Response of LiF thermoluminescent dosimeters to sup(99m)Tc gamma rays

The energy dependence of lithium fluoride ribbon dosimeters was investigated using sup(99m)Tc solution sources and a 60Co teletherapy source. The response per Roentgen for the 140 keV gamma rays was greater than that for the 1.17 and 1.33 MeV gamma rays by a factor of 1.084 +- 0.022. Of this 8% increase in response, 2% could be assigned to the absorption properties of lithium fluoride. Therefore the response per LiF rad to sup(99m)Tc photons divided by that for the 60Co photons was 1.064 +- 0.022. The effect of the rate of delivery of the radiation on the response was investigated and found to be negligible. Linear energy transfer effects are discussed as a plausible source of the residual 6% response increase. (author)