Radiochemical Determination of Long-Lived Radionuclides in Proton-Irradiated Heavy Metal Targets: Part II Tungsten.

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.

Radiochemical Determination of Long-Lived Radionuclides in Proton-Irradiated Heavy-Metal Targets: Part I-Tantalum.

In this study, distillation, precipitation, and ion-exchange methods were chosen for the separation of the long-lived ß-emitters 129I, 36Cl and the α-emitters 154Dy, 148Gd, 150Gd, and 146Sm from Ta targets irradiated with protons up to 2.6 GeV to determine their production cross sections. Measurements of 129I/127I and 36Cl/35Cl ratios were performed with accelerator mass spectrometry. After separation of the lanthanides, the molecular plating technique was applied to prepare thin samples to obtain highly resolved α-spectra. Autoradiography and focused ion beam/scanning electron microscopy techniques were used to characterize the lanthanide deposited layer. Experimental cross-section data are compared with theoretical predictions obtained with INCL++ and ABLA07 code, and a satisfactory agreement is observed.

Potential Releases of 129I, 236U, and Pu Isotopes from the Fukushima Dai-ichi Nuclear Power Plants to the Ocean from 2013 to 2015.

After the Fukushima Dai-ichi nuclear accident, many efforts were put into the determination of the presence of 137Cs, 134Cs, 131I, and other gamma-emitting radionuclides in the ocean, but minor work was done regarding the monitoring of less volatile radionuclides, pure beta-ray emitters or simply radionuclides with very long half-lives. In this study we document the temporal evolution of 129I, 236U, and Pu isotopes (239Pu and 240Pu) in seawater sampled during four different cruises performed 2, 3, and 4 years after the accident, and we compare the results to 137Cs collected at the same stations and depths. Our results show that concentrations of 129I are systematically above the nuclear weapon test levels at stations located close to the FDNPP, with a maximum value of 790 × 107 at·kg-1, that exceeds all previously reported 129I concentrations in the Pacific Ocean. Yet, the total amount of 129I released after the accident in the time 2011-2015 was calculated from the 129I/137Cs ratio of the ongoing 137Cs releases and estimated to be about 100 g (which adds to the 1 kg released during the accident in 2011). No clear evidence of Fukushima-derived 236U and Pu isotopes has been found in this study, although further monitoring is encouraged to elucidate the origin of the highest 240Pu/239Pu atom ratio of 0.293 ± 0.028 we found close to FDNPP.

Oral Vitamin D Supplements Increase Serum 25-Hydroxyvitamin D in Postmenopausal Women and Reduce Bone Calcium Flux Measured by 41Ca Skeletal Labeling.

BACKGROUND: Ensuring adequate vitamin D status in older adults may reduce the risk of osteoporosis. The serum 25-hydroxyvitamin D [25(OH)D] concentration is the recommended biomarker of vitamin D status, but the optimal serum 25(OH)D concentration for bone health in postmenopausal women remains unclear. OBJECTIVE: The aim of this study was to apply the highly sensitive (41)Ca skeletal labeling technique and the measurement of urinary (41)Ca:(40)Ca ratios to determine the serum 25(OH)D concentration that has greatest benefit on bone calcium flux in postmenopausal women. METHODS: We administered a mean intravenous (41)Ca dose of 870 pmol to healthy postmenopausal women [n = 24, age (mean ± SD): 64 ± 6.0 y] without osteoporosis. After 6 mo, at the nadir of their wintertime serum 25(OH)D status, each of the women sequentially consumed daily oral cholecalciferol supplements of 10, 25, and 50 µg/d (in this order), each for 3 mo. We assessed serum 25(OH)D concentrations monthly and urinary (41)Ca:(40)Ca ratios biweekly. (41)Ca:(40)Ca ratios were measured with low-energy accelerator mass spectrometry. With the use of pharmacokinetic analysis, we determined the effect of varying serum 25(OH)D concentrations on (41)Ca transfer rates. RESULTS: At baseline, the mean (95% CI) serum 25(OH)D concentration was 16.2 (13.5, 18.8) µg/L. After the first, second, and third intervention periods, mean (95% CI) serum 25(OH)D increased to 29.8 (27.2, 32.4), 36.9 (34.2, 39.7), and 46.6 (41.2, 52.0) µg/L, respectively. Supplementation was associated with a downward shift in the urinary (41)Ca:(40)Ca ratio compared with the predicted (41)Ca:(40)Ca ratio without vitamin D supplementation. In the model, the most likely site of action of the increase in serum 25(OH)D was transfer from the central compartment to a fast exchanging compartment. At this transfer rate, predicted values were a concentration with half-maximal effect of 2.33 µg/L and an estimate of the maximal effect of 31.7%. After the first, second, and third intervention periods, the mean changes in this transfer rate were +18.0%, +25.7%, and +28.5%, respectively. CONCLUSION: In healthy postmenopausal women, increasing serum 25(OH)D primarily affects calcium transfer from the central compartment to a fast exchanging compartment; it is possible that this represents transfer from the extracellular space to the surface of bone. A serum 25(OH)D concentration of ~40 µg/L achieves ~90% of the expected maximal effect on this transfer rate. This trial was registered at clinicaltrials.gov as NCT01053481.

Unlocking the Potential of CuAgZr Metallic Glasses: A Comprehensive Exploration with Combinatorial Synthesis, High-Throughput Characterization, and Machine Learning.

In this work, the CuAgZr metallic glasses (MGs) are investigated, a promising material for biomedical applications due to their high strength, corrosion resistance, and antibacterial activity. Using an integrated approach of combinatorial synthesis, high-throughput characterization, and machine learning (ML), the mechanical properties of CuAgZr MGs are efficiently explored. The investigation find that post-deposition oxidation in inter-columnar regions with looser packing causes high oxygen content in Cu-rich regions, significantly affecting the alloys' mechanical behavior. The study also reveals that nanoscale structural features greatly impact plastic yielding and flow in the alloys. ML algorithms are tested, and the multi-layer perceptron algorithm produced satisfactory predictions for the alloys' hardness of untested alloys, providing valuable clues for future research. The work demonstrates the potential of using combinatorial synthesis, high-throughput characterization, and ML  techniques to facilitate the development of new MGs with improved strength and economic feasibility.

Seismic history of western Anatolia during the last 16 kyr determined by cosmogenic 36Cl dating.

Western Anatolia is one of the most seismically active regions worldwide. To date, the paleoseismic history of many major faults, in terms of recurrence intervals of destructive earthquakes, their magnitude, displacement, and slip rates is poorly understood. Regional crustal extension has produced major horst-graben systems bounded by kilometer-scale normal faults locally in carbonates, along which vertical crustal displacements occurred. In this study, we explore the seismic history of western Anatolia using 36Cl exposure dating through study of well-preserved carbonate normal fault scarps. To accomplish this, 36Cl concentrations in 214 samples from fault plane transects on the Rahmiye and Ören fault scarps were measured and compared with existing 36Cl measurements of 370 samples on five fault scraps in western Anatolia. At least 20 seismic events have been reconstructed over the past 16 kyr. The age correlation of the seismic events implies four phases of high seismic activity in western Anatolia, at around 2, 4, 6, and 8 ka. Slips are modeled ranging between 0.6 to 4.2 m per seismic event, but are probably the result of clustered earthquakes of maximum magnitude 6.5 to 7.1. While the average slip rates have values of 0.3 to 1.9 mm/yr, incremental slip rates of the faults range greater than 0.1 to 2.2 mm/yr, showing more activity mostly through late Holocene. Our finding reveals high capability of cosmogenic 36Cl dating to explore seismic behavior of active faults beyond the existing earthquake records. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s00015-022-00408-x.

Cosmogenic radionuclides reveal an extreme solar particle storm near a solar minimum 9125 years BP.

During solar storms, the Sun expels large amounts of energetic particles (SEP) that can react with the Earth's atmospheric constituents and produce cosmogenic radionuclides such as 14C, 10Be and 36Cl. Here we present 10Be and 36Cl data measured in ice cores from Greenland and Antarctica. The data consistently show one of the largest 10Be and 36Cl production peaks detected so far, most likely produced by an extreme SEP event that hit Earth 9125 years BP (before present, i.e., before 1950 CE), i.e., 7176 BCE. Using the 36Cl/10Be ratio, we demonstrate that this event was characterized by a very hard energy spectrum and was possibly up to two orders of magnitude larger than any SEP event during the instrumental period. Furthermore, we provide 10Be-based evidence that, contrary to expectations, the SEP event occurred near a solar minimum.

Nonuniform Late Pleistocene glacier fluctuations in tropical Eastern Africa.

Today's ice caps and glaciers in Africa are restricted to the highest peaks, but during the Pleistocene, several mountains on the continent were extensively glaciated. However, little is known about regional differences in the timing and extent of past glaciations and the impact of paleoclimatic changes on the afro-alpine environment and settlement history. Here, we present a glacial chronology for the Ethiopian Highlands in comparison with other East African Mountains. In the Ethiopian Highlands, glaciers reached their maximum 42 to 28 thousand years ago before the global Last Glacial Maximum. The local maximum was accompanied by a temperature depression of 4.4° to 6.0°C and a ~700-m downward shift of the afro-alpine vegetation belt, reshaping the human and natural habitats. The chronological comparison reveals that glaciers in Eastern Africa responded in a nonuniform way to past climatic changes, indicating a regionally varying influence of precipitation, temperature, and orography on paleoglacier dynamics.

Controls on the 36Cl/Cl input ratio of paleo-groundwater in arid environments: New evidence from 81Kr/Kr data.

Measurements of the long-lived 81Kr and 36Cl radioisotopes in groundwater from the Negev Desert (Israel) were used to assess the 36Cl/Cl input ratios and Cl- contents for paleorecharge into the Nubian Sandstone Aquifer (NSA). The reconstructed Cl- content of the recharge flux was on the order of 300-400 mg/L. An initial 36Cl/Cl ratio of 50 × 10-15 was assessed for the groundwater replenishment in the Negev Desert since the late Pleistocene, in agreement with the 36Cl/Cl ratios in recent local rainwater. This is despite possible changes in the climatic conditions and the 36Cl production rates in the atmosphere over this timeframe. This similarity in values is explained by the major role played by the erosion and weathering of near-surface materials in the desert environment that dominate the hydrochemistry of rains, floods, and the consequent groundwater recharge. Spatial variation in the reconstructed initial 36Cl/Cl ratio is accounted for by the differences in the mineral aerosol sources for specific recharge areas of the NSA. Accordingly, regional variations in the 36Cl/Cl input in groundwater reservoirs surrounding the Mediterranean Sea indicate various processes that govern the 36Cl/Cl system. Finally, the results of this study highlight the great advantage of integrating 81Kr age information in evaluating the initial 36Cl/Cl and Cl- input, which is essential for the calibration of 36Cl radioisotope as an available long-term dating tool for a given basin.

Cosmogenic in situ 14C-10Be reveals abrupt Late Holocene soil loss in the Andean Altiplano.

Soil sustainability is reflected in a long-term balance between soil production and erosion for a given climate and geology. Here we evaluate soil sustainability in the Andean Altiplano where accelerated erosion has been linked to wetter climate from 4.5 ka and the rise of Neolithic agropastoralism in the millennium that followed. We measure in situ cosmogenic 14C directly on cultivated hilltops to quantify late Holocene soil loss, which we compare with background soil production rates determined from cosmogenic 26Al and 10Be. Our Monte Carlo-based inversion method identifies two scenarios to account for our data: an increase in erosion rate by 1-2 orders of magnitude between ~2.6 and 1.1 ka, or a discrete event stripping ~1-2 m of soil between ~1.9 and 1.1 ka. Coupled environmental and cultural factors in the Late Holocene signaled the onset of the pervasive human imprint in the Andean Altiplano seen today.

Fault Scarp Dating Tool - a MATLAB code for fault scarp dating using in-situ chlorine-36 supplemented with datasets of Yavansu and Kalafat faults.

We publish a MATLAB code used to analyze concentration profile of cosmogenic 36Cl accumulated in-situ through a rupture history of the fault scarps in western Turkey (Mozafari et al., 2019). The code is a version of the forward modeling Matlab code -Fault Scarp Dating Tool- (Tikhomirov, 2014). The code models a 36Cl profile accumulated in the fault scarp surface through a guessed rupture history, and compares the modeled and measured 36Cl profiles with statistical tests. Rupture histories are randomly generated in bounded solution space using Monte-Carlo method or optimized using Random Walk algorithm to achieve the best fit of the modeled and measured 36Cl profiles. The code has a user-friendly interface, a build-in help and an example of input data.

Fast long-term denudation rate of steep alpine headwalls inferred from cosmogenic 36Cl depth profiles.

Quantifications of in-situ denudation rates on vertical headwalls, averaged over millennia, have been thwarted because of inaccessibility. Here, we benefit from a tunnel crossing a large and vertical headwall in the European Alps (Eiger), where we measured concentrations of in-situ cosmogenic 36Cl along five depth profiles linking the tunnel with the headwall surface. Isotopic concentrations of 36Cl are low in surface samples, but high at depth relative to expectance for their position. The results of Monte-Carlo modelling attribute this pattern to inherited nuclides, young minimum exposure ages and to fast average denudation rates during the last exposure. These rates are consistently high across the Eiger and range from 45 ± 9 cm kyr-1 to 356 ± 137 cm kyr-1 (1σ) for the last centuries to millennia. These high rates together with the large inheritance point to a mechanism where denudation has been accomplished by frequent, cm-scale rock fall paired with chemical dissolution of limestone.

Radionuclides in surface waters around the damaged Fukushima Daiichi NPP one month after the accident: Evidence of significant tritium release into the environment.

Following the Fukushima nuclear accident (2011), radionuclides mostly of volatile elements (e.g., 131I, 134,137Cs, 132Te) have been investigated frequently for their presence in the atmosphere, pedosphere, biosphere, and the Pacific Ocean. Smaller releases of radionuclides with intermediate volatility, (e.g., 90Sr), have been reported for soil. However, few reports have been published which targeted the contamination of surface (fresh) waters in Japan soon after the accident. In the present study, 10 surface water samples (collected on April 10, 2011) have been screened for their radionuclide content (3H, 90Sr, 129I, 134Cs, and 137Cs), revealing partly unusually high contamination levels. Especially high tritium levels (184 ±â€¯2 Bq·L-1; the highest levels ever reported in scientific literature after Fukushima) were found in a puddle water sample from close to the Fukushima Daiichi nuclear power plant. The ratios between paddy/puddle water from one location only a few meters apart vary around 1% for 134Cs, 12% for 129I (131I), and around 40% for both 3H and 90Sr. This illustrates the adsorption of radiocesium on natural minerals and radioiodine on organic substances (in the rice paddy), whereas the concentration differences of 3H and 90Sr between the two waters are mainly dilution driven.

Measurement of the 43Sc production cross-section with a deuteron beam.

43,44Sc/47Sc is one of the most promising theranostic pairs in nuclear medicine. The co-emission of 1157 keV γ-rays with 99.9% branching ratio by 44Sc and the presence of its metastable state 44 mSc push to favour the adoption of 43Sc for Positron Emission Tomography (PET) diagnostic procedures to lighten the dose to the patient and to the personnel. The ß+ emitter 43Sc can be produced at a medical cyclotron by proton bombardment of an enriched 43Ca or 46Ti oxide target. 43Sc can be also produced by deuteron bombardment of an enriched 42Ca oxide target. Only a few medical cyclotrons currently in operation offer deuteron beams. Some can be adapted to operate both a proton or a deuteron source. To compare these three production routes, an accurate knowledge of the cross-sections is essential. In this paper, we report on the cross-section measurement of the reaction 42Ca(d,n)43Sc performed at the 6 MV HVEC EN-Tandem of the Ion Beam Physics group at ETH in Zürich. A study of the production yield by using commercially available enriched target materials is also presented.

Radioecological investigation of 3H, 14C, and 129I in natural waters from Fuhrberger Feld catchment, Northern Germany.

Ongoing radionuclide releases from nuclear facilities, e.g. from reprocessing plants, but also from nuclear reactors require monitoring of the environment. Particularly drinking water reservoirs are prone to possible radionuclide accumulation fostering the need for routine surveillance. In this work, we investigated tritium (3H), radiocarbon (14C), and iodine-129 (129I) activity levels in natural aquatic samples at the water protection area of Fuhrberger Feld near Hannover city, Northern Germany. For that aim, a low-level liquid scintillation counting (LSC) technique was used to measure 3H in the water samples based on a distillation process after alkaline permanganate treatment. Isotopic ratios for both 14C and 129I were measured by accelerator mass spectrometry (AMS) after chemical separation and purification of the samples. Mean 3H levels in precipitation (8.8 ± 3.4 TU) were found to be comparable to its levels in precipitation data in Germany. Rivers and small streams revealed similar mean 3H value (11.0 ± 3.3 TU) as in lake water (10.6 ± 3.4 TU). Variations in 3H concentrations in groundwater samples were observed and discussed. 14C levels in all groundwater samples were below the atmospheric natural level of 100 pMC indicating no anthropogenic input of radiocarbon. The 129I/127I isotopic ratios in all investigated water samples were in the order of 10-8 to 10-7, which is significantly higher than the pre-nuclear natural equilibrium isotopic ratio (∼1.5 × 10-12). In strong contrast to all other regional groundwaters, the Fuhrberger Feld groundwater has much higher values of 129I concentration and 129I/127I isotopic ratio close to the ones of surface water. The overall annual effective dose via ingestion for all nuclides in the investigated groundwater remains substantially below the reference dose level of 0.1 mSv a-1.