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The trace element content of single fluid inclusions in quartz from Tsushima granite in Japan was determined with particle-induced X-ray emission (PIXE) to investigate the chemical features of Ti in hydrothermal fluids derived from granites. Most of the fluid inclusions were polyphase and vapor-rich fluid inclusions, and both types contained Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Ge, Br, Rb, Sr, Ba, and Pb. Concentrations of Ti were of up to a few tens ppm wt Ti for polyphase inclusions and up to one hundred ppm for vapor-rich fluid inclusions. The Ti content indicated the possibility of transportation of a certain amount of Ti by granitic hydrothermal fluids. [ABSTRACT FROM AUTHOR]

A tremendous amount of radioactivity was discharged because of the damage to cooling systems of nuclear reactors in the Fukushima No. 1 nuclear power plant in March 2011. Fukushima and its adjacent prefectures were contaminated with fission products from the accident. Here, we show a geographical distribution of radioactive iodine, tellurium, and cesium in the surface soils of central-east Japan as determined by gamma-ray spectrometry. Especially in Fukushima prefecture, contaminated area spreads around Iitate and Naka-Dori for all the radionuclides we measured. Distributions of the radionuclides were affected by the physical state of each nuclide as well as geographical features. Considering meteorological conditions, it is concluded that the radioactive material transported on March 15 was the major contributor to contamination in Fukushima prefecture, whereas the radioactive material transported on March 21 was the major source in Ibaraki, Tochigi, Saitama, and Chiba prefectures and in Tokyo. [ABSTRACT FROM AUTHOR]

We propose a methodology for estimating the residence time of groundwater based on bomb-produced 36Cl. Water samples were collected from 28 springs and 2 flowing wells located around Mt. Fuji, Central Japan. 36Cl/Cl ratios in the water samples, determined by accelerator mass spectrometry (AMS), were between 43 × 10−15 and 412 × 10−15. A reference time series of the above-background (i.e., bomb-derived) 36Cl concentration was constructed by linearly scaling the background-corrected Dye-3 data according to the estimated total bomb-produced 36Cl fallout in the Mt. Fuji area. Assuming piston flow transport, estimates of residence time were obtained by comparing the measured bomb-derived 36Cl concentrations in spring water with the reference curve. The distribution of 36Cl-based residence times is basically consistent with that of tritium-based estimates calculated from data presented in previous studies, although the estimated residence times differ between the two tracers. This discrepancy may reflect chlorine recycling via vegetation or the relatively small change in fallout rate, approximately since 1975, which would give rise to large uncertainties in 36Cl-based estimates of recharge for the period, approximately since 1975. Given the estimated ages for groundwater from flowing wells, dating based on a 36Cl bomb pulse may be more reliable and sensitive for groundwater recharged before 1975, back as far as the mid-1950s. [ABSTRACT FROM AUTHOR]

This study investigates the potential of 36Cl in tracing young groundwater with residence times of up to ∼50 years. Groundwater samples were obtained from 16 irrigation wells in paddy fields located within an upland-lowland system in the Yoro River basin, Central Japan. The 36Cl/Cl ratios were in the range of 17 to 362 x 10-15. Among the samples with higher Cl- concentrations (>10 mg/L), two samples showed high nitrate concentrations as well (>30 mg/L). Except for these samples, the distribution of 36Cl in groundwater was essentially consistent with previous tritium concentration data measured in 1982 and 1994, considering the time that has elapsed since these earlier measurements were performed. 36Cl/Cl values were less than 30 x 10-15 in lowland areas, with higher values in and around upland areas. The results indicate longer residence times in the regional groundwater flow system (>50 years) than those estimated in previous studies, especially in the area west of the Yoro River. The results demonstrate the ability of 36Cl to trace young groundwater flow, particularly because high values of bomb-derived 36Cl/Cl are easily discriminated from pre-bomb water with low 36Cl/Cl values. Because of its very long half-life (3.01 x 105 years), 36Cl remains even after tritium is no longer available. [ABSTRACT FROM AUTHOR]

Abstract: This study attempted to quantify long-term subaerial denudation of bare carbonate rock surfaces by using in situ-produced cosmogenic 36Cl in calcite. Carbonate samples were collected from the topmost 5cm of exposed pinnacles at several non-glaciated karst areas in subtropical to subarctic regions in Japan. Concentrations of natural Cl and 36Cl in calcite were determined by accelerator mass spectrometry with isotope dilution with 35Cl-enriched carrier spike. The nuclide concentrations were of the order of 105–106 atomg−1, and converted to total denudation rates averaged over a 105 yr-timescale of chemical and physical processes acting on the karst surfaces. The denudation rates were 20–60mmkyr−1, being lowest in the central part of Japan. This tendency indicates the alternation of relative importance of chemical (dissolution) and physical (frost shattering) processes in denudation, depending on site-specific factors such as mean temperature, annual precipitation, and freeze–thawing intensity. [Copyright &y& Elsevier]

Fluid inclusions in quartz from miarolitic cavities, pegmatites, and quartz veins in Miocene biotite-granite plutons, Kofu, Japan, were analyzed by particle-induced X-ray emission to examine chemistries and behaviors of granite-derived fluids in island-arc granite. Most inclusions are aqueous two-phase inclusions, and halite-bearing polyphase inclusions are also observed in quartz veins in the upper part of the plutons. From element contents of fluid inclusions in the miarolitic cavities, the original fluid released from the granite plutons during solidification is inferred to have concentrations of Mn, Fe, Cu, Zn, Ge, Br, Rb, Pb, and Ba of several tens to hundreds of parts per million by weight (ppm) and a salinity of about 10 wt% NaCl equivalent. We estimated the formation conditions of the fluid to have been at about 1.3–1.9 kb and 530–600°C on the basis of the homogenization temperatures of the inclusions and the solidification conditions of the plutons. The polyphase inclusions probably originated from hypersaline fluid by boiling of part of the released fluid during its ascent in the plutons. The polyphase inclusions contain several hundreds to tens of thousands of ppm of Fe and Mn, and tens to several hundreds of ppm of Cu, Zn, Br, Rb, and Pb. The salinities are about 35 wt% NaCl equivalent. Compositional variations in two-phase inclusions from the miarolitic cavities and quartz veins are primarily explained by mineral precipitation with dilution by surface water exerting a secondary influence. Thus, chemistries and behaviors of the granite-derived fluids in the plutons can be explained by mineral precipitation, boiling, and dilution of the originally released fluid. [ABSTRACT FROM AUTHOR]

Abstract: Essential parameters for the applications of 36Cl as a tracer in groundwater studies include the initial 36Cl/Cl ratio, at the time of recharge, and/or the natural background deposition flux of 36Cl in the recharge area. To facilitate the hydrological use of 36Cl in central Japan, this study aimed to obtain a precise estimate of the long-term average local 36Cl flux and to characterize its seasonal variability. The 36Cl in precipitation was continuously monitored in Tsukuba, central Japan over a period of >5 years. The 36Cl flux showed a clear seasonal variation with an annual peak during the spring, which was attributed to the seasonal variability of tropopause height. The long-term average 36Cl flux (32±2atomsm−2 s−1), estimated from the measured data, was consistent with the prediction from the 36Cl latitudinal fallout model scaled using the global mean production rate of 20atomsm−2 s−1. The initial 36Cl/Cl ratio was estimated to be (41±6)×10−15, which is similar to that of pre-bomb groundwater in the Tsukuba Upland. An observation period covering an 11-year solar cycle would yield more accurate estimates of the values, given the increased 36Cl flux during the solar minimum. [Copyright &y& Elsevier]

The anthropogenic long-lived radionuclide 129 I is receiving increased attraction as a new oceanic tracer in addition to usage as a fingerprint of radionuclide contamination of the marine environment. To demonstrate the robustness of 129 I as an oceanic tracer in the Northwest Pacific area, specifically in the Japan Sea, the input history of 129 I to surface seawater was reconstructed using a hermatypic coral core sample from Iki Island in the Tsushima strait. Iodine isotopes in each annual band were measured using AMS and ICP-MS after appropriate pre-treatments of small amounts of coral powder. The 129 I/ 127 I ratios in the 1940s were almost at background levels (<1 × 10 -11 ) and increased abruptly in the early 1950s. Thereafter, the ratios continuously increased with some fluctuations; the maximum ratio, 7.13 ± 0.72 × 10 -11 , being found in the late 1990s. After that period, the ratios remained nearly constant until the present time (2011). The 129 I originated mainly from the nuclear weapons testings of the 1950s and the early 1960s, and from airborne releasing by nuclear reprocessing facilities. The dataset obtained here was used to construct a simple model to estimate the diffusion coefficient of 129 I in the Japan Sea. The 129 I/ 236 U ratios over the observation period were also reconstructed to help constraining sources of 129 I to the marine environment. Based on the results, the 129 I/ 236 U ratio obtained here could be an endmember of the water mass in the Kuroshio Current area of the Northwest Pacific Ocean., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Evaluation of radiation exposure from diet is necessary under the assumption of a virtual accident as a part of emergency preparedness. Here, we developed a model with complete consideration of the regional food trade using deposition data simulated by a transport model, and estimated the dietary intake of radionuclides and the effectiveness of regulation (e.g., restrictions on the distribution of foods) after the Fukushima accident and in virtual accident scenarios. We also evaluated the dilution factors (i.e., ratios of contaminated foods to consumed foods) and cost-effectiveness of regulation as basic information for setting regulatory values. The doses estimated under actual emission conditions were generally consistent with those observed in food-duplicate and market-basket surveys within a factor of three. Regulation of restricted food distribution resulted in reductions in the doses of 54⁻65% in the nearest large city to the nuclear power plant. The dilution factors under actual emission conditions were 4.4% for radioiodine and 2.7% for radiocesium, which are ~20 times lower than those used in the Japanese provisional regulation values after the Fukushima accident. Strict regulation worsened the cost-effectiveness for both radionuclides. This study highlights the significance and utility of the developed model for a risk analysis of emergency preparedness and regulation.

To evaluate the deposition density and extent of subsurface infiltration of (129)I and (137)Cs in the restricted area that was highly contaminated by the accident of Fukushima Dai-ichi Nuclear Power Plant, cumulative inventories of (129)I and (137)Cs, concentrations of (129)I and (137)Cs, and (129)I/(137)Cs ratio in 30-cm-long soil columns were compared with pre-accident levels from the same area. The cores were collected before and after the accident from locations of S-1 (4 km west of FDNPP) and S-2 (8 km west of FDNPP). Deposition densities of (129)I and (137)Cs in the soil following the accident were 0.90-2.33 Bq m(-2) and 0.80-4.04 MBq m(-2), respectively, which were 14-39 and 320-510 times larger than the pre-accident levels of (129)I (59.3-63.3 mBq m(-2)) and (137)Cs (2.51-7.88 kBq m(-2)), respectively. Approximately 90% of accident-derived (129)I and (137)Cs deposited in the 30-cm soil cores was concentrated in the surface layer from 0 to 44-95 kg m(-2) of mass depth (0-4.3-6.2 cm depth) and from 0 to 16-25 kg m(-2) of mass depth (0-1.0-3.1 cm depth), respectively. The relaxation mass depths (h0) of 10.8-11.2 kg m(-2) for (129)I estimated in the previous study were larger than those of 8.1-10.6 kg m(-2) for (137)Cs at both sites, owing to the larger infiltration depth of radioiodine mainly by the gravitational water penetration in the surface soil in our study sites. Approximately 7-9% of the accident-derived (129)I was present in the lower layer from 44 to 100 kg m(-2) (4.3-8.6 cm depth) at S-1, and from 95 to 160 kg m(-2) (6.2-10.2 cm depth) at S-2. Approximately 1% of (137)Cs seems to infiltrate deeper than (129)I in the lower layer at each site in contrast to the surface layer., (Copyright © 2015 Elsevier Ltd. All rights reserved.)