A preliminary investigation has been undertaken to study the impact of blending irradiated and unirradiated products on luminescence detection of irradiated herbs and spices. Samples of six products (oregano, basil, sage, paprika, ginger and cinnamon) were prepared combining irradiated material at three different concentration levels - 10%, 1% and 0.1% with unirradiated product under controlled conditions. The luminescence sensitivities of both the irradiated and unirradiated products were varied systematically, producing 9 sensitivity combinations at each of the three concentration levels. \ud \ud Samples were selected following an analysis of the sensitivity distributions of both PSL and TL from archival data sets at SURRC. Retained samples were combined under controlled conditions from materials believed to be unirradiated on the basis of previous PSL and TL analyses. Portions of these samples were irradiated to a 10 kGy gamma dose, and then recombined to produce the blended samples. Thus a total of 162 blended samples was produced for analysis. All samples were subjected to PSL screening measurements, and to TL analysis following standardised and validated procedures. The PSL analysis followed the EU standard method, which has been used in earlier MAFF supported interlaboratory trials. TL analyses were conducted relative to EN1788 and MAFF V27 protocols.\ud PSL screening results showed that all samples could be identified in either intermediate or positive bands in 10% concentration; the proportion detected falling to 68% of samples containing 1% irradiated material, and 33% of samples containing 0.1% concentrations. Signal strengths were generally higher for high sensitivity materials, as expected, although the low concentration blends showed high variations.\ud \ud TL analyses were evaluated relative to both the 1998 revised EN1788 criteria, currently undergoing consultation prior to adoption, and the 1996 criteria which form the current EN standard. The 1998 criteria, in keeping with MAFF V27 place emphasis on peak shapes, and recognise the possibility that glow ratios can be adversely affected by blending. When this is done 96% of samples with 10% irradiated material could be detected. Falling to 75% with 1% irradiated material, and 54% with 0.1% concentrations. These figures compare favourably with those based on strict interpretation of the current (1996) EN1788 criteria where only 84%, 35% and 15% of these blends would have been identified as irradiated at the three respective concentration levels. These overall results confirm the importance of using peak shape as a primary classification tool, where blended materials are encountered. However when taken to critical limits this can introduce subjective elements to classification. Glow 1 peak shapes could be shown to comprise mixtures of two signal components – the higher temperature forms associated with residual geological luminescence in the silicate assemblages used for analysis, and the lower temperature components associated with the irradiated fractions. The data sets broadly confirm the expected behaviour of these components as a function of the sensitivities and concentrations of the irradiated components and the unirradiated matrices.\ud \ud Overall it can be seen that standard methods are able to detect a significant portion of irradiated blends at concentrations above 1-10%. Below these concentrations there is a significant probability of non-detection, particularly for low sensitivity components
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