Advanced Spectroscopic Investigation Of Color Centers In Lif Crystals Exposed To 6 Mv X-Ray Clinical Beams

Polished LiF crystals were irradiated by using 6MV X-rays produced by a clinical linear accelerator. The irradiation doses (absorbed dose to water) covered the 1-100 Gy range. Optical absorption spectra show stable formation of primary F defects, while the M absorption band, located at around 450nm and due to the aggregate F-2 and F-3(+) color centers, was not detectable. By using the Smakula formula, a concentration of 1.2 x 10(16) and 1.9 x 10(16) F/cm(-3) was obtained for LiF crystals irradiated at 50 and 100 Gy, respectively. Under argon laser excitation at 457.9 nm, photoluminescence spectra of the irradiated LiF crystals exhibited the characteristic F-2 and F-3(+) broad emission bands. The integrated photoluminescence intensity of F-2 and F-3(+) defects as a function of the irradiation dose shows a linear behaviour in the investigated dose range. This result is confirmed by the measurements of the F-2 and F-3(+) integrated photoluminescence intensity performed by using a conventional fluorescence optical microscope under blue lamp illumination. These preliminary experimental results are encouraging for further investigation of nominally pure LiF crystals as clinical dosimeters based on optical reading of photoluminescence emitted by radiation-induced color centers.