Uranium Series Nuclides Research Articles

Substantially excess uranium in the waters of an intertidal salt marsh: A case study of eastern Chongming Beach

Knowledge of the geochemical behavior of uranium is key to an accurate tracing of the decay chain of the uranium series nuclides for material transportation processes on different temporal scales. However, direct observations for understanding dissolved uranium input in tidal water are very limited. Therefore, dissolved uranium was measured in tidal creek water, overlying water, and pore water collected from the central cross section of eastern Chongming Beach, Changjiang Estuary, from November 2012 to October 2013, to observe the spatiotemporal distribution of uranium. The results indicated that the behavior of dissolved uranium is conservative in the tidal creek waters during the flooding process, and an excess of dissolved uranium is observed during the ebbing process; excess uranium phenomena are dominant in the overlying and pore waters throughout the year, particularly at the middle and high tidal flats. The element concentration profiles in pore water showed that uranium release follows Mn oxide reduction in the subsurface suboxic zone. Hence, the exchange process between tidal water and pore water, coupled with ebb tide, represents a potential path for uranium release into the estuary. The three-end-member (Changjiang River, seawater, and pore water) model estimates that 35% of the amount of uranium in ebbing water is derived from pore water. The exchange rate between tidal water and pore water is 196.4 nmol/(cm2·d), with an export flux of 2.34 × 104 mol/a. We suggest that the release of uranium from intertidal salt marshes is an important uranium source in estuarine and coastal regions.

Field biotite weathering rate determination using U-series disequilibria

The chemical weathering rate of silicates is a key parameter of several geochemical processes; however, the long-term field measurement of these rates remains challenging. Currently, there are several methods for quantifying field weathering rates, but each presents it's own unique set of difficulties. In this study uranium-series nuclides were used to investigate long-term biotite weathering in a soil profile. For this purpose, pseudomorph grains of biotites (including weathering products) were hand-picked from four horizons of a soil profile and from underlying granitic saprolite from the experimental Breuil-Chenue site (France).Unexpected behaviors of U and Th nuclides were recorded from these samples. An unambiguous leaching of 232Th occurs during the weathering of biotite, while reduced U release relative to Th was observed, implying an efficient redistribution of U between the primary mineral and weathering products within the pseudomorphs. The measured U-series activity ratios reflect a regular and self-consistent pattern evolution. However, the “U-series-derived-weathered-stage” is not always coherent with the weathering features of major elements and/or with the location of the samples within the soil profile. For instance, biotite from the saprolite displays U-series activity ratios typical of significantly weathered samples, while major elements present rather limited signs of weathering. These results suggest an incongruent leaching of U and Th isotopes and suggest that U- and Th-series nuclides probe some water-mineral interactions that occur before macroscopic mineral tansformation.Using an open-system leaching model, coupled (234U/238U), (234U/230Th), and (226Ra/230Th) disequilibria measured from the samples allow us to calculate a weathering duration range of 6–52 ky for most weathered samples of this soil profile. The biotite weathering rate deduced from these data ranges from 7.8 × 10−17 mol·m−2·s−1 to 6.5 × 10−16 mol·m−2·s−1, which is consistent with the range of field rates previously reported. This rate was compared to the weathering rate of biotites induced by the substitution of vegetation occuring 35 years ago in a nearby soil profile, which was about 2–3 orders of magnitude higher than the long-term rate reported above. This feature is perfectly consistent with the decrease in the weathering rate with time that was previously widely documented but that still remains debated. Our results allude to a valuable use of U-series isotopes for mineral-weathering field rate determination and report a decrease in silicate weathering rates over long- (10,000s of years) and short-term (10s of years) weathering events recorded from the same site. The results show that short term laboratory experiments can be representative of field processes, and suggest that some forms of mineral weathering reactivation, similar to that observed during laboratory experiments, may naturally occur in soils in response to high frequency perturbation processes such as land cover change.

The application of abundance sensitivity filters to the precise and accurate measurement of uranium series nuclides by plasma mass spectrometry

Application of retardation filters has revolutionized the use of multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) for the measurement of U-series disequilibria. Here, we present an evaluation of the application of retardation energy filters coupled with ion counting detectors for the measurement of U-series disequilibria by MC-ICPMS. We show that: 1) The RPQ minimizes backgrounds caused by ions experiencing irregular flight paths at high masses of uranium series nuclides. This reduced background is important for low count rate measurements and has enabled us to develop an improved method for the determination of 226Ra/228Ra ratios using a dual SEM/RPQ collector block. 2) Systematic biases exist for isotope ratios of 234U/238U and 230Th/232Th without the use of RPQs; thus, the RPQ is important for measurement of both of these isotope ratios. 3) That the RPQ makes possible 210Pb measurements in geologic samples using MC-ICPMS, but that this application is limited to samples that have low common Pb, such as carbonates and silica sinter. Additionally, we present mass spectrometric and gamma counting data for U-Th-Ra disequilibria in rock standard reference materials including AGV-2, AThO, BCR-1, BCR-2, BHVO-2, BIR-1a, DTS-1, PCC-1, RGM-2, TML, and W-2a. Comparing this new data with values from published literature enables us to provide consensus or recommended values for U, Th, and 226Ra concentrations and 230Th/232Th ratios for each of these standards. We note that this is the first compilation of recommended radium concentrations for rock standard reference materials.

地層水等におけるウラン系列核種とコロイド挙動

地層水等におけるウラン系列核種とコロイド挙動

Spatial distribution of gamma radiation levels in surface soils from Jaduguda uranium mineralization zone, Jharkhand, India, using γ-ray spectrometry, and determination of outdoor dose to the population

The concentrations of natural radionuclides in surface soil samples around selected villages of Jaduguda were investigated and compared with the radioactivity level in the region. Concentrations of 238U, 232Th, and 40K were determined by a gamma ray spectrometer using the HPGe detector with 50% relative efficiency, and the radiation dose to the local population was estimated. The average estimated activity concentrations of 238U, 232Th, and 40K in the surface soil were 53.8, 44.2 and 464.2 Bq kg−1 respectively. The average absorbed dose rate in the study area was estimated to be 72.5 nGy h-1, where as the annual effective dose to the population was 0.09 mSv y-1. A correlation analysis was made between measured dose rate and individual radionuclides, in order to delineate the contribution of the respective nuclides towards dose rate. The radio-elemental concentrations of uranium, thorium and potassium estimated for the soils, in the study area, indicated the enrichment of uranium series nuclide. The results of the present study were subsequently compared with international and national recommended values.

Radiological implications of NORM in the production of rare-earth compounds

The composite rare earth chloride produced from monazite contain low levels of natural radionuclides and is being used as the input material for the production of individual rare earth compounds which have wide applications. Gross alpha, beta and 228 Ra activity concentrations in composite rare earth chloride and individual rare earth compounds such as oxides of Ce, Nd, Pr, Sm, Gd etc are presented. The significant radionuclide of environmental concern is identified as 228 Ra and the activity level varied between 0.1 and 7.8Bq.g −1 in different compounds. Sporadic 228 Ra levels up to 16Bq.g −1 was observed in Lanthanum oxide. The external gamma exposure rates and airborne activity due to thorium and thoron progeny in the process locations are studied. The activity levels in liquid effluent and potential exposure scenarios are indicated. Radiation protection and management of wastes generated by industries that process minerals and raw materials containing naturally occurring radioactive materials (NORM) are of concern in the context of long term environmental implications of waste disposal. Chemical compounds of rare-earth (RE) elements (La to Lu) have wide applications in daily life. They are commercially exploited from minerals such as monazite, bastnasite, xenotime, allanite etc. Most of these natural ores and minerals contain low or significant levels of thorium and uranium series nuclides. The thorium content varies from 0.1% to 10% and uranium content varies from very low percentage to 0.8% depending on the mineral and region of occurrence (1). Monazite (Ce,La,Th)PO4, a phosphate mineral containing nearly 9% thorium as ThO2 is the starting material for the production of rare earth compounds in India. Caustic digestion followed by selective extraction in HCl is the method used to separate composite rare-earths chloride. Limited studies on the radiation protection aspects in rare-earths industry are reported (2, 3). A variety of diversified RE compounds that have wide applications in daily life and advanced scientific research are produced from the composite RE chloride by different chemical processes such as precipi- tation, solvent extraction and ion-exchange methods. The present studies are carried out in a rare-earths producing plant typically convert composite RE chloride to different compounds such as RE fluoride, oxide, carbonate and other individual rare earths compounds with emphasis on radiological aspects.

Uranium-series Crystal Ages

As the collected papers in this volume aptly demonstrate, chemical and textural records contained within crystals have become increasingly useful tools for understanding the evolution of magmatic systems. An essential component of studies of the dynamics of magmatic systems is the ability to place the thermal, physical, and compositional evolution of magmas in a temporal context. Studies of the kinetics of crystal growth and reaction, and of diffusive re-equilibration of crystals and melts, can provide information about the duration of magmatic processes such as magma ascent (Rutherford 2008), crystal growth (Hammer 2008), and residence of crystals in melts other than the ones in which they crystallized (Costa 2008). However, the only method of extracting information from young crystals about the absolute age of magmatic processes is isotopic dating. The timescales of many sub-volcanic magmatic processes such as magma transport, differentiation, crystallization, and storage within the crust, appear to be commensurate with the half-lives of uranium-series (U-series) nuclides, and therefore this isotopic system offers the greatest potential to quantify timescales and rates of magmatic processes. We focus here on crystal dating using the decay products of 238U and 235U, including 238U-230Th-226Ra-210Pb disequilibria, 235U-231Pa disequilibria, and U-Pb dating of young crystals. In this chapter, we review the principles of U-series dating of crystals, the types of information that have been gained so far from U-series dating, and the potential for combining U-series crystal ages with other crystal-scale and magma-scale information to unravel the dynamics of magmatic systems. ### Principles of U-series dating U-Pb dating is based on the accumulation of 206Pb and 207Pb over time due to decay of 238U and 235U, respectively, and is conceptually similar to most isotopic dating techniques. U-Pb dating of zircon, both by TIMS and in …

Determination of Lanthanoids and Uranium in Groundwater from Southeast Sweden by Neutron Activation Analysis and Their Behavior Including Uranium Series Nuclides

Determination of Lanthanoids and Uranium in Groundwater from Southeast Sweden by Neutron Activation Analysis and Their Behavior Including Uranium Series Nuclides

Characterization and geochemical behaviour of uranium series nuclides in sandy sediments at Kanamaru area, Yamagata and Niigata Prefectures, Japan

Uranium series nuclides in the Tertiary arkosic sands from a high rainfall area in Japan were determined and their characteristics and behaviour were studied. Uranium was concentrated in the upper ( c. 241 ppm) and lower ( c. 581 ppm) layers although no specific U mineral was observed. The filtration experiment showed that U in the groundwater is in the dissolved form rather than colloidal or particulate forms. Most U in the concentrated layers was in easily soluble fractions (such as AcONa/AcOH soluble) while the U content in the water around the site was low. The fact that the 230 Th/ 234 U activity ratios of a sample in the upper layer were much greater than unity suggests that U migration occurred within 0.3 Ma. However, the 234 U/ 238 U and 230 Th/ 234 U activity ratios of samples in the lower layer were close to unity, suggesting that the material has not been strongly leached. Using chemical leaching techniques, a small disequilibrium among the fractions is observed, even though the bulk sample was near equilibrium. It is inferred that sorption of U is more effective than precipitation in this area.

Minimum speed limit for ocean ridge magmatism from 210Pb–226Ra–230Th disequilibria

Although 70 per cent of global crustal magmatism occurs at mid-ocean ridges-where the heat budget controls crustal structure, hydrothermal activity and a vibrant biosphere-the tempo of magmatic inputs in these regions remains poorly understood. Such timescales can be assessed, however, with natural radioactive-decay-chain nuclides, because chemical disruption to secular equilibrium systems initiates parent-daughter disequilibria, which re-equilibrate by the shorter half-life in a pair. Here we use 210Pb-226Ra-230Th radioactive disequilibria and other geochemical attributes in oceanic basalts less than 20 years old to infer that melts of the Earth's mantle can be transported, accumulated and erupted in a few decades. This implies that magmatic conditions can fluctuate rapidly at ridge volcanoes. 210Pb deficits of up to 15 per cent relative to 226Ra occur in normal mid-ocean ridge basalts, with the largest deficits in the most magnesium-rich lavas. The 22-year half-life of 210Pb requires very recent fractionation of these two uranium-series nuclides. Relationships between 210Pb-deficits, (226Ra/230Th) activity ratios and compatible trace-element ratios preclude crustal-magma differentiation or daughter-isotope degassing as the main causes for the signal. A mantle-melting model can simulate observed disequilibria but preservation requires a subsequent mechanism to transport melt rapidly. The likelihood of magmatic disequilibria occurring before melt enters shallow crustal magma bodies also limits differentiation and heat replenishment timescales to decades at the localities studied.

Open-System Coral Ages Reveal Persistent Suborbital Sea-Level Cycles

Sea level is a sensitive index of global climate that has been linked to Earth's orbital variations, with a minimum periodicity of about 21,000 years. Although there is ample evidence for climate oscillations that are too frequent to be explained by orbital forcing, suborbital-frequency sea-level change has been difficult to resolve, primarily because of problems with uranium/thorium coral dating. Here we use a new approach that corrects coral ages for the frequently observed open-system behavior of uranium-series nuclides, substantially improving the resolution of sea-level reconstruction. This curve reveals persistent sea-level oscillations that are too frequent to be explained exclusively by orbital forcing.

Uranium-series chronology and cosmogenic 10Be– 36Cl record of Antarctic ice

We present new uranium-series and cosmogenic nuclide age data obtained by sensitive thermal ionization and accelerator mass spectrometric techniques for samples of dusty polar ice from Allan Hills, Antarctica. These data are used to further evaluate the applicability of these nuclides for direct radiometric dating of polar ice. In order to minimize artifacts during sample processing we developed an improved method utilizing ethylenediaminetetraacetic acid (EDTA) to stabilize uranium-series nuclides dissolved in polar ice during ice melting and filtration. Our measurements revealed low uranium-series daughter abundances and large uranium-series ( 234U/ 238U, 230Th/ 234U, 226Ra/ 230Th, 231Pa/ 235U) disequilibria in the filtered <0.05-μm fraction of these ice samples. Both the long-lived uranium-series disequilibria and 10Be/ 36Cl ratios are most likely recently inherited from precipitation. The short-lived daughter 226Ra is the exception and is enhanced in the <0.05-μm fraction, presumably due to recoil effects from dust bands present in the ice. Based on a simplified recoil model, ice ages of approximately 30 ka are obtained from our data. Absence of measurable 238U– 234U– 230Th– 226Ra disequilibria in the volcanic dust bands also suggests that ice ages are greater than 10 ka, consistent with recoil-based ages. Our relatively young ice ages can be compared with previously published relatively old terrestrial ages of meteorites from this area and suggests that meteorites at Allan Hills have experienced a multi-stage history of ice accumulation and/or ice flow. Our results also suggest that large uranium-series disequilibria can be inherited from precipitation, which may provide a method for dating clear ice samples.

堆積物_-_環境水におけるウラン系列核種の動態 _-_金丸地域の一例

堆積物_-_環境水におけるウラン系列核種の動態 _-_金丸地域の一例

Techniques for Measuring Uranium-series Nuclides: 1992-2002

Advances in geochemistry and geochronology are often closely linked to development of new technologies for improved measurement of elemental and isotopic abundance. At the beginning of the past decade, thermal ionization mass spectrometric (TIMS) methods were just beginning to be applied for long-lived uranium-series nuclide measurement (Edwards et al. 1987; Goldstein et al. 1989; Bard et al. 1990), with considerable advances in measurement speed, precision, and sensitivity over decay-counting methods. This opened up a vast number of applications in uranium-series geochronology and geochemistry of young sediments, volcanic rocks, and aqueous systems. Over the past decade there have continued to be advances in thermal ionization techniques, and the advent of alternative mass spectrometric methods, particularly multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS), has continued to improve the quality of uranium-series studies. So the past decade has been a particularly dynamic time for not only development of mass spectrometric techniques, but initiation of other methods related to long-lived uranium-series nuclide measurement. In the area of sample preparation, further development of microwave digestion methods had led to advances in speed and cost of analysis. In chemical separations, development of extraction chromatographic resins for isolating specific elements have simplified many separation problems and consequently improved analytical characteristics including sensitivity, speed of analysis, waste generation, and cost. With regard to instrumental analysis, advances in both decay-counting and mass spectrometry instrumentation have improved either measurement sensitivity or precision, speed of analysis, or analytical cost. One could argue that instrumental developments will continue to drive scientific breakthroughs in the application of uranium-series nuclides as tracers and chronometers in the earth and other sciences. In this chapter we discuss improvements documented in the literature over the past decade in these areas and others. Chemical procedures, decay-counting spectroscopy, and mass spectrometric techniques published prior to 1992 were …

Glacial to Holocene changes in carbonate and clay sedimentation in the equatorial Pacific Ocean estimated from thorium 230 profiles

Uranium series nuclide concentrations have been measured on sediments from five box cores from an equatorial Pacific transect. 230Thexcess activities show discontinuities at the Holocene‐glacial boundary as dated by 14C. The glacial sedimentation rates determined by 230Th and 14C are 2.5‐3.0 cm/kyr. The Holocene rates from 230Th are much lower than those dated by 14C (1.9–2.3 cm/kyr) because of carbonate dissolution. 230Th sedimentation fluxes exceed water column supply by factors of 1.2–1.8 in the Holocene and 1.8–3.0 in the glacial sections. A number of models have been applied to calculate carbonate dissolution rates. The results show that carbonate dissolution rates in the Holocene (in g/cm²kyr) equal 1.5 × 10−3 exp (1.4D) where D is water depth in kilometers. A point‐by‐point estimation of sediment fluxes through time show that clay accumulation rates in the area have been near constant at 0.1–0.2 g/cm²kyr over the past 20 kyr whereas carbonate accumulation rates have decreased dramatically from 0.6–1.0 g/cm²kyr in the glacial sections of the cores to 0.2–0.6 g/cm²kyr in the Holocene. The errors caused by the uncertainties in the age of the termination of the last glacial period have been investigated and results show that a range of 11–14 kyr leads to an error upper limit of about 30% in the estimation of CaCO3 dissolution rates. The response time of CaCO3 and 230Thex concentrations in the mixed layer of sediments due to an impulse of change in CaCO3 dissolution rate has also been discussed, showing that the observed changes in carbonate dissolution may be explained in terms of a single or a continuous change, depending upon the thickness of the mixed layer.

Study on Role of 234Th in Uranium Series Nuclides Migration

ABSTRACTThe role of 234Th, a daughter nuclide of 238U having a half life of 24 days, in the migration of uranium series nuclides has been studied to understand the mechanism which gives a higher migration velocity of 238U than that of 234U. We assume that 234Th is adsorbed at two different sites; one, where 234Th is reversibly adsorbed, and the other, where 234Th is irreversibly fixed. Calculations have shown that the fixation of ^Th to a rock can cause the apparent migration velocity of 234U to be reduced compared to that of 238U and this agrees with observed field data. Changes in the fixation rate constants affect the relative mobility of 238U and 234U, and this can account for the different migration behavior at different depths in the Koongarra ore deposit.

Uranium-series nuclides in the Golden fault, Colorado, U.S.A.: dating latest fault displacement and measuring recent uptake of radionuclides by fault-zone materials

Concentrations and isotopic ratios of U, Th and Ra were measured in a fault zone near Golden, Colorado where major displacement occurred between about 190 and 615 ka. Faulting created new surfaces for leaching and provided the pathways for U-rich ground water. Uranium and 230Th, the latter produced by the decay of dissolved 234U, are adsorbed by fault gouge, hematite-stained sand and brecciated sand- and claystones. The observed U enrichment is as much as six times baseline value and the simultaneous enrichment of 230Th is estimated at about ninefold relative to 238U. The adsorption of radionuclides chemically analogous to Th, such as Pu (IV) and Np, and 237Np decay products, on fault-zone materials would contribute to the immobilization of high-level radioactive waste in the vicinity of a repository in the event of leakage from engineered barriers into fractured rock-mass.

Migration Behavior of Uranium Series Nuclides in Altered Quartz-Chlorite Schist

ABSTRACTThe migration behavior of uranium series nuclides in an altered quartz-chlorite schist has been studied by utilizing data on the activity distributions of uranium series nuclides at Koongarra in the Northern Territory of Australia. The variation of 230Th/234U activity ratios (ARs) with distance along surface (2 m depth), intermediate (16 m) and deep (31 m) layers show different trends in the three layers parallel to the water flow. The relationship between the 234U/238U and 230Th/238U ARs reveals that the mobility of the uranium series nuclides is in order 238U, 234U and 230Th, and that the retardation factors oft 234U are greater than those of 238U by a factor of 1.1, 1.9 and 1.0 in the surface, intermediate and deep layers, respectively. X-ray diffraction patterns show different mineral assemblages, which are the alteration products of chlorite at the three layers. These results imply that the migration behavior of uranium series nuclides at each depth would be related to the alteration of chlorite.

Comment on “Ra-Th disequilibria systematics: Timescale of carbonatite magma formation at Oldoinyo Lengai volcano, Tanzania”

This paper discusses potential flaws in study by Williams, Gill, and bruland (1986) dealing with the extreme disequilibria between uranium and thorium series nuclides in alkalic carbonatite lava specimens. It discusses the apparent discrepencies between chemical compositions of lava which were reported from the same eruption. Clarification is made on the actual timing of eruptions in this volcanic region and the effects this would have on the petrogenesis interpretation of these rocks.

Source-Term Comparison Using the Arest and Syvac-Vault Models: Effects of Decay-Chain In-Growth and Precipitation

ABSTRACTA series of calculations of radionuclide release was performed with the AREST and SYVAC-Vault models (SVM) in order to assess concurrance. Specifically, the effects of precipitation and decay chain in-growth on the predicted release of nuclides from waste packages containing spent nuclear fuel were compared between each code. The results for maximum release rates generally agreed within a factor of 10. The differences in results can be explained based on the differences in geometry and boundary conditions between the two codes. Both codes showed nearly identical enhancement factors in release rates of uranium-series nuclides (U-238, U-234, Th-230, Ra-226) arising from the effect of decay-chain in-growth. Calculated enhancement factors in release rates for precipitation of a new uranium-bearing solid within the waste package were also in good agreement between AREST and SVM.