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KMID : 0857019990140010113
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Kosin Medical Journal
1999 Volume.14 No. 1 p.113 ~ p.122
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Improvement of Precision in TL Response with an Automated TLD Reader
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Kim Soo-Kil
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Abstract
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Background : Whilst TLD is one of the most convenient methods of dosimetry, it is a somewhat imprecise technique with several draw-backs. An increase in the variability of TLD dose measurements prompted a study of the precision of dose measurements with an automatic TLD reader. An optimum calibration procedures decreasing the effects of uncertainties should be determined.
Methods : The dependence of sensitivity of the TLD response to calibration techniques and repeated cycles of irradiation was investigated. Measurements were performed using a batch of twenty seven TLDs, chosen at random from the stock. They were irradiated to 1 Gy with a 6 MV photon beam placing the dosimeter inside a PMMA solid phantom under a thickness of 15mm (full build-up depth). TLD readings of the responses were measured directly in the TLD reader.
Results : When TLDs were selected homogeneously in the batch, our data indicate a large improvement of precision in TLD sensitivity, up to a factor of 2. When TLDs are calibrated with sensitivity factor in a TLD reader, precision levels of 3.7% and 1.4% of the sensitivities are for large batch and for a small batch respectively. Two different batches of TLD-100 showed a similar regression in sensitivity with increasing cycles of irradiations and readouts.
Conclusion : Two calibration techniques of homogenization and sensitivity factors have been examined in order to improve the precision of TLDs by elimination random error. An application of homogenization and sensitivity calibration techniques has allowed us to reach a standard deviation of less than 1.4% in the small batch. This study allows us to state that an application of both calibration techniques is the best one for obtaining better precision, reproducibility of TL signal.
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KEYWORD
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TLD sensitivity, homogeneity, calibration, precision
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