Detection of radiation treatment of spices and herbs of Asian origin using thermoluminescence of mineral contaminants

Eight types of spices and herbs or their mixtures of Asian origin have been investigated for detection of irradiation treatment using thermoluminescence (TL) of insoluble mineral contaminants adhering to the samples. These samples were irradiated by 60Co γ-rays (at absorbed doses 1, 5 and 10 kGy) as well as by 10-MeV electrons using an accelerator (at a dose of 5.4 kGy). The integrated TL intensities of glow curves from the irradiated samples were found to be much higher than those from unirradiated samples. These results were normalized by administering a re-irradiation γ-ray dose of 1 kGy and calculating the ratio of the integral of the first glow curve (of unirradiated or irradiated samples) to that of the second glow curve (after re-irradiation). This ratio is less than 0.02 for all unirradiated samples and more than 0.3 for all irradiated samples (more than 1 for samples irradiated to 5 kGy or at higher doses), thereby making discrimination between irradiated and unirradiated samples possible. If one also compares the different temperature regions of the glow-curve maxima of unirradiated and irradiated samples, unequivocal discrimination is achieved for those previously irradiated to doses equal to or greater than 1 kGy.