Dose dependence and thermal stability of the thermoluminescence emission in inorganic dust from mint and camomile

The inorganic phase extracted from mint and camomile samples obtained from commercial products in Mexico was selected according to different grain sizes and exposed to 60Co gamma radiation at different doses in the range 0.5–12 kGy. Thermoluminescence (TL) glow curves show a single broad peak, centred around 175 °C for prompt readouts. X-ray diffraction analysis indicates the inorganic dust is mainly composed by quartz, Na,K-feldspars and amphiboles, which use to be characterized by TL emissions associated to continuous distribution of trapping centres. The high fading of the TL signal during the first days of storage at room temperature can be related to the shallowest part of the distribution while the deepest traps originate the asymptotic behaviour for longer storage times. The TL intensity also increases significatively with the grain size, being linear with the absorbed dose at least up to 10 kGy.