# Photo-Stimulated Luminescence Approach for Effective Identification of Irradiated Fruit
## 3 Results and Discussion
### Inter-Laboratory Validation  
For the inter-laboratory test, eight types of fruit were analyzed, namely, two of fresh fruit, two of dried fruit and four of nuts: oranges, kiwis and raisins, which gave good results in the preliminary tests; dried figs, which replaced the dried dates not available in the market when the test was organized; hazelnuts, peanuts, pistachios and walnuts, successfully tested in previous studies (see par 1). The samples were analyzed by all four laboratories within the first seven weeks from irradiation; two laboratories repeated the analyses on the irradiated samples (different aliquots) some months after the irradiation. For fresh fruit (kiwis and oranges), the analyses were not repeated due to the deterioration during the storage. For pistachios irradiated with 1 kGy and hazelnuts, the analyses after 12 months could not be performed due to the product shortage. The results are reported in Figures 2-9 and in Tables 3 and 4. As can be seen in Figures 2-9, the data obtained in the first analysis by the four laboratories were generally in agreement, with small differences in the total counts due to the high uncertainty of the PSL measurement. In some cases, the data symbols overlapped due to the occurrence of very close values. One laboratory (Lab 3), however, showed systematically lower counts, likely due to a different sensitivity of the photomultiplier. Most of the products analyzed in this test showed different PSL sensitivities to radiation from those expected (Table 3). Kiwi and orange samples gave many intermediate responses showing much lower sensitivities compared to the results of the preliminary study. 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, irradiated hazelnut and walnut samples provided intermediate responses, not observed by [PERSON] et al. (2019) [20], especially at the lowest dose (25%). However, it must be considered that the dose used in that study (5 kGy) was higher. On the contrary, irradiated peanuts and pistachios gave total counts much higher than the ones previously obtained by [PERSON] et al. (2019) [20], despite the samples being irradiated with lower doses in the present work. In the case of pistachios, the higher levels of total counts (millions) might be due to the higher content of salt, which is, as known, a luminescent material very sensitive to ionizing radiation. Ultimately, these findings confirmed that different batches of the same fruit might show very different PSL results due to the reasons discussed above (see Section 3.1). In all the figures, with the exception of those relating to kiwis and oranges, the data obtained from analyses performed some months after irradiation by two laboratories are  
Figure 2: Results of the interlaboratory test for kiwi: (**a**) 0.5 kGy; (**b**) 1 kGy. also reported. As can be seen, despite showing an overall slight reduction in the total counts, these last PSL responses were concordant with those of the first analysis, thus indicating that the method could be applied on some products even a year after irradiation. As for the non-irradiated samples, in the majority of the cases, the results were negative; however, some intermediate results were obtained from the more sensitive matrices. For pistachio, also due to the salt, 43.75% of intermediate responses were obtained. Figure 3: Results of the interlaboratory test for orange: (**a**) 0.5 kGy; (**b**) orange 1 kGy. Figure 4: Results of the interlaboratory test for hazelnut: **(a)** 0.5 kGy; **(b)** 1 kGy. Figure 5: Results of the interlaboratory test for walnut: (**a**) 0.5 kGy; (**b**) 1 kGy. Figure 6: Results of the interlaboratory test for peanut: (**a**) 0.5 kGy; (**b**) 1 kGy. Figure 7: Results of the interlaboratory test for pistachio: **(a)** 0.5 kGy; **(b)** 1 kGy. Figure 8: Results of the interlaboratory test for dried fig: (**a**) 0.5 kGy; (**b**) 1 kGy.