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

Abstract

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 (μ_en/ρ), 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 μ_en/ρ 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.

Keywords: Energy response; Mass energy absorption coefficient; Monte Carlo; Thermoluminescence dosimetry.