The thermoluminescence of irradiated polyethylene and other polymers

Abstract

The thermoluminescence glow curves of various polymers have been observed in the temperature range 77 $^\circ$K to ice point after $^{60}$Co $\gamma$-irradiation, and a number of them are reproduced. A detailed study of polyethylene thermolummescence was made. The glow curve of this material in the absence of oxygen comprises three glow peaks, the $\alpha$, $\beta$, $\gamma$ peaks, whose luminescence intensities are proportional to irradiation dose for doses below 50 krads. The $\alpha$, $\beta$, $\gamma$ peaks all decay exponentially at constant temperature, and a study of the kinetics involved shows that all these peaks have the same activation energy at the lowest temperatures. At higher temperatures the $\beta$ and $\gamma$ peaks each show two different transition points, one in the visible region and one in the ultra-violet, which appear to be related to two of the known structural transitions of polyethylene. The glow curves of a variety of different polyethylenes were recorded. By comparison of these it was found that the relative heights of the $\alpha$, $\beta$, $\gamma$ peaks are dependent on the degree of crystallinity of the materials but that the normal chemical impurities present in commercial polyethylenes have no effect on their glow curves.