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A Pt skin effect, i.e., an enrichment of Pt within the first 1–2 nm from the surface, is observed in as-prepared electrodeposited Ni-rich Ni–Pt thin films. This effect, revealed by Rutherford backscattering (RBS), is present for both dense thin films and mesoporous thin films synthesized by micelle-assisted electrodeposition from a chloride-based electrolyte. Due to the Pt skin effect, the Ni-rich thin films show excellent stability at the hydrogen evolution reaction (HER) in acidic media, during which a gradient in the Pt/Ni ratio is established along the thickness of the thin films, while the activity at the HER remains unaffected by this structural change. Further characterization by elastic recoil detection with He ions analysis shows that hydrogen profiles are similar to those of Pt: a surface hydrogen peak coincides with the Pt skin, and a gradient in hydrogen concentration is established during HER in acidic media, together with a considerable uptake in hydrogen. A comparative study shows that in alkaline media, hydrogen evolution has little to no effect on the structural properties of the thin films, even for much longer times of exposure. The mesoporous thin films, in addition to their higher efficiency at HER compared to dense thin films, also show lower internal stress, as determined by Rietveld refinement of grazing incidence X-ray diffraction patterns. The latter also reveal a fully single-phase and nanocrystalline structure for all thin films with varying Ni contents.

This work exhibits the very first experimentally determined cross sections for 26Al and 41Ca as proton-induced spallation products of metallic vanadium targets. Additionally, the authors describe a radiochemical separation of 26Al and 41Ca from the vanadium matrix and present the theoretically calculated cross-section values as a reference for the experimental ones.

This study represents the first use of the artificial radionuclides 129I and 236U, released into the ocean mainly from Nuclear Reprocessing Plants, as a dual tracer in the vicinity of Iceland with novel estimation of ocean circulatory pathways and mixing in the region. Iceland lies at the gateway to the Arctic where warm, saline Atlantic waters interact with waters of Arctic origin in ways that have critical consequences for the strength and stability of the Atlantic Meridional Overturning Circulation. Many of these interactions are not yet fully understood, such as how Atlantic water circulates around the Arctic Ocean and Nordic Seas and the composition and fate of the major overflows of the Greenland‐Scotland Ridge. Using new and previous measurements of 129I and 236U in seawater, we present a new method of appraising water mass provenance and mixing in the form of the 129I–236U dual mixing plot. With this method, we estimate that at least half the Atlantic‐origin water entering the Arctic Ocean circulates around the Canada Basin before exiting at Fram Strait and that this outflow is increased by about 40% by mixing with Return Atlantic Water “short‐circuiting” the Arctic Ocean at Fram Strait. We present tracer‐based evidence that water carried by the East Greenland Current has an unbroken pathway to the Faroe‐Shetland Channel and that Iceland‐Scotland Overflow Water (ISOW) entrains 60% Labrador Sea Water during transit past southeast Iceland. We present an unambiguous way to differentiate ISOW from DSOW after they partially merge in the Irminger Sea. This study is the first to use a pair of man‐made nuclear products to study ocean currents near Iceland. Understanding these currents is important because Iceland sits where warm Atlantic waters meet colder Arctic waters, affecting a key ocean circulation system and the global climate. However, many details about how these waters move and mix are still unclear. Using new and previous measurements of these tracers in seawater, we demonstrate a new method to estimate the origins of currents and how they mix. We estimate that the outflow of Atlantic‐origin water from the Arctic Ocean at Fram Strait is increased by about 40% by Atlantic water bypassing the Arctic Ocean altogether at this location. Some of this Atlantic‐origin water then flows all the way from Iceland to Shetland in an unbroken pathway and the water that spills over the Iceland‐Scotland ridge increases by 60% by mixing with water from the Labrador Sea southeast of Iceland. Finally, we present a new way to distinguish this Iceland‐Scotland Overflow Water from similar water that overflows the ridge at Denmark Strait. Recirculating Atlantic Water contributes about 40% to Atlantic layer of the East Greenland CurrentAtlantic‐origin waters can be traced from the East Greenland Current to the Faroe‐Shetland ChannelIceland‐Scotland Overflow Water and Denmark Strait Overflow Water are traceable separately after joining Deep Western Boundary Current Recirculating Atlantic Water contributes about 40% to Atlantic layer of the East Greenland Current Atlantic‐origin waters can be traced from the East Greenland Current to the Faroe‐Shetland Channel Iceland‐Scotland Overflow Water and Denmark Strait Overflow Water are traceable separately after joining Deep Western Boundary Current

Anthropogenic radionuclides 129I and 236U are used to investigate pathways of the Atlantic Water flow in the Canada Basin, estimate transport timescales, and investigate mixing dynamics within the Atlantic Water layer and the overlying Pacific Water. Transit Time Distribution (TTD) model mean ages indicate water takes 25–35 years to reach the Canada Basin from the entrance of the Arctic, with limited lateral and vertical mixing along the core of the Arctic Ocean Boundary Current. Mode ages obtained from the model yield shorter transport times of 20–32 years. These age estimates agree with previous studies using these radionuclides and ventilation tracers in this region, indicating a steady‐state flow of Atlantic Water for the last 15 years. The distribution of the isotopes in the Atlantic layer indicates two pathways Atlantic Water may take into the basin, supported by the distribution of ages in the TTD model. End‐member mixing models indicate that the Pacific Winter water acquires a 20%–40% Atlantic Water signal of the radionuclides, upwelled over short periods, most likely along the shelf and Barrow Canyon region. Man‐made nuclear products are used to trace the path of Atlantic water from the Atlantic Ocean to the Canada Basin in the Arctic, determine its transit time, and how it interacts with itself and Pacific Water that enters through the Bering Strait. The model suggests water takes 25–35 years to flow from the entrance of the Arctic to the Canada Basin, while a second estimate of age suggests slightly shorter transit times. The results of this study show that Atlantic Water flow has not changed significantly in the last 15 years. The distribution of the isotopes and ages also indicates two possible pathways water may take to the basin. An additional finding is that Pacific Winter Water carries a tracer concentration of 20%–40% of Atlantic Water, probably from Atlantic Water upwelling along the shelf, and in the Barrow Canyon region. 129I and 236U trace Atlantic sourced water in the Canada BasinUpwelling of tracer labeled Atlantic Water into the Pacific Winter Water distinguishes the layer from Pacific Summer WaterTransit time distributions yield ages of 25–35 years for the core Atlantic Water 129I and 236U trace Atlantic sourced water in the Canada Basin Upwelling of tracer labeled Atlantic Water into the Pacific Winter Water distinguishes the layer from Pacific Summer Water Transit time distributions yield ages of 25–35 years for the core Atlantic Water

In this study, proton-irradiated tungsten targets, up to 2.6 GeV, were investigated for the purpose of the experimental cross-section measurements. Radiochemical separation methods were applied to isolate the residual long-lived alpha-emitters 148Gd, 154Dy, and 146Sm and the beta-emitters 129I and 36Cl from proton-irradiated tungsten targets. The molecular plating technique has been applied to prepare 148Gd, 154Dy, and 146Sm samples for alpha-spectrometry. Production cross-sections of 129I and 36Cl were determined by means of accelerator mass spectrometry. The results are compared with theoretical predictions, obtained with the INCL++–ABLA07 codes, showing good agreement for 36Cl and 148Gd, while a factor of 4 difference was observed for 154Dy, similar to the results obtained for tantalum targets.

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. 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

Compared to stratospheric SO2injection for climate intervention, alumina particle injection could reduce stratospheric warming and associated adverse impacts. However, heterogeneous chemistry on alumina particles, especially chlorine activation via ClONO2+HCl→surfCl2+HNO3${\text{ClONO}}_{2}+\text{HCl}\stackrel{\text{surf}}{\to }{\text{Cl}}_{2}+{\text{HNO}}_{3}$, is poorly constrained under stratospheric conditions, such as low temperature and humidity. This study quantifies the uncertainty in modeling the ozone response to alumina injection. We show that extrapolating the limited experimental data for ClONO2+ HCl to stratospheric conditions leads to uncertainties in heterogeneous reaction rates of almost two orders of magnitude. Implementation of injection of 5 Mt/yr of particles with 240 nm radius in an aerosol‐chemistry‐climate model shows that resulting global total ozone depletions range between negligible and as large as 9%, that is more than twice the loss caused by chlorofluorocarbons, depending on assumptions on the degree of dissociation and interaction of the acids HCl, HNO3, and H2SO4on the alumina surface. Global warming caused by increasing greenhouse gases could be temporarily reduced by introducing aerosol particles into the stratosphere. The most frequently studied approach to climate intervention uses H2SO4‐H2O aerosols, which, however, could result in undesirably strong warming of the stratosphere and significant ozone depletion. This might be improved by injecting solid particles, for example, made of aluminum oxide. However, here we show that the extremely limited availability of experimental studies on heterogeneous chemistry on alumina under the influence of stratospheric concentrations of HCl, HNO3, H2SO4, and H2O leads to large uncertainties in the impact of alumina injection on stratospheric ozone. In order to quantify these uncertainties, we integrated the currently available knowledge about the most important heterogeneous reaction ClONO2+HCl→surfCl2+HNO3${\text{ClONO}}_{2}+\text{HCl}\stackrel{\text{surf}}{\to }{\text{Cl}}_{2}+{\text{HNO}}_{3}$into an aerosol‐chemistry‐climate model. We conclude that the uncertainty in the resulting heterogeneous reaction rate is more than two orders of magnitude depending on the partitioning of HCl, H2SO4, and HNO3on the alumina surface. This could lead to global ozone column depletion ranging between almost negligible and up to 9%, which would be more than twice as much as the ozone loss caused by chlorofluorocarbons in the late 1990s. Heterogeneous chemistry on solid alumina particles is highly uncertain and depends strongly on the partitioning of acids onto the surfaceThe reaction rate of ClONO2with HCl on alumina particles is uncertain by up to two orders of magnitude under stratospheric conditionsInjection of 5 Mt/yr of alumina particles could double global ozone reductions compared to chlorofluorocarbons in the late 1990s Heterogeneous chemistry on solid alumina particles is highly uncertain and depends strongly on the partitioning of acids onto the surface The reaction rate of ClONO2with HCl on alumina particles is uncertain by up to two orders of magnitude under stratospheric conditions Injection of 5 Mt/yr of alumina particles could double global ozone reductions compared to chlorofluorocarbons in the late 1990s

The concentrations of the long-lived nuclear reaction products 129I and 36Cl have been measured in samples from the MEGAPIE liquid metal spallation target. Samples from the bulk target material (lead-bismuth eutectic, LBE), from the interface of the metal free surface with the cover gas, from LBE/steel interfaces and from noble metal absorber foils installed in the cover gas system were analysed using Accelerator Mass Spectrometry at the Laboratory of Ion beam Physics at ETH Zürich. The major part of 129I and 36Cl was found accumulated on the interfaces, particularly at the interface of LBE and the steel walls of the target container, while bulk LBE samples contain only a minor fraction of these nuclides. Both nuclides were also detected on the absorber foils to a certain extent (≪ 1% of the total amount). The latter number is negligible concerning the radio-hazard of the irradiated target material; however it indicates a certain affinity of the absorber foils for halogens, thus proving the principle of using noble metal foils for catching these volatile radionuclides. The total amounts of 129I and 36Cl in the target were estimated from the analytical data by averaging within the different groups of samples and summing up these averages over the total target. This estimation could account for about half of the amount of 129I and 36Cl predicted to be produced using nuclear physics modelling codes for both nuclides. The significance of the results and the associated uncertainties are discussed.

A reconstruction of historical discharges of 236U into the Northeast Atlantic Ocean by nuclear installations is presented. The nuclear reprocessing facilities Sellafield (SF), Great Britain (GB) and La Hague (LH), France and potentially also the nuclear fuel processing installation Springfields (SP), GB represent the main contributors of 236U in the Northeast Atlantic Ocean. Because data on 236U releases is lacking, 236U discharges from SP and SF are estimated based on the U‐isotopic systematics found in the discharges from LH. The resulting reconstruction of 236U releases indicates that, until 2013, a total of (95 ± 32) kg of 236U was discharged from SF, SP, and LH. In a second step, the reconstructed 236U releases are combined with 129I data from literature and oceanic and atmospheric box models are used to derive the 129I/236U and 236U/238U input functions that, for example, can be used to calculate tracer ages of Atlantic Waters in the Arctic Ocean. Our conceptual results show that the combination of 129I/236U and 236U/238U generally allows the estimation of tracer ages over the past approximately 25 years if contributions of 236U from global fallout are considered. Finally, as a proof of concept, the new method is applied to calculate tracer ages of Arctic Ocean surface samples (collected in 2011/2012) and the results are in good agreement with literature data. We conclude that the combination of 129I/236U with 236U/238U in a dual tracer approach provides a sensitive tool for the calculation of tracer ages and ventilation rates in the North Atlantic region. First reconstruction of the oceanic 236U input by nuclear reprocessingPresentation of a new 129I/236U and 236U/238U‐based dual tracer conceptCalculation of 129I/236U and 236U/238U‐based tracer ages in the Arctic Ocean

A 3-MV pelletron tandem accelerator is the heart of the Vienna environmental research accelerator (VERA). The original design of the beam transport components allows the transport of ions of all elements, from the lightest to the heaviest. For light ions the suppression of neighboring masses was sufficient to measure isotopic ratios of 14C/12C and 26Al/27Al as low as 10−15and 10Be/9Be down to 10−13. To suppress neighboring masses for the heaviest radionuclides in the energy range of 10–20 MeV, the resolution of VERA was increased both by improving the ion optics of existing elements at the injection side and by installing a new high-resolution electrostatic separator at the high-energy side. Interfering ions which pass all beam filters are identified with a Bragg-type ionization detector and a high-resolution time-of-flight system. Two ultra-thin diamond-like carbon (DLC) foils are used in the start and stop detector, which substantially reduces losses due to beam straggling. This improved set up enables us to measure even the heaviest long-lived radionuclides, where stable isobaric interferences are absent (e.g. 236U and 244Pu), down to environmental levels. Moreover, the advantage of a ‘small’ and well manageable machine like VERA lies in its higher stability and reliability which allows to measure these heavy radionuclides more accurately, and also a large number of samples.

Blue ice moraines are common supraglacial landforms in Antarctica and they are considered to record the ice volume fluctuations. In this study, we use photogrammetry and the analysis of multiple cosmogenic nuclides (10Be, 26Al, and in-situ 14C) in boulders on three blue ice moraines to explore the timing of ice volume fluctuations in the Sør Rondane Mountains, Queen Maud Land, and provide insights into the role of sediment sources in the reconstruction of their chronology. In the field, we observe that the blue ice moraines are composed of subglacially and supraglacially transported sediments. Cosmogenic 10Be and 26Al exposure ages of 14 surface samples, collected from boulders on three blue ice moraines, range from 15.4 ± 1.1 to 659.5 ± 33.9 ka. 26Al/10Be ratios vary between 3.53 ± 0.20 and 7.01 ± 0.32, and many of these ratios indicate complex exposure histories. In contrast, among nine in-situ 14C exposure ages, five vary between 4.2 ± 0.1 and 22.0 ± 1.3 ka, and four are saturated. We conclude that the accumulation of these blue ice moraines commenced before or during the global Last Glacial Maximum. Our results indicate that surficial sediment sources can yield exposure ages that are older than real exposure age, and exhibit a wider scatter. This can alter the reconstructed chronology of these landforms. The analysis of in-situ 14C has a high potential in tracking the pace of their evolution, especially since the Last Glacial Maximum.