Determination of X-ray Effective Energy and Absorbed Dose Using CaF2:Mn and LiF:Mg, Ti Thermoluminescent Dosemeters

The results of the X-ray effective energy determination using the energy dependence of the response ratio of two thermoluminescent dosimeters are presented. CaF2:Mn dosimeters with a large, and LiF:Mg,Ti with a much lower energy dependence, were used. The calibration factors were obtained by irradiating the dosimeters with 137Cs gamma rays, and their energy dependences were measured with X-ray beams with the known effective energies and also with the 241Am gamma ray source. The measured values, i.e. the energy calibration curves, were compared with the calculation using the ratios of mass energy absorption coefficients and pertaining uncertainties were discussed. The results show that for determination of the effective energy of X-ray beams in the energy range from 33 to 116 keV effective energies it is possible to use CaF2/LiF pair of TLDs. For the evaluation of the effective energy it is possible simply to compare the measured results with the theoretical curve of the ratios of photon mass energy-absorption coefficients for CaF2 and LiF. For more precise determinations with the lower uncertainty (about ± 1.5 - 2 keV), the calibration curve obtained from the measured results should be used. Also, in addition to the determination of the X-ray effective energy, this method enables determination of absorbed dose in the specified material compensated for the systematic error due to the energy dependence inherent to each type of detector used. (author)