Feasibility studies on the use of MgB4O7:Ce,Li-based films in 2D optically stimulated luminescence dosimetry

The objective of this work is to demonstrate the feasibility of 2D dosimetry using optically stimulated luminescent (OSL) films based on MgB4O7:Ce,Li and to identify current limitations of this material for this application. A small quantity of test films was produced and read using a laser-scanning OSL reader after irradiation. The OSL luminescence and dosimetric properties were also investigated. The results demonstrate the advantage of the fast luminescence lifetime associated with Ce3+ emission (similar to 31.5 ns) for 2D dosimetry based on laser-scanning readout, since it minimizes the need for pixel-bleeding correction. The signal could be bleached satisfactorily using a fluorescence lamp and a long-pass filter. A dose response curve could be obtained with pieces of films simulating steep dose gradients and the dose response obtained using the signal from the center of such piece films was linear up to 10 Gy. Short and long-term phosphorescence components were observed in the luminescence signal of MgB4O7:Ce,Li, but their contribution with respect to the fast OSL signal is relatively small and should decrease with increasing laser scan rates. In spite of the high OSL sensitivity and linear response, the main disadvantage of MgB4O7:Ce,Li at the moment is the lack of a better understanding of the processes responsible for the sensitivity changes and fading of the OSL signal. Although the bleaching applied here allowed to reduce the residual OSL signal to minimum levels (<1 mGy), the sensitivity of the films increased with previous dose. Fading has also been observed affecting the initial OSL intensity to a larger extent than the OSL area. This work also highlights the need to investigate in more detail the luminescence mechanisms of MgB4O7:Ce,Li to better understand how the performance of such films can be improved.