For proper environmental radiation monitoring, a method to simultaneously determine ambient dose equivalent rate and radioactivity concentration in the air by using a newly developed scintillation spectrometer, namely a CeBr₃ spectrometer was investigated. The performance of the proposed method, including energy dependence, angular dependence and the linearity of the spectrometer (i.e. the dose rate dependence of its response), was verified by a series of measurements, conducted according to the procedure of inter-comparison of detectors used for early warning network performed by the European Radiation Dosimetry Group (EURADOS). Measurement results show that the proposed method is suitable for environmental radiation monitoring purposes. After thorough tests, the investigation on obtaining activity concentration in air from the pulse height spectrum of γ-ray was demonstrated in the laboratory by using a point-like sealed ¹³³Ba source to simulate an artificial increase of ambient dose equivalent rate due to a radioactive cloud containing ¹³¹I and ¹³³Xe. The photon fluence rate was obtained from the pulse height spectrum by using the unfolding method, and the activity concentration in air for radionuclides of interest could be estimated from the obtained photon fluence rate by applying the conversion coefficient evaluated via a Monte Carlo calculation.

To confirm the contamination by radiocaesium, the concentrations of ¹³⁷Cs and ¹³³Cs of Japanese persimmon fruits and soils were measured in several orchards. Over 3 years, the ¹³⁷Cs concentration tended to decrease in many orchards, and there was no significant difference in the transfer factor. Additionally, 5 to 7 years after the accident, the effect of above-ground contamination seemed to be decreasing, and radiocaesium contamination by roots was likely negligible. The ¹³³Cs concentration in the soil was similar in all orchards; however, the ¹³³Cs concentration of fruits in one orchard was higher than that in the other orchards.

Plants absorb nutrients from both inorganic and organic components, but the use of organic components remains largely unknown due to their complexity. However, the mechanism of action of organic components has been elucidated through the detailed experimental results using isotope-labeled organic components, such as stable isotopes of carbon and nitrogen (¹³C and ¹⁵N) and radioisotopes of carbon (¹⁴C). In this article, we explained the properties, absorption and metabolism of organic compounds used by plants with the latest research reports, and the contribution of isotope tracer experiments to elucidate the effectiveness of organic compounds for plant growth.

Systematic measurement of tritium (T) concentration and oxygen, hydrogen stable isotope ratios (δ¹⁸O, δD) in precipitation is one of the most effective methods for estimating the environmental behavior. In this manuscript, various studies regarding T, δ¹⁸O and δD conducted in Japan in recent years (mainly since 2010) including our research were investigated. Consequently, the following matters have been mainly clarified. (1) The notable seasonal changes of T concentration in precipitation including “spring peak” was generally observed in each sampling area. (2) The tendency that “the higher the latitude of sampling area, the greater the concentration of T (i.e., latitude effect) was also generally observed. (3) It was confirmed that the T concentration in the precipitation temporarily increased due to Fukushima Daiichi Nuclear Power Plant accident in March 2011. However, the concentration of T has returned to the normal level after May of the year concerned. (4) The value of δ¹⁸O or δD alone did not show distinct seasonal characteristics, but d-excess (=δD−8×δ¹⁸O) calculated from these values was inclined to increase in winter. These results suggest that the precipitation environment in Japan may be strongly influenced by seasonal air masses.