Thermoluminescence and electron spin resonance investigations of minerals for the detection of irradiated foods

Thermoluminescence (TL) measurements are used to detect irradiated foods. They are performed by investigating the minerals that contaminate certain products. Pure quartz, feldspars, and mineral mixtures, which are to be expected in foods, were examined for their radiation sensitivity, dose response, stability of signals, and changes of sensitivity induced by prior heating and prior irradiation. The sensitivity of all samples investigated varied over a range of 3 logs. Dose dependency and signal stability as a function of storage temperature and light exposure were similar for all samples. Prior heating and irradiation treatments significantly affected the sample sensitivity, which might be a reason for the high variability of results known from routine food control. The composition of the mixtures was analyzed by X-ray diffraction spectroscopy. It was found that almost all samples contained a significant amount of quartz in addition to minor amounts of feldspars. ESR measurements were performed to attempt to detect and identify the trapped charges responsible for TL. However, the differences in signal stability, dose dependency, and sensitivity imply that the ESR signals do not correlate with the presence of these charges.