Temporal Signal Stability of KCl:Eu2+ Storage Phosphor Dosimeters
Z XIAO*, H Chen, R Hansel, H Li, Washington University School of Medicine, St. Louis, MOTU-A-BRB-2 Tuesday 8:00:00 AM - 9:55:00 AM Room: Ballroom B
Purpose: It is known that the PSL (photo-stimulated luminescence) signal fades with time after x-ray irradiation and eventually reaches a plateau. The purpose of this work is to determine whether x-ray generated electrons stored in non-dosimetric shallow traps can be liberated prior to dose readout. If so, we would achieve a rapid signal stabilization so the wait time could be shortened to, for example, one hour or less.
Methods: Pellet-style KCl: Eu2+ dosimeters were fabricated in-house for this study. PSL signal stability after x-ray irradiation was studied by interfering with a thermal annealing and optical annealing with near infra-red light, respectively prior to dosimetric readout.
Results: Without optical annealing, PSL faded with time at a rate of 13.6%/hr for the first 2 hrs and 6%/hr for the next 3 hrs after irradiation and eventually reached a fading rate of about 0.5%/hr after 12 hrs. PSL intensity decreased with increasing NIR optical annealing time; however, there was only marginal improvement in the PSL stabilization rate, indicating that the shallow electron traps that are responsible for the fast-fading for the first few hours were not efficiently emptied. 15-minute thermal annealing treatments at either 60 or 70°C stabilized the PSL to a slow decay rate of approximately 0.4%/hr over a time period of 24 hrs post irradiation. Moreover, 90% of PSL sensitivity can be retained. More stable PSL signal, 0.18%/hr and 0.08%/hr decay rate for 90 and 120°C thermal annealing, respectively, can be achieved at the expense of PSL sensitivity.
Conclusions: Thermal annealing immediately after x-ray irradiation is an effective way to remove electrons stored in the shallow traps. This study is expected to guide the future design of storage phosphor dosimeter readers, which could incorporate a thermal annealing pre-read cycle. As a result, a long wait time would be avoided.