Shoji Hirai

Neutron activation analysis for ultra low contents of uranium and thorium in aluminium and silica

Highly sensitive neutron activation analysis of uranium and thorium in high quality silica and aluminium has been investigated using the Japan Materials Testing Reactor (JMTR), having a thermal neutron flux higher than 1014 n/cm2/s. In order to determine ultra-low contents of uranium and thorium,239Np and233Pa as activation products were separated by using anion exchange and LaF3 coprecipitation methods. As a result, a number of interfering radioactive isotopes containing double neutron capture product such as183Ta were removed completely from the isolated239Np and233Pa fraction and the detection limits for uranium and thorium were found to be 2·10−12 g and 4·10−13 g, respectively.

Certified reference materials of agricultural products and foods bearing radioactivity from the Fukushima nuclear accident

Abstract Certified reference materials (CRMs) for food analysis were developed in an inter-laboratory experiment for validation of measurement of radiocesium in foodstuffs. Since 2012, five series of CRMs were developed, including for brown rice grain, soybean powder, beef flake, shiitake mushroom powder and marine fish (meat and bone parts). This paper discusses the strategy of development, including choice of CRMs developed and the preparation and certification procedures applied for CRM development. In particular, some detailed data are presented for the most popular CRMs developed: brown rice grain, soybean powder and beef flake.

Natural alpha-active isotopes contained in modern memory device materials

Coprecipitation methods with SmF3 and BaSO4 were developed in order to evaluate the radioequilibrium of natural decay nuclides series in high purity silica and lead. The present study revealed that228Th,230Th, and231Pa in silica and210Po, probably210Pb, in lead were enriched in much higher concentrations than their precursor nuclides.

Determination of ultra trace uranium and thorium in high purity aluminium by NAA.

半導体構成材料中に含まれるU,Th及びその娘核種から放出されるα粒子によって,半導体メモリーの蓄積データが反転する,いわゆるソフトエラーの問題が指摘されて以来,その対策の検討が行われている.この中で,材料の精製技術の発展に伴い,極微量U,Th及びα放射体の分析法の確立が強く要求されている.現在,これらの分析法の中でも高感度分析法として知られているNAAでさえ,非破壊法(INAA)では目的核種以外の核種からの生成放射能の影響で,0.n ppb程度までしか定量が行えない.本研究では,検出限界を下げるために,中性子放射化後,イオン交換分離操作を行い,U及びThからの生成核種である239Np及び233Paを選択的に分離し,その後γ線測定する方法で数十pptレベルまでのU,Thを定量する方法(RNAA)を開発したので報告する.

Mössbauer analysis of iron ore and rapidly reduced iron ore treated by micro-discharge using carbon felt

Several samples of iron ores produced in Australia and Brazil were analyzed by Mössbauer spectrometry. Almost all iron ores are composed of hematite, goethite, and fine grains of the oxides, of which the ratios are different among production area. The amount ratio of hematite and goethite, determined by Mössbauer spectrometry, were almost consistent with those obtained by a conventional chemical analysis especially for iron ore with less goethite. Iron ores were treated by a micro discharge using carbon felt (MD/CF). It is found that FeO, Fe(CO3), and Fe3O4 are produced by MD/CF. The treatment by MD/CF is efficient in rapid reduction of iron ores.

Preparation and certification of certified reference materials of fish meat and ashed bone for determination of 90Sr and radiocesium after Fukushima Daiichi Nuclear Power Plant

Certified reference materials (CRMs) of the fish meat powder and the fish bone ash for validation of measurement of anthropogenic nuclides (134Cs, 137Cs and 90Sr) related the Fukushima Daiichi nuclear power plant accident were developed using an inter-laboratory comparison. This paper discusses the strategy of development including selection of raw material, the preparation and certification procedures applied for CRM production. In particular, some detailed data are presented for the homogeneity study and inter-laboratory experiment for the certification. The results of inter-laboratory comparison not only to certify CRMs but also showed analytical performance of the anthropogenic nuclides in Japanese laboratories.

Comparative analysis of distributions of radioactive cesium and potassium and stable cesium, potassium, and strontium in brown rice grains contaminated with radioactive materials released by the Fukushima Daiichi Nuclear Power Plant accident

The distributions of 137Cs, 134Cs, and 40K as well as stable Cs, K, and Sr in bran, germ, and endosperm of brown rice contaminated by fallout from the Fukushima Daiichi Nuclear Power Plant were studied. It was found that 137Cs, 134Cs, and 40K were accumulated in germ at the highest concentration and the concentration ratios of Cs and K in bran, germ, and endosperm were approximately identical to one another, while the highest concentration of Sr was detected for bran. Possible chemical forms of the metal elements in rice grains were discussed based on their extraction behavior with water and MgCl2 aqueous solution.