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We have investigated vertical distributions of Ag, I, Te, and Cs and existence in beach soil collected three months after the Great East Japan Earthquake. All the nuclides passed through tsunami deposit and original beach soil, then reached fine particle layer lying beneath them in the three months. Moreover, depth profiles of all the nuclides did not exhibit exponential decrease. Behavior of I, Te, and Cs were explained with distribution coefficients ( K) but that of Ag was not explained. Particulate form was observed for the Cs; number of the particle was proportional to the Cs concentration in the soil sample. [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]

We have developed a laser coupling with an electron cyclotron resonance (ECR) ion source for trace element analysis of mineral samples at University of Tsukuba. A compact Q-switched Nd:YAG laser at 1064 nm wavelength with a pulse width of 8 ns and a maximum energy of 50 mJ is employed to ablate the sample materials as a means of introducing samples into the ECR plasma. Preliminary experiments were performed to focus the laser beam on a pure metallic target (Cu). The mean kinetic energy of the laser produced Cu ions is measured to 470 eV for the laser energy of 50 mJ by a simple time-of-flight method. Design for a laser coupling with an ECR ion source as a new application of mass spectrometry are reported. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract A 6 MV tandem accelerator at the University of Tsukuba, Japan, has been working on multi-nuclide (10Be, 14C, 26Al, 36Cl, 41Ca, and 129I) accelerator mass spectrometry (AMS) since 2016. This paper reports improvement of isobar suppression techniques for 36Cl AMS. Previous studies have shown that a Cu sample holder with AgBr backing is the most suitable for 36Cl AMS to decrease isobaric 36S interference. Therefore, the method of AgBr preparation was considered, and we found that preparation under acidic conditions was most appropriate to reduce 36S in 36Cl AMS. Cl charge states and their analysis method were considered to improve peak separation. 36 Cl 8 + was chosen for detection because it allows clear separation of 36S from the 36Cl spectrum. Furthermore, 36S spectrum tails could be removed using a third anode (dE3) signal. As a result, a 36Cl/Cl background of ∼ 3 × 10 - 15 was achieved. [ABSTRACT FROM AUTHOR]

Quantification of the development of solution dolines provides important information for understanding the long-term evolution of karst landscapes. This study reports the initial results of an investigation of the long-term denudation rates along the side slopes of a solution doline based on analyses of cosmogenic 36Cl in calcite. The denudation rates increase in proportion with increasing size of the topographic contributing area, thereby supporting the hypothesis that the rate of surface lowering in carbonate terrains is controlled by water convergence in the epikarst. A simple model based on the empirical correlation between denudation rate and contributing area is successful in explaining the form of several solution dolines located close to the analyzed doline. The model reveals that these solution dolines, which have varying diameters, developed over similar time scales of the order of 105 yr. [ABSTRACT FROM AUTHOR]

Environmental contaminations of 129 I were continuously monitored in various sample preparation rooms for accelerator mass spectrometry at the University of Tsukuba. Monitoring of 129 I was performed in the rooms used for the treatment of samples in the past, in order to compare with the results obtained in the sample preparation rooms. Ambient levels of atmospheric 129 I in each room were estimated from the measured concentrations in the alkali trap solutions. This article reports the results of one year of monitoring the temporal changes of stable iodine ( 127 I) and 129 I contamination rates in the alkali trap solutions. It was found that 129 I contamination rates were lower than approximately 10 4 atoms cm -2 day -1 in the rooms where ether no samples or only samples with environmental background levels of 129 I were handled. Values from 10 4 to 10 5 atoms cm -2 day -1 were recorded in another room where environmental samples, such as the samples derived from nuclear power plant accidents, were treated. Higher levels of 129 I, ranging from 10 6 to 10 7 atoms cm -2 day -1 , were recorded in rooms used for treating neutron-activated iodine. The experimental results show that the 129 I level depended on the 129 I sample-preparation histories for the respective rooms. It is possible to estimate the 129 I contamination risk from the atmosphere to the samples by knowing the 129 I level in the preparation room.

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.)

Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO 2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets.

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.)