The airborne dispersion of 223Ra and its descendent nuclides from an aqueous 223Ra2+ solution containing sodium chloride/citrate was investigated. The dispersion of 223Ra was not detected, and γ-rays of 211Pb and 211Bi caused by the 219Rn dispersion were observed by means of γ-ray spectrometry. The detected radioactivity of 211Pb was found to decrease as the inner diameter of the vessel containing the 223Ra solution was decreased because of the decreasing surface area of the solution exposed to the air. The dispersal rate of 219Rn from the aqueous solution was determined by the ratio of the number of the dispersed 219Rn atoms calculated from the detected radioactivity of 211Pb on the samples. The values at room temperature were in the range of (1.6 ± 0.1) × 10−3–(2.0 ± 0.1) × 10−2. These rates were found to decrease with decreasing exposed surface area of the vessel used.
Monthly fieldwork was conducted in the paddies of Fukushima Prefecture in 2016, to obtain samples of the paddy soil and rice plants. The monthly change in the radioactivity concentrations of 137Cs, 134Cs, and 40K of the samples was investigated, using a germanium semiconductor detector. Three-phase transfer factors (TFs) of 137Cs from the paddy soil to the roots (TF1), from the roots to the leaves (TF2), and from the leaves to the ears (TF3) of rice plants were calculated. The results showed that the radioactivity concentration of 137Cs and 134Cs in the paddy soil varied seasonally, while the concentration of 40K showed an almost opposite seasonal change compared to 137Cs and 134Cs. The radioactivity concentration of 137Cs and 134Cs in the roots increased 60 days after planting, while the concentration of 40K decreased. Furthermore, the radioactivity concentration of 137Cs, 134Cs, and 40K in the leaves and ears decreased over time. Correlations of the TFs of 137Cs with the radioactivity concentration of 40K suggested that 137Cs and 40K were competitively absorbed by the roots, however, they were transported to the leaves and ears in the same manner. In conclusion, the transportation of 137Cs (TF2 and TF3) in rice plants was high despite the low absorption of 137Cs (TF1) in the early stage of rice growth. Therefore, it is recommended that the potassium concentration in the paddy should be high during the early stage of growth to prevent radioactive cesium contamination.
In the present study, we reported the investigation of radiocesium migration from steep slope surrounding catchment to water body based on the radiocesium distribution and soil to sediment ratio. It was confirmed that the radiocesium was derived from the Fukushima accident by considering the 134Cs to 137Cs ratio corrected to the released day which is about 1. We found the higher radiocesium inventory in higher elevation area and steep slope forest catchment, revealing the atmospheric dry initial deposition-derived radiocesium and high retention of the forest zone. The radiocesium distribution data revealed that the radiocesium migrated more from the transition zone to the water body than from forest catchment, and accumulated in the deeper layer of sediment. The lower value of 137Cs soil to sediment ratio provided an evidence of radiocesium migration from the catchment and its accumulation in the sediment. The physicochemical property of surface soil was revealed as one of the possible factors of radiocesium high retention in forest catchment.
Actinium-225 is one of the most promising nuclides in the field of nuclear medicines for treatments of cancers, whereas the transfer rate of 225Ac during chemical treatments, required for the radiological protection of the radiation workers, has not been determined. In this study, firstly, the chemical operations and the chemical status required for dealing with 225Ac for nuclear medicines were selected, and secondly, the dispersal rate, the surface contamination, and the concentrations of radionuclides in the waste water of 225Ac were determined. The total dispersal rates were determined as low values (2～4) × 10−6 h−1 and high values (2～4) × 10−5 h−1, depending on the classes of operations, and that in the exhaust as 1 × 10−7 h−1. These values are about an order of magnitude smaller than that of the “in surface” for normal chemical operations.
To support the safe return of residents after the TEPCO Fukushima Daiichi Nuclear Power Plant accident, cleaning methods and materials for the removal of radiocesium (137Cs) from household surfaces were compared. A spot contaminated with 137Cs on a vinyl floor sheet or a glass plate was wiped in different moisture conditions with different cleaning materials, including a paper sheet, cellulose sponge, polyester sheet, and a polyesterpolyamide sheet. Radioactive solid particles on a vinyl sheet were wiped with miniature mops made of cellulose sponge, polyester microfiber, or cotton yarn. There was little difference in the removal of radioactivity among cleaning materials when the contaminated spot was wiped in wet conditions. The removal of contaminated particles depended on the structure of the mop. The use of an abrasive and a detergent worked well for the vinyl sheet and the glass plate, respectively. These observations suggested that, in appropriate conditions, effective decontamination was achievable by regular indoor cleaning with commercially available cleaning devices.