Phototransfer thermoluminescence applied to the re-estimation of low dose levels of ionizing radiation for personnel dosimetry
Herr, Andrew Douglas.
Thesis (M.S.)--Georgetown University, 2010.; Includes bibliographical references.; Text (Electronic thesis) in PDF format. The characteristics and proven track record of thermoluminescence dosimetry (TLD) has made it one of the standards for personnel dosimetry. However, when TLD dosimeters are read, the majority of the information contained in them is lost. Dose re-estimation is the use of information left on the chips after the initial readout to estimate the dose received. This is useful in case the initial data are lost and for quality control purposes. Techniques in this field have focused on direct readouts of residual information contained on the chips and on using ultraviolet (UV) phototransfer to move information from inaccessible high-temperature traps to lower-temperature traps, the technique which was used in this work.; This study sought to improve upon earlier published re-estimation systems for LiF:Mg,Ti for use in personnel dosimetry systems. In order to do so, the parameters of a phototransfer thermoluminescence (PTTL) based re-estimation system were optimized to the extent possible without affecting the normal parameters of dosimeter readouts. Parameters of the PTTL system which were investigated for optimization included UV exposure, heating rate, and maximum readout temperature in an attempt to increase the net PTTL yield, the ratio of the PTTL signal minus the photoinduced thermoluminescence (PITL) background to the primary thermoluminescence signal, or (PTTL-PITL)/TL.; Based on the optimization results, the re-estimation protocol was then tested to determine the lowest dose level it could re-estimate and its accuracy. Re-estimation of doses as low as 2.44 mGy with better than ±20% accuracy was demonstrated with a lowest detectable dose of 1.05 mGy and the potential for extension to lower dose levels. Importantly, this protocol is easily implementable into a pre-existing LiF:Mg,Ti-based dosimetry system and is one of the simplest protocols which can achieve sub-10mGy re-estimation. No additional training is required and additional capital costs would be small to any existing dosimetry program. Thus, the protocol described herein improves the accuracy and ease of implementation of a re-estimation system for personnel dosimetry and can be adopted by any dosimetry program which requires improved dose re-estimation capabilities.
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