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A single-stage accelerator mass spectrometer (GXNU-AMS) developed for radiocarbon and tritium measurements was installed and commissioned at Guangxi Normal University in 2017. After several years of operational and methodological upgrades, its performance has been continuously improved and applied in multidisciplinary fields. Currently, the measurement sensitivity for radiocarbon and tritium is 14C/12C ∼ (3.14 ± 0.05) ×10–15 and 3H/1H ∼ (1.23 ± 0.17)×10–16, respectively, and the measurement accuracy is ∼0.6%, which can meet the measurement requirements in the nuclear, earth, environmental and life science fields. This study presents the performance characteristics of GXNU-AMS and several interesting application studies. more...

For assessment of the potential of the Beppu Bay sediments as a Global boundary Stratotype Section and Point (GSSP) candidate for the Anthropocene, we have integrated datasets of 99 proxies. The datasets for the sequences date back 100 years for most proxy records and 1300 years for several records. The cumulative number of occurrences of the anthropogenic fingerprint reveal unprecedented increases above the base of the 1953 flood layer at 64.6 cm (1953 CE), which coincides with an initial increase in global fallout of 239Pu+240Pu. The onset of the proliferation of anthropogenic fingerprints was followed by diverse human-associated events, including a rapid increase in percent modern 14C in anchovy scales, changes in nitrogen and carbon cycling as recorded by anchovy δ15N and δ13C, elevated pollution of heavy metals, increased deposition of novel materials (spheroidal carbonaceous particles, microplastics, polychlorinated biphenyls), the occurrence of hypoxia (Re/Mo ratio) and eutrophication (biogenic opal, TOC, TN, diatoms, chlorophyll a), unprecedented microplankton community changes (compositions of carotenoids, diatoms, dinoflagellates), abnormally high spring air temperatures as inferred from diatom fossils, and lithological changes. These lines of evidence indicate that the base of the 1953 layer is the best GSSP level candidate in the stratigraphy at this site. more...

A new system for preparing 14C samples was established for a compact accelerator mass spectrometer (GXNU-AMS) at Guangxi Normal University. This sample preparation system consists of three units: a vacuum maintenance unit, a CO2 purification unit, and a CO2 reduction unit, all of which were made of quartz glass. A series of radiocarbon (14C) preparation experiments were conducted to verify the reliability of the system. The recovery rate of graphite obtained was more than 80%. The carbon content in the commercial toner and wood sample was linearly fitted to the CO2 pressure in the measurement unit of the system. The results showed a good linear relationship, indicating that the reliability of the sample preparation system. AMS measurements were conducted on a batch of standard, wood, and dead graphite samples prepared using this system. The results showed that the beam current of 12C- for each sample was more than 40 μA, the carbon contamination introduced during the sample preparation process was ∼ 2 × 10–15, and that the new sample preparation system is compact, low-contamination, and efficient and meets the GXNU-AMS requirements for 14C samples. more...

Many waterflooding oil fields, injecting water into an oil-bearing reservoir for pressure maintenance, are in their middle to late stages of development. To explore the geological conditions and improve oilfield recovery of the most important well group of the Hu 136 block, located on the border areas of three provinces (Henan, Shandong, and Hebei), Zhongyuan Oilfield, Sinopec, central China, a 14C cross-well tracer monitoring technology was developed and applied in monitoring the development status and recognize the heterogeneity of oil reservoirs. The tracer response in the production well was tracked, and the water drive speed, swept volume of the injection fluid were obtained. Finally, the reservoir heterogeneity characteristics, such as the dilution coefficient, porosity, permeability, and average pore-throat radius, were fitted according to the mathematical model of the heterogeneous multi-layer inter-well theory. The 14C-AMS technique developed in this work is expected to be a potential analytical method for evaluating underground reservoir characteristics and providing crucial scientific guidance for the mid to late oil field recovery process. more...

Polycyclic aromatic hydrocarbons (PAHs), originating mainly from the incomplete combustion of fossil fuels and biomass and the leakage of petroleum products, are hazardous pollutants with adverse carcinogenic and mutagenic potential for marine organisms. The Yangtze River estuarine–inner-shelf area in the East China Sea is one of the largest reservoirs of PAHs and connected with the semi-enclosed Sea of Japan through the shallow, narrow Tsushima Strait. The main sources of PAHs in the Sea of Japan are the East Asian landmass and East China Sea, with the major PAH transport pathways being atmospheric transport of the westerly and northwesterly winter monsoon and marine transport in the Tsushima Warm Current. Investigation of the environmental behavior of PAHs in the Sea of Japan is critical in assessing the ecological risks of PAHs, as the sea is among the most fertile fishing grounds, however, the contributions of surface PAHs transported via atmosphere and ocean current are unclear. This study aimed to elucidate variation factor of dissolved PAHs in the surface Sea of Japan during 2017–2022, and analyzed 1) surface PAH distribution, 2) PAH source, 3) air-sea PAH exchange flux, and 4) ocean current driven PAHs flux through the Tsushima Strait. Surface seawater samples of 10–15 L were collected at 148 sites in the Sea of Japan, and its adjacent seas including the Tsushima Strait and Kuroshio Current area (Sesoko, Okinawa Island) from 2017 to 2022. Particulate and dissolved phases were separated by filtration through 0.5 µm glass fiber filter (GFF), and the latter was concentrated in C18 disks. Particulate and dissolved PAHs were respectively extracted from the GFF and C18 disks with dichloromethane and measured by HPLC system with fluorescence detector. Total concentrations of the 14 dissolved PAHs (Σ14PAHdiss) in the central Sea of Japan were in range 0.26–5.87 ng L−1, with the mean of 3.26±0.36 ng L−1 in 2017, 3.70±1.44 ng L−1 in 2019, 0.51±0.10 ng L−1 in 2020, 1.29±0.53 ng L−1 in 2021, and 0.69±0.35 ng L−1 in 2022. In 2020, although atmospheric PAH deposition flux were increased to 4.0 ton month−1 from 2019 (3.4 ton month −1) at the Sea of Japan, mean Σ14PAHdiss in the surface seawater were parallelly decreased to 0.51 ng L−1 at the central Sea of Japan, 0.86 ng L−1 at the Tsushima Strait, and 0.46 ng L−1 at the Kuroshio Current area. The contribution of PAH-rich and low salinity continental shelf water from the East China Sea in the Tsushima Strait was decreased to 36% in 2020 from 58% in 2019 on the basis of salinity mass-balance and ocean current simulation. Moreover, PAHs inflow flux through the Tsushima Strait were in range 2.2–8.8 ton month−1, and decreased to 2.2 ton month−1 in 2020. Thus, the decrease in surface Σ14PAHdiss levels at the central Sea of Japan in 2020 was mainly caused by the decrease in PAHs flux via the Tsushima Warm Current, which flow into the Sea of Japan from the East China Sea. more...

PAHs have high dissolved concentrations (Σ13PAHdiss) at the northern area off the Sakhalin Island (33-78 ng L−1) where oil and natural gas is extracted (Chizova et al.,2013). East Sakhalin Current (ESC) starting northern of the Sakhalin Island and reaching the southern Okhotsk Sea during autumn-winter, presents a latent risk of PAHs transboundary pollution. The southern Okhotsk Sea is also fed by Soya Warm Current (SWC, Summer) originating in the Sea of Japan. The seasonal interchange of SWC and ESC makes the area an excellent fishing ground, with 352,000 tons of scallops, crabs, salmon, and other major species of fish caught annually. 50+ seawater samples (~10 L) were collected from 2017 to 2022 with collaboration of the Japan Fisheries Research and Education Agency to evaluate the PAHs migration around southern Okhotsk Sea. Dissolved PAHs were concentrated, from pre-filtered (0.5 µm) samples, using C18 membranes and measured with a HPLC-fluorescence. Low-background γ-spectrometry of 234Th and 228Ra were measured at the Ogoya-Underground Laboratory, Kanazawa University using HPGe-detectors. 129I was measured using accelerator mass spectrometry at the University of Tsukuba. 234Th is constantly produced from 238U in seawater, thus the disbalance of the particle-reactive 234Th (t1/2=24.1 d) tells the scavenging due to new production. 228Ra (t1/2=5.75 y) is produced by the decay of 232Th, in the shallow continental shelves. 129I (t1/2=15.7x 106 y) is released from nuclear fuel reprocessing facilities and transported by the westerlies to the West-Pacific’s marginal seas. The Σ13PAHdiss averaged 2.59 (0.87−5.56) ng L−1. Using isomers ratios and statistical analyses, PAHs’ sources were inferred as primarily pyrogenic for all samples. Oceanographic structure was characterized by a coastal area [high salinity (>33.0 PSU), high 228Ra (0.80−1.90 mBq L−1) and low PAHs (−1)], dominated by the SWC and an offshore area [low salinity (228Ra (0.25−0.80 mBq L−1) and high PAHs (>2 ng L−1)], dominated by the ESC-influenced Okhotsk Sea Surface Water. Σ13PAHdiss were not necessarily low (1.71−5.15 ng L−1) at the endmember of SWC, and thus surface migration and isopycnal mixing does not fully explain PAHs distribution. 234Th/238U ratio was 0.65 at the endmember of SWC, 0.51 ± 0.03 in the offshore area, but only 0.36 ± 0.10 in the coastal area. Chlorophyll-a, PO43-, and SiO2 at the coastal (1.38 ± 0.76 mg m3, 0.07 ± 0.05 μM, 1.77 ± 0.65 μM, respectively) and offshore (0.61 ± 0.57 mg m3, 0.20 ± 0.08 μM, 3.64 ± 1.44 μM, respectively) areas also indicated higher primary productivity at the former, and thus scavenging of dissolved PAHs at the coastal area of southern Okhotsk Sea was nominated as a major geochemical process at the southern Okhotsk Sea. The high primary productivity and downward carbon export is key for the successful of scallop farming, but the co-scavenging of organic pollutants found by this study emphasizes the environmental risk that Sakhalin I, II present. 228Ra’s origins are multiple at the West-Pacific’s marginal seas, therefore a multiple-tracer assessment including the seaice’s role will be prepared when 129I analysis are completed. more...

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. more...

Strontium-90 is one of the most important fission products due to the potential health risks of its uptake and retention in the human body. Conventional analysis techniques involve β counting, whic... more...

Hydrogen concentrations in thin self-supporting samples of polyphenylene sulfide and muscovite have been determined by nuclear-elastic recoil detection analysis of transmission layout. The analysis procedure is based only on the database of stopping power and recoil cross section for material analysis, without using any reference sample of known H content. For the polyphenylene sulfide sample, the determined value of $(2.87\pm 0.26)\times 10^{22}\,{\rm H}/$cm$^{3}$ is in good agreement with the calculated value of $3.01 \times 10^{22}\,{\rm H}/$cm$^{3}$. For the muscovite sample, the H concentration originating each from bound water and absorbed water is uniform over the entire thickness of the sample. The determined concentration $(9.43 \pm 0.75) \times 10^{21}$ H$/$cm$^{3}$ of the muscovite agrees excellently with the value of $9.36 \times 10^{21}$ H$/$cm$^{3}$ obtained from other quantitative analyses typically applied for minerals. The present results demonstrate the capability of accurate determination of H contents in materials and minerals by transmission ERDA., Comment: 15 pages, 6 figures more...

We measured the yield of Auger electrons emitted through Coster–Kronig transitions from Rydberg states 1 s 2 p ( 3 P ) nl ( n = 7 , 8 ) and 1 s 2 2 p ( 2 P ) nl ( n = 5 , 6 , 7 ) of emergent atomic ions C q + under irradiation of 3.5-MeV/atom C+ and C 2 + ions on thin C foil targets. The Auger electron yields are suppressed for C 2 + irradiation compared with C+ irradiation and the relative yield becomes larger as n increases. Thus, amount of scattered electrons having lower relative energy in the projectile rest frame becomes larger. The results obtained in this study support the influence of projectile velocity on the cluster effect of secondary electron yields. more...

The Guangxi Zhuang Autonomous Region in southern China is one of the most typical karst relief areas with various forms, and tiankeng is one of the most typical karst relief forms of the Quaternary Period. In this work, accurate measurements of tiankeng exposure ages were made. The exposure ages of carbonate rocks from the five largest tiankengs in the world, the DaShiwei, HuangJing, ChuanDong, DaTuo, and DaCao tiankengs, were determined by accelerator mass spectrometry to be at least 20–400 thousand years, which provides significant proof for activity of new tectonic movement of the Eurasian continent in the Quaternary. more...

Tiankeng, a typical Karst relief of the Late Quaternary Period, in the south of China, plays an important role when researching the surface shape and evolution of the Karst relief. The accumulation of Chlorine-36 (T1/2 = 301 ka) through the interaction of cosmic ray particles with Ca, K and Cl in rocks allow it to be used as the ideal nuclide for determination of the exposure age and erosion rate of limestone. In this work, an improved 36Cl sample preparation method for Tiankeng limestone was presented. The Isotope Dilution-AMS technique allows for the simultaneous measurement of 36Cl and Cl with a single AMS sample preparation. The barium introduced during the sample preparation was removed to avoid ionizer poisoning and attain a higher and more stable beam current. The method is particularly suitable for limestone samples, as well as for soil, sediment and water samples. more...

The jungles of Linyun and Longlin Autonomous Prefecture, located in the heart of the southwestern Guangxi Zhuang Autonomous Region of China, are home to the oldest tea trees (Camellia sinensis) in the world. In the absence of regular annual rings, radiocarbon (14C) dating is one of the most powerful tools that can assist in the determination of the ages and growth rates of these plants. In this work, cores were extracted from large ancient tea trees in a central Longlin rain forest; extraction of carbon was performed with an automated sample preparation system. The 14C levels in the tree cores were measured using accelerator mass spectrometry (AMS) at the University of Tsukuba. These measurements indicated that contrary to conventional views, the ages of trees in these forests range up to ~700 years, and the growth rate of this species is notably slow, exhibiting a long-term radial growth rate of 0.039±0.006 cm/yr. It was demonstrated that 14C analyses provide accurate determination of ages and growth rates for subtropical wild tea trees. more...

The first preliminary test of the 14C-accelerator mass spectrometry (AMS) system at the University of Tsukuba was successfully performed using a gas/solid hybrid ion source and an automated sample preparation system with an elemental analyzer (EA). The maximum 12C− current of ∼11 µA was achieved using the optimized CO2 flow rate to the hybrid ion source. The machine background of 14C/12C for the AMS system reached to ∼2.4 × 10−16 (∼0.02 percent modern carbon, pMC) using unprocessed mineral graphite. Moreover, the blank level of 14C/12C including the combustion process for an IAEA-C1 graphite sample was 4.6 × 10−16 (0.05 pMC), demonstrating the low blank level of the automatic sample preparation system. In contrast, the blank level of 14C/12C including the combustion process for an IAEA-C1 CO2 sample was 5.0 × 10−15 (0.49 pMC), an order of magnitude worse than that for the graphite sample. The measurement uncertainty for the gas ion source was 0.6%, 2–3 times worse than that for the solid ion source (0.2%–0.3%). more...

We report on the preliminary studies for two-dimensional (2D) mapping of hydrogen and other elements in materials with transmission ERDA and PIXE using a microbeam of 8 MeV 4He. The extremely enhanced forward recoil cross section of hydrogen in the non-Rutherford scattering allows 2D mapping of hydrogen in the sample. The mapping by PIXE, which provides complementary information to the mapping by ERDA, was obtained simultaneously. The present work probably leads to 3D mapping of hydrogen in bulk materials, i.e., the present spatial 2D plus depth as an additional dimension, since the energy of the outgoing hydrogen corresponds to the depth where the hydrogen is originally located. more...

We study morphological changes on the Si surface induced by the C60 ion beam under various irradiation conditions. The fluence and incident energy of the C60 ion beam was 1 × 1016–1 × 1019 ions/m2 and 50 keV–9 MeV, respectively. The beam’s incident angle to the surface normal was 0° or 60°. As a result of the changes in these variables, three types of nanostructures were observed: concave and convex, stringlike, and ripple structures. Structure shapes or sizes varied with changes in the parameters. Almost all cases showed concave and convex structures at an incident angle of 0°. At a 60° incident angle, stringlike or ripple structures were formed. Stringlike structures were formed at higher incident energy, while ripple structures were formed at lower incident energy. We found that both stringlike and ripple structures can form from sputtering and thermal effects. The formation of string structure requires a thicker amorphous layer and the proper balance of sputtering and annealing. more...

Radioiodine is one of the most important radionuclides released by the accidents of Fukushima Dai-ichi nuclear power plant (FDNPP). Iodine-131 elevated ambient radiation dose rate immediately after the accident, but it is extinguished due to its short half-life. The long-lived 129I can be used as a tracer to retrospectively infer the level of 131I. Understanding of environmental behavior of 129I is important for preparedness against nuclear disaster. This study presents sampling campaigns on the Abukuma River during two high flow events, and discusses riverine 129I behavior based on comparisons with that of 137Cs. The study site was the Kuroiwa site locating at midstream of the Abukuma river. Its catchment area was 2886 km2 and mean 129I inventory in the catchment was 0.041 Bq m-2. Five and seven river water samples were taken during high-flow events in July 2018 (JUL18) and October 2018 (OCT18), respectively. Suspended sediment and filtrate samples were obtained by decantation and subsequent filtration with 0.45 μm-mash membrane filter, respectively. The suspended sediment and filtrate samples were measured for 137Cs activity concentrations with HPGe detector and then measured for 129I/127I ratio with accelerator mass spectrometer and for 127I concentration with ICP-QQQ-MS. Mean 129I activity concentration in suspended sediment during JUL18 and OCT18 were 1.0 and 0.43 mBq kg-1, respectively. In terms of temporal trends, 129I activity concentration in suspended sediment lowered in the peak water discharge phase, contrastive to those of 137Cs which were the highest at peak water discharge phase. Mean dissolved 129I activity concentrations during JUL18 and OCT18 were 0.18 and 0.067 μBq L-1, respectively. Both 129I and 137Cs activity concentrations in dissolved form tended to decrease with time during two high-flow events. Mean apparent distribution coefficient (Kd) during JUL18 and OCT18 were 4.3 ×104 and 6.1 ×103 L kg-1, respectively. The Kd values of 129I were lower than those of 137Cs and it reveal relatively-high solubility of 129I. Total exportation of 129I from the catchment during JUL18 and OCT18 were estimated as 1.0 × 104 and 2.3 × 104 Bq, respectively. Exported 129I in dissolved form accounted for 80 and 27% of total exportations, respectively. By contrast, more than 95% of 137Cs was exported in particulate form in the events. These results indicated an importance of dissolved form for understanding environmental behavior of radioiodine. more...

To evaluate the environmental impact of 14C discharged to the atmosphere from the Tokai nuclear facility during normal operational periods, cores were extracted from an 80-yr-old pine tree that grew close to the Tokai Nuclear Power Plants (Tokai NPP and Tokai-2 NPP) and the Tokai Reprocessing Plant (Tokai RP), and the 14C levels in the annual rings were measured using accelerator mass spectrometry (AMS). The 14C activity ranged from 232 to 403 Bq kg−1 C in the tree rings formed during the period 1959–2013. The activities in the periods 1959–1965 and 2011–2013 represent the background levels, and the activities recorded between 1966 and 2010 are significantly elevated compared with these background levels, indicating uptake by the tree of 14C discharged from the Tokai nuclear facility. The excess 14C activity values of 1.1–70 Bq kg−1 C for the period 1966–2010 are positively correlated with the estimated total annual 14C discharges of 0.019–2.0 TBq from the Tokai NPP, Tokai-2 NPP, and Tokai RP (R2 = 0.72; n = 40). This activity of more...

A horizontal-type 6 MV Pelletron tandem accelerator was installed at the University of Tsukuba, Japan, in September 2014. The first test of the multi-nuclide accelerator mass spectrometry system was performed in March 2016, after two years of construction. This is the first report of its performance. The particle detection system was designed for high-sensitivity detection of 10Be, 14C, 26Al, 36Cl, 41Ca, and 129I. A five-electrode ΔE-E gas-ionization detector was installed as the end station of the detection system. The system background for 14C measurements, with the 4+ charge state at 5.0 MV, has a 14C/12C ratio of ∼2.4 × 10−16. 10Be, 26Al, 36Cl, 41Ca, and 129I have also been successfully detected. The 41Ca/Ca background is ∼3 × 10−15 as a result of improved isobaric separation techniques. more...

The anthropogenic long-lived radionuclide 129I 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 129I as an oceanic tracer in the Northwest Pacific area, specifically in the Japan Sea, the input history of 129I 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 129I/127I ratios in the 1940s were almost at background levels ( more...

A series of nuclides (14C, 26Al, and 36Cl) was measured using the 12UD Pelletron tandem accelerator before replacement by the horizontal 6 MV tandem accelerator at the University of Tsukuba Tandem Accelerator Complex (UTTAC). This paper considers the modification of the accelerator mass spectrometry (AMS) measurement parameters to suit the current 6 MV tandem accelerator setup (e.g., terminal voltage, detected ion charge state, gas pressure, and entrance window material in detector). The Particle and Heavy Ion Transport code System (PHITS) was also used to simulate AMS measurement to determine the best conditions to suppress isobaric interference. The spectra of 41Ca and 41K were then successfully separated and their nuclear spectra were identified; the system achieved a background level of 41Ca/40Ca ∼ 6 × 10 - 14 . more...

A new submicron scanning nuclear microprobe beam line was constructed in early 2016 at the accelerator facility of the University of Tsukuba, Japan. A microbeam scanning endstage (OM-2000, Oxford Microbeams, Oxford, UK) was installed at the end of this system. The distance from the object slit to the target position is 8730 mm and the working distance is 180 mm. This ion microbeam system will be used mainly for X-ray imaging of two-dimensional distributions of light elements in structural materials using particle-induced X-ray emission (PIXE). A silicon drift detector (SDD) with a thin window of Si3N4 was installed to detect characteristic X-rays emitted from light elements such as B, C, and N, which are common additive elements in structural materials. In addition, a superconducting tunnel junction (STJ) array detector is going to be installed to perform PIXE measurements more efficiently. By combining a microbeam scanning technology with the X-ray detectors, we plan to obtain two-dimensional maps of additive light elements in structural materials. Experiments for obtaining proton microbeams are ongoing, and a 6 MeV proton beam with a diameter of between 12 and 20 μm has been obtained to date. more...

Environmental contaminations of 129I were continuously monitored in various sample preparation rooms for accelerator mass spectrometry at the University of Tsukuba. Monitoring of 129I 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 129I 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 (127I) and 129I contamination rates in the alkali trap solutions. It was found that 129I contamination rates were lower than approximately 104 atoms cm-2 day-1 in the rooms where ether no samples or only samples with environmental background levels of 129I were handled. Values from 104 to 105 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 129I, ranging from 106 to 107 atoms cm-2 day-1, were recorded in rooms used for treating neutron-activated iodine. The experimental results show that the 129I level depended on the 129I sample-preparation histories for the respective rooms. It is possible to estimate the 129I contamination risk from the atmosphere to the samples by knowing the 129I level in the preparation room. more...

Three methods to detect neutrons emitted from an electrostatic accelerator were examined. These were gold foil activation, thermoluminescent dosimeters (TLDs), and CR-39. The gold-foil activation method has previously been proven effective in the measurement of neutrons emitted from cyclotron sources. In the case of electrostatic accelerators, a greater amount of fast neutrons and a smaller amount of thermal neutrons are observed compared to a cyclotron accelerator. Therefore, the error in calculating the thermal neutron flux became unacceptably large. By comparison the CR-39 detectors were apparently unable to measure thermal neutrons well, because some tracks were also generated by fast neutrons causing a signal interference. In the case of TLDs, as the material was not sensitive to fast neutrons, it was not affected by them, and hence could adequately measure the thermal neutron flux. However, it was found that in some cases its measurements could be offset by the influence of high dose rate of gamma rays. more...

This manuscript describes our experimental work being carried out to develop the previously published T-ERDA technique to measure H distribution in solids [Yamazaki et al., AIP Adv. 9 (2019) 105111]. From the experiments for the samples with H markers, we have identified the factors that degrade the depth resolution for analysis of H distribution, depending on the acceptance conditions of the detector., Comment: 13 pages, 5 figures more...

Fluid inclusions in quartz samples from a miarolitic cavity, two quartz veins, and a hydrothermal ore vein in the Tsushima granite, Japan, were analyzed by particle-induced X-ray emission to examine the chemistry and process of formation of hydrothermal fluids in an island-arc granite. Most of the inclusions were polyphase or vapor, and there were smaller numbers of two-phase aqueous inclusions. The inclusions contained Cl, K, Ca, Ti, Mn, Fe, Cu, Zn, Ge, Br, Rb, Sr, Ba, and Pb. For each inclusion, there was a strong positive correlation between Cl content and contents of other elements identified. Concentration ranges for most elements (other than Rb and Ge) in polyphase inclusions from the miarolitic cavity were comparable to those from cavities in alkaline granites; those from the ore vein were comparable to large-scale continental hydrothermal ore deposits. The lower Rb and higher Ge contents in the polyphase inclusions of the Tsushima granite may be characteristic of hydrothermal fluids from calc-alkaline granites in an island-arc setting. Br/Cl ratios (by weight) for the vapor and two-phase inclusions were 0.0013–0.0030 and differed among the three geological settings. Br/Cl ratios of polyphase inclusions increased with increasing Cl content in single-crystal and polycrystalline quartz, and high values of more than 0.0100 were found. The high Br/Cl ratios and the differences among the geological settings sampled may be due to pressure dependences of partitioning of Cl and Br between fluid and magma during fluid segregation and between liquid and vapor during boiling. Using a simple model based on these dependences, we calculated Br/Cl ratios greater than 0.01 in brine generated at pressures more...

The Fukushima Daiichi Nuclear Power Plant (F1NPP) accident in 2011 released radionuclides into the atmosphere in both aerosol and gaseous form. Subsequent studies of contamination in the environment have focused on the bulk radioactivity in samples. Comparatively little is known about the relative contribution and patterns of soluble versus particulate deposition of the radionuclides. We investigated a sample of heavily contaminated surface soil from a site 20 km northwest of the F1NPP and isolated four radioactive particles from the surrounding soil. These particles had a maximum particle area equivalent diameter of 6.4 μm and a maximum 137Cs radioactivity of 67.5 ± 0.1 Bq per particle. They were larger than the particles identified in aerosol samples shortly after the accident at a location 170 km southwest of the F1NPP. Two of the particles were spherical and two were fragmental. Silicates were a major component of the Fukushima radioactive particles. These characteristics clearly differ from the so-called hot particles observed at the Chernobyl accident in 1986. Clarifying the physical and chemical properties of the radionuclides released from the F1NPP accident is important for assessing the potential long-term impacts to humans. more...

The anthropogenic long-lived radionuclide

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. more...

We have performed an experiment on charged droplet formation in a humidified N2 gas with trace SO2 concentration and induced by 20MeV proton irradiation. It is thought that SO2 reacts with the chemical species, such as OH radicals, generated through the reactions triggered by N2+ production. Both droplet number and droplet size increased with SO2 consumption for the proton irradiation. The total charged droplet numbers entering the differential mobility analyzer per unit time were proportional to the 0.68 power of the SO2 consumption. These two findings suggest that coagulation among the small droplets contributes to the formation of the droplets. The charged droplet volume detected per unit time is proportional to the SO2 consumption, which indicates that a constant amount of sulfur atoms is contained in a unit volume of droplet, regardless of different droplet-size distributions depending on the SO2 consumption. more...

Accelerator mass spectrometry (AMS) is one of method used for 90 Sr determination. It would enable rapid 90 Sr measurements from environmental samples such as water, soil, and milk. However, routine analysis of 90 Sr using AMS has not yet been achieved because of difficulties associated with isobaric separation and production of intense negative ion beams characterized by currents from hundreds of nanoamperes to several microamperes. We have developed a rapid procedure for preparing samples with optimum compositions for use with AMS, which enables production of intense Sr beam currents from an ion source. Samples of SrF 2 were prepared from a standard Sr solution and agricultural soil. The time required to prepare a SrF 2 sample from a soil sample was 10 h. Negative 88 SrF 3 − ions were successfully extracted at 500 nA from mixed samples of SrF 2 and PbF 2 . In the present work, negative ions of 90 Zr, included as an impurity, were accelerated with a tandem accelerator operated at a terminal voltage of 5 MV. Ions characterized by a charge state of 6+ were channeled into a gas counter. An atomic ratio of 90 Zr/ 88 Sr of 3 × 10 −8 was estimated for the soil sample. No signal was detected from the assay of PbF 2 , which was pressed in an aluminum cathode, for a mass number of 90. PbF 2 revealed good performance in the production of negative SrF 3 − molecular ion beams and detection of 90 Sr with a gas counter. more...

In March 2011, vast amounts of radionuclides were released into the environment due to the Fukushima Daiichi Nuclear Power Plant (F1NPP) accident. However, very little work has been done concerning accident-derived long-lived nuclides such as 129I (T1/2 = 1.57 × 107 year) and 36Cl (T1/2 = 3.01 × 105 year). 129I and 131I are both produced by 235U fission in nuclear reactors. Being isotopes of iodine, these nuclides are expected to behave similarly in the environment. This makes 129I useful for retrospective reconstruction of 131I distribution during the initial stages of the accident. On the other hand, 36Cl is generated during reactor operation via neutron capture reaction of 35Cl, an impurity in the coolant or reactor component. Resulting 36Cl/Cl ratio within the reactor is thus much higher compared to that in environment. Similar to 129I, 36Cl is expected to have leaked out during the accident and it is important to evaluate its effects. In this study, 129I concentrations were determined in several surface soil samples collected around F1NPP. Average 129I/131I ratio was estimated to be 26.1 ± 5.8 as of March 11, 2011, consistent with calculations using ORIGEN2 code and other published data. 36Cl/Cl ratios in some of the soil samples were likewise measured and ranged from 1.1 × 10−12 to 2.6 × 10−11. These are higher compared to ratios measured around F1NPP before the accident. A positive correlation between 36Cl and 129I concentration was observed. more...

The deposition density and extent of subsurface infiltration of 129I were investigated within the area highly contaminated by the March 2011 accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in Japan. Depth profiles of 129I activity and 129I/127I ratios were measured in 5-cm-long soil cores that were collected 20–27 months after the accident from three sites (S-1, S-2, and S-3) within 10 km to the west and northwest of the FDNPP. These profiles were compared with the background levels of 129I from the same areas. The deposition densities of 129I were 2.17 Bq m−2 at S-1, 0.80 Bq m−2 at S-2, and 1.41 Bq m−2 at S-3, which are, respectively, about 160, 60, and 100 times larger than the background level (12.8–14.8 mBq m−2). The average 129I/127I ratios in each soil core after the accident (S-1: 2.1 × 10−6; S-2: 4.2 × 10−7; S-3: 2.3 × 10−6) were similar to the value typically found in contaminated surface soil within 80 km of the FDNPP. Therefore, accident-derived 129I deposited at S-1 (4.3 km west of the FDNPP) was 2.7 times larger than at S-2 (8.2 km west of the FDNPP), and 1.5 times larger than at S-3 (7.5 km northwest of the FDNPP). Depth profiles showed that the 129I activity and 129I/127I ratios decayed exponentially with depth. ∼90% of accident-derived 129I deposited in the soil cores was concentrated in the upper 25.2–26.4 kg m−2 of mass depth (2.1–3.1 cm depth). The relaxation mass depths (h0) of 129I were 9.49–11.2 kg m−2 at the three sampling sites, and these values are comparable to those of accident-derived 131I (10.4 kg m−2) at a site 40 km northwest of the FDNPP. more...

We have investigated vertical distributions of 110mAg, 131I, 129mTe, and 137Cs 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 131I, 129mTe, and 137Cs were explained with distribution coefficients (Kd) but that of 110mAg was not explained. Particulate form was observed for the 137Cs; number of the particle was proportional to the 137Cs concentration in the soil sample. more...

We have measured microscopic 3-dimensional distribution of plasma-charged hydrogen in polycrystalline Al. The measurements have been carried out nondestructively by using elastic recoil detection analysis under transmission geometry of a collimated 8 MeV 4He2+ beam. The recoil cross section as large as 2 × 103 mb/sr due to the nuclear elastic collision allowed observation of the spatial distribution of hydrogen in the Al sample of 80 μm thickness. The distribution maps of hydrogen clearly visualize hydrogen bubbles of 10–20 μm diameter in the surface layer of about 12 μm thickness. The critical concentration of hydrogen minimally needed for growth of the hydrogen bubble of ten-μm size has been determined to be 1.6 × 1020 cm−3. more...

We have measured the backward yield of secondary electrons induced by 1 MeV C 2 + coincident with the emerging projectiles. The total electron yield decreased by a few percent with the number of detected projectiles, which indicates the contribution of inner-shell electron excitation to the secondary-electron yield. The inner-shell contribution for the C 2 + impact was approximately the same as that for the C + impact, whereas the cluster effect on the total secondary electron yield remains. more...

We report on a new route for synthesizing metastable anatase tantalum oxynitride (TaON) in thin film form on lattice-matched (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7 (LSAT) single crystals by using nitrogen plasma assisted pulsed laser deposition. Epitaxial stress from the substrate stabilized the anatase structure without the need for doping an impurity, such as Sc or Mg, which is required in conventional bulk synthesis by ammonolysis. X-ray diffraction measurements and cross-sectional transmission electron microscope (TEM) observations demonstrated the growth of phase-pure anatase TaON thin films with the epitaxial relationships (001)TaON ∥ (001)LSAT and [100]TaON ∥ [100]LSAT. A high growth temperature (≥750 °C) and a balanced supply of oxygen and nitrogen are crucial for obtaining high-quality anatase TaON thin films. The films grown at 800 °C exhibited good n-type conduction with a resistivity of ∼1 × 10–2 Ω cm. The source of the carrier electrons was likely anion vacancies. The Hall mobility of anatase TaON (... more...

We apply the capillary beam-focusing method for the C 60 fullerene projectiles in the velocity range between 0.14 and 0.2 a.u. We study the C 60 transmission properties through two different types of capillaries: (1) borosilicate glass microcapillary with an outlet diameter of 5.5 μm, and (2) Al 2 O 3 multi-capillary foil with a pore size of about 70 nm and a high aspect ratio of about 750. We measured the transmitted particle composition by using the electrostatic deflection method combined with the microchannel plate imaging technique. For the experiments with the single microcapillary, the main transmission component is found to be primary C 60 beams that are focused in the area equal to the capillary outlet diameter. Minor components are charge-exchanged C 60 ions and charged or neutral fragments (fullerene-like C 60-2 m and small C n particles), and their fractions decrease with decreasing the projectile velocity. It is concluded that the C 60 transmission fraction is considerably high for both types of the capillaries in the present velocity range. more...

Tiankeng is a typical Karst relief of the late Quaternary Period. Studies on the exposure ages of Tiankeng are very important in geographical research to elucidate the formation condition, the developing process, and the features of biological species. 36 Cl on the surface layer of the rupture cross-section of Tiankeng is largely produced by cosmogenic high-energy neutron induced reactions 40 Ca(n, αp) and 39 K(n, α), and has accumulated since the formation of the Tiankeng. Low-energy neutron reaction 35 Cl(n, γ) contributes a small portion of 36 Cl. In this work, the concentration of the cosmogenic 36 Cl in rock samples taken from Dashiwei Tiankeng, Leye County, Guangxi Zhuang Autonomous Region, China, was measured jointly by Accelerator Mass Spectrometry (AMS) laboratories of CIAE and University of Tsukuba in an effort to estimate the formation time (or exposure age) of the Tiankeng. The results show that the exposure time of Da Shiwei Tiankeng is about 26 ± 9.6 ka (without erosion correction). The sampling strategy and procedures, experimental set-up, and preliminary results will be presented in detail. more...

We study the transmission properties of fast cluster ions (Cn+ (n = 2–4) with velocities ranging from 0.89 to 1.79 a.u.) through a single tapered capillary with an outlet diameter of 13.7 μm. We investigate the projectile-velocity dependence of the transmission fraction from the measurements of transmitted particle energy spectra. It is found that the non-fragmentation fraction of C2+ projectiles increases with decreasing velocity, indicating that fragmentation occurs mainly via close collisions with the surfaces of the capillary wall. For Cn+ (n = 2–4) ions with the same incident velocity, the cluster-size dependence of the non-fragmentation fraction shows even–odd alternation, implying that the fraction includes contributions from stable clusters surviving the grazing scattering process at the capillary surface. We also find that the angular distribution of transmitted particles is narrower for cluster projectiles compared with atomic projectiles. more...

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 × 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 × 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 × 105 years), 36Cl remains even after tritium is no longer available. more...

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 36 Cl 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 10 5 yr. more...