In this study, standardization of ¹⁴C is carried out using the CIEMAT/NIST method with a conventional liquid scintillation counter, which is the national standard, and a triple-to-double coincidence ratio (TDCR) counter developed by the National Institute of Advanced Industrial Science and Technology (AIST). An efficiency calculation for the CIEMAT/NIST method was conducted by the program CN2004. The TDCR calculation was conducted at AIST using a custom-made program. The activity measured by the TDCR counter was in good agreement with that measured by the conventional national standard within the given uncertainties. These two measurement methods will be used for calibration services at AIST according to the purpose.

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Part of radioactive substance-containing water leaked from the reactor buildings of TEPCO Fukushima Daiichi Nuclear Power Plant has flowed into seawater area in front of Unit 1 to 4. A direct immersion of adsorbent in seawater and subsequent recovery of it from seawater are effective in removing radioactive substances from seawater in simple, steady, and safe modes. We suggested the immersion of a braid of caesium-adsorptive fiber in the seawater area for the removal of radioactive caesium ions. Here, the preparation of the caesium-adsorptive fiber by radiation-induced graft polymerization and its performance of caesium removal are described.

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Removal of radioactive strontium from seawater contaminated with radioactive substances by use of adsorbents is a tough task from the following two reasons. First, radioactive strontium ions at an extremely low concentration dissolve in seawater that originally contains non-radioactive strontium at a concentration of approximately 8 mg/L. Second, calcium and magnesium ions that belong to the same alkaline-earth metal ions as strontium ions dissolve in seawater at 600- and 100-fold higher molar concentrations than strontium ions. Therefore, a high capacity for strontium in seawater is a crucial requisite for the adsorbent. Here, we describe the preparation of strontium-adsorptive fiber by radiation-induced graft polymerization and its performance of strontium removal.

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The concept of frustration has driven the modern research fields of magnetism and strongly correlated electron systems. In frustrated magnets, even at a much lower temperature than the scale of magnetic bonding energy, a spin system does not form a normal static long-range order but forms a novel liquid-like state. The representative state is molecular spin excitation modes in spinel oxides, which refers to the picture of spin motions confined in a beautiful geometrical figure within 1 nm. We introduce molecular spin excitations from the discovery to recent results around our inelastic neutron scattering studies.

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For underwater in-situ measurement of radiations, radiation measurement instruments are required to be designed as water and pressure resistant. In addition to the development of underwater radiation measurement system taking into account the operating environment, operation techniques of underwater equipment such as towed γ-ray spectrometer are essential to get two dimensional mapping of radiation distribution in sediment of bottom of sea or water. In this paper, in-situ radiation measurement techniques, used from the 1960s to the present for geophysics studies, marine sediment transport studies, marine mineral exploration, and anthropogenic radionuclide survey, are reviewed. Recent techniques for mapping of distribution of radionuclides in seafloor or water bottom deployed to measurement of radionuclides released from the accident at Fukushima Daiichi Nuclear Power Plant, Tokyo Electric Power Company, are also described.

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