Graduate Thesis Or Dissertation
 

Efficacy of Reusing NanoDot OSL Dosimeters Using Optical Bleaching

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/41687k61c

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  • Use of optically stimulated luminescence detectors (OSLDs) is rapidly increasing in the area of in vivo dosimetry. OSLDs are relatively new to the market compared to their main competitor, thermoluminescent detectors (TLDs). Currently, not all characteristics of OSLDs have been fully investigated. Landauer’s nanoDot OSLDs were used in conjunction with their MicroStar reader to ascertain a nanoDot's ability to be reused. Annealing an OSLD signal with heat has been documented to work well. Due to the plastic casing on nanoDots, the high heat needed for annealing would destroy the OSLD. For this reason, nanoDots need to be bleached with light if they are to be reused. The strength of the light used was investigated by comparing the effects of bleaching with 15 W and 25 W lights. OSLDs use light to read out the signal, so each reading depletes some fraction of the signal. The rate of depletion per reading was looked at and compared to other data (Jursinic 2007). Most importantly, the effects of accumulated dose on the sensitivity of OSLDs were explored. This was done at different accumulated dose rates. Differences between the two wattages of light were found to play a minimal role on the total time needed for ample bleaching. The loss of signal per reading of the nanoDot was determined to be 0.04% per readout, which closely agrees with the Jursinic paper (2007). The sensitivity of the chip was shown to be stable up to 1080 cGy of accumulated dose. After this threshold point, the sensitivity of the OSLD decreases at a rate of 0.00456 cGy lost per cGy accumulated above 1080. This can be used to make a correction that can be added to the dose read out in nanoDots with accumulated doses above 1080 cGy. The use of the correction relies on the assumption that different OSLDs behave similarly under different accumulated dose rates and that differences in manufacturing between nanoDots are small enough to be negligible.
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