[en] To measure radioactivities in soil contaminated by the accident of the Fukushima Daiichi Nuclear Power Plant, efficiency calibration of Ge detectors for "1"3"1I, "1"3"4Cs, and "1"3"7Cs in volume sources was investigated. Gamma-ray detection efficiencies for these nuclei were determined precisely using standard soil samples containing "1"3"4Cs, "1"3"7Cs, "1"7"5Hf, and "8"8Zr. These standard sources were prepared by admixing radioactive solutions with soil, and point sources were made from the same solutions to determine their radioactivity concentrations. The efficiency for the 364 keV γ ray of "1"3"1I was extracted from the experimental efficiencies of "1"3"7Cs and "1"7"5Hf. Cascade summing corrections for γ rays of "1"3"4Cs in soil samples were evaluated experimentally. To easily calculate the cascade summing corrections for volume sources, we examined a simplified method using averaged efficiencies, and evaluated its validity through a comparison of the calculated correction factors with the experimental ones. (author)

[en] The dispersal rates of ²¹¹At, which is a promising nuclide for targeted alpha therapy, from aqueous solutions and chloroform were studied to provide experimental evidence for the reasonable evaluation of its airborne concentration in a radiation-controlled area. Using a collection unit for dispersed ²¹¹At during ventilation, radioactivity of the trapped ²¹¹At was quantified. The dispersal rates of ²¹¹At in chloroform as well as acidic, neutral, and alkaline solutions, in addition to a neutral solution containing ascorbic acid, were determined. Thin-layer chromatography was also performed to identify the formed chemical species of ²¹¹At. The dispersal rate of ²¹¹At was very low in the neutral solution containing ascorbic acid and in chloroform. The chemical forms of ²¹¹At in aqueous solutions are also briefly discussed. (author)

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[en] We have measured radioactivities in soils contaminated by the severe accident of Fukushima Daiichi Nuclear Power Plant. The soil samples were taken at the 83 points distributed around the north area of Ibaraki prefecture. Radioactivities in the soils were measured by gamma-ray spectrometry, and distributions of "1"3"1I and "1"3"4","1"3"7Cs in this area were clarified. The highest radioactivity of 130 kBq/m"2 of "1"3"7Cs was observed at the boundary among Tochigi, Fukushima, and Ibaraki prefecture, while it was about 3 kBq/m"2 at the center of Ibaraki. (author)

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[en] 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. (author)

[en] A gas-jet transport system has been coupled to the RIKEN gas-filled recoil ion separator GARIS to startup superheavy element (SHE) chemistry at RIKEN. The performance of the system was appraised using an isotope of element 104, ²⁶¹Rf, produced in the ²⁴⁸Cm(¹⁸O,5n)²⁶¹Rf reaction. Alpha-particles of ²⁶¹Rf separated with GARIS and extracted to a chemistry laboratory were successfully identified with a rotating wheel apparatus for α spectrometry. The setting parameters such as the magnetic field of the separator and the gas-jet conditions were optimized. The present results suggest that the GARIS/gas-jet system is a promising approach for exploring new frontiers in SHE chemistry: (i) the background radioactivities of unwanted reaction products are strongly suppressed, (ii) the intense beam is absent in the gas-jet chamber and hence high gas-jet efficiency is achieved, and (iii) the beam-free condition also allows for investigations of new chemical systems.