Effect of spectral shape in the relative efficiency of LiF: Mg,Ti exposed to 20 keV effective energy X-rays

This work is aimed at studying the possible dependence of the thermoluminescent response of LiF:Mg,Ti (TLD-100) on the X-ray beam spectrum. TLD-100 chips were irradiated with 20 keV effective energy filtered tungsten X-ray spectra, generated by a tube operated at 30, 40, 50, 60, 70 and 80 kV, and the response was measured relative to the response to 60Co gammas. TLDs were exposed in air at air kerma values between 50 and 300 mGy. Glow curve deconvolution into 8 peaks (3, 4, 5, 6a, 6b, 7, 8 and 9) was performed in order to evaluate the response of individual peaks and regions of interest in the glow curve. Results show that all peaks display a linear response, at least up to 200 mGy, for all X-ray beam qualities. The relative response of the total glow curve area, the dosimetric region (peaks 3 + 4 + 5) and peaks 5 to 9 is statistically constant for beams generated by voltages from 30 to 70 kV; for 80 kV, the values are lower by about 20% for peaks 8 and 9 and 9% for the rest. The relative efficiency for the glow curve area, the dosimetric region and peaks 5 (1.15, 1.10 and 1.13), peaks 8 and 9 (2.05 and 1.55) do not depend on the beam spectrum between 30 and 70 kV, while for 80 kV the efficiency is lower. For peaks 6a, 6b and 7, relative efficiencies (1.91, 2.94 and 2.60) are voltage independent.