D2 smaller than 0.14. Hp(10) in such cases could be arrived at by multiplying Hp(0.07) value by a correction factor obtained from the ratio of conversion coefficients for Hp(10) and Hp(0.07) for the encountered effective x-ray energy estimated from the ratio of D1/D2. In mixed fields of high energy gamma rays (¹³⁷Cs/⁶⁰Co) and beta radiation, beta doses should be evaluated as per the prevalent method and this should be added to Hp(10) recorded from readout of discs under metal filter (D1) for reporting Hp(0.07). (author)

[en] Residual TL (RTL) in different reading cycles for CaSO₄ : Dy Teflon TLD Badges has been studied using semi automatic TLD badge reader based on N₂ gas heating for the exposure range from a few μGy (50) to a few Gy (10.23) of ⁶⁰Co/¹³⁷Cs and the possibility of re-estimation of dose using RTL was investigated. The RTL was found to be more appropriate for re-estimation of doses up to 3Gy. The RTL was found to be function of flow rate of the gas. The standard annealing protocol of 4h at 230 deg C was also studied after lst, 2nd and 3rd read out and was found to be adequate only up to a dose of 0. 06Gy above which the background of the card after annealing was found to be increasing with dose and was a function of number of reading cycles. (author)

[en] This paper discusses the performance of the Blind Test carried out in the last five years at Kaiga Generating Station. The analysis of the results by the method of ANSI as well as trumpet curve for both TLD and DRD, used for monitoring, has been presented. The excellent performance achieved over the period shows that the present system is capable of making measurements with high level of accuracy and consistency by the standards prescribed by the international bodies. Good performance of both TLD and DRD indicates the scope of revision of TLD-DRD discrepancy identification criteria. The paper provides a new method for identification of TLD-DRD dose discrepancy, on the basis of results. (author)

[en] Individual monitoring is one of the most important aspects of a radiation protection programme. In India, an official and centralized personnel monitoring service to radiation workers started in 1952. With the indigenous development of a TLD badge system in 1975 at Bhabha Atomic Research Centre, decentralization of monitoring service was initiated. At present, about 40,000 radiation workers are monitored using this system through twelve TLD units located in different parts of the country, including a private accredited laboratory. Regulatory and other inspecting bodies have often asked outstation TLD units to produce a duly approved document on the procedures being practiced for the assessment of personal doses. A need for such a document has also been felt to ensure the uniformity in processing of dosemeters, recording and reporting of doses by different TLD units and to provide guidelines regarding the infrastructure requirement. This document in the form of a handbook has been prepared to cater to the above needs. The handbook is expected to provide necessary guidelines not only to the newcomers/ forthcoming units and the existing laboratories but also to help the regulators, inspectors and assessors. (author)

[en] PC based auto TLD reader system has been developed recently for the prevalent TLD cards based on CaSO₄:Dy teflon. The improvements made in design of the reader and the subsequent advantages, it offers, have been discussed. It offers better accuracy in low dose estimation apart from providing permanent records and saving time and manpower. The glow curve recorded for each disc can be analyzed at any time as per the need. The benefits of the accompanying software are also discussed. (author)

[en] In India, personnel monitoring of radiation workers for X-, beta- and gamma-radiation is carried out using three element CaSO₄:Dy Teflon disc based TLD card. TLD cards are manufactured from different production batches of CaSO₄:Dy phosphor. Although care is taken to maintain the uniformity in sensitivity of powder batch, still variation in sensitivity of cards/disc has been observed. Spread of sensitivity in a batch of TLD cards depends upon various factors including variation in amount of phosphor in the disc, homogeneity of phosphor Teflon mixture, compacting pressure applied to discs, incorporation of impurities in the discs, etc. Further, long term dosimetry performance of the cards depends on quality of Nickel platting on the cards, proper clipping of the discs in the card plate. All these factors are specifically checked while testing new TLD cards. The paper presents the procedure adopted and results of testing of 10000 TLD cards procured recently. The input from the above procedure of testing was given to the supplier to review the production process and achieve high quality and minimize the sensitivity variation. Further this testing procedure enhances the confidence in the use of TLD cards for personnel monitoring

[en] This paper is focussed on the results obtained in the last three external quality assurance cycles conducted for the TLD units at six nuclear power stations and the various measures taken for the improvement of the quality and reliability of the personnel monitoring service conducted by these units. In addition to the ANSI criteria the trumpet curve analysis method was introduced for testing the performance of the TLD units. The performance of all the units had been well within the permitted tolerance level and for some units highly satisfactory performance with a tolerance level value below 0.1 was observed. A constant interaction with concerned implementing units and efforts of the TLD units in implementing new suggested measures resulted in bringing down the number of TLD-DRD discrepancy cases by about a factor of 2 in the past four years. (author)

[en] Lead Apron as individual shielding is used primarily in Radiology for protection of personnel against ionizing radiation. Occasionally lead apron of specific design are being used in reactor environment where one-sided radiation fields are encountered. The protection provided by Apron has been evaluated using personnel dosimeter. Based on the results the utility of lead Apron has been discussed in view of ALARA. The paper discusses the results and the recommendations for use in reactor environment. (author)