Impact of dosimeter size on energy dependence: An experimental study on glass TLDs

Abstract

Practical Use of a dosimeter in a range of photon energies necessitates identification of radiation field as well as energy response of the dosimeter. Energy dependence of absorbed dose is caused by the unequal absorption properties of the material from various radiation energies, while the process of dosimeter response generation may also be energy dependent. The aim in this work is to measure the energy dependence of the response of sub-millimeter size glass silica fibre thermoluminescent dosimeters and to check whether there is a relation between energy dependence and the size of the dosimeter. Small size TLDs of capillary rod shape with the external/internal diameters of 870/544, 386/241 and 127/79 μm and 3 mm length prepared by a precision cutting process and appropriate preconditioning, were irradiated at various photon energies. Irradiations were performed in free-in-air condition at the secondary standard dosimetry laboratory (SSDL) of the Malaysian Nuclear Agency using X-ray narrow series spectra and gamma rays from a137Cs source as the reference photon energy. Theoretical energy dependence calculated by using the cavity theory was found in an acceptable agreement with the experimental results. The results show an increasing degree of energy dependence with the dosimeter size in the studied size range. This can be explained based on the low dimensions of the dosimeter that are comparable with the range of secondary electrons produced in the dosimeter, while luminescence efficiency may also play a role.