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The activation product chlorine-36 (36Cl) is an important radionuclide within the context of the disposal of nuclear wastes, due to its long half-life and environmental mobility. Its behaviour in a range of potential cementitious encapsulants and backfill materials was studied by evaluating its uptake by pure cement hydration phases and hardened cement pastes (HCP). Limited uptake of chloride was observed on calcium silicate hydrates (C-S-H) by electrostatic sorption and by calcium monosulphoferroaluminate hydrate (AFm) phases, due to anion exchange/solid solution formation. Diffusion of 36Cl through cured monolithic HCP samples, representative of cementitious materials considered for use in deep geological repositories across Europe, revealed a markedly diverse migration behaviour. Two of the matrices, a ground granulated blast furnace slag/ordinary Portland cement blend (GGBS–OPC) and an ordinary Portland cement (CEM I) effectively retarded 36Cl migration, retaining the radionuclide in narrow, reactive zones. The migration behaviour of 36Cl within the cementitious matrices is not strictly correlated to the measured sorption distribution ratios (Rd-values), suggesting that physical factors related to the microstructure can also have a distinct effect on diffusion behaviour. The findings have implications when selecting cementitious grouts and/or backfill materials for 36Cl-bearing radioactive wastes. [ABSTRACT FROM AUTHOR]

Cave carbonate mineral deposits (speleothems) contain trace elements that are intensively investigated for their significance as palaeoclimate and environmental proxies. However, chlorine, which is abundant in marine and meteoric waters, has been overlooked as a potential palaeo-proxy, while cosmogenic 36Cl could, in principle, provide a solar irradiance proxy. Here, total Cl concentrations analysed from various speleothems were low (3–14 mg/kg), with variations linked to crystal fabrics. High-resolution synchrotron radiation micro X-ray fluorescence (μ-XRF) trace element mapping showed Cl often associated with Na, Si, and Al. We propose that speleothems incorporate Cl in two fractions: (1) water soluble (e.g., fluid inclusions) and (2) water insoluble and strongly bound (e.g., associated with detrital particulates). However, disparities indicated that alternate unidentified mechanisms for Cl incorporation were present, raising important questions regarding incorporation of many trace elements into speleothems. Our first measurements of 36Cl/Cl ratios in speleothems required large samples due to low Cl concentrations, limiting the potential of 36Cl as a solar irradiance proxy. Critically, our findings highlight a knowledge gap into how Cl and other trace elements are incorporated into speleothems, how the incorporation mechanisms and final elemental concentrations are related to speleothem fabrics, and the significance this may have for how trace elements in speleothems are interpreted as palaeoclimate proxies. [ABSTRACT FROM AUTHOR]

The knowledge of the residence time of formation water is fundamental to understanding the subsurface flow and hydrological setting. To better identify the origin and evolution of coal seam water and its impact on gas storage and production, this study collected coalbed methane co‐produced water in the southeast Qinshui Basin and detected chemical and isotopic compositions, especially 36Cl and 129I concentrations. The calculated tracer ages of 129I (5.2–50.6 Ma) and 36Cl (0.13–0.76 Ma) are significantly younger than the age of coal‐bearing formation (Pennsylvanian ‐ Cisuralian), indicating freshwater recharge after coal deposition. The model that utilises 129I/I and 36Cl/Cl ratios to constrain the timing of recharge and the proportion of recharge water reveals that over 60% of pre‐anthropogenic meteoric water entered coal seams since 10 Ma and mixed with residue initial deposition water, corresponding to the basin inversion in Cenozoic. The spatial distribution of major ion concentrations reveals the primary recharge pathway for meteoric water from coal outcrops at the eastern margin to the basin center. This study demonstrates the occurrence of higher gas production rates from wells that accept water recharge in recent times and suggests the possible potential of the non‐stagnant zones for high gas production. [ABSTRACT FROM AUTHOR]

• Status report of JAEA-AMS-TONO in the last four years (2017–2020). • Two accelerator mass spectrometers (JAEA-AMS-TONO-5MV and JAEA-AMS-TONO-300 kV) in operation. • Application studies including dating of geological samples. • Technical development of isobar separation and sample preparation. The JAEA-AMS-TONO facility at the Tono Geoscience Center, Japan Atomic Energy Agency has two accelerator mass spectrometers (AMSs): JAEA-AMS-TONO-5MV and JAEA-AMS-TONO-300 kV. The JAEA-AMS-TONO-5MV has a 5 MV Pelletron™ accelerator (15SDH-2, National Electrostatics Corp., US) and was installed in 1997. The JAEA-AMS-TONO-300kV is a state-of-the-art multi-nuclide AMS with a 300kV Tandetron™ accelerator (4103Bo-AMS, High Voltage Engineering, Europa B.V., Netherlands) and was installed in 2020 in response to an increase of samples. The AMSs have been used to measure radiocarbon, beryllium-10, aluminium-26 and iodine-129 in geological samples in studies on long-term geological stability as a basic research and development related to the geological disposal of high-level radioactive waste. Recently, test measurement of chlorine-36 using the JAEA-AMS-TONO-5MV are proceeding. Furthermore, we are currently promoting the development of techniques for isobar separation in AMS and for sample preparation. To remove isobaric interference, fast ion surface channeling is applied and a prototype for downsizing of the AMS based on this technique has been built. Also, small sample graphitization for 14C has been attempted by using an automated graphitization system (AGE3, Ionplus, Switzerland) equipped with an elemental analyzer (Vario Micro cube, Elementar Analysensysteme GmbH, Germany). [ABSTRACT FROM AUTHOR]

Many radionuclides were released to the environment during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in Japan in March 2011, including 36Cl, and were transported in the atmosphere and deposited over large areas. However, there have been few studies of the 36Cl release from the FDNPP, and the actual amounts released and deposited have not been accurately quantified. Concentrations of 36Cl in rainwater samples collected monthly at Tsukuba, Japan, during the period January 2010 to September 2011, were determined by accelerator mass spectrometry and used to calculate depositions. In March 2011, the monthly deposition of 36Cl was (1.03 ± 0.02) × 10–4 Bq m−2, 18 times higher than the average for March in previous years. Monthly 36Cl deposition was correlated with that of 129I (r = 0.7) and 137Cs (r = 0.8) measured in the same rainwater samples from April to August 2011. The total amount of 36Cl released by the FDNPP accident was estimated to be (1.4 ± 0.2) × 108 Bq based on the 129I/36Cl deposition ratio of March 2011. [ABSTRACT FROM AUTHOR]

We examine the relationship of channel steepness to incision rate from channels eroding into a previously tilted, planar, and progressively exhumed unconformity surface. Channel and unconformity slopes are measured from a suite of channels developed on erosionally resistant Paleozoic limestone exhumed by the removal of Cenozoic sediments from the Baybeiche Range bordering the Naryn basin in the western Tian Shan. The compiled data set, sampling 5 orders of magnitude of upstream drainage area (0.03 to 227 km2), is used to derive the exponent, n, relating channel steepness to channel incision rate and the ratio, K/V, of the rate constant for channel incision of the resistant substrate, K, to the erosion rate, V, of the cover strata. We show that for a typical value of intrinsic concavity (slope-area exponent, θ=0.5), erosion rates that are proportional to specific stream power (n=1) satisfy the data set. However, valley width data suggest that the intrinsic concavity is higher (θ=0.8) and that incision data can also be fit if erosion is proportional to basal shear stress (n=2/3). Our results do not support values of n significantly greater than one. Using36Cl exposure age dating of the unconformity surface, we independently demonstrate that the Cenozoic cover strata have been progressively stripped downward from the unconformity surface at a vertical rate of 1 to 2 m/kyr. Using V=1 m/kyr, we constrain the rate constant, K, to between 6 ± 1 and 9 ± 2 ×10 -4kyr-1 for incision of resistant limestone bedrock in this field setting. Key Points Channel incision relation to steepness calibrated from tilted bedrock surface Chlorine-36 exposure age-dating shows bedrock surface exhumed at 1 to 2 m/kyr Low n values, consistent with shear stress (n=2/3) satisfy field data ©2014. American Geophysical Union. All Rights Reserved.

Current status of MALT (Micro Analysis Laboratory, Tandem accelerator, The University of Tokyo) and recent achievements both in development and application are reported. Multi-nuclide AMS (10Be, 14C, 26Al, 36Cl, 129I) system is available and shows good performance as well as PIXE, NRA, ERDA/RBS systems. 236U-AMS system was developed and the background of 236U/238U = 3 × 10−10 was so far achieved. A test bench beam line for Laser Photo Detachment was also constructed for the development of the future isobar separation technique. Among various application fields using AMS, the study of iodine isotope system, both natural and anthropogenic, has been the most energetically promoting research field at MALT in recent years. We proposed natural equilibrium isotopic ratio 129I/127I as 2.0 × 10−13 in marine environment. We also contributed to reconstruction of initial 131I deposition distribution due to the Fukushima Daiichi Nuclear Power Plant accident. [ABSTRACT FROM AUTHOR]

On Crete—as is common elsewhere in the Mediterranean—carbonate massifs form high mountain ranges whereas topography is lower in areas with meta‐clastic rocks. This observation suggests that differences in denudational processes between carbonate‐rich rocks and quartzofeldspathic units impart a fundamental control on landscape evolution. Here we present new cosmogenic basin‐average denudation rate measurements from both 10Be and 36Cl in meta‐clastic and carbonate bedrock catchments, respectively, to assess relationships between denudation rates, processes, and topographic form. We compare total denudation rates to dissolution rates calculated from 49 new and previously published water samples. Basin‐average denudation rates of meta‐clastic and carbonate catchments are similar, with mean values of ~0.10 mm/a and ~0.13 mm/a, respectively. The contribution of dissolution to total denudation rate was <10% in the one measured meta‐clastic catchment, and ~40% for carbonate catchments (~0.05 mm/a), suggesting the dominance of physical over chemical weathering at the catchment scale in both rock types. Water mass‐balance calculations for three carbonate catchments suggests 40–90% of surface runoff is lost to groundwater. To explore the impact of dissolution and infiltration to groundwater on relief, we develop a numerical model for carbonate denudation. We find that dissolution modifies the river profile channel steepness, and infiltration changes the fluvial response time to external forcing. Furthermore, we show that infiltration of surface runoff to groundwater in karst regions is an efficient way to steepen topography and generate the dramatic relief in carbonates observed throughout Crete and the Mediterranean. Key Points: Quantifying chemical and mechanical denudation in meta‐clastic and carbonate bedrockDominance on mechanical denudation in karstic terrainsDissolution and infiltration in carbonate terrains influence the shape and response of river profiles to external forcing [ABSTRACT FROM AUTHOR]

Quantifying denudation rates under different climatic and tectonic settings is fundamental to understanding landscape evolution. Carbonate rocks may respond differently to climatic and tectonic forcings than other rock types because of their tendency to dissolve congruently. Yet, there is little information on the long-term denudation rate of carbonates and their controlling factors in different settings. Here, we present the first long-term denudation rates for carbonates in the south of the Central Anatolian Plateau. We quantified the outcrop denudation rates using in-situ cosmogenic 36Cl measured in 13 rock samples to evaluate spatial variations and potential controls on the style and rate of denudation. 36Cl-derived denudation rates range from 1.92 ± 0.31 to 45.77 ± 3.91 mm/ka. On the plateau, denudation rates are strongly correlated with precipitation and are lower than the theoretical maximum dissolution rates predicted assuming zero evaporation, implying that climate exerts the major control on carbonate denudation. These results indicate that chemical weathering is the prevalent denudation style. The denudation pattern shows spatial variability with a decreasing trend from SW to NE consistent with climate zones. High-to-moderate denudation rates occur in the continental climate, while the lowest denudation rates occur in the arid plateau interior. In the Mediterranean coastal region, measured denudation rates are higher than the predicted maximum dissolution rates, reflecting the mechanical removal of overlying rock or soil. The low denudation rates in the plateau interior indicate a slowly evolving landscape with an arid climate. The physical properties of rocks showed the weakest control on carbonate denudation. In the Central Taurides, significant infiltration of surface runoff resulted in strong subsurface karstification at the expense of surface drainage. This process caused disequilibrium between uplift and denudation and resulted in the preservation of high-elevation topography. Therefore, in the actively uplifting plateau margin, the influence of tectonics on carbonate denudation has been interfered with the impact of precipitation and subsurface karstification. • 36Cl-derived denudation rate of carbonate rocks ranges from 1.92 to 45.77 mm/ka. • Precipitation exerts a major control on denudation of carbonate rocks. • Chemical weathering is the dominant style of denudation on the plateau. • Denudation pattern shows spatial variability with a decreasing trend from SW to NE. • The efficient drainage of runoff by karstification delayed the response to uplift. [ABSTRACT FROM AUTHOR]

Constraining the age of young lavas, which generally fall outside the effective range of traditional geochronology methods, remains a key challenge in volcanology, limiting the development of high-resolution eruption chronologies. We present an in situ cosmogenic 3He and 36Cl surface-exposure chronology, alongside new minimum-limiting 14C ages, documenting young eruptions at five sites in the Western Cordillera, southern Peru. Four 3He-dated lavas on the Nevado Coropuna volcanic complex (hitherto thought to be dormant) indicate that the central dome cluster is young and potentially active; two Holocene lavas on the easternmost dome are the youngest directly dated lavas in Peru to date. East of Coropuna, lava domes and block-lava flows represent the most extensive output to date of Nevado Sabancaya, one of Peru's most active volcanoes. Two 3He measurements confirm the Holocene age of these deposits and expand the chronology for one of the youngest major lava fields in Peru. 36Cl surface-exposure ages from the Purupurini dome cluster and Nevado Casiri document middle-late-Holocene episodes of effusive activity, while basal 14C ages from a lava-dammed wetland constrain an effusive eruption at Mina Arcata, north of Coropuna, to the late-glacial period. These new data advance the recent Western Cordillera volcanic record whilst demonstrating both the considerable potential and fundamental limitations of cosmogenic surface-exposure methods for such applications. [ABSTRACT FROM AUTHOR]

Abstract Documenting the sources and residence times of water that contributes to streamflow is important for understanding processes in river catchments. The residence times of bank storage and return flow and its influence on river water chemistry in the upper Barwon River of southeast Australia were investigated using stable (18O, 2H, and 13C) and radioactive (3H and 36Cl) isotopes, major ion geochemistry, river discharge data, and electrical conductivity (EC)-discharge hysteresis. Elevated 3H activities following high winter flows indicate that bank storage and return flow contributes to river discharge for at least several months. However, EC-discharge hysteresis patterns suggest that individual storm events make additional contributions to bank storage and return flow throughout the year over periods of a few weeks. 3H activities in the upper Barwon River are >1.75 TU throughout the year, suggesting that the contribution of older regional groundwater, which has 3H activities <0.04 TU, is relatively minor in comparison to bank return flows. However, downstream trends in total dissolved solids (TDS) concentrations, δ13C values and R36Cl values demonstrate that regional groundwater inflows deliver solutes to the river. Estimates of regional groundwater inflows are mainly in the range 8–33% of total stream flow. The R36Cl values of river water in the upper Barwon catchment are between 37 and 46, which are significantly higher than those of modern rainfall (∼20). The high R36Cl values may reflect retardation of bomb-pulse 36Cl due to plant uptake and recycling in the soil zone, which suggests Cl residence times of up to ∼60 years. The results of this study demonstrate that river water is comprised of both young and old water and that managing rivers and near-river environments should include careful consideration of both inputs. Highlights • Bank storage and return flow following high winter streamflow has a residence time of several months, if not longer. • Bank storage and return flow following individual storm events has a residence time on the order of a few wees • High chlorine-36 ratios in river water may be due to plant uptake and recycling of bomb-pulse 36-Cl in soils. [ABSTRACT FROM AUTHOR]

The amounts of technogenic carbon and chlorine contained in reactor graphite and in the biosphere are compared. The total amount of 14C on Earth and in the atmosphere, according to a rough estimate, is 2.0 × 108 Ci, while in all reactor graphite in Russia this value is no more than 3 × 107 Ci. The amount of 36Cl in reactor graphite is approximately (0.2–5) × 103 Ci, which is many times less than its content in the ocean, 7.16 × 108 Ci. Therefore, when disposing of reactor graphite waste in a near-surface storage, the yield of 14C and 36Cl will not lead to significant disproportions in their accumulation in the biosphere [ABSTRACT FROM AUTHOR]

Abstract Erosion rates offer insight on landscape development and the relative importance of chemical and physical processes of weathering. Minimal chemical weathering makes Antarctica an ideal location in which to compare the physical weathering of carbonate rocks to other lithologies. Here we report the first cosmogenic nuclide-derived erosion rates for carbonate rocks in Antarctica. Carbonate samples collected in the southernmost Ellsworth Mountains reflect a 36Cl erosion rate of 0.22 ± 0.02 mm/ka. This erosion rate is consistent with other reported Antarctic erosion rates, but is lower than 36Cl erosion rates derived from other arid regions in the world. These results are integrated with a continent-wide reanalysis of 28 cosmogenic nuclide erosion rate studies (>200 measurements), which comprise numerous rock types and multiple cosmogenic nuclides. By combining cosmogenic nuclide-derived erosion rates across studies, the larger trends provide insight into factors (e.g. lithology, glacial history, and availability of abrasive material) affecting subaerial erosion rates in Antarctica. Statistical analysis of the compiled data set shows differences based on lithology, with sandstone having the largest range of erosion rates. The compiled data also reveals higher erosion rates in areas with a large potential sediment supply, like the Dry Valleys. Samples collected from boulders yield lower erosion rates than those collected from bedrock, likely due to a combination of physical processes that affect boulders and bedrock differently, and glacial history, which can affect the apparent cosmogenic-nuclide derived erosion rate. Highlights • Low cosmogenic 36Cl erosion rates from carbonate bedrock in Antarctica. • Statistical analysis of compiled Antarctic erosion studies shows lithologic dependence. • Boulder erosion rates are lower than bedrock erosion rates. • Higher erosion in the Dry Valleys is likely due to sediment supply. • Consistent, low erosion rates support the dominance of mechanical processes. [ABSTRACT FROM AUTHOR]

The residence times of groundwater and chloride and the processes contributing to the development of saline (total dissolved solids (TDS) up to 45,379 mg/L) groundwater within the Barwon River Catchment of southeast Australia were investigated using major ion, stable isotope (δ 18 O, δ 2 H, and δ 13 C) and radioactive isotope ( 3 H, 14 C, 36 Cl) geochemistry. The elevated groundwater salinity in the region is primarily due to evapotranspiration and recycling of solutes in saline lakes with minor contributions from weathering of halite, silicate and calcite minerals. Groundwater residence times estimated from 14 C vary from modern to ~ 20 ka; for groundwater with lower 14 C activities, the estimated residence times vary significantly depending on the assumed flow model and the 14 C activity of recharge. Chloride residence times downgradient of Lake Murdeduke (a saline through-flow lake in the centre of the catchment) are greater than the corresponding groundwater residence times due to the recycling of Cl within the lake. Precise estimates of chloride residence time could not be determined using 36 Cl due to R 36 Cl in precipitation being lower than that of groundwater. This is most likely due to R 36 Cl values in rainfall having been higher in the past than they are at present due to climate variability. δ 18 O, δ 2 H, and δ 13 C values also suggest that the region has experienced increasingly more evaporative conditions with time. The results of this study demonstrate that, while Cl is a useful tracer of hydrological processes, it must be applied carefully in arid and semi-arid regions of the world. In particular, recharge rates calculated using chloride mass balance may be underestimated where recycling of Cl has occurred. [ABSTRACT FROM AUTHOR]

Geochronological constraints on the deglaciation of former marine based ice streams provide information on the rates and modes by which marine based ice sheets have responded to external forcing factors such as climate change. This paper presents new 36 Cl cosmic ray exposure dating from boulders located on two moraines (Glen Brittle and Loch Scavaig) in southern Skye, northwest Scotland. Ages from the Glen Brittle moraines constrain deglaciation of a major marine terminating ice stream, the Barra-Donegal Ice Stream that drained the former British-Irish Ice Sheet, depending on choice of production method and scaling model this occurred 19.9 ± 1.5–17.6 ± 1.3 ka ago. We compare this timing of deglaciation to existing geochronological data and changes in a variety of potential forcing factors constrained through proxy records and numerical models to determine what deglaciation age is most consistent with existing evidence. Another small section of moraine, the Scavaig moraine, is traced offshore through multibeam swath-bathymetry and interpreted as delimiting a later stillstand/readvance stage following ice stream deglaciation. Additional cosmic ray exposure dating from the onshore portion of this moraine indicate that it was deposited 16.3 ± 1.3–15.2 ± 0.9 ka ago. When calculated using the most up-to-date scaling scheme this time of deposition is, within uncertainty, the same as the timing of a widely identified readvance, the Wester Ross Readvance, observed elsewhere in northwest Scotland. This extends the area over which this readvance has potentially occurred, reinforcing the view that it was climatically forced. [ABSTRACT FROM AUTHOR]

The Cosmic-Ray Produced Nuclide Systematics on Earth Project (CRONUS-Earth Project) has reused a limited number of ‘legacy’ 10 Be, 26 Al, and 36 Cl samples of latest Pleistocene age for the assessment of cosmogenic nuclide production rates independently derived by the CRONUS-Earth Project. The studies re-evaluated here include ones from the Sierra Nevada, California, originally measured by Nishiizumi et al. (1986), Evans et al. (1997), and Phillips et al. (2009). We have also analyzed a limited number of new samples from the same area. We have reevaluated the geological context of the legacy samples, their chronological controls, and the consistency of the data. The locations and settings of the 1986 samples for 10 Be and 26 Al calibration can be verified to within reasonable degree of precision using comparison of published locations and field photos with Google Earth imagery. Two cosmogenic sites, Greenstone Lake and Baboon Lakes, were also the localities where key 14 C samples for glacial chronology were collected, giving confidence in the application of the 14 C constraints to the cosmogenic nuclide samples. A considerable amount of more distant radiocarbon dating work supports an age of 15,750 ± 500 years for the exposure of the cosmogenic calibration samples associated with the Tioga 4 glacial retreat. These samples do all appear to be on surfaces that were exposed by final Tioga glacier retreat (15,750 ± 500 years), but below the limits of the Recess Peak advance (13,550–13,050 years). The 36 Cl samples reported by Phillips et al. (2009) and Evans et al. (1997) were from the terminal moraine of the last Tioga glacier advance (16,100 ± 500 years), the final Tioga glacier retreat (15,750 ± 500 years), and the Recess Peak glacial episode (13,300 ± 250 years). When ages are calculated for these samples using the final CRONUS-Earth Project production rates and scaling models, they are in good agreement with the independent radiocarbon age control, with the exception of the 36 Cl ages from the Recess Peak episode, which average about 15% young. The most likely reasons for this discrepancy are either inadequate understanding of snow shielding or error in the assignment of the age of the Recess Peak glacial advance. [ABSTRACT FROM AUTHOR]

The Cosmic-Ray prOduced NUclide Systematics on Earth Project (CRONUS-Earth Project) has reused a limited number of ‘legacy’ 10 Be and 36 Cl samples from late Pleistocene moraines in the Sierra Nevada for the testing and evaluation of cosmogenic nuclide production rates derived by the CRONUS-Earth Project. A secure glacial chronology for the range is necessary for this purpose. Evidence for the timing of glacial fluctuations is provided by direct radiocarbon ages marking glacial termini at various times and by chronologies on lacustrine cores, marine cores, and speleothem records. Evaluation of these records yields a relatively consistent picture. Tioga 3 glaciers were close to their maximum extent from >20 to about 17 ka. Close to 17 ka they retreated rapidly, then began to readvance at ∼16.8 ka. The Tioga 4 readvance culminated at about 16.2 ka and rapid retreat ensued, with the equilibrium line altitude rising by 400 m by 15.7 ka and the range probably virtually ice-free by a short time thereafter. There is no evidence of ice readvance until the Recess Peak glaciation. Dating of this readavance is inconsistent, with direct dates on glacial features and some lacustrine and speleothem records placing it between 14.0 and 13.0 ka, but many regional records are more consistent with an advance during the interval 13.0 to 12.6 ka. After consideration of all the evidence I have assigned ages of 15.75 ± 0.5 ka for Tioga 4 retreat and 13.3 ± 0.25 for the maximum extent of the Recess Peak glaciation. [ABSTRACT FROM AUTHOR]

This study aims at determining the chlorine and chlorine-36 fallout rates in an experimental beech forest site located in NE France (48°31′55″ N, 5°16′8″ E). A monthly record of Cl and 36 Cl concentrations in rainfall samples collected above the canopy was performed during two years, from March 2012 to February 2014. The results show that the Cl concentrations mainly originate from sea-spray while the 36 Cl concentrations originate from the stratosphere and therefore present a seasonal dependency. Abrupt and important inputs of 36 Cl from the stratosphere indeed yield sharp increases of the recorded concentrations during the spring-summer. We also show that a too short sampling period might bias the determined 36 Cl fallout rate. To smooth the seasonal and sporadic bursts of 36 Cl, a minimum of 6 months sampling period is required. A mean 36 Cl fallout rate of (77 ± 21) atoms m −2 s −1 can be deduced from our study, which is 45% higher than the modelled value. This discrepancy suggests more studies aiming at measuring the 36 Cl fallout rate worldwide are necessary. [ABSTRACT FROM AUTHOR]

The present study aims to estimate the residence time of groundwater based on bomb-produced36Cl.36Cl/Cl ratios in the water samples are determined by inductively coupled plasma mass spectrometry and liquid scintillation counting.36Cl/Cl ratios in the groundwater were estimated to be 1.0–2.0 × 10−12. Estimates of residence time were obtained by comparing the measured bomb-derived36Cl concentrations in groundwater with the background reference. Dating based on a36Cl bomb pulse may be more reliable and sensitive for groundwater recharged before 1975, back as far as the mid-1950s. The above36Cl background concentration was deduced by determining the background-corrected Dye-3 ice core data from the frozen Arctic data, according to the estimated total36Cl resources. The residence time of 7.81 × 104y is obtained from extrapolated groundwater flow velocity.36Cl concentration in groundwater does not reflect the input of bomb pulse36Cl, and it belongs to the era before 1950. [ABSTRACT FROM PUBLISHER]

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Models of the production of cosmogenic nuclides typically incorporate an adjustable production rate parameter that is scaled for variations in production with latitude and altitude. In practice, this production rate parameter is set by calibration of the model using cosmogenic nuclide data from sites with independent age constraints. In this paper, we describe a calibration procedure developed during the Cosmic-Ray Produced Nuclide Systematics on Earth (CRONUS-Earth) project and its application to an extensive data set that included both new CRONUS-Earth samples and samples from previously published studies. We considered seven frameworks for elevation and latitude scaling and five commonly used cosmogenic nuclides, 3 He, 10 Be, 14 C, 26 Al, and 36 Cl. In general, the results show that the calibrated production rates fail statistical tests of goodness-of-fit. One conclusion from the calibration results is that two newly developed scaling frameworks and the widely used Lal scaling framework provide qualitatively similar fits to the data, while neutron-monitor based scaling frameworks have much poorer fit to the data. To further test the fitted models, we computed site ages for a number of secondary sites not included in the primary calibration data set. The root-mean-square percent differences between the median computed ages for these secondary sites and independent ages range from 7.1% to 27.1%, differences that are much larger than the typical uncertainties in the site ages. The results indicate that there are substantial unresolved difficulties in modeling cosmogenic nuclide production and the calibration of production rates. [ABSTRACT FROM AUTHOR]

The Huancané II moraines deposited by the Quelccaya Ice Cap in southern Peru were selected by the CRONUS-Earth Project as a primary site for evaluating cosmogenic-nuclide scaling methods and for calibrating production rates. The CRONUS-Earth Project is an effort to improve the state of the art for applications of cosmogenic nuclides to earth-surface chronology and processes. The Huancané II moraines are situated in the southern Peruvian Andes at about 4850 m and ∼13.9°S, 70.9°W. They are favorable for cosmogenic-nuclide calibration because of their low-latitude and high-elevation setting, because their age is very well constrained to 12.3 ± 0.1 ka by 34 radiocarbon ages on peat bracketing the moraines, and because boulder coverage by snow or soil is thought to be very unlikely. However, boulder-surface erosion by granular disintegration is observed and a ∼4% correction was applied to measured concentrations to compensate. Samples from 10 boulders were analyzed for 10 Be, 26 Al, and 36 Cl. Interlaboratory bias at the ∼5% level was the largest contributor to variability of the 10 Be samples, which were prepared by three laboratories (the other two nuclides were only prepared by one laboratory). Other than this issue, variability for all three nuclides was very low, with standard deviations of the analyses only slightly larger than the analytical uncertainties. The site production rates (corrected for topographic shielding, erosion, and radionuclide decay) at the mean site elevation of 4857 m were 45.5 ± 1.6 atoms 10 Be (g quartz) −1 yr −1 , 303 ± 15 atoms 26 Al (g quartz) −1 yr −1 , and 1690 ± 100 atoms 36 Cl (g K) −1 yr −1 . The nuclide data from this site, along with data from other primary sites, were used to calibrate the production rates of these three nuclides using seven global scaling methods. The traditional Lal formulation and the new Lifton-Sato-Dunai calibrations yield average ages for the Huancané samples that are in excellent-to-good agreement with the radiocarbon age control (within 0.7% for 10 Be and 36 Cl and 6% for 26 Al). However, all of the neutron-monitor-based methods yielded ages that were too young by about 20%. The nuclide production ratios at this site are 6.74 ± 0.34 for 26 Al/ 10 Be in quartz and 37.8 ± 2.3 (atoms 36 Cl (g K) −1 ) (atom 10 Be (g SiO 2 ) −1 ) −1 for 36 Cl/ 10 Be, in sanidine and quartz, respectively. [ABSTRACT FROM AUTHOR]

Geological surface-exposure dating using cosmogenic-nuclide accumulation became a practical geochronological endeavor in 1986, when the utility of 10 Be, 26 Al, 36 Cl, and 3 He were all demonstrated. In response to the lack of a common basis for quantifying analytical consistency and calibrating cosmogenic-nuclide production, the CRONUS-Earth Project in the U.S. was started in 2005, along with a European partner project, CRONUS-EU. The goal of the CRONUS-Earth Project was to improve the accuracy and precision of terrestrial cosmogenic nuclide dating in general, focusing especially on nuclide production rates and their variation with altitude, latitude, and time, and to attempt to move from empirically based methods to ones with a stronger basis in physics. The CRONUS-Earth Project conducted extensive intercomparisons of reference materials to attempt to quantify analytical reproducibility at the community level. We found that stated analytical uncertainties nearly always underestimate the actual degree of variability, as quantified by the over-all coefficient of variation of the intercalibration data. The average amount by which the actual coefficient of variation exceeded the analytical uncertainty was a factor of two (100%), but ranged from 15% to 300% depending on the nuclide and material. Coefficients of variation ranged from 3−4% for 10 Be to 6–8% for 36 Cl, 14 C, and 21 Ne, to 5–11% for 26 Al. Both interlaboratory bias and within-laboratory excess spread of the data played a role in increasing variability above the stated analytical uncertainties. The physical basis for cosmogenic nuclide production was investigated through numerical modeling and the measurement of energy-dependent neutron cross sections for nuclide interactions. We formulated new, physically based, scaling models, denoted LSD and LSDn, by generalizing global numerical simulations of cosmic-ray processes. The CRONUS-Earth Project identified new geological calibration sites, including one at low latitude and high elevation (Huancané, Peru), and replicated nuclide measurement at numerous laboratories. At many sites multiple nuclides were measured, providing much more confidence in the equivalence of surface-exposure ages calculated from differing nuclides. The data were interpreted using an original cosmogenic-nuclide calculator, CRONUScalc, that incorporates the new physically based scaling. The new data and model produced significantly better fits than previous efforts, but do not fully resolve apparent spatial variations in production rates. The CRONUS-Earth and CRONUS-EU Projects have provided a firm foundation for assessing the strengths and weaknesses of cosmogenic-nuclide analytical methods, adjusted the AMS standards for 10 Be and consequently revised the half-life, and have provided improved calibration data sets and interpretative tools. [ABSTRACT FROM AUTHOR]

As cosmogenic nuclide applications continue to expand, the need for a common basis for calculation becomes increasingly important. In order to accurately compare between results from different nuclides, a single method of calculation is necessary. Calculators exist in numerous forms with none matching the needs of the CRONUS-Earth project to provide a simple and consistent method to interpret data from most commonly used cosmogenic nuclides. A new program written for this purpose, CRONUScalc, is presented here. This unified code presents a method applicable to 10 Be, 26 Al, 36 Cl, 3 He, and 14 C, with 21 Ne in testing. The base code predicts the concentration of a sample at a particular depth for a particular time in the past, which can be used for many applications. The multi-purpose code already includes functions for performing production rate calibrations as well as calculating erosion rates and surface exposure ages for single samples and depth profiles. The code is available under the GNU General Public License agreement and can be downloaded and modified to deal with specific atypical scenarios. [ABSTRACT FROM AUTHOR]

[Display omitted] • Physical and geochemical changes are measured beneath a playa across a hydroperiod, with environmental tracers and physical properties used to evaluate fluid flux beneath the interplaya after the hydroperiod. • A variety of methods are used to evaluate fluid flux rates to account for different flow paths and changing fluid flux rates before, during, and after the hydroperiod. • Fluid flux rates beneath the playa are significantly higher than beneath the interplaya. • Despite different soils and substrate, playas in the Central High Plains have similar hydrological function as those in the Southern High Plains. Playa lakes have been promoted as potential point sources of recharge to the High Plains aquifer, but information about recharge rates is only available for the Southern High Plains, where soils and substrate differ significantly from the Central High Plains. The goal of this study is to determine the degree to which functioning playas contribute to recharge of the aquifer in the Central High Plains. This is accomplished through a multifaceted study across a single 34–43 day-long playa hydroperiod, combining physical and geochemical evidence to measure fluid flux through the playa and geochemical evidence of fluid flux through the nearby interplaya. The hydroperiod resulted in increased matric potential and decreases in chloride and other anion concentrations in the vadose zone beneath the playa, and increases in groundwater levels downgradient, likely indicating recharge to the aquifer over the course of the short event. Anion concentrations are significantly higher in the interplaya compared with the playa, while fluid flux estimates are significantly higher beneath the playa. The fluid fluxes determined in this study are consistent with estimates from elsewhere in the High Plains region. The combination of physical and geochemical data decreased the uncertainty and improved the overall conclusion that recharge rates are higher beneath the playa than the interplaya, providing evidence that playas in the Central High Plains function similarly to those in the Southern High Plains. [ABSTRACT FROM AUTHOR]

MALT (Micro Analysis Laboratory, Tandem accelerator, The University of Tokyo) was designed for a ‘highly sensitive and precise elemental and isotopic microanalysis system’ using an ion-beam generated by a Pelletron™ 5UD tandem accelerator. Currently, a multi-nuclide AMS ( 10 Be, 14 C, 26 Al, 36 Cl, 129 I) system is available and shows good performance in both precision and sensitivity, and the accelerator serves for PIXE, NRA, ERDA/RBS measurements as well. The total operation time of the accelerator has been over 95,000 hours since the start of MALT, 20 years ago. After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, many projects related to 129 I have been conducted. The retrospective reconstruction of the 131 I distribution at the accident from 129 I is one of the most important missions for dose evaluation of the residents. The accident-derived 129 I is also quite useful as a tracer for the general iodine dynamics in the environment. As a new tool for environmental assessment related to nuclear activity, including the global fallout from past atmospheric nuclear bomb testing, effects from the spent fuel reprocessing plant, and nuclear accidents such as Chernobyl and FDNPP, a 236 U-AMS system is now under development. [ABSTRACT FROM AUTHOR]

The ages of recent effusive eruptions on Erebus volcano, Antarctica are poorly known. Published 40 Ar/ 39 Ar ages of the 10 youngest “post-caldera” lava flows are unreliable because of the young ages of the flows (<10 ka) and the presence of excess 40 Ar. Here we use cosmogenic 3 He and 36 Cl to provide new ages for the 10 youngest flows and 3 older summit flows, including a newly recognized flow distinguished by its exposure age. Estimated eruption ages of the post-caldera flows, assuming no erosion or prior snow cover, range from 4.52 ± 0.08 ka to 8.50 ± 0.19 ka, using Lifton et al. (2014) to scale cosmogenic production rates. If the older Lal (1991)/Stone (2000) model is used to scale production rates, calculated ages are older by 16–25%. Helium-3 and chlorine-36 exposure ages measured on the same samples show excellent agreement. Helium-3 ages measured on clinopyroxene and olivine from the same samples are discordant, probably due in part to lower-than-expected 3 He production rates in the Fe-rich olivine. Close agreement of multiple clinopyroxene 3 He ages from each flow indicates that the effects of past snow coverage on the exposure ages have been minimal. The new cosmogenic ages differ considerably from published 40 Ar/ 39 Ar and 36 Cl ages and reveal that the post-caldera flows were erupted during relatively brief periods of effusive activity spread over an interval of ∼4 ka. The average eruption rate over this interval is estimated to be 0.01 km 3 /ka. Because the last eruption was at least 4 ka ago, and the longest repose interval between the 10 youngest eruptions is ∼1 ka, we consider the most recent period of effusive activity to have ended. [ABSTRACT FROM AUTHOR]

The cosmonuclide 36 Cl is relevant for hydrological applications due to its conservative chloride form. 36 Cl measurements are commonly performed by Accelerator Mass Spectrometry (AMS) while stable chlorine concentration measurements are usually performed by ion chromatography (IC). They can also be achieved by Isotope Dilution-Accelerator Mass Spectrometry (ID-AMS) which offers the advantage of the simultaneous determination of both Cl and 36 Cl contents. The range of applicability of this method has been assessed on rock samples but, to our knowledge, no experimental tests were conducted on water samples characterized by low chloride contents. This study aims at investigating the accuracy and precision of the ID-AMS method for such low chlorine water samples for which chloride and 36 Cl determinations remain highly challenging. First, internal and external errors were evaluated on the measured ratios and uncertainties on Cl and 36 Cl concentrations were assessed at ± 5% and ± 7% respectively using standard error propagation calculations. Focused on the 0.1 to 10 mg·L − 1 concentration range, the Cl concentrations of thirty-five gravimetric standards were determined by ID-AMS leading to a 1:1 line (R 2 = 0.99) and a 1-sigma uncertainty on [Cl − ] of ± 5%, consistently with the propagated uncertainty. Finally, the optimal sample volume to reach accurate 36 Cl and Cl measurements with ID-AMS for water sample concentrations within the 0.1 to 10 mg·L − 1 range has been theoretically estimated. [ABSTRACT FROM AUTHOR]

Well-dated bedrock surfaces associated with the highstand and subsequent catastrophic draining of Pleistocene Lake Bonneville, Utah, during the Bonneville flood are excellent locations for in situ cosmogenic nuclide production rate calibration. The CRONUS-Earth project sampled wave-polished bedrock and boulders on an extensive wave-cut bench formed during the Bonneville-level highstand that was abandoned almost instantaneously during the Bonneville flood. CRONUS-Earth also sampled the Tabernacle Hill basalt flow that erupted into Lake Bonneville soon after its stabilization at the Provo level, following the flood. New radiocarbon dating results from tufa at the margins of Tabernacle Hill as part of this study have solidified key aspects of the exposure history at both sites. Both sites have well-constrained exposure histories in which factors such as potential prior exposure, erosion, and shielding are either demonstrably negligible or quantifiable. Multi-nuclide analyses from multiple labs serve as an ad hoc inter-laboratory comparison that supplements and expands on the formalized CRONUS-Earth and CRONUS-EU inter-laboratory comparisons (Blard et al., 2015; Jull et al., 2015; Vermeesch et al., 2015). Results from 10 Be, 26 Al, and 14 C all exhibit scatter comparable to that observed in the CRONUS-Earth effort. Although a 36 Cl inter-laboratory comparison was not completed for Jull et al. (2015), 36 Cl from plagioclase mineral separates exhibits comparable reproducibility. Site production rates derived from these measurements provide valuable input to the global production rate calibration described by Borchers et al. (2015). Whole-rock 36 Cl concentrations, however, exhibit inter-laboratory variation exceeding analytical uncertainty and outside the ranges observed for the other nuclides (Jull et al., 2015). A rigorous inter-laboratory comparison studying the systematics of whole-rock 36 Cl extraction techniques is currently underway with the goals of delineating the source(s) of this discrepancy and standardizing these procedures going forward. [ABSTRACT FROM AUTHOR]

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Summary A multiple tracer study was conducted in the coastal plain of Horonobe, northern Hokkaido, Japan. To accomplish reliable estimates of groundwater residence time, multiple tracer approach, employing both gaseous and nongaseous environmental tracers, and lumped parameter models (LPMs) were applied in combination. Environmental tracers including 3 H, 3 H/ 3 He, 36 Cl, and SF 6 were analyzed and compared with values estimated from LPMs to select the most appropriate tracer and models to describe groundwater flow regime in the study area. Time series of 36 Cl/Cl input in the study area were reconstructed and used in the LPMs. From comparison of the analyzed and modeled results, an index of 3 H/ 3 He was selected as the most appropriate for investigation of the study area. The relationship between the 3 H/ 3 He index and 36 Cl/Cl indicated reliability of the 3 H/ 3 He index, but 36 Cl/Cl values of the samples were lower than the models. This discrepancy was caused by underestimation of Cl − concentration of recharging water in the calculation of 36 Cl/Cl input. SF 6 mixing ratios of the samples were slightly higher than the models and it suggested involvement of terrigenic SF 6 . Three well groups, northern Shimonuma wells (NSW), southern Shimonuma wells (SSW), and Hamasato wells (HW), were respectively consistent with exponential piston flow model (EPM), binary mixing model (BMM), and exponential mixing model (EMM). Relational expressions between the 3 H/ 3 He index and mean residence time or mixing fraction of young groundwater (assumed to contain no tritiogenic 3 He) with old groundwater (all 3 H decayed to tritiogenic 3 He) were obtained based on the models. The mean residence time determined from the 3 H/ 3 He index and the expressions were 19–78 years for NSW and 1–648 years for HW. The mixing fraction of young groundwater was less than 10% at all SSW. Nongaseous tracers, including 36 Cl are not influenced by factors specific for gaseous tracers, such as excess air and degassing. Analyses of multiple tracers, including both gaseous and nongaseous tracers, and comparison using LPMs were effective to show plausibility of the estimated residence time, and they contributed to understanding of groundwater flow regime in the study area. [ABSTRACT FROM AUTHOR]

For the first time in Turkey, we report an early advance of glaciers before the broadly defined global Last Glacial Maximum (LGM). Forty-one moraine boulders from three glacial valleys on Mount Akdağ (36.54°N, 29.57°E, 3016 m), southwest coast of Turkey, were dated with cosmogenic 36Cl. Valleys on the north side of the mountain were filled with few km long glaciers that terminated at elevations of about 2000 m above sea level (a.s.l). The pre-LGM glaciations reached their maximum positions (2150 m a.s.l) by 35.1 ± 2.5 ka ago (1σ; ka = 1000 calendar years). The glaciers readvanced during the global LGM and reached their farthest locations (2050 m a.s.l) by around 21.7 ± 1.2 ka ago. Later, glaciers retreated and shortly stabilized during the Lateglacial at around 15.1 ± 0.9 ka ago. Using the glacier modeling and paleoclimate proxies from the Eastern Mediterranean, we estimated that if temperatures during the LGM were 8–11 °C colder than modern, which is suggested by paleotemperature proxies from the region, precipitation was up to two times more than that of today. Previous estimates on southwest coast of Turkey indicate a similar precipitation value while central Turkey requires drier conditions, implying regional heterogeneity on LGM climates in Turkey. [ABSTRACT FROM AUTHOR]

Our current understanding of water fluxes and flow paths within the mountain block is limited, and improved understanding is necessary to assess hydrology more accurately above the mountain front. Source waters and the processes controlling their mixing were characterized in the Merced River basin within Yosemite National Park, California, using 36Cl and Cl−, supported by 222Rn, δ18O, δD, and streamflow data. Streams, snow, groundwater, and springs were sampled seasonally from July 2004 to October 2007. Three source water end-members were identified: (i) near surface runoff of recent meltwater containing bomb-pulse 36Cl (36ClBP), (ii) shallow, evapotranspired groundwater, and (iii) groundwater containing Cl− derived through extended rock interaction. Both groundwater end-members mix in Yosemite Valley and then later discharge to the Merced River. Near surface runoff dominates all stream hydrographs during snowmelt, whereas the two groundwater end-members become significantly more important during base flow. Tributaries consist of mixtures of the shallow evapotranspired groundwater and near surface runoff, whereas the Merced River is composed of the mixture of all source water end-members. Snow is not an obvious end-member, and elevated 36ClBP in the near surface runoff suggests that 36ClBP was retained efficiently, and is being slowly released as meltwater interacts with the soil. The use of 36Cl as a natural tracer is important in revealing the processes controlling streamflow generation in large montane catchments and the results will be helpful in configuring and calibrating hydrologic models. [ABSTRACT FROM AUTHOR]

Abstract: Some potential applications of the isotopes 36Cl and 236U require higher sensitivity than is normally required or achieved. For 36Cl, one such application is the measurement of the 36Cl/Cl ratio of seawater. We show that, with appropriate precautions to reduce the effect of ion-source memory, it is possible to reach blank levels below 10−16 in the 36Cl/Cl ratio. Measurements of a series of seawater and sea salt samples yield a blank-corrected 36Cl/Cl ratio of present-day sea water of 0.71±0.08×10−15. For 236U, one potential application is as a prospecting tool, where sensitivities in the 236U/238U ratio at the 10−13 level are desirable. We demonstrate that this sensitivity can be achieved for 24MeV uranium ions with time-of-flight detection over a 6.0m flight path. [Copyright &y& Elsevier]

Abstract: Because the intensity and energy spectrum of the cosmic ray flux are affected by atmospheric depth and geomagnetic-field strength, cosmogenic nuclide production rates increase considerably with altitude and to a lesser degree with latitude. The scaling methods used to account for spatial variability in production rates assume that all cosmogenic nuclides have the same altitude dependence. In this study we evaluate whether the production rates of cosmogenic 36Cl, 3He and 21Ne change differently with altitude, which is plausible due to the different threshold energies of their production reactions. If so, nuclide-specific scaling factors would be required. Concentrations of the three cosmogenic nuclides were determined in mafic phenocrysts over an altitude transect between 1000 and 4300m at Kilimanjaro volcano (3°S). Altitude dependence of relative production rates was assessed in two ways: by determination of concentration ratios and by calculation of apparent exposure age ratios for all nuclide pairs. The latter accounts for characteristics of 36Cl that the stable nuclides 3He and 21Ne do not possess (radioactive decay, high sensitivity to mineral composition and significant contributions from production reactions other than spallation). All ratios overlap within error over the entire transect, and altitudinal variation in relative production rates is not therefore evident. This suggests that nuclide-specific scaling factors are not required for the studied nuclides at this low-latitude location. However, because previous studies have documented anomalous altitude-dependent variations in 3He production at mid-latitude sites, the effect of latitude on cross-calibrations should be further evaluated. We determined cosmogenic 21Ne/3He concentration ratios of 0.1864±0.0085 in pyroxenes and 0.377±0.018 in olivines, agreeing with those reported in previous studies. Despite the absence of independently determined ages for the studied lava surfaces, the consistency in the dataset should enable progress to be made in the determination of the production rates of all three nuclides as soon as the production rate of one of the nuclides has been accurately defined. To our knowledge this is the first time that 36Cl has been measured in pyroxene. The Cl extraction method was validated by measuring 36Cl in co-existing plagioclase phenocrysts in one of the samples. [Copyright &y& Elsevier]

Abstract: Heat generated by high level radioactive wastes could alter the performance of a clay repository. It was intended to investigate the effect of such a thermal period on the diffusive properties of Callovo–Oxfordian claystones. Thus, through-diffusion experiments with HTO, Cl-36, Na-22 and Cs-137 were performed before, during and after stages of heating at 80°C that lasted for up to one year. A special attention was paid to limit the occurrence of any chemical disturbance. Therefore (i) the temperature was raised to 80°C, then progressively brought back to 21°C, thanks to three intermediate temperature stages, and (ii) specific synthetic solutions were used for each temperature, chemistry of which being close to the equilibrium state, especially with respect to the carbonate and sulphate minerals. It was found that experiments carried out at 80°C showed a clear increase of the effective diffusion coefficient values for the four tracers with respect to those obtained at 21°C (by a factor of 3 for HTO and Cl-36, 5 for Na-22 and 2 for Cs-137). On the other hand, the porosity and rock capacity values did not exhibit any significant discrepancy between 21°C and 80°C, indicating no observable damage of both the pore conducing network and the sorption properties of clay minerals. The Stokes–Einstein relationship, based on the temperature dependency of the viscosity of bulk water, could be used to describe the temperature dependence of the diffusion of HTO and Cl-36 but failed to describe the diffusive evolution of the two sorbing cations, Na-22 and Cs-137. Furthermore, experiments performed after the thermal period led to diffusive properties well matching those obtained before heating. All these results suggest that at the lab scale the heating of rock samples would not alter the claystone containment properties. [Copyright &y& Elsevier]

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]

Abstract: Can accelerator mass spectrometry (AMS) studies validate risk assessments of the long-term behaviour of contaminants such as radionuclides? AMS measurements on samples from the 1.3 billion-year-old Cigar Lake uranium ore deposit provide one approach to address this question. In Cigar Lake, elevated concentrations of uranium enhance the in situ neutron flux that produces 36Cl and other radionuclides. We calculated the production of 36Cl using a Monte Carlo neutron transport code. We then tested for the loss of 36Cl from ore samples collected from an 8m stratigraphic section through the deposit by comparing the predicted values (assuming equilibrium between production and decay) with the concentrations measured by AMS. The 36Cl:Cl atom ratios within the ore were more than two orders of magnitude higher than in the surrounding host rock and ranged from 4 to 64×10−12. The 36Cl concentrations in the ore, rock, clay and fracture infilling minerals all agree with the values predicted by the Monte Carlo simulations. We conclude that 36Cl has very limited mobility. Even in matrix adjacent to more permeable fractures, there is no evidence that the measured isotopic ratios deviate significantly from the predicted values. [Copyright &y& Elsevier]

Abstract: This paper reports the results of trial measurements of the concentration of cosmogenic 36Cl in an ice core recovered from Dome Fuji Station, Antarctica. Ten ice samples were extracted from depths corresponding to the Last Glacial Maximum and the early Holocene, with each sample comprising ∼150g for a core length of 0.5m (∼30–40yr resolution). Analyses of 36Cl concentrations by accelerator mass spectrometry were successfully performed within±10% precision, even for samples with low 36Cl/Cl values (∼3×10–14). The average 36Cl concentrations were 16×103 atoms g–1 for the Last Glacial Maximum, and 7×103 atoms g–1 for the early Holocene. The apparent 36Cl depositional flux at Dome Fuji Station during these periods was estimated to be approximately 2.5–3.5×104 atoms cm–2 yr–1. [Copyright &y& Elsevier]

Abstract: The present status of the AMS activities at the Australian National University is described. Particular attention is paid to methods and equipment that have evolved substantially since earlier reports. [Copyright &y& Elsevier]

Abstract: We present the current status and research programs of a multinuclide accelerator mass spectrometry (AMS) system on the 12UD Pelletron tandem accelerator at the University of Tsukuba (Tsukuba AMS system), Japan. A maximum terminal voltage of 12MV is available for the AMS system. The Tsukuba AMS system can measure environmental levels of long-lived radioisotopes of 14C, 26Al, 36Cl and 129I by employing a molecular pilot beam. Recently, enhancements in AMS techniques and equipment, including sample preparation, the ion source and the data acquisition system, have improved the performance of 36Cl-AMS. The standard deviation of fluctuations is typically ±2%, and the machine background level for the 36Cl/Cl ratio is lower than 1×10−15 with a halite sample. We have measured over 500 samples in 1year, including samples for earth and environmental sciences and nuclear safety research. [Copyright &y& Elsevier]

Abstract: A radio-frequency quadrupole ion guided reaction cell, incorporated into a system for generating, decelerating and accelerating anions for analysis by accelerator mass spectrometry is described. Tests of this system for the suppression of the unwanted isobar 36S in the analysis of 36Cl and the measurement of a standard 36Cl reference material are reported. [Copyright &y& Elsevier]