Koichi Takamiya

Analysis of cesium isotope compositions in environmental samples by thermal ionization mass spectrometry – 1. A preliminary study for source analysis of radioactive contamination in Fukushima prefecture

Cesium was recovered from plant samples obtained from Fukushima prefecture. The isotopic ratios of 134Cs/137Cs and 135Cs/137Cs were analyzed by thermal ionization mass spectrometry with a single filament method using a TaO activator. Samples containing 5 Bq of 137Cs were analyzed with typical analytical errors of approximately 0.5% for 134Cs/137Cs and approximately 0.1% for 135Cs/137Cs. Measurements of both ratios showed profiles that were characteristic of the measurements of among other environmental samples reported in the literature. The results showed the isotopic ratios of 134Cs/137Cs and 135Cs/137Cs were applicable for the source analysis of radioactive Cs in Fukushima prefecture.

Measurement of air dose rates over a wide area around the Fukushima Dai-ichi Nuclear Power Plant through a series of car-borne surveys

A series of car-borne surveys using the Kyoto University RAdiation MApping (KURAMA) and KURAMA-II survey systems has been conducted over a wide area in eastern Japan since June 2011 to evaluate the distribution of air dose rates around the Fukushima Dai-ichi Nuclear Power Plant and to evaluate the time-dependent trend of decrease in air dose rates. An automated data processing system for the KURAMA-II system was established, which enabled rapid analysis of large amounts of data obtained using about 100 KURAMA-II units. The initial data used for evaluating the migration status of radioactive cesium were obtained in the first survey, followed by other car-borne surveys conducted over more extensive and wider measurement ranges. By comparing the measured air dose rates obtained in each survey (until December 2012), the decreasing trend of air dose rates measured through car-borne surveys was found to be more pronounced than those expected on the basis of the physical decay of radioactive cesium and of the air dose rates measured using NaI (Tl) survey meters in the areas surrounding the roadways. In addition, it was found that the extent of decrease in air dose rates depended on land use, wherein it decreased faster for land used as building sites than for forested areas.

Neutron-capture cross-sections of 244Cm and 246Cm measured with an array of large germanium detectors in the ANNRI at J-PARC/MLF

The neutron neutron-capture cross cross-sections of 244Cm and 246Cm were measured by the time-of-flight method in the energy range of 1–300 300 eV with an array of large germanium detectors in the Accurate Neutron-Nucleus Reaction measurement InstrumentANNRI at Material and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research ComplexJ-PARC/MLF. The 244Cm resonances at around 7.7 and 16.8 8 eV and the 246Cm resonances at around 4.3 and 15.3 3 eV were observed in the capture reactions for the first time. The uncertainties of the obtained cross cross-sections are 5.8% at the top of the first resonance of 244Cm and 6.6% at that of 246Cm. The rResonance analyses were performed for low-energy ones using the code SAMMY. The prompt γ-ray spectra of 244Cm and 246Cm were also obtained. Eight and five new prompt γ-ray emissions were observed in the 244Cm(n, γ) and 246Cm(n, γ) reactions, respectively.

Prediction of groundwater contamination with 137Cs and 131I from the Fukushima nuclear accident in the Kanto district.

We measured the concentrations of (131)I, (134)Cs, and (137)Cs released from the Fukushima nuclear accident in soil and rainwater samples collected March 30-31, 2011, in Ibaraki Prefecture, Kanto district, bordering Fukushima Prefecture to the south. Column experiments revealed that all (131)I in rainwater samples was adsorbed onto an anion-exchange resin. However, 30% of (131)I was not retained by the resin after it passed through a soil layer, suggesting that a portion of (131)I became bound to organic matter from the soil. The (137)Cs migration rate was estimated to be approximately 0.6 mm/y in the Kanto area, which indicates that contamination of groundwater by (137)Cs is not likely to occur in rainwater infiltrating into the surface soil after the Fukushima accident.

Development of a rapid source preparation method for high-resolution α-particle spectrometry

In order to prepare sources of short-lived actinides for alpha-particle spectrometry, a coprecipitation method with Sm hydroxide was developed. The preparation procedure can be completed within 5 min with a high chemical yield of over 90%. It was found that the uniformity of the produced sources was sufficient to provide a high resolution of better than 20 keV. Under this method, we successfully measured the alpha-particle spectrum of short-lived Cf isotopes produced in the (238)U((12)C, xn) reaction.

Alpha-decay from the 3.5 eV isomer of 229Th

The alpha-decay of a low energy isomer of 229Th at about 3.5 eV was sought by producing it through the (g,n) reaction on a 230Th target. Thorium isotopes in the reaction products were isolated and purified by anion exchange chromatography in a concentrated nitric acid medium to remove lanthanides fission products. The thorium fraction was further purified by samarium fluoride coprecipitation and the precipitate was mounted as a source for a-spectroscopy. Decaying a-signals were observed in the energy region that was expected for 229mTh, i.e., between 4.83 and 5.08 MeV. The half-life of the decaying component was determined from repeated experiments to be 13.9±3 hours.

235U/238U Isotopic ratio in plant samples from Fukushima Prefecture

Abstract Uranium was recovered from plant samples obtained from Fukushima Prefecture, and the 235U/238U isotopic ratio was analyzed using thermal ionization mass spectrometry. The possibility of soil and biosphere contamination with U by the nuclear accident at Fukushima Daiichi nuclear power plant was evaluated. The isotopic ratio of U in the plant samples was the same as the natural abundance, which suggests that no significant contamination with U occurred.

Determination of isotopic ratios of plutonium and uranium in soil samples by thermal ionization mass spectrometry

Isotopic ratios of plutonium and uranium in soil samples were investigated, in order to understand the level of contamination with plutonium and uranium released at the accident of Fukushima Daiichi nuclear power plant. At first, plutonium and uranium were recovered from the standard reference soil/sediment materials by extraction/ion-exchange chromatography, and their isotope compositions were analyzed by TIMS. By applying our analytical technique to soil samples obtained from Fukushima prefecture, a possibility of atmospheric release of nuclear fuel material during the accident of FDNPP was discussed. The contamination with uranium was under detection limit, while that with plutonium was observed.

Development of a simple and rapid method of precisely identifying the position of 10B atoms in tissue: an improvement in standard alpha autoradiography

Boron neutron capture therapy (BNCT) can be utilized to selectively kill cancer cells using a boron compound that accumulates only in cancer cells and not in normal cells. Tumor-bearing animals treated by BNCT are routinely used to evaluate long-term antitumor effects of new boron compounds. Alpha-autoradiography is one of the methods employed in the evaluation of antitumor effects. However, a standard alpha-autoradiography cannot detect the microdistribution of 10B because of the difficulty associated with the superposition of a tissue sample image and etched pits on a track detector with the etching process. In order to observe the microdistribution of 10B, some special methods of alpha-autoradiography have been developed that make use of a special track detector, or the atomic force microscope combined with X-ray and UV light irradiation. In contrast, we propose, herein, a simple and rapid method of precisely identifying the position of 10B using the imaging process and the shape of etched pits, such as their circularity, without the need to use special track detectors or a microscope. A brief description of this method and its verification test are presented in this article. We have established a method of detecting the microdistribution of 10B with submicron deviation between the position of etched pits and the position of reaction in a tissue sample, for a given circularity of etched pits.

Adsorption of fission products on a metal surface in nitric acid solutions: Radiochemical study using a multitracer

Adsorption behavior of fission products in nitric acid solution on various alloys and metals was studied by using a multitracer produced by neutron irradiation of UO2. The adsorption behavior of the fission products 99Mo, 131I, 132Te, 140La, and 143Ce, and 239Np was simultaneously studied. Some chemical decontamination tests were also examined. Clear adsorption of 99Mo, 131I, and 132Te was observed, whereas adsorption of 140La, 143Ce, and 239Np was not. The adsorption characteristics were discussed by considering anion-exchange reaction and surface complexation.