Tracer experiments using radioisotope are powerful for the analysis of mineral uptake mechanisms in plant roots. In this study, we aimed to establish a quantitative method for measuring ion fluxes, i.e. net flux, influx, and efflux, which can be used to phenotyping of the mutants and natural variations. Consistency of obtained flux values for Mg²⁺ and Na⁺ was examined, and it was found that radioisotope absorption time of 20 s gave influx rate and an absorption time of more than 15 min gave net flux rate in rice roots. Furthermore, it was suggested that the longest possible radioisotope labeling time is necessary to increase the accuracy of the calculated efflux rate.

In Namie Town, Fukushima Prefecture, decontamination was carried out after the Fukushima Daiichi Nuclear Power Station accident. After remediation, the restricted residential area and the area preparing for the lifting of evacuation orders in the eastern part of Namie Town were lifted, and residents started returning home beginning on March 31, 2017. Various self-consumed crops, including homegrown agricultural crops and edible wild plants, were collected from the decontaminated fields and surrounding areas in 2019 and 2020. Activity concentrations of radiocaesium were measured in 181 samples of grain, potatoes, beans, vegetables, and fruits. Internal radiation exposure to humans from ingestion of the crops were calculated. Activity concentrations of ¹³⁷Cs in the homegrown agricultural crops ranged from 0.18 to 46 Bq kg⁻¹ fresh weight, which were all below the standard limit of 100 Bq kg⁻¹, while in the wild plants collected from around the fields ¹³⁷Cs ranged from 3.2 to 175 Bq kg⁻¹ fresh weight. The additional internal radiocaesium radiation dose for adult males in 2020 from ingestion of the various self-consumed crops was 0.032 mSv, accounting for approximately 5％ of the total additional internal and external radiation dose of 0.64 mSv due to the accident. The internal radiation dose from the intake of the homegrown agricultural crops, excluding wild plants, was 0.012 mSv, which was about 1/3 of that from the intake of both self-consumed crops and wild plants, and well below 1 mSv.

The concept of the wholesomeness of irradiated foods and previous studies on their toxicological safety in Europe, the U.S., and Japan over many years are described. In particular, the recent Japanese research on the safety of 2-alkylcyclobutanones (2-ACBs), which are specifically produced from lipids in foods by irradiation, was described in comparison with the previous studies in Europe and the United States. In the Japanese study, the test conditions were based on those of the previous studies in Europe and the U.S., and more stringent dosing conditions were used in the study. Genotoxicity tests on cells, including cells collected from animals, were all negative. On the other hand, screening tests using cultured cells showed that both 2-dDCB and 2-tDCB were positive for carcinogenic promotion activity, but more advanced tests using laboratory animals showed that all tests were negative. Based on the above, it can be concluded that no findings were obtained that would overturn the current opinion of international organizations regarding the safety of 2-ACBs in irradiated foods.

Food irradiation is prohibited in Japan except in potato sprout inhibition. However, Low-energy electron beams (Soft electron) of less than 1 MeV can be irradiated to food because these electrons adapt to the Atomic Energy Basic Law in Japan. In addition, absorbed dose of food in edible part must be set to under 0.10 Gy. We examined the absorbed dose of the edible part in eggs when sterilizing their shells with Soft electron. The irradiation conditions with these electron beams were evaluated by experimentation and Monte Carlo simulation. The resulting eggshell depth dose distributions indicate that the acceleration voltages between 80 and 200 kV were optimal for eggshell sterilization. It was also found that the acceleration voltages between 80 and 150 kV were suitable for the reduction of dosage to the egg’s edible tissues (≤0.10 Gy).

The control of bacterial spores resistant to sterilization is important for the microbiological safety and integrity of foods. Spores are considered sub-lethally injured during the sterilization process but remain alive and can germinate and grow under non-stress conditions during storage and distribution. In this study, Our research team aimed to establish a method to control such injured bacterial spores, the survival of injured Bacillus subtilis spores after heat or gamma-ray irradiation treatment was investigated. we compared the damage mechanisms of spores subjected to heat treatment and γ-ray irradiation and the developmental dynamics of the injured spores. This study found that γ-ray irradiation suppressed the generation of injured spores better than heat treatment.

In Japan, the number of patients treated with high-dose-rate brachytherapy is small per facility. The use of radiation equipment in RALS rooms is restricted to the acquisition of images required for high-dose-rate brachytherapy, which is a treatment purpose permitted by the current domestic law. The difficulty of installing dedicated CT scanner in RALS rooms has been a stumbling block to the widespread use of IGBTs.

Therefore, we conducted a questionnaire survey to determine the effective use of CT in RALS rooms. Because the RALS room CT is used for a limited number of hours and days, there were many requests for its use in CT imaging for treatment planning of external irradiation.

We concluded that the availability of RALS room CT, in addition to image acquisition for brachytherapy, will lead to the further spread of IGBTs in Japan.

For the purpose of utilizing the high voltage of a Geiger-Mueller (GM) tube survey meter for corona electric discharge experiment, the relation between the applied high voltage and corona discharge current for the different curvatures of the tips of the electrodes was examined both experimentally and theoretically. As a result, a new electric discharge phenomenon “triggered corona discharge” with the help of the usage of a leaf electroscope and tribo-electricity was found. Performance of science experiment such as corona electric discharge after radiation education experiments using the same GM tube survey meter is an effective use of the equipment and also helpful to understand “ionization phenomenon” from different perspectives of nuclear radiation, electric discharge and tribo-electricity.

Exposure to ionizing radiation results in the generation of reactive intermediate species such as cation radicals, anion radicals, and free radicals that can induce DNA damage. Epigallocatechin gallate (EGCG) and epicatechin (EC) are natural radiation-protective agents. The radiation protection effects of EGCG and EC against γ-ray and helium ion irradiation were studied using plasmid pUC118 and wild-type yeast. The percentage of strand breaks of pUC118 in the presence or absence of EGCG or EC were evaluated by agarose gel electrophoresis, and the protective effects of EGCG in yeast cells exposed to radiation were assessed by the survival ratio. The percentage of non-damaged plasmid DNA after irradiation increased in the presence of both EGCG and EC, indicating that these compounds can reduce DNA damage induced by γ-ray and helium ion irradiation. Our results show that EGCG and EC may provide effective protection against the harmful effects of ionizing radiation.

High effective atomic-numbers (Z_eff) and light outputs are required for gamma-ray scintillator, and we have developed novel materials such as Cs₂HfI₆ (Z_eff:58) and Ce³⁺-doped (Gd, La)₂Si₂O₇ (Z_eff:56) with high light outputs of approximately 64,000 photons/MeV and 50,000–60,000 photons/MeV, respectively.