It is known that the heavy uranium isotope enriches in tetravalent state in the reduction of hexavalent to tetravalent uranium catalyzed by enzymes in bacteria. In contrast, abiotic reductions do not show such fractionation. Using this fact, it is expected to understand the biogeochemical events of the era from the isotope composition of uranium in the ancient deposits. However, the mechanism of isotope fractionation has not been uncovered. In this study, we focus on the biotic reduction by bacteria and calculate the isotope fractionation coefficient ε using ab initio methods. We assume that all the elementary reactions of the reduction pathway are in thermal equilibrium in our calculations. We consider the reduction pathway that forms a uranium di-nuclear complex bound to an enzyme residue which is reduced by electron transfer from an enzyme and disproportionation. The ε value between initial substance (UO2(CO3)34-) and product (non-crystalline CaU(PO4)2) is about three times larger than the experimental result. Since our result is obtained assuming that all elementary reactions are in thermal equilibrium, the disagreement with the experiment suggests that non-equilibrium isotope effect may occur in any elementary reaction.

Volcanic gases consist of carbon dioxide, sulfur dioxide, hydrogen sulfide, and so on. Since their chemical composition and release amount provide important information on volcanic activity, various observation techniques are studied. In recent years, methods using a semiconductor or a chemical sensor have drawn attention because a compact and simple observation system can be constructed. However, these sensors have problems with long-term stability, response and selectivity. In this study, we focused on the localized surface plasmon resonance (LSPR) sensor. It conventionally has a good response and stability, but low sensitivity to volcanic gases. We developed the LSPR sensors whose detection limits were 5 ppm and 0.6 ppm for hydrogen sulfide and sulfur dioxide, respectively, by coating adsorbents with high gas adsorption capacity and selectivity for these gases.

Since 1950’s, human being started to use nuclear power, with various anthropogenic nuclides being discharged into the environment. These nuclides have been recorded in natural archives to be a clear sign of the onset of the Anthropocene. This period coincides with the era that human began to affect the environment. However the details of the records are fairly complicated, and it is important to analyze them for the definition of the Anthropocene.

This paper discusses the use of ultraviolet (UV) light sources to oxidize dissolved organic carbon (DOC) from freshwater and seawater. The UV oxidation method is especially well-suited to seawater analysis, where dissolved salt concentrations far exceed DOC concentrations. The UV oxidation method commonly used for AMS seawater DOC - 14C analysis normally uses a UV light source in excess of 1000 W, however UV light sources that range from 8 W to 450 W show promise as a low-cost alternative. To demonstrate this, we prepared standard solutions with varying concentrations of the organic pH indicator, phenol red (C19H14O5S), and irradiated them under a UV light source for 30 minutes to 58 hours. Although the UV irradiation readily dissociated the phenol red, as observed by the loss of color in the solutions, it did not fully oxidize the carbon to CO2. However, we were able to convert 94% of the carbon to CO2 with the addition of hydrogen peroxide (H2O2). Hydrogen peroxide is especially effective because UV irradiation forms hydroxyl radicals, which are potent oxidants. The 8 W UV technique requires at least 24 hour irradiation times, however the light sources are relatively compact, do not produce appreciable heat or ozone, and a single light source can be shared between samples. We discuss the physics of UV oxidation under our experimental conditions and the design of a UV oxidation system and its applications. We also present results for dissolved humic acids and seawater samples processed under our system.

⁹⁰Sr is an important radioactive nuclide for environmental impact assessment on atomic accidents or nuclear bomb tests. However, it is difficult to measure ⁹⁰Sr rapidly by the usual method. ⁹⁰Sr-AMS has been developed with the 6 MV tandem accelerator mass spectrometry system at the University of Tsukuba. SrF₃^- could be extracted about 400 nA from SrF₂ samples mixed with PbF₂. ⁹⁰Sr⁸⁺ with an energy of 51.8 MeV was detected by the gas ionization detector. The detection limit of ⁹⁰Sr isotopic ratio was achieved about 6 × 10^-13 (~3 mBq) by AMS.

Recently, the increase of cosmic ray flux was found around 5480 BC using the ¹⁴C measurements for tree rings with 1- to 2-y resolution. It is assumed that it may be caused by the large solar flares but we cannot specify the detail cause of this event. In this study, we aim to elucidate the cause of 5480 BC cosmic ray event by measuring ¹⁰Be and ³⁶Cl in the ice core which was drilled at the Dome Fuji Station in Antarctica, and investigate the variation of cosmic ray flux around 5480 BC. The result of ³⁶Cl concentration variation using the Accelerator Mass Spectrometry (AMS) system in the University of Tsukuba is reported in this presentation. In addition, the performance of ¹⁰Be-AMS and the future plan is also presented.

³⁶Cl is a cosmogenic nuclide, which is produced by the reactions of Ar with cosmic rays. Therefore, the deposited ³⁶Cl on the ground is expected to be correlated with the cosmic-ray intensity. In this study, we measured ³⁶Cl in rainwater with accelerator mass spectrometry (AMS) and evaluated the ³⁶Cl flux monthly from 2010 to 2014. The results confirmed that the ³⁶Cl flux was correlated with sunspot number (r = -0.4) on the assumption that ³⁶Cl fell down to the ground for two years. Besides, in 2011, a large amount of ³⁶Cl was observed, which was considered to be released from the Fukushima Daiichi Nuclear Power Plant accident.

Some effects of Anthropocene is utilized for scientific studies successfully. Iodine-129 (I-129, H.L. 15.7kyr) is one of them. We tried to make I-129 as a marine biological marker. In this study, data sets of I-129 isotopic ratio in marine biota and seawater will be reported and be discussed its utilities and problems.

Insoluble cesium bearing Type A particles, which were detected in Fukushima and metropolitan areas, are believed to have been generated by the Fukushima Daiichi accident. The particles are known to have silica-rich matrix containing elements such as Zn, Fe, Cs, Rb, Sn, K, and Cl, and are typically glass spheres having a diameter of 1-5 microns. However, the material origins are not well known for Si, Zn, K and Cl and sometimes misunderstood, possibly causing confusion in generation mechanisms discussion. In this paper, we discuss probable material origins for the Type A particles, considering the generation mechanisms in relation to the progression of Fukushima Daiichi Accident.

In the present study, we explore a new application of barite (BaSO4) as a sequestering phase for selenite (Se(IV)) and selenate (Se(VI)) ions from aqueous solutions. Barite is a common phase in many geological environments, and it can be used to remove toxic and/or radioactive elements from aqueous solutions, but it has not been widely used in environmental studies. This study describes the mechanisms of Se distribution between barite and water, thus providing a good estimate of its ability to effectively remove Se(IV) and Se(VI) from aqueous solutions (more than 80%) using the optimized experimental parameters examined here.