# Photo-Stimulated Luminescence Approach for Effective Identification of Irradiated Fruit
## 4 Conclusions  
In this work, the applicability of the PSL method CEN EN 13751 was verified for 15 types of fruit. Preliminary tests were conducted on 10 matrices of fresh and dried fruit: fresh kiwi, lemon, mango, orange, papaya, pineapple and tangerine, dried date, dried prune and raisin. An inter-comparative test was organized, in which four official control laboratories analyzed eight matrices, namely, kiwi, orange, dried fig, raisin, hazelnut, peanut, pistachio and walnut, carrying out a total of 384 tests, i.e., 256 on aliquots of irradiated samples and 128 on aliquots of non-irradiated samples. The results indicated a considerable difference in the radiation PSL sensitivity of the products. Very good results were obtained with dried fruits. In particular, irradiated pistachios, peanuts, dried figs and raisins gave very intense PSL signals with total counts up to millions, which confirmed the possibility of extending the applicability of the EN 1375 method to these matrices. For pistachios, the high levels of total counts (millions) could also be due to the content of salt, which is a luminescent material with very high sensitivity to ionizing radiation. The other products provided several non-positive results, mainly at the lower dose (0.5 kGy). Kiwi samples gave 50% of intermediate responses at 0.5 kGy and 12.5% at 1 kGy, with orange samples giving 87.5% at 0.5 kGy and 93.5% at 1 kGy. Additionally, the irradiated \begin{table}
\begin{tabular}{c c c c c c} \hline
**Fruit** & **Aliquot** & **Lab1** & **Lab2** & **Lab3** & **Lab4** \\ \hline kiwi 0.5 kGy & A & 4571 & 6760 & **1509** & 6257 \\  & B & 7427 & 2767 & 810 & 5083 \\  & C & 4700 & 3093 & 2120 & **67,091** \\  & D & **41,768** & **11,481** & **1904** & 5369 \\ \hline kiwi 1 kGy & A & 8517 & 7070 & 8019 & A \\  & B & 3779 & 7822 & **5503** & B \\  & C & 6225 & 5528 & **23,458** & C \\  & D & **19,146** & **18,850** & 21,408 & D \\ \hline orange 0.5 Gy & A & 891 & & & \\  & B & 1487 & & & \\  & C & 1284 & & & \\  & D & **7738** & & & \\ \hline orange 1 Gy & A & 3983 & 1086 & 3983 \\  & B & 2360 & 2522 & 2360 \\  & C & 1184 & **2022** & 1184 \\  & D & **12,390** & 1614 & **12,390** \\ \hline \end{tabular}
\end{table} 
Table 4: Inter-comparison PSL results obtained from oranges and kiwis: the values in bold were obtained from the peel close to the stem. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Fruit**} & \multicolumn{3}{c}{**0 kGy**} & \multicolumn{3}{c}{**0.5 kGy**} & \multicolumn{3}{c}{**1 kGy**} \\ \cline{2-9}  & **\% N** & **\% I** & **\% P** & **\% N** & **\% I** & **\% P** & **\% N** & **\% I** & **\% P** \\ \hline kiwis & 100 & 0 & 0 & 50 & 50 & 0 & 12.5 & 87.5 \\ oranges & 100 & 0 & 0 & 6.25 & 87.5 & 6.25 & 0 & 93.75 & 6.25 \\ dried figs & 75 & 25 & 0 & 0 & 0 & 100 & 0 & 0 & 100 \\ raisins & 93.75 & 6.25 & 0 & 0 & 0 & 100 & 0 & 0 & 100 \\ hazelnuts & 87.5 & 12.5 & 0 & 0 & 25 & 75 & 0 & 25 & 75 \\ walnuts & 93.75 & 6.25 & 0 & 0 & 25 & 75 & 0 & 0 & 100 \\ peanuts & 50 & 50 & 0 & 0 & 0 & 100 & 0 & 0 & 100 \\ pistachios & 56.25 & 43.75 & 0 & 0 & 0 & 100 & 0 & 0 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Inter-comparison results: percentages of negative, intermediate and positive PSL responses obtained from the samples irradiated at the different doses. hazelnut and walnut samples provided intermediate responses, especially at the lowest dose (25%). However, with the exception of pineapple, the absence of false negative results, in principle, would not prevent the application of the method to these products. It should be emphasized, in fact, that the intermediate result does not exclude the possibility of a correct classification of the sample because, as in the case of a positive response, the analytical protocol for the official control requires a second test with a confirmation method.