## 3 Results and Discussion
The largest signal increase was observed in the vacuum-stored AAT samples placed at RT with light exposure (see Figure 4B) in comparison to those without light exposure (refer to Figure 4A,C,D),  
Figure 4: Comparison of the effects of repeated L(+)-ascorbic acid (AAT) or water treatments (WT) and X-ray irradiations (IR) to the ESR peak-to-peak intensities in samples stored under four different location conditions, as described in steps 1–4 of Experiment 1. Each point of the AAT samples in the plot was calculated as the average of three samples and subtracted from the WT control sample. The error bars on the AAT samples were obtained as the standard deviation of three samples, while one standard deviation was used for the WT sample. Note that “soon after AAT1” and “soon after IR1” were performed on the same day, as well as the “7d after IR1”, “soon after AAT2”, and “soon after IR2”. The notations RT and LT correspond to room temperature (20 \({}^{\circ}\)C) and low temperature (\(-\)20 \({}^{\circ}\)C), respectively. The with (w/) and without (w/o) light imply that the samples were placed in ambient illumination and in darkness, respectively. which may be related to the sensitivity of fingernails to ambient illumination [1; 2]. Generally, the WT samples, on the other hand, were found to be stable with no drastic signal growth under vacuum storage, but the combination with the LT condition was able to achieve a more stable signal with very minimal (almost zero) signal changes. For completeness, the second treatment (AAT2 or WT2) and irradiation (IR2) procedures (steps 3-4 of Experiment 1) were applied in the same way and in the same sets of samples, also shown in Figure 4. The radiation sensitivity of the AAT samples changed with repeated treatment and irradiation. The absolute signal intensities were significantly reduced (>50%) for all AAT samples. Although it can also be noticed that the increase rate of the signal regrowth was slower with improved signal stability in comparison to the first treatment and irradiation, the reduction of sensitivity to radiation still possesses a major disadvantage. The signal intensities of the vacuum-stored AAT samples at RT with light exposure also continued to increase during storage time. In contrast, the continuous signal regrowth with post-irradiation storage time and concomitant changes to the radiation sensitivity was not observed in the WT samples after repeated treatment and exposure to radiation, as also shown in Figure 4.  
To summarize the obtained results in Experiment 1, we found that all the samples following AAT exhibited an increase in their signal intensities. This increase in the ESR peak-to-peak intensity suggests that the use of AA for sample treatment may provide an enhancement effect to the radiation-dependent signal of interest needed for reliable ESR fingernail dosimetry. While the AA was also observed to be very unstable at ambient conditions (i.e., temperature, humidity, and light), the enhanced intensity due to the signal generated by the AA treatment was significantly dependent upon the storage conditions of the samples. With such well-controlled storage conditions, the degree of variability in the enhancement effect caused by the AA can be used to estimate the absorbed dose in fingernails. According to the experimental results obtained in Experiment 1, the growth and stability of the ESR signal intensity in AAT samples were dependent upon the storage and location conditions, with the most variable dependence observed in samples with light exposure. To understand the behavior of the signal growth in AAT samples that were exposed to light with a UV component, we considered initially examining the effect of UV exposure in unirradiated and untreated fingernail samples. Figure 5 shows the time evolution of the ESR signals obtained from five different sample sets following exposure to UV for 30 min, as described in step 1 of Experiment 2 (see Figure 2). Note that each sample set was exposed to UV separately and stored under various storage conditions.