The UV–visible absorption spectra of virgin and gamma ray-irradiated thermally treated and non-thermally treated CR-39 polymeric track detectors are measured using a UV–visible spectrometer. Annealing experiments are carried out on CR-39 polymer films exposed to60Co. The prime aim of this research is to find a relationship between the gamma ray dose and the corresponding changes in the optical properties of thermally treated CR-39 after being irradiated by gamma rays. These results will be of use for the optical representation of CR-39, as well as for investigations of the alterations of polymers caused by thermal annealing after exposure to gamma rays. From our analysis of the dependence of the absorbance on the annealing time and exposure dose, we find that the obtained results are consistent and systematic across all samples. The optical absorbance in the UV–visible range (190–450 nm) has a linear dependence on the gamma ray dose, as shown using thermally treated CR-39 detectors. Consequently, a semi-empirical relation between the wavelengths of UV– visible light and gamma ray dose at certain absorbance is established for the gamma ray dose estimation. This new technique is particularly very useful in measuring medium doses ranging from 200 to 1,000 kGy, where optical absorbance in non-annealed CR-39 is not well resolved because of superimposed absorbance. We also provide evidence that there is a considerable interaction effect between the gamma ray dose and temperature, which causes the CR-39 material to respond quite differently than when it is subjected to temperature alone. In this paper, the results provide a new approach to measuring the specific property changes induced by both thermal annealing and exposure to gamma rays, allowing a unique detection of gamma ray doses over the range 200 to 1000 kGy.