Preliminary Investigation into the regeneration of luminescent signal in nanoDot OSLDs.

PURPOSE Reuse of optically stimulated luminescent dosimeters (OSLDs) has been suggested in prior works by using a light source to erase the dosimeter's signal (optical bleaching) and recharacterizing the dosimeter's sensitivity based on its dose history. However, depending on the wavelength of the bleaching source and the dosimeter's dose history this may be problematic due to the presence of deep dosimetric traps and the phototransfer mechanism observed in Al2 O3 . In this work we examine the regeneration of signal in OSL nanoDots, with prior irradiation history, following their bleaching from a light source containing blue wavelengths. METHODS Irradiations were performed on 33 nanoDots at a dose range of 5-3000 cGy using 6 MV and 1000-3000 cGy using 220 kV x rays, with three nanoDots irradiated at each dose value. Following their irradiation, nanoDots were bleached using blue light for a period of 1 h. The postbleached signal in nanoDots was measured over a 27-day period to track any changes in their measured signal due to the migration of charge carriers from deep dosimetric traps to shallower traps of the dosimeter. RESULTS The growth extent and growth rate observed in bleached nanoDots were observed to be dependent on the dosimeter's accumulated dose history and energy of the radiation source. The 12 nanoDots with prior irradiation history of 500, 1000, 2000, and 3000 cGy from 6 MV x rays exhibit an increase in measured signal that range from 220 to 5229 PMT counts when measured the first day postbleaching to 408-8710 PMT counts when measured on the 27th day postbleaching, which may be substantial depending on the application regarding the dosimeter's reuse. CONCLUSION These findings caution against the reuse and optical bleaching of nanoDots with prior irradiation history exceeding 100 cGy and demonstrate an energy, accumulated dose, and time dependence in the regeneration of signal in postbleached nanoDots with prior irradiation history.