The energy dependence of BaSO4: Eu nanophosphors for thermoluminescence dosimetry of orthovoltage X-rays and low energy protons

Abstract

Accurate dosimetry of ionizing radiation requires careful consideration of the absorption properties of the dosimeter material in question. The energy dependence of a dosimeter signifies the variation in dosimeter signal per absorbed dose to water with radiation type and energy. The nanophosphor BaSO4: Eu is a radiosensitive material for thermoluminescence (TL) dosimetry. However, the energy dependence of the material for orthovoltage X-rays and low energy protons has not previously been investigated, which is the purpose of the current work. We irradiated BaSO4 doped with 0.5 mol% of europium with 100, 160 and 225 kV X-rays and 2 and 9 MeV protons. Co-60 γ-rays were used for reference irradiation. Absolute dose-to-water dosimetry was ensured with an ion chamber. Delivered calibration doses ranged from 0.01 to about 2 Gy. TL output was measured at a heating rate of 5 K/s, where the maximum intensity of the dominant glow peak at about 212 °C defined the dosimeter signal. The signal was found to increase linearly with absorbed dose for both radiation types and all energies. The measured energy response, defined as the ratio of the TL calibration slope at a given radiation type and energy to that following Co-60 γ-irradiation, varied between 47 and 62 for X-rays and between 0.41 and 0.61 for protons. Theoretical modelling of the energy response and proton detector efficiency gave similar trends. The findings show that BaSO4 is an energy-dependent material, especially for X-rays, but may still prove valuable for accurate dose determination if the dosimeter is calibrated in the user beam.