Mass energy absorption coefficients and energy responses of magnesium tetraborate dosimeters for 0.02 MeV to 20 MeV photons using Monte Carlo simulations

摘要

Thermoluminescence dosimeters containing boron, such as magnesium tetraborate (MgB4O7), are of interest because of their very high sensitivity, near tissue-equivalent absorption coefficients, low cost, easy handling, and very large linearity range for absorbed dose. Another important parameter that should be considered when working with thermoluminescent dosimeter (TLD) is the mass energy absorption coefficient (mu(en)/rho), which is a close approximation to the energy available for production of chemical, biological and other effects associated with exposure to ionizing radiation, therefore important in estimating dose in medical and health physics. In this study the mass energy absorption coefficients and energy responses of undoped and some doped magnesium tetraborates were calculated by Monte Carlo N-particle transport code for a range of photon energies between 20 keV and 20 MeV. The calculated parameters for MgB4O7, MgB4O7:Dy and MgB4O7:Dy,Li were evaluated in comparison with standard TLDs as Al2O3:C and TLD-100 (LiF: Mg, Ti) and ICRU tissue data. The influence of the dopant concentration in the MgB4O7 matrix on the energy dependence of TLD was also investigated. The analyses indicated a good agreement between the simulations and theoretical calculations. The mu(en)/rho and energy dependence of the materials are higher in the low energy range (E < 100 keV), which is related to the high probability of interaction between radiation and matter due to photoelectric absorption. With regard to the influence of dysprosium concentration in the MgB4O7 matrix an increase in the energy dependence of MgB4O7 for higher concentrations of dopants was observed in the low energy range.