Energy dependence of TLD-900 dosimeters exposed to low energy X-rays

•The energy dependence of TLD-900 dosimeters to low energy X-rays is investigated.•Values of X-ray to gamma relative TL response are presented.•This work includes measurements as well as analytical and Monte Carlo calculations.•Interpretation considers (absorbed-dose)- and (intrinsic)- energy dependence.•Present results are useful for a proper correction of dose in clinical applications.

This work investigates the energy dependence of CaSO4:Dy (TLD-900) thermoluminescent dosimeters to low energy X-rays. Dosimeters were exposed to X-ray radiation qualities between 30 and 250 kVp for three air kerma values: 100, 250 and 500 mGy. The detector thermoluminescent response as a function of air kerma and the detector's relative kerma sensitivity with respect to 60Co as a function of effective energy were obtained. Monte Carlo and analytical calculations were also performed. A maximum relative kerma sensitivity of 12 is found for a 22 keV effective energy corresponding to the 50 kVp X-ray beam. Monte Carlo and analytical calculations accurately describe trends in the energy dependence curve as a function of photon energy though they predict lower values for the relative kerma sensitivity. Maximum difference is observed at the lowest energy measured (16 keV) where experimental data is 2.1 and 2.3 times greater than Monte Carlo and analytical calculations, respectively. The difference between measurements and Monte Carlo-calculated predictions is attributed to the intrinsic energy dependence of TLD-900. Values of intrinsic energy dependence estimated from the measured relative TL kerma sensitivity together with the MC and analytical calculated values of kerma energy dependence were found to be independent of beam quality in the region from 33 to 142 keV effective energies.