Isotopes 232Th Research Articles

The Effect of Nanofluid Coolant and Thorium-added Fuel on Burnup Dependent Isotopic Compositions in VVER-1000 Reactor

Recently, the use of nanofluids has gained importance in studies aimed at increasing reactor efficiency while also addressing safety concerns in nuclear technology. Various studies have investigated the effects of adding nanoparticles of different types and proportions to the coolant water on the thermal and neutronic characteristics of power reactors using conventional UO2 fuels. Given the abundance of thorium compared to uranium, research on thorium-based fuels has become increasingly significant. In this study, the criticality and isotope changes in a VVER-1000 reactor loaded with 5% ThO2 and 95% UO2 by mass as fuel, and 0.1% by volume of Al2O3, CuO, and TiO2 nanoparticles as the coolant, were investigated. Neutronic analysis was performed using the MCNP5 and MONTEBURNS2.0 codes. The analysis results indicated that the operational lifespan of the reactor with only water coolant and thorium-based fuel was shortened due to the presence of nanoparticles. Furthermore, it was observed that while there was no significant change in the amount of fissile 235U and fertile 238U isotopes, the consumption of fertile 232Th isotope in the reactor increased with the insertion of nanoparticles into the coolant.

Natural radioactivity of the crust as an important factor of the chemical evolution of the early Earth

The long-lived (billions of years) 40K, 235U, 238U, and 232Th isotopes have a high energy capacity and represent a potent internal source of energy. Together with the external action of the Sun, the natural radioactivity was apparently an important component of evolution of the early Earth and development of Earth's life. The decay of isotopes initiated radiation chemical reactions involving water, which were accompanied by the formation of hydrogen and oxygen and the transformation of Earth's inorganic matter into organic compounds, including prebiotic molecules. Water radiolysis in the Earth's crust continuously produces H2, which is now considered as the main electron donor (food) for microorganisms several kilometers below the Earth's surface. Here we calculate the initial radioactivity of the early Earth's crust from the relative abundances of elements and dynamics of variation of the radioactivity and energy release upon the decay of particular radioactive isotopes. The energy released upon the decay of heavy 235U, 238U, and 232Th throughout the existence of the Earth (4.6 billion years) was 4.5 × 1030 J, while the energy released upon the decay of 40K was approximately 1.0 × 1030 J. The energy release per year during the first billion years decreased from 3.0 × 1021 J to 1.5 × 1021 J for heavy isotopes and from 0.70 × 1021 J to 0.45 × 1021 J for 40K. Over the last billion years, the energy decreased approximately threefold. Analysis of the data on the radiation chemical formation of hydrogen in the wet components of the Earth's crust (cements, zeolites, geopolymers, and other) and bottom sediments indicates that hydrogen is formed upon direct action of radiation on water in yields characteristic of pure water. According to calculations, over the past 4 billion years, approximately 1.7 × 1022 M of hydrogen was formed. Furthermore, ∼93 % of H2 was due to the decay of uranium and thorium, while the contribution of 40K did not exceed 7 %. The global rate of hydrogen formation in the Earth's crust is ∼ 1.5 × 1012 mol per year. A mechanism involving ionic and radical products of water radiolysis was proposed to describe the formation of prebiotic molecules (amino acids, sugars, etc.) from carbon-, nitrogen-, and sulfur-containing inorganic compounds.

A novel, spongy mesoporous hybrid bio-adsorbents derived from agricultural waste for highly selective thorium recovery

The expansion of engineering and development of porous materials for the bio-adsorbents synthesis from agro-waste-derived as superior efficient extractors is a significant economic and environmental breakthrough. Here, a novel spongy mesoporous hybrid silica (SMS-L) was successfully prepared from wheat straw by developed dissolution/precipitation methodology. This manuscript aims to extract/preconcentrate 232Th isotope from Egyptian cataclastic rock (ECR) using SMS and SMS-L bio-adsorbents. The proposed bio-adsorbents/extractors provide high adsorption capacity toward the 232Th isotope ions depending on the pH value of the extraction process. The optimum conditions of leaching (batch procedure), adsorption and elution (batch and permanent-bed columnar procedures) were investigated through a series of practical experiments. The physical parameters like isotherm, kinetic, and thermodynamics were studied. The SMS and SMS-L are considered promising bio-adsorbents for the adsorption/trapping of 232Th isotope from real leach solutions of ECR. These characteristic features may attribute to (i) the recycling and management of sustainable wheat straw wastes, (ii) the low-cost and eco-friendly, (iii) superior adsorption capacity of 232Th isotope, (iv) selective-trapping of 232Th isotope ions among other competitive ions such as Cr3+, Pb2+, Sr2+, Zn2+, Zr4+, Ba2+, Cu2+, Ni2+, V3+ and REEs, and (v) the structural stability of SMS and SMS-L bio-adsorbents even after 10 adsorption-desorption recycles without marked reduction in the Th(IV)-extraction efficacy. This report offers a foundation for additional advancement in clean energy applications.

Natural Radioactivity and Chemical Evolution on the Early Earth: Prebiotic Chemistry and Oxygenation

It is generally recognized that the evolution of the early Earth was affected by an external energy source: radiation from the early Sun. The hypothesis about the important role of natural radioactivity, as a source of internal energy in the evolution of the early Earth, is considered and substantiated in this work. The decay of the long-lived isotopes 232Th, 238U, 235U, and 40K in the Global Ocean initiated the oxygenation of the hydro- and atmosphere, and the abiogenesis. The content of isotopes in the ocean and the kinetics of their decay, the values of the absorbed dose and dose rate, and the efficiency of sea water radiolysis, as a function of time, were calculated. The ocean served as both a "reservoir" that collected components of the early atmosphere and products of their transformations, and a "converter" in which further chemical reactions of these compounds took place. Radical mechanisms were proposed for the formation of simple amino acids, sugars, and nitrogen bases, i.e., the key structures of all living things, and also for the formation of oxygen. The calculation results confirm the possible important role of natural radioactivity in the evolution of terrestrial matter, and the emergence of life.

Status report on AMS measurements of plutonium isotopes using the 1MV Tandetron Accelerator at IFIN-HH

Accelerator Mass Spectrometry is the most sensitive measurement method that allows us to determine 239, 240, and 244Pu radioisotopes in environmental samples with extremely low isotopic concentrations. By measuring plutonium isotopes, we focus our research activity on two main directions, monitoring of environmental nuclear pollution and nuclear astrophysics.This report gives an overview of the progress that was made in the determination of plutonium isotopes at IFIN-HH, and it starts with the studies performed for the transport and measurement of actinides using the 1MV Tandetron Accelerator. The 238U and 232Th isotopes were used as pilot beams for the determination of ion transport parameters, after which the isotopic ratios 239Pu/242Pu, 240Pu/242Pu, and 244Pu/242Pu were measured using the new Plutonium Standard ColPuS. The results obtained for the isotopic ratios agree with the consensus values of the standard. In addition, we developed radiochemical procedures for thorium, plutonium, and uranium separation, the chemical recoveries of uranium and thorium using UTEVA and TEVA resins are presented, where we used an Agilent ICP-MS system (Inductively Coupled Plasma Mass Spectrometry). The radiochemical separation is important mainly for obtaining target materials that can provide microscopic pilot beams as U and/or Th. Finally, a short overview is provided of the molecular interference challenges that are encountered when measuring plutonium isotopes.

Investigation of octupole deformed fragments decaying from even-even isotopes of Th*222–230

Background: In earlier studies, spherical and quadrupole deformed nuclei with closed shells were found to be the most probable fission fragments in the decay of heavy-mass compound nuclei at low excitation energies. Recently, the disintegration of heavy-mass actinides gave evidence of pear-shaped fission fragments, in the mass-asymmetric region, due to extra stability provided by the shell-stabilized octupole deformed $^{144}\mathrm{Ba}$ $(Z=56)$ nucleus.Purpose: In our theoretical work, we have done an exercise to analyze the possibility of octupole deformed fragments in the decay of light- and heavy-mass isotopes of thorium, i.e., $^{222,224,226,228,230}\mathrm{Th}^{*}$.Method: To carry forward the above idea, the mass and charge dispersions of chosen Th isotopes have been analyzed by including deformations (up to ${\ensuremath{\beta}}_{3}$) and related cold optimum orientations within the dynamical cluster-decay model (DCM), which is based on the collective clusterization approach of quantum mechanical fragmentation theory. The above analysis is worked out at low excitation energy, which corresponds to the cold synthesis criteria.Results: In the decay of considered Th isotopes, the minima of fragmentation potential and peaks of preformation probability appear in two regions, near symmetric and asymmetric, respectively due to the presence of quadrupole (${\ensuremath{\beta}}_{2}$) and octupole deformations (${\ensuremath{\beta}}_{3}$) of decay fragments. However, the emission of ${\ensuremath{\beta}}_{3}$-deformed fission fragments is prominent in the heavier isotopes of Th, i.e., $^{226,228,230}\mathrm{Th}^{*}$. The above result is in agreement with the experimentally obtained mass and charge distributions.Conclusions: The disintegration of thorium isotopes into octupole deformed fragments in the asymmetric region signifies their relative stability, which is enhanced for $^{144}\mathrm{Ba}$ ($Z=56$) or in its vicinity.

РАДОНОВЫЕ ВОДЫ БОЛЬШОЙ БЕЛОКУРИХИ: СОВРЕМЕННОЕ ИСПОЛЬЗОВАНИЕ И ПЕРСПЕКТИВНЫЕ УЧАСТКИ РАЗВИТИЯ КУРОРТА

At present, a tourist and recreational cluster is being formed around the federal resort of Belokurikha, which includes the adjacent territories of the Smolensk, Altai and Soloneshensky municipal districts of the Altai Territory. To determine the directions of spatial development in the cluster, information is needed on the prospects for discovering new sources of radon waters. The purpose of the study is to assess the current level of use of radon waters by the resort of Belokurikha, to identify geological and geochemical prospecting indicators of radon waters and to assess the prospects for their detection within the tourist cluster "Bolshaya Belokurikha". A field study of the territory and sampling of granitoids from the Belokurikhinsky pluton were carried out. The analysis of isotopes of uranium and thorium from granitoids was carried out according to the classical method at the Center for Isotope Research of the Russian Geological Research Institute (St. Petersburg). The analysis of the current water use was carried out based on the data of the Hydroservice of the resort of Belokurikha on water consumption for 2019. The volume of radon water consumption by the sanatoriums of the Belokurikha resort in 2019 varied throughout the year from 435.1 m3 / day in August to 282.1 m3 / day in December. This does not exceed the operational reserves of the Belokurikhinskoye deposit, which are 600 m3 / day. Potential areas for the detection of radon waters are confined to the deep sub-latitudinal Belokurikha fault, which runs along the border of the Pre-Altai plain and the Altai Mountains, and especially to the zones of intersection of faults of different directions. This is the main geological prospecting indicator. The geochemical prospecting indicator is the increased content of uranium in rocks. The highest concentrations of 238U and 232Th isotopes in the granitoids of the Belokurikhinsky pluton were found for aplites and pegmatites. Thus, the entire strip of the transition zone from the Biysk-Barnaul depression to the mountain-folded structure of Altai has prospects for radon waters, due to a complex of features for prospecting and factors of water formation with the participation of the vadose component and of deep waters leaching minerals with increased radioactivity from aplites and pegmatites. Prospective sites for carrying out detailed prospecting for radon waters are located in Belokurikha-2 in the area of the village Ulyanovka and near the village of Danilovka. Here, in addition to indirect prospecting indicators, there are also direct ones (radon content in waters).

Transformations of actinides fission product yields due to post-scission emission of nuclear particles: 232Th

The “many ensembles” method was proposed to investigate the influence of nuclear particles’ post-scission emission on mass and charge distributions of fission products. The post-scission approximation was used: each of these ensembles consists of the fission fragments after emission of chains of different lengths, both the beta (β±) particles and neutrons. The theory allows one to find the most probable two-fragment clusters of fission products and study their evolution after the post-scission emission of nuclear particles. The isotope 232Th was chosen as an example, the fission fragments of which have been intensively studied experimentally. It is shown that the post-scission emission of nuclear particles eventually leads to the convergence of the asymmetric peaks, which looks like enhanced symmetric fission mode over the asymmetric mode for fission product yields. A comparison of the theoretical results and experimental data for the 232Th fission fragments indicates their satisfactory matching.

Specific Activity and Radiation Hazard of Radionuclides in Wheat and Bean Produced Near Shazand, Iran

Introduction: Radionuclides found in foods are harmful to human health. Wheat and bean are among the most important food ingredients in the world. Therefore, this study aimed to determine the specific activity of natural radionuclides in wheat and bean produced near the refinery complex plant. Material and Methods: In order to determine the specific activity of radionuclides, the gamma-ray spectrometry method was used employing a high-purity germanium detector with a relative efficiency of 80%. Results: Our findings showed that the specific activity of the 226Ra isotope of radium had the ranges 232Th isotope of thorium was in the range of not detected (ND)-4.09 and ND-3.62 Bq/kg with the mean values of 2.19 and 2.69 Bq/kg for wheat and bean samples, respectively.The specific activity of the 40K isotope of potassium was obtained as 103.19-168.94 and 129.22-568.98 Bq/kg with the mean values of 142.21 and 458.37 Bq/kg for wheat and bean samples, respectively. The annual effective dose for wheat and bean intake was 0.11-0.52 and 0.02-0.18 mSv, respectively. Furthermore, the mean of excess lifetime cancer risk for wheat and bean samples was calculated as 1.06×10-3 and 0.11×10-3, respectively. The latter values are lower than the world average for bean samples. Conclusion: According to the results of this study, the radiological parameters of wheat were higher than the global average and reference value, which may be due to ash dispersion in this area. For bean, these parameters were lower than the mean value. As a result, it could be concluded that bean is not considered as a threat to consumer health.

Atmospheric Dust Inputs, Iron Cycling, and Biogeochemical Connections in the South Pacific Ocean From Thorium Isotopes

AbstractOne of the primary sources of micronutrients to the sea surface in remote ocean regions is the deposition of atmospheric dust. Geographic patterns in biogeochemical processes such as primary production and nitrogen fixation that require micronutrients like iron (Fe) are modulated in part by the spatial distribution of dust supply. Global models of dust deposition rates are poorly calibrated in the open ocean, owing to the difficulty of determining dust fluxes in sparsely sampled regions. We present new estimates of dust and Fe input rates from measurements of dissolved and particulate thorium isotopes 230Th and 232Th on the FS Sonne SO245 section (GEOTRACES process study GPpr09) in the South Pacific. We first discuss high‐resolution upper water column profiles of Th isotopes and the implications for the systematics of dust flux reconstructions from seawater Th measurements. We find dust fluxes in the center of the highly oligotrophic South Pacific Gyre that are the lowest of any mean annual dust input rates measured in the global oceans, but that are 1–2 orders of magnitude higher than those estimated by global dust models. We also determine dust‐borne Fe fluxes and reassess the importance of individual Fe sources to the surface South Pacific Gyre, finding that dust dissolution, not vertical or lateral diffusion, is the primary Fe source. Finally, we combine our estimates of Fe flux in dust with previously published cellular and enzymatic quotas to determine theoretical upper limits on annual average nitrogen fixation rates for a given Fe deposition rate.

Concentrations of Trace Elements in Daily Life Water Consumed in Angono, Rizal, Philippines

Objective. The present study aims to determine the concentrations of seven trace elements [chromium (Cr), arsenic (As), cadmium (Cd), cesium (Cs), lead (Pb), thorium (Th), and uranium (U)] in tap, well, spring, river, and lake waters in the town of Angono, Rizal in the Philippines, consumed for drinking, cooking, bathing, and washing. In the town of Angono, both of the tap and purified tap waters produced in the refilling station are consumed as the water for drinking.Methods. Water samples from six unpurified tap, six purified taps, 10 wells, two springs, two rivers, and one lake water were obtained in October 2015. Samples were analyzed using solution nebulization inductively coupled plasma mass spectrometry. Results were evaluated for health risks of the trace elements in the water samples using WHO guideline values. The provisional WHO guideline values are as follows: Cr: 50 µg/L, As: 10 µg/L, Cd: 3 µg/L, Pb: 10 µg/L, and U: 30 µg/L. That of Cs has not been proposed yet. The WHO guideline value for the naturally occurring radioactive isotope 232Th in drinking water is 1 Bq/L, which is equivalent to 250 μg/L.Results. The concentrations of the trace elements in the tap water samples were <0.5% of the WHO guideline values, except Cs and Cd, with those of Cd being ~9% of the WHO guideline value. Purified tap waters contained the seven trace elements in lower concentrations, with the exception of Pb, which may have been added in small amounts from equipment used for water purification. The concentrations of the trace elements in water samples from the wells and springs in Angono were more variable than those of the tap waters, and these were also below the WHO guideline values. The concentrations of Cs in all water samples were <0.3 µg/L. The trace-element concentrations of the waters from Angono River and Laguna Lake were almost the same as those of the well and spring waters. Conclusion. At present, the concentrations of trace elements in daily life water consumed in Angono are at safe levels.

First results of the 230Th(n,f) cross section measurements at the CERN n_TOF facility

The study of neutron-induced reactions on actinides is of considerable importance for the design of advanced nuclear systems and alternative fuel cycles. Specifically, 230Th is produced from the α-decay of 234U as a byproduct of the 232Th/233U fuel cycle, thus the accurate knowledge of its fission cross section is strongly required. However, few experimental datasets exist in literature with large deviations among them, covering the energy range between 0.2 to 25 MeV. In addition, the study of the 230Th(n,f) cross-section is of great interest in the research on the fission process related to the structure of the fission barriers. Previous measurements have revealed a large resonance at En=715 keV and additional fine structures, but with high discrepancies among the cross-section values of these measurements. This contribution presents preliminary results of the 230Th(n,f) cross-section measurements at the CERN n_TOF facility. The high purity targets of the natural, but very rare isotope 230Th, were produced at JRC-Geel in Belgium. The measurements were performed at both experimental areas (EAR-1 and EAR-2) of the n_TOF facility, covering a very broad energy range from thermal up to at least 100 MeV. The experimental setup was based on Micromegas detectors with the 235U(n,f) and 238U(n,f) reaction cross-sections used as reference.

238U and 232Th isotopes in groundwater of Jordan: Geological influence, water chemistry, and health impact

An extensive pioneer study was conducted to determine the activity concentration of 238U and 232Th in 94 groundwater samples to examine the influence of geological formations on the activity concentrations of 238U and 232Th and to investigate a relationship with the major chemical elements in groundwater. The study also aims to estimate the annual effective dose and health impact due to the intake of these radionuclides in the groundwater of Jordan. The mean activity concentrations of 238U and 232Th in groundwater were found to be 33 ± 5 mBq L−1 and 0.017 ± 0.002 mBq L−1, respectively. The highest mean of 238U and 232Th activity concentrations were found for lower Cretaceous geological formation, while Tertiary and Quaternary geological formations have the lowest mean 238U and 232Th activity concentration, respectively. The output of (ANOVA) and post hoc tests revealed the existence of significant influence of geological formations on 238U activity concentrations, while insignificant influence on 232Th activity concentrations was found in the groundwater of Jordan. The groundwater of Jordan was dominated by HCO3−1, Cl−1, Ca+2, and Na+1. The mean annual effective dose due to the ingestion of radionuclides 238U and 232Th in groundwater were found 1.143 μSv lower than recommended by WHO. The ingestion dose deduced is dominated by 238U of 99% where the average contribution from 232Th amounted to 1%. The results of the study will serve as a baseline data of 238U and 232Th activity concentrations in groundwater based on geological formations of Jordan.

Simple procedure for optimizing model of NaI(Tl) detector using Monte Carlo simulation

This study proposed a simple procedure for optimizing the model of NaI(Tl) detector. The procedure considers using linear functions for describing the dependence of efficiency on each specification of detector using Monte Carlo simulation. The measurements were performed to determine the efficiency of detector using point calibration sources. Using these efficiencies, the optimized specifications were interpolated based on the above linear functions. The validation of optimized model was carried out by experimentally determining the efficiencies of detector and estimating the radioactivities of 40K, 238U, and 232Th isotopes in reference samples. The obtained results showed good agreement between experiment and simulation.

Critical concentration of the exotic nuclei in the 232Th chain for the alpha analysts

The critical concentration plays an important role in the consideration of the analysts, such as gamma or alpha analyzers, for the isotopic analysis. Since the 232Th isotope and its a-decay daughters are abundant in the environments of soils, rocks and water, it is necessary to investigate the content of these isotopes to reduce the risks of health. In this work, the critical concentrations of the mentioned radioactive nuclei were estimated based on their radioactivities for the alpha analysts. The a-decay half-lives of the nuclei in the decay chain of the 232Th isotope were re-examined for the radioactivities. The semi-empirical formulae proposed by Viola-Seaberg, Royer and Poenaru were applied to the estimation. The predicted half-lives were normalized by their average values and compared to the data (NuDat) of the National Nuclear Data Center, Brookhaven National Laboratory. The results show that there exist a large uncertainty, 15% - 95% dispersed from the average values (in decimal logarithmic scale), of the half-lives evaluated by each models. Most of average half-lives are close to the NuDat data except the multi-decay-mode isotopes. The relationships between the estimated half-lives and the NuDat data are deduced as linear functions. The decay-constant deviations due to the half-life uncertainty are in the range of 1% - 120% from the average values. The large radioactivity uncertainty due to the half-lives estimated by the three models should be paid an attention for considering the environmental samples for the analysis of the natural exotic isotopes using alpha spectrometers. By assuming an efficiency of 100%, the critical concentration for the alpha analyst of the 232Th nucleus is found to be in the range 1.5 – 2.5 microgram/(l or kg).

Detectors for direct Dark Matter search at KamLAND

The current status of laboratory for Dark Matter search at the Kamioka mine and specialized facility for production of NaI(Tl) detectors is described. Techniques developed for purification and growth of ultra-low background NaI(Tl) crystals are reported. Achieved activity levels of the 210Pb, 40K, 238U, 232Th isotopes in the latest NaI(Tl) Dark Matter detector prototypes and the DAMA/LIBRA detectors are compared.

Correlation among the nuclear structure and effective symmetry energy of finite nuclei

The structural evolution and correlation of ground state properties with the effective nuclear matter characteristics for the even-even isotopes of Th and U nuclei are investigated within axially and triaxially deformed Relativistic-Hartree-Bogoliubov approaches. The density dependent meson exchange (DD-ME), point coupling (DD-PC) and non-linear (NL3⁎) force parameters are used for the present analysis. The potential energy surface is calculated by the quadratic constraint method to analyze the structural evolution by mean of shape transitions over an isotopic chain. The Coherent Density Fluctuation Model is used to formulate the nuclear matter characteristics such as symmetry energy and neutron pressure by weightening the density for finite nuclei. Further, we have predicted the possible modes of decay (α-decay and/or β-decay) in order to understand the stability of these nuclei. The calculated results are compared with experimental and other theoretical models, wherever available. We found a peak for effective symmetry energy and neutron pressure at N=150 for all the force parameters, which may correlate with the shell/sub-shell closures in an isotopic chain.

Shallow particulate organic carbon regeneration in the South Pacific Ocean

Particulate organic carbon (POC) produced in the surface ocean sinks through the water column and is respired at depth, acting as a primary vector sequestering carbon in the abyssal ocean. Atmospheric carbon dioxide levels are sensitive to the length (depth) scale over which respiration converts POC back to inorganic carbon, because shallower waters exchange with the atmosphere more rapidly than deeper ones. However, estimates of this carbon regeneration length scale and its spatiotemporal variability are limited, hindering the ability to characterize its sensitivity to environmental conditions. Here, we present a zonal section of POC fluxes at high vertical and spatial resolution from the GEOTRACES GP16 transect in the eastern tropical South Pacific, based on normalization to the radiogenic thorium isotope 230Th. We find shallower carbon regeneration length scales than previous estimates for the oligotrophic South Pacific gyre, indicating less efficient carbon transfer to the deep ocean. Carbon regeneration is strongly inhibited within suboxic waters near the Peru coast. Canonical Martin curve power laws inadequately capture POC flux profiles at suboxic stations. We instead fit these profiles using an exponential function with flux preserved at depth, finding shallow regeneration but high POC sequestration below 1,000 m. Both regeneration length scales and POC flux at depth closely track the depths at which oxygen concentrations approach zero. Our findings imply that climate warming will result in reduced ocean carbon storage due to expanding oligotrophic gyres, but opposing effects on ocean carbon storage from expanding suboxic waters will require modeling and future work to disentangle.

A New Chronology of Late Quaternary Sequences From the Central Arctic Ocean Based on “Extinction Ages” of Their Excesses in 231Pa and 230Th

AbstractMerging the late Quaternary Arctic paleoceanography into the Earth's global climate history remains challenging due to the lack of robust marine chronostratigraphies. Over ridges notably, low and variable sedimentation rates, scarce biogenic remains ensuing from low productivity and/or poor preservation, and oxygen isotope and paleomagnetic records differing from global stacks represent major impediments. However, as illustrate here based on consistent records from Mendeleev‐Alpha and Lomonosov Ridges, disequilibria between U‐series isotopes can provide benchmark ages. In such settings, fluxes of the particle‐reactive U‐daughter isotopes 230Th and 231Pa from the water column, are not unequivocally linked to sedimentation rates, but rather to sea‐ice rafting and brine production histories, thus to the development of sea‐ice factories over shelves during intervals of high relative sea level. The excesses in 230Th and 231Pa over fractions supported by their parent U‐isotopes, collapse down sedimentary sequences, due to radioactive decay, and provide radiometric benchmark ages of approximately 300 and 140 ka, respectively. These “extinction ages” point to mean sedimentation rates of ∼4.3 and ∼1.7 mm/ka, respectively, over the Lomonosov and Mendeleev Ridges, which are significantly lower than assumed in most recent studies, thus highlighting the need for revisiting current interpretations of Arctic lithostratigraphies in relation to the global‐scale late Quaternary climatostratigraphy.

A procedure for the sequential determination of radionuclides in soil and sediment samples

We present a new radiochemical procedure for the sequential determination of Sr, Am, Pu, Th and U radionuclides. For the validation, seven IAEA certified reference materials were analyzed for 239Pu, 240Pu, 241Pu, 238U and 232Th isotopes by ICP-MS, 243Am by alpha spectrometry and 90Sr by low level gas proportional counting. The sequential method was then used for determining the radionuclide profiles in one sediment core collected in the River Rhine, near Augst, downstream of the Swiss nuclear power plants.