Application of thin thermoluminescent dosimeters for gamma-ray heating measurements in high atomic number materials

A theoretical model was developed to calculate the ratio of absorbed gamma-ray doses in thermoluminescent dosimeters (TLDs) to that in the surrounding medium. This model is based on Burlin's general cavity ionization theory. The important features improved included taking into account the secondary electron scattering at the cavity-medium interface and subdividing primary electrons into three groups (photoelectrons, Compton-recoil electrons, and pair-production electrons). According to this theoretical model, the TERC/IV computer code was prepared for calculating absorbed dose ratios (f-ratios). This involved modifying the TERC/III code which was based upon Burlin's general cavity theory. A comparison of f-ratios from the TERM/IV code and other computer codes with that from experimental results were made for lead, copper, and aluminum surrounding stacks of 0.38 x 3.18 x 3.18 mm3 TLD-100 dosimeters irradiated using a 60Co gamma-ray source. Results of this research showed that the gamma-ray energy dependence can be alleviated by decreasing the TLD thickness. Comparisons of reactor spectrum dose-weighted f-ratios and gamma-ray source energy f-ratios were also performed. These results provide that if thin TLDs are calibrated using a properly selected gamma-ray source, e.g. 137Cs or 60Co, instead of the exact reactor gamma-ray spectrum, the error caused by employing thin TLDs to measure gamma-ray heating in these reactor regions could be reduced