This study investigated the induction of DNA double-strand breaks (DSBs) in the hTERT-immortalized normal human diploid epithelial cells (RPE1-hTERT) continuously exposed to 6000 Bq/ml of tritiated water (HTO) and organically bound tritium (OBT). The relationship of the DSBs induction with the intracellular amount as well as the localization of tritium was also examined. Tritium-labeled thymidine (3H-Thy) and palmitic acid (3H-PA) were used as OBT. The average number of DSBs, which were indicated as co-localized foci of 53BP1 with phosphorylated H2AX, per cell was higher in the order of treatments with 3H-Thy, 3H-PA, and HTO. This order was consistent with that of tritium localization in the insoluble nuclear fraction but not with the intracellular amount of tritium. In addition to the intracellular amount of tritium, we showed that the subcellular localization of tritium is an important factor in cellular effects stimulated by DSBs.

A survey meter was developed to reliably detect and visualize surface contamination of suits and objects by α-nuclides in high γ/n-rays background radiation environment. The survey meter features a semi-opaque ZnS:Ag scintillator mounted directly onto a multi-anode photomultiplier tube (MA-PMT) and amplification circuits, ensuring output gain equalization for all channels. α-ray events induce localized light emission in thin-film scintillators. By directly mounting the scintillator, diffusion of light before reaching the MA-PMT is suppressed, concentrating it in just a few channels, thereby facilitating discrimination from background radiation. This design also enables clear visualization of the shape of surface contamination. The prototyped survey meter is capable of responding up to 2.1 × 107 cpm, with no γ-ray response even in high-radiation environments exceeding 1 Sv/h. In actual environments with high background radiation, contamination of ~1/100th of the surface contamination density limit of 4 Bq/cm2 could be reliably detected.

The radon (Rn) and thoron (Tn) concentrations and other environmental parameters were measured in the vicinity of active faults in two regions with different geology structure of Japan. The range of measured values was from 1.2 to 74 kBq m$^{-3}$, 1.1 to 38.9 kBq m$^{-3}$, 0% to 4.35%, and 2$\times $10$^{-13}$ to 4$\times $10$^{-11}$ m$^{2}$, for Rn, Tn, CO$_{2}$, and soil permeability, respectively. Significant differences in the measured parameters were observed, suggesting that Rn concentrations near faults are strongly influenced by geological structure and fault type. Based on statistical analysis, good correlations were found between Rn, Tn, and CO$_{2}$ (carried gas ) concentrations. It is planned to continue the study with measurements at a number of additional sites.

ApcMin/+ mouse was a model mouse for human familial adenomatous polyposis, and irradiation at an early age increases tumors in the small and large intestine. To study the effects of antioxidant administration on tumor incidence after continuous whole-body exposure to gamma rays, ApcMin/+ mice were exposed to a medium-dose-rate, 200 mGy/d, from postnatal Day 0 to 21 of age or a high-dose-rate of 0.65 Gy/min (total dose 4.2 Gy) on postnatal Day 7. The dams and pups were supplied with the N-acetylcysteine (NAC) in drinking water (7 g/L), from gestation Day 15 until weaning (21 days-old). A significant increase in the number of intestinal tumors were observed in ApcMin/+ mice irradiated with high dose-rate gamma rays as compared with the non-irradiated controls, but there was no significant difference in tumor counts between the non-irradiated controls and the medium-dose rate irradiation groups. NAC administration did not have any significant effect at least at this dose. These results suggest that the supplementation of anti-oxidant at the early stage of tumorigenesis does not suppress the formation of irradiation-induced small intestinal tumors.

The new electrolytic enrichment system with compact glass cell was designed. Three (Ni-Fe-Ni) electrodes are used, and electrolysis is carried out at a rate of 2.45 g per h with constant current density of 120 mA per cm2. This enrichment system allows the enrichment for small, limited sample volumes (e.g. Tritiated Water (HTO) recovered from air). With an initial water volume of 100 ml, the tritium enrichment factor of 7 within 2 days and a detection limit of 0.12 Bq per L can be obtained by Liquid Scintillation Counter (LSC) measurement for 1000 minutes, which is better than the direct measurement with 50 ml sample water using large vial. It is also possible to perform the high enrichment process. The initial sample volume of 700 ml enriched for 12 days by manual refilling yields a tritium enrichment factor of around 43 and detection limit of 0.02 Bq per L for 1000 minutes of LSC measurement.

In recent decades, technological advances have been made in the field of radiotherapy and with it the emergence of new dosimetric systems for their calibration and commissioning, among other uses. Such is the case of the measurement in the build-up region, where there is no charged-particle equilibrium, which is reflected in the increase in surface dose for patient treatments and potential skin toxicities as a secondary effect. This study utilizes optically stimulated dosemeters (nanoDot) and the radiochromic film (EBT3) to measure skin doses in patients with head and neck cancer who received radiotherapy. Accurately depicting 15 patients with different diagnoses from 3 linear accelerators using 3D, intensity modulated radiation therapy, or volumetric arc therapy/RapidArc technology, these results were compared with those calculated in the treatment planning system (TPS) and obtaining a percentage of variation for the EBT3 ranged from 0.30% to 6.15%, while that observed for the nanoDot was from 0.51% to 4.88%. This difference may be attributed to the reproducibility of placement in patients. Therefore, for clinical use, nanoDot dosemeters are a viable alternative for in vivo dosimetry where rapid validation of planning system results is required.

DNA mutations are one of the effects of radiation exposure. A large amount of radioactive materials was released into the environment from the Fukushima Daiichi Nuclear Power Plant after a major earthquake and tsunami. Wild animals and plants living in highly radiation-contaminated areas are constantly exposed to high doses of radiation, and concerns occur about its effects on their health and the next generations. As a pilot study, double-digest restriction site-associated DNA (ddRAD) sequencing was conducted to assess the incidence of mutations in wild large Japanese field mice collected from the evacuation area. The optimal combination of restriction enzymes, encompassing the functionally important coding regions, was selected using in silico analysis. These enzymes were used for ddRAD sequence analysis of females and their fetuses to evaluate mutation rates. The results indicated that no significant differences were observed in mutation rates between mothers and fetuses in the study areas.

A spectroscopy method of alpha particles with the track geometry parameters in CR-39 plastic nuclear track detectors is proposed. The relationship between the track registration sensitivity and incident angle of each etch pit is analyzed. The components of alpha particles emitted from radon, thoron and 241Am can be roughly separated when the etching level is not exceeded beyond the range in CR-39. This work aims at improving the dose assessment accuracy from exposure to indoor radon and thoron.

TEPCO planned the release of Advanced Liquid Processing System (ALPS)-treated water, which is decontaminated stagnated water by ALPS, to the Pacific Ocean in 2023 after diluting it more than a hundred times in accordance with the policy of the Japan government. Since the low level of I-129 can remain in ALPS-treated water, the background I-129 concentration in seaweed samples around 1F NPS before the release of ALPS-treated water was recorded in this study. The iodine in seaweed samples was extracted via TMAH alkali-dissolution, and the I-129 concentration was measured by 8900 Triple Quadrupole ICP-MS. The resulting I-129 concentration was <5.4 × 10-2 Bq/kg-wet (sargassum) and <2.7 × 10-2 Bq/kg-wet (laminaria), respectively.

This study aimed to determine the annual effective dose resulting from radon and thoron progeny inhalation. The levels of radon, thoron, and progeny were assessed in residences situated in the Doi Lo region of Chiang Mai, Thailand. Indoor radon and thoron concentrations were detected using passive discriminative detectors. Using a progeny deposition rate detector, this study evaluates radon and thoron progeny [equilibrium-equivalent radon concentration (EERC) for radon and equilibrium-equivalent thoron concentration (EETC) for thoron]. Data were collected from 44 dwellings between March and May 2020. The results found that indoor radon concentrations ranged from 17 to 118 Bq m-3, while thoron concentrations ranged from 12 to 72 Bq m-3. The radon progeny (EERC) ranged from 4 to 173 Bq m-3, whereas thoron progeny (EETC) ranged from 1 to 15 Bq m-3. The total annual effective dose received from radon and thoron progeny inhalation varied from 0.5 to 5 mSv y-1.

222Rn is recognized as a matter of international concern for human health risk. Because 220Rn as well as 222Rn coexist in the natural environment, thoron sometimes influences the experiment for radon measurement. It is important to measure radon and thoron separately to evaluate the risk of the exposure to 222Rn. As a discriminative measurement method for 222Rn and 220Rn, a simple technique with a single scintillation cell is well known. However, in recent years, the influence of atmospheric environment on the geometrical efficiency of the scintillation cell has not yet been investigated. In this study, environmental dependence of geometrical efficiency for the scintillation cell in 222Rn and 220Rn measurement was investigated using the Lucas type scintillation cell and Monte Carlo particle simulation. It was found that the influence of temperature and pressure on the geometrical efficiencies were larger than that of relative humidity.

This study summarises the responses to information on thyroid cancer, which possibly provoked misunderstanding and unfounded rumour, described in a letter issued by five former Japanese Prime Ministers on 27 January, 2022. Fukushima Medical University (FMU) implemented countermeasures and follow-up in three phases in response to the letter. In Phase 1, FMU shared scientific facts on the relationship between radiation exposure and thyroid cancer, as well as the response of FMU towards those who read the letter and were concerned about the description. Furthermore, FMU organised lectures and workshops to facilitate peer support among medical and non-medical staff, which were publicised through a newspaper article. In Phase 2, the peer support programme targeting patients with thyroid cancer was launched. In Phase 3, FMU participated in a TV programme to explain the medical aspects of thyroid cancer and the importance of providing peer support to patients with cancer, featuring individuals with experiences as medical staff and survivors.

As the International Commission on Radiological Protection lowers the equivalent dose limit for lens of the eye of radiation workers, the importance of radiation protection for the lens of the eye has been increased. In the case of poor working condition, such as high temperatures and humid environments at nuclear power plants, wearing an eye dosemeter near the worker's eye may interfere with work. In addition, it would not be reasonable for all workers to wear an eye dosemeter to evaluate the lens equivalent dose even in areas with an expected low exposure dose in the NPPs. Therefore, it is necessary to develop an indirect assessment method for lens equivalent dose. The purpose of this study is to develop an indirect assessment method for a lens equivalent dose using correlation factors between whole-body dose and eye. The correlation factors are calculated by MCNP simulation results.

Researchers have stressed that crops may absorb radioactive cesium (Cs) in the soil and translocate it to its edible parts. Therefore, a method was developed to suppress Cs absorption through high K fertilisation. However, this method is less effective for rice plants after ear emergence, thus demanding the application of a suppression method at this stage. In this study, we test whether immersion of ears in a Ca solution during its ripening period could suppress the translocation of Cs from roots to brown rice. The results show that the translocation of Cs absorbed from the hydroponic solution to brown rice is reduced based on the Ca concentration applied to the ears. In addition, differences in the inhibition of translocation were observed among the different Ca salts. In addition, the effect of immersion of ears in Ca solution on Cs translocation was effective at lower concentrations than that effective for K.

The concentration of the radioactive cesium (134Cs and 137Cs) in soils and in atmospheric fallouts has been measured at the Koriyama campus, Nihon University, after the Fukushima Dai-ichi Nuclear Power Plant accident for 13 y, from October 2011 till September 2023 and now ongoing. The concentration of them decreased very rapidly due to decontamination activities and weathering effects, with an environmental half-life of 1.21 and 2.82 y in soils, with those of 1.58 and 2.08 y in atmospheric fallouts for 134Cs and 137Cs, respectively. The behavior of the decrease was not simple, due to particles raised from the surface soil in wooded areas that had not been thoroughly decontaminated or that had been accumulated due to the re-release of radioactive cesium by trees after decontaminated activity.

To understand the regional properties of atmospheric 7Be and 210Pb concentrations at Hirosaki, aerosol samples were collected weekly for the investigation. Total suspended particles (TSP) concentration ranged from 0.14 to 1.19 mg m-3 with a mean value of 0.29 ± 0.08 mg m-3. The activity concentrations during the observation period have shown a similar trend between 7Be and 210Pb, comparable to reported studies. The activity concentrations of 7Be and 210Pb ranged from 0.46 to 4.94 mBq m-3 with an average of 2.22 mBq m-3 and from 0.26 to 1.29 mBq m-3 with an average of 0.64 mBq m-3, respectively. The relation between precipitation and radionuclide concentrations indicated that precipitation is an essential factor in the radionuclide removal process. The rainfall/snowfall had a significant impact on the deposition, and the process was greatly affected by the changes in the features of raindrops and snowflakes, such as intensity, shape, surface area, and falling speed.

Radioactive ruthenium may be accidentally released from spent nuclear fuel reprocessing plants to the surrounding environment. However, research on the chemical behavior of radioactive Ru in the environment is limited, and the complex chemical properties of this element complicate the application of extraction methods for the analyses of its chemical forms. To obtain basic information regarding the outcome of radioactive Ru in the environment, we investigated the changes in the form of stable Ru added to soil through X-ray absorption fine-structure (XAFS) analysis. This study uses ruthenium tetroxide (RuO4), ruthenium dioxide (RuO2), ruthenium nitrosyl nitrate (Ru(NO)(NO3)3) and ruthenium chloride (RuCl3) as test sources. These are added to ultrapure water, soil solution or fresh soil samples, which are analyzed using XAFS immediately or 5 days after Ru addition. The Ru K-edge X-ray absorption near edge structure spectra acquired immediately after Ru addition differed with respect to the source. The XAFS results suggest that RuO4 immediately changes to tetravalent form after deposition from air to soil. For RuCl3, the ionic structure in the vicinity of Ru is affected by the soil even if the valence does not change immediately. By contrast, RuO2 and Ru(NO)(NO3)3 are highly stable in soil. The results show that the chemical forms of RuO2 and Ru(NO)(NO3)3 added to the soil solution and soil are retained for 5 days, whereas those of RuCl3 and RuO4 are affected by the soil solution and soil within a short period. These results emphasize the need to focus on the chemical form of Ru deposits and the form change after Ru addition when investigating the environmental fate of radioactive Ru.

Applicability of biomimetic approach with simulation of plant uptake for assessment of radiocesium availability in soil was investigated. The soil spiked with 137Cs tracer was contacted with wicking material and copper-substituted prussian blue (Cu-PB), which simulate transpirationally induced mass flow and concentration gradient-induced diffusion of radiocesiumin the soil, respectively. Comparison of the removed 137Cs to the wick and the wick + Cu-PB from the soil during the contact period of 12 weeks suggested that the diffusion process has larger contribution than the mass flow process in radiocesium dynamics in root zone. The change of the removed rate of 137Cs from the soil was reflected that its availability decreased with the time elapsing and with subjecting repeated wet-dry treatment. The results suggest that the biomimetic approach can be applicable to the realistic evaluation of the availability of radiocesium in soil.

This study aimed to measure tritium (3H) concentrations in Thailand. Nationwide tap water samples were collected in July 2021. Rainwater samples were collected monthly during May-October 2020, April-October 2021, and February-March 2022 in Chonburi province and in Chiang Mai province during July-November 2021, January 2022, and March-June 2022. The measurements of 3H activity concentrations were conducted by Osaka Sangyo University (OSU) and were compared with measurements by the Thailand Institute of Nuclear Technology (TINT). The results from OSU and TINT showed that 3H concentrations in tap water were matched in the ranged from 0.08 ± 0.03 to 0.28 ± 0.04 Bq L-1, while those in rainwater samples collected from Chonburi province and Chiang Mai province are also matched in the ranged from 0.11 ± 0.02 to 0.21 ± 0.03 Bq L-1 and 0.19 ± 0.02 to 0.57 ± 0.04 Bq L-1, respectively. Our measured result suggests that 3H concentration in tap water and rainwater shows a similar relation depending on latitude.

Japan's first commercial nuclear fuel reprocessing plant is expected to release radioiodine into the atmosphere, and orchard grass plants grown in the vicinity of this plant may absorb this radioiodine. In this study, we investigated the mechanism underlying the absorption and volatilization of iodine in the leaves of orchard grass. Our findings suggest that iodine can be transferred from the leaves of this grass to the atmosphere via two routes: direct volatilization and absorption followed by volatilization. Previous studies on rice and oats also show that iodine can be absorbed by the roots and volatilized from the plant's body. Although orchard grass absorbs iodine via the leaves, the chemical form of volatilized iodine may differ from that absorbed via the roots. We applied a NaI solution to the leaves of orchard grass and analyzed the volatilized iodine. The experimental results showed that the iodine was volatilized as methyl iodide.

Radon and thoron exhalation rates from samples are estimated by the standard closed-loop technique using online radon monitors. Conventionally, the mass balance equation is formulated by considering the closed air volume of the sample chamber and the detector chamber put together. This model serves the purpose of estimating the radon/thoron exhalation rates for the prescribed pump flow rate of 1 L min-1 using RAD7 online monitor. The flow rate requirement is crucial for thoron measurement due to its short half-life. In the present work, an alternate model is proposed which simulates the dynamics of radon/thoron concentration dictated by the air entry and exit rate and brings out the effect of pump flow rate. This model is more of academic interest, where sample chamber and detector chamber are considered as two separate entities since they are separated by tubing. The mass balance equation is reformulated considering the air entry and exit in and out the individual chambers. The radon buildup in the sample chamber and detector chamber were treated separately by two coupled differential equations. The equations were numerically solved. The model reiterated the fact that the lower flow rates do not affect the buildup profile of relatively long-lived 222Rn (half-life 3.8 d) and its steady-state concentration attained in the closed air volume. However, experiments carried out for flow rates 0.3 and 0.5 L min-1 with RAD7 monitor using powdered granite sample with higher 226Ra and 232Th concentrations gave contradicting results. The radon effective removal rate was found to decrease with increase in flow rate from 0.3 to 1 L min-1. This issue was investigated, and it was speculated that the thoron interference problem might not be properly addressed for flow rates <1 L min-1. This was ascertained by observing the effective radon removal rate in the absence of thoron by conducting radon decay experiments with different flow rates. For the case of short-lived thoron (half-life 55 s), the model described the dynamics of thoron concentration in the closed loop and the steady-state concentrations attained in the detector and sample chamber. As expected, the model showed that due to decay losses during transit of thoron between the chambers, the steady-state concentrations attained in the chambers considerably differ from each other even for 1 L min-1 flow rate.