Development of a sequential method for the determination of238U,234U,232Th,230Th,228Th,228Ra,226Ra,and210Pb. in environmental samples

A sequential analytical method for the determination of²³⁸U,²³⁴U,²³²Th,²³⁰Th,²²⁸Th,²²⁸Ra,²²⁶Ra and²¹⁰Pb in environmental samples was developed. Uranium and thorium isotopes are first chromatographically sepaaated using tri-n-octyl phosphine oxide (TOPO) supported on silica gel. The uranium isotopes are determined by alpha-spectrometry following extraction with TOPO onto a polymeric membrane. Thorium isotopes are co-precipitated with lanthanum fluoride before counting in an alpha spectrometer. Radium isotopes and²¹⁰Pb are separated by co-precipitation/precipitation with mixed barium/lead sulphate. Radium-226 is determined by gross alpha counting of the final BaSO₄ precipitate and²²⁸Ra by gross beta counting of the same source. Lead-210 is determined through beta counting of its daughter product²¹⁰Bi.     

Quantification of <Superscript>234</Superscript>Th recovery in small volume sea water samples by inductively coupled plasma-mass spectrometry

Summary Development of a small volume (2-4 liter) technique for measuring ²³⁴ Th in sea water has been instrumental in bringing to light small-scale structures in upper-ocean particle removal processes previously missed by standard ²³⁴ Th measurement techniques. Further development of this method to evaluate removal efficiencies of ²³⁴ Th via MnO₂ precipitation quantified using ICP-MS are presented in this work. Advantages to this approach are precise knowledge of ²³⁴ Th recovery, while maintaining high sample throughput afforded by ICP-MS analyzes. The improved technique includes the acidification of 4-liter sea water samples and the addition of ²³⁰ Th as a yield monitor prior to MnO₂ precipitation. Subsequent filtration and beta-counting of the high-energy daughter, ^234mPa, was followed by a final background count after 6 half-lives (144 d) of decay. Filtered precipitates were dissolved with H₂O₂, and an internal standard of ²²⁹ Th was added. Samples were purified using anion-exchange chromatography to remove high levels of manganese, and recoveries were determined by measured ratios of ²³⁰ Th/²²⁹ Th by ICP-MS. Application of this procedure for ²³⁴ Th derived export in the recent Southern Ocean Iron Experiment showed average recoveries of 91%. Corrections for rare low recoveries (25-80%) noticeably change ²³⁴ Th profiles, thus impacting subsequent elemental flux calculations.     

Disk mini-adsorbers with radial flow for determination of 234Th concentration in seawater

A modified method has been developed for measuring the ²³⁴Th concentration in seawater, which is based upon the use of MnO₂-impregnated disk mini adsorbers with radial flow connected in-line and the direct beta counting of ²³⁴Th and/or its daughter ^234mPa. This allows determining the ²³⁴Th concentration in a relatively small volume of seawater (20–50 L) with the possibility to check the extraction efficiency in every individual sample. The field testing, which was carried out at different areas of Sevastopol Bay during different seasons, has shown applicability of the proposed method to evaluate particle fluxes in marine environments within a wide range of concentrations of suspended matter.     

Testing a new small-volume technique for determining 234Th in seawater

Thorium-234 is a naturally occurring radionuclide that has been widely studied in ocean sciences. These studies use the disequilibrium between the soluble parent uranium-238 (T _1/2 = 4.5·10⁹ y), and its particle reactive daughter, ²³⁴Th (T _1/2 = 24.1 d), to quantify the in-situ removal rates of ²³⁴Th on sinking particles. Here, we present additional experiments that test a new 2-l procedure in which ²³⁴Th is co-scavenged with a MnO₂ precipitate. Unlike other techniques, this method can be easily applied at-sea with an overall precision and accuracy of 5%. Our experiments have sought to elucidate the effects of delaying reagent addition and precipitate filtration, differences in sample bottle types, and issues related to sample backgrounds and ²³⁴Th particulate sampling. Most of these experiments were conducted using water collected on repeated occupations of station ALOHA (22°45.0'N, 158°00.0'W), 100 km North of Oahu, Hawaii.     

Estimation of 90Sr in reprocessed uranium oxide samples

Summary A method has been developed for the estimation of ⁹⁰Sr in reprocessed uranium oxide samples obtained from the Purex processing of natural uranium spent fuel discharged from the research reactor. The method employs a combination of precipitation and solvent extraction procedure to eliminate other beta-impurities prior to resorting to the estimation of ⁹⁰Sr by beta-counting. ¹⁰⁶Ru was eliminated by volatalizing with perchloric acid, uranium was removed by carrier precipitation with strontium as sulphate. The sulphate precipitate was converted to carbonate and dissolved in nitric acid. ²³⁴Th and ²³⁴Pa were eliminated by synergistic solvent extraction using tri-n-butyl phosphate and thenoyl trifluoroacetone extractant mixture in xylene. An iron scavenging step was included to remove any residual impurities. Finally, strontium is precipitated as SrC₂O₄^. H₂O. The separated ⁹⁰Sr activity was followed to check the equilibrium growth of ⁹⁰Y.     

Variations of U/Th-series nuclides with associated chemical factors in the hot spring area of northern Taiwan

The relationship of the activity ratios (ARs) of U/Th-series nuclides and associated factors (pH, Eh, and the concentrations of Cl^- and SO₄ ^2-) in the hot spring area of Taipei were determined. The contents of U and Th in water decreased with increasing pH. The ²³⁴U/²³⁸U ARs have been ascribed to alpha recoil and selective leaching of ²³⁴U, while the ²³⁴U/²³⁸U disequilibrium was not significant with regard to the statistical error. Variations of ²³⁰Th/²³⁴U ARs can be attributed to the different chemical properties of ²³⁰Th and ²³⁴U. The disequilibrium of ²²⁶Ra/²³⁰Th can be ascribed to the complexation of thorium with Cl^- and SO₄ ^2-, and to the co-precipitation of radium with sulfates. The disequilibrium of²²⁸Th/²³²Th can be due to the co-precipitation of ²²⁸Ra with (Ba,Pb)SO₄ and to the migration of ²²⁸Th from the sediment into the water.     

Development and validation of a methodology for uranium radiochronometry reference material preparation

The paper describes a methodology for a reference material preparation to be used for the determination of the production date (i.e. the time elapsed since the last chemical processing) of uranium materials based on the ²³⁰Th/²³⁴U radiochronometer. The reference material was prepared from highly enriched uranium by a complete separation of thorium decay products, thus zeroing the initial daughter nuclide concentration at known time. The complete elimination of thorium from the starting material was verified by gamma spectrometric measurements and by addition of a ²³²Th tracer to the material and its re-measurement in the final product after the separation. The validation of the methodology was carried out subsequently by comparing the ingrown daughter nuclide ²³⁰Th and the measured ²³⁰Th/²³⁴U ratio after recorded times following the last chemical separation with the calculated values obtained on the basis of their respective half-lives. The prepared reference material can be used as a quality control material for age determination of uranium in nuclear forensics and safeguards as well as for method validation.     

A device for uranium series leaching from glass fiber in HEPA filter

For the disposal of a high efficiency particulate air (HEPA) glass filter into the environment, the glass fiber should be leached to lower its radioactive concentration to the clearance level. To derive an optimum method for the removal of uranium series from a HEPA glass fiber, five methods were applied in this study. That is, chemical leaching by a 4.0?M HNO₃?C0.1?M Ce(IV) solution, chemical leaching by a 5 wt% NaOH solution, chemical leaching by a 0.5?M H₂O₂?C1.0?M Na₂CO₃ solution, chemical consecutive chemical leaching by a 4.0?M HNO₃ solution, and repeated chemical leaching by a 4.0?M HNO₃ solution were used to remove the uranium series. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after leaching for 5?h by the 4.0?M HNO₃?C0.1?M Ce(IV) solution were 2.1, 0.3, 1.1, and 1.2?Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after leaching for 36?h by 4.0?M HNO₃?C0.1?M Ce(IV) solution were 76.9, 3.4, 63.7, and 71.9?Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after leaching for 8?h by a 0.5?M H₂O₂?C1.0?M Na₂CO₃ solution were 8.9, 0.0, 1.91, and 6.4?Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after consecutive leaching for 8?h by the 4.0?M HNO₃ solution were 2.08, 0.12, 1.55, and 2.0?Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after three repetitions of leaching for 3?h by the 4.0?M HNO₃ solution were 0.02, 0.02, 0.29, and 0.26?Bq/g. Meanwhile, the removal efficiencies of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th from the waste solution after its precipitation?Cfiltration treatment with NaOH and alum for reuse of the 4.0?M HNO₃ waste solution were 100, 100, 93.3, and 100%.     

Use of Adogen-464 in some parent — daughter separations by reverse phase extraction chromatography

Seperation of few carrier-free daughter isotopes from their respective parents, e.g.,¹³²I from¹³²Te,¹⁴⁰La from¹⁴⁰Ba and²³⁴Th from²³⁸U, using Adogen-464, a high molecular weight quaternary ammoaium salt by reversed phase extraction chromatographic technique is reported.     

Separation of 234th from inactive thorium, uranium and iron by adsorption on Bi(IO3)3, Bi(IO4)3 or Pb(IO3)2

Summary Conditions are described under which rapid and quantitative separation of ²³⁴Th occurs by adsorption on Bi(IO₃)₃, Bi(IO₄)₃, Pb(IO₃)₂. The activity is retained even in presence of considerable amounts of inactive thorium, uranyl and ferric ions. It appears that the activity is adsorbed by counter-ion exchange followed by inhomogeneous mixed crystal formation.

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Trennung des ²³⁴Th von inaktivem Thorium, Uran und Eisen durch Adsorption an Bi(JO₃)₃, Bi(JO₄)₃ oder Pb(JO₃)₂

Zusammenfassung Bedingungen für eine rasche Trennung werden beschrieben. Die Aktivität wird selbst in Anwesenheit wesentlicher Mengen von inaktivem Thorium, Uranyl- und Eisen(III)-ionen an dem Wismut- oder Bleiniederschlag zurückgehalten. Der Vorgang wird durch Gegenionen-Austausch und inhomogene Mischkristallbildung erklärt.

     

The Comprehensive Nuclear Test-Ban-Treaty and the radiological risk to on-site inspection teams

The solvent extraction behavior of thorium traces from the hydrochloric acid media with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) is described using ²³⁴Th as a tracer. The influence of certain variables such as extractant concentration, acidity, equilibrium time as well as UO₂ ²⁺ ions on the extraction of thorium has been investigated systematically. The back-extraction behavior of thorium from the organic phase has also been tested. The results reveal that the percent extraction of ²³⁴Th decreases with increasing hydrochloric acid concentration and thorium is easily back-extracted with an 4-6 mol/l aqueous HCl solution. At the same time, the effect of thorium extraction with PMBP was tested employing radioisotopes as multi-tracers in the irradiation of natural uranium with 14-15 MeV neutrons. The results show that thorium can be completely separated from a large amount of uranium and most of the other main reaction products.     

Preparation of234Th(UX1) by extraction of238U. determination of thorium with arsenazo-III

Summary Radiochemical procedures have been worked out to prepare²³⁴Th(UX₁) with and without carrier from uranium using N-oxide of 4-(5-nonyl)pyridine in sulphuric acid media. This reagent has also been employed in the development of a combined solvent extraction-ion exchange-spectrophotometric method for the determination of thorium in various samples.

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Zusammenfassung Radiochemische Methoden zur Herstellung von²³⁴Th(UX₁) aus Uran mit und ohne Träger und unter Verwendung von 4-(5-Nonyl)pyridin-N-oxid in schwefelsaurer Lösung wurden ausgearbeitet. Dieses Reagens wurde auch für die Ausarbeitung einer Thoriumbestimmung in verschiedenartigen Proben auf der Grundlage von Extraktion, Ionenaustausch und Spektro-photometrie verwendet.

     

234Th-derived particulate organic carbon export in the Prydz Bay, Antarctica

²³⁴Th activities in sea water were measured using Fe(OH)₃ co-precipitation and beta counting at six stations in Prydz Bay in March 2008 during the 24th Chinese National Antarctic Research Expedition. Total ²³⁴Th activities ranged from 0.96 to 2.44 dpm L^?1 with an average of 1.61 dpm L^?1, showing an apparent deficit with respect to ²³⁸U due to scavenging and export with particles. With a one-dimensional steady state model, ²³⁴Th export fluxes were converted to particulate organic carbon (POC) export using bottle ratios of POC concentrations to particulate ²³⁴Th activities on suspended particles. POC fluxes at the depth of 100 m varied between 33 and 297 mmol m^?2 day^?1, comparable to prior work in the same region and higher than those of some other sea areas in the Southern Ocean, and indicated efficient running of biological pump in Prydz Bay. The results could be helpful to expand the knowledge of carbon cycle in seasonally ice-covered coastal regions around Antarctica.     

Geochemical and gamma spectrometric analysis of ores and hostrocks of the Kanawa uranium occurrence in NE Nigeria

The Kanawa mineralization is one of the numerous low grade U-occurrences in the Gubrunde horst, NE Nigeria. Eighty nine samples consisting of ore and host rocks have been analyzed for 12 elements and 3 isotopes by atomic absorption spectrometry, colorimetry and direct -spectrometric methods and the data described using multivariate statistical techniques. The results show an enhancement of U, Mn, P₂O₅, Fe₂O₃, CaO,²¹⁰Pb,²²⁶Ra and²³⁴Th in the ore zones. The element/isotopic associations (U–P₂O₅–²¹⁰Pb–²²⁶Ra–²³⁴Th), (Na₂O–K₂O–MgO), (Fe₂O₃–MnO–CaO–Cu) were established in the mineralized rhyolites, while (P₂O₅–²¹⁰Pb–²²⁶Ra–²³⁴Th), (Na₂O–K₂O–MgO–Zn) and Fe₂O₃–Mn–U) occur in the altered/unmineralized rocks. The variation in the pattern of association of Cu, U, Zn and CaO could be ascribed to their remobilization, depletion, enrichment or introduction in the ore zone by hydrothermal solutions. The elements/isotopes U, Zn, Cu, P₂O₅,²²⁶Ra,²¹⁰Pb,²³⁴Th or their ratios could in addition to Pb, Ba, Ce, Sm be used as pathfinder elements in prospecting concealed ores in NE Nigeria.     

Intercalibrated radionuclide activities in spiked water samples of the IAEA worldwide open proficiency test

Proficiency testing is one of methods for regularly assessing the accuracy of the analytical data produced by laboratories for particular measurements. In 2008 and 2010, we participated in the IAEA 2008 and 2010 worldwide open proficiency tests on the determination of natural radionuclides in water spiked with ²²⁶Ra, ²³⁴U and ²³⁸U for activity analysis and with ⁹⁰Sr and ²³⁰Th for gross alpha/beta analysis. Feedback statistics from the IAEA final report showed that the radioactivities of all of the samples fell within an acceptable range according to the IAEA. For ²²⁶Ra analysis, our result showed that ²²⁹Th–²²⁵Ra is suitable as a chemical tracer, although there are doubts that different co-precipitation efficient between parent ²²⁹Th and its daughter nuclide ²²⁵Ra in published literature. The impact factors of the analysis results, such as the lower limit of detection, standard substances, the background and efficiency for daily determination, are discussed in detail.     

Influence of daughter radionuclides on Purex-process parameters

Experimental and calculated data are presented which concern the limiting influence of²³⁹Np,²³⁷U,²³³Pa,²³⁴Th,²²⁸Th (with daughter radionuclides) on the final decontamination of uranium, plutonium and neptunium from -emitters in Purex-process for NPP fuel reprocessing. It was found, in particular, that in the investigated flowsheet²²⁸Th follows neptunium(IV) and²³³Pa accompanies plutonium. The influence of accumulated daughter -emitters on ionization characteristics of end products in storage up to 100 years was studied. It is shown that stored regenerated uranium and plutonium may require repeated reprocessing just before refabrication.     

Natural radionuclides in groundwaters

The²³⁴U and²³⁰Th radionuclides are highly retarded by factors of 10⁴ to 10⁵ in basalt groundwater (Hanford) and briny groundwaters from Texas, and geothermal brine from the Salton Sea Geothermal Field (SSGF). In basalt groundwaters (low ionic strength), Ra is highly sorbed, while in brines (high ionic strength), Ra is soluble. This is probably because the sorption sites are saturated with Na⁺ and Cl^– ions, and RaCl₂ is soluble in brines.²¹⁰Pb is soluble in SSGF brine, probably as a chloride complex. The²³⁴U/²³⁰Th ratios in basalt groundwaters and brines from Texas and SSGF are nearly unity, indicating that U is in the +4 state, suggesting a reducing environment for these aquifers.     

Determination of americium-243 through its daughter product neptunium-239

The extraction of Np(IV), Zr, Nb, Cs, Ce(III) and Am(III) from nitric acid solutions containing oxalate and phosphate ions by solutions of 1-phenyl-3-methyl-4-benzoylpyrazolon-5 (PMBP) and tri-n-butyl phosphate (TBP) in benzene has been investigated. A solution 0.1M in respect to PMBP and 0.25M in respect to TBP was found to extract 99% of neptunium from aqueous solutions 1M in respect to H₃PO₄ and 0.5M in respect to HNO₃. Under these conditions, the extraction of the other investigated elements does not exceed 0.1%. Based on this finding, a procedure was developed to determine²⁴³Am through its daughter product²³⁹Np in solutions containing large quantities of curium and its fission products. The sensitivity of the procedure is 1·10⁻⁷ mg of²⁴³Am in the sample. The²⁴³Am content is obtained by calculation from measurements of the γ-activity of the extracted²³⁹Np. The purification ratio of²³⁹Np is∼10⁵ from Zr, Nb and Ru, ∼10⁸ from Ce and Cm and >10¹² from Cs.     

Radioactive series disequilibria in underground uranium deposits of the Singhbhum Shear Zone, Eastern India

Radionuclides of the ²³⁸U series (²²⁶Ra, ²¹⁰Pb, ²³⁴Th and ²³⁴U), ²³⁵U series (²²⁷Ac and ²³¹Pa) and ²³²Th series (²²⁸Th and ²²⁸Ra) series were measured by High Resolution Gamma Spectrometry system in twenty-five uranium ore samples from underground uranium deposits in the Singhbhum Shear Zone of Eastern India. The activity concentrations were observed to vary within a wide range in most of the deposits, as is the case in most rocks of crustal origin. The uranium ore from these deposits were not of high ore grade (U concentrations ranged from 0.015 to 0.082%). Activity ratios of key daughter–parent pairs from the decay chains, viz. ²²⁶Ra/²³⁸U, ²²⁶Ra/²¹⁰Pb, ²³¹Pa/²³⁵U, ²²⁷Ac/²³⁵U, ²³⁰Th/²³⁸U, ²³⁴U/²³⁸U, ²²⁶Ra/²³⁰Th and ²²⁸Th/²²⁸Ra indicated migration/accumulation of uranium and radium in some samples. The ²²⁶Ra/²³⁰Th ARs suggested that the deposits were not closed to groundwater movement for a maximum time period of 8ky. Thiel plot of the ²³⁴U/²³⁸U vs. ²³⁰Th/²³⁸U activity ratios indicated uranium accumulation and complex processes of uranium redistribution.     

Influence of freezing on physicochemical forms of natural and technogenic radionuclides in Chernozem soil

Sharp variations of different climatic parameters influence the transport, transfer, and deposition of contaminants in nature. Investigations of the impact of environmental temperature on the fractionation of radionuclides in soil are necessary for adequate assessment of their distribution and bioavailability in case of a nuclear accident. The impact of a sharp decrease of environmental temperature shortly after radioactive contamination on the physicochemical fractionation of natural and technogenic radionuclides in Chernozem soil and its influence on their potential migration ability and bioavailability in case of subsequent warming were evaluated. The soil was contaminated in a laboratory with ²⁴¹Am, ⁶⁰Co, ¹³⁷Cs, ²²⁸Ra, ²³⁴Th, and U and two temperature regimes were used for storage. Changes of the radionuclides association with various soil phases in the first weeks after contamination were studied. Physicochemical forms of ²⁴¹Am, ⁶⁰Co, ²²⁸Ra, ²³⁴Th, and U were determined using two sequential extraction procedures. The ion-exchangeable forms of ¹³⁷Cs were evaluated by single extraction with 1 M NH₄NO₃. The data showed that the freezing, following the radioisotope contamination of the soil, causes an increase of the amount of potentially mobile forms of radiocobalt, radiocesium, radium, and thorium and has an insignificant impact on the fractionation of americium and uranium.