Characterization of uranium isotopic abundances in depleted uranium metal assay standard 115

Certified reference material (CRM) 115, Uranium (Depleted) Metal (Uranium Assay Standard), was analyzed using a TRITON Thermal Ionization Mass Spectrometer to characterize the uranium isotope-amount ratios. The certified ²³⁵U/²³⁸U “major” isotope-amount ratio of 0.0020337 (12) in CRM 115 was determined using the total evaporation (TE) and the modified total evaporation (MTE) analytical techniques. In the MTE method, the total evaporation process is interrupted on a regular basis to allow correction of background from peak tailing, internal calibration of the secondary electron multiplier detector versus the Faraday cups, peak-centering, and ion source re-focusing. For the “minor” ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope-amount ratio measurements using MTE, precision and accuracy comparable to conventional analyses are achieved, without compromising the quality of the ²³⁵U/²³⁸U isotope-amount ratios. Characterized values of the ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope-amount ratios in CRM 115 are 0.000007545 (10) and 0.000032213 (84), respectively. The ²³³U/²³⁸U isotope-amount ratio in CRM 115 is estimated to be <5 × 10^?9. The homogeneity of the CRM 115 materials is established through the absence of any statistically significant unit-to-unit variation in the uranium isotope-amount ratios. The measurements leading to the certification of uranium isotope-amount ratios are discussed.     

Chromatographic separation of uranium

Summary A solvent mixture of methanol and saturated ammonium acetate solution (18:2) is employed for the separation of uranium in ppm quantities from iron (up to 1000 fold excess) by paper chromatography. The separation from both iron and copper can be achieved by using a solvent mixture of methyl ethyl ketone, acetic acid, and diluted nitric acid (1613).

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Zusammenfassung Zur papierchromatographischen Trennung von ppm-Mengen Uran von Eisen (in bis zu 1000 fächem Überschuß) wird ein Laufmittel aus Methanol und gesätt. Ammoniumacetatläsung (182) benutzt. Die Trennung von Eisen und Kupfer wird mit einem Gemisch aus Methyläthylketon, Essigsäure und verd. Salpetersäure (1613) durchgeführt.

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The author is highly thankful to Prof. Bh. S.V. Raghava Rao for his valuable suggestions and guidance throughout the progress of this work.Thanks are also due to the Department of Geology, Andhra University for supplying the samples and to the Counsil of Scientific and Industrial Research, New Delhi for the award of a fellowship.     

Determination of isotopic uranium in food and water

The U.S. Food and Drug Administration (FDA) conducts surveys of foods both domestic and imported for the presence of radioactivity. It does not routinely analyze for the actinides, specifically uranium, as it has been shown by previously by studies as reported by WELFORD and others that the concentration in food is very low. This was the result of a "Tri-City" study. However, at specific sites, the FDA has been requested to analyze for uranium. The concern is that either 'enriched' or 'depleted' uranium has been introduced into the environment and possibly contaminated the food supply. In addition some concern has been raised that water from wells or other sources used for processing food may contain uranium, both natural, depleted or enriched. This paper will discuss the methodology for the determination of isotopic uranium, specifically for uranium-238 (depleted) and/or uranium-235 (enriched) in the analyses of food and water samples and the results of these surveys.     

Anion-exchange separation of uranium from the lanthanidfs

The anion-exchange behavior of uranium and the lanthanides in acetie acid-organic solvent mixtures is described. The distribution coefficients of the elements in 13 organic solvents containing acetic acid as the coniplexing agent were measured, and methods for the quantitative separation of uranium, from the rare-earth elements are proposed.     

Mass spectrometry determination of the isotopic composition of uranium hexafluoride

An absolute method for the determination of isotopic composition of substances in multiple collector mass spectrometers was proposed. The detailed analysi of terms used in the method for the determination of the isotopic composition of uranium hexafluoride was given. Parabolic nature of occurring constant measurement error, obtained in theory, was proved by test data for ²³⁵U within a wide range of its concentrations. In order to use the method of measurements in practice, the registration of constant error, through linear discriminatory relations Δc _i (c _i ), preliminary determined using uranium hexafluoride with standard isotopic composition, was proposed. The advantages of the developed method in comparison with the traditional analysis procedures, applied at present, were considered.     

Cation-exchange separation of uranium in dimethylsulphoxide medium

Cation-exchange chromatography in a dimethylsulphoxide (DMSO) medium is a suitable means for separating uranium from metal ions, including copper, iron, nickel and molybdenum. Quantitative separations of uranium from 26 elements can best be effected on a column of Dowex 50W-X8 (200-400 mesh), using as the eluent a 20% v/v DMSO solution which is 0.6Min hydrochloric acid and 0.25M in sodium acetate. Only calcium is eluted with the uranium and all other elements studied are eluted either before or after uranium. The elution characteristics of uranium and of other metal ions were investigated with respect to changes in eluent and resin compositions. Separations were much less effective at higher concentrations of sodium ion or DMSO. None of the organic solvents methanol, ethanol, methyl glycol, acetone, dioxan or acetic acid was found to produce favourable separation conditions. Results with Dowex 50 resins of lower or higher cross-linkage were inferior to those obtained with the X8 resin.     

Determination of isotopic composition of uranium in the CMX-4 samples by SIMS

Journal of Radioanalytical and Nuclear Chemistry - From the 16 laboratories participating in CMX-4, three laboratories (Buonarroti, Matisse, and Pollock) have utilized secondary ion mass...     

A preliminary investigation of the operational and isotopic speciation of uranium in sediments

Uranium was determined in extracts of inter-tidal sediment, obtained from a contaminated harbour, using the three-stage sequential extraction procedure recommended by BCR. The element was found mainly in association with reducible, or reducible and oxidisable, phases and the overall concentration was enhanced (up to 6.7 μg g^–1 dry weight) with respect to typical, UK levels. The ²³⁸U/²³⁵U ratio has been measured in digests of stream sediments obtained from the vicinity of a uranium enrichment plant. Significant enhancement in ²³⁵U with respect to the natural ²³⁸U/²³⁵U ratio (137.88:1) was observed at some locations.     

Radiochemical separation of antimony by isotopic exchange

Isotopic exchange has been used to develop a simple and rapid procedure for radiochemical separation of antimony. A number of variables which affect the yield were studied and optimised, and antimony yields of 96% were obtained at 30 degrees . Acids and alkalies decrease this yield considerably because they dissolve part of the precipitate. The mode of preparation of the antimony oxide precipitate and the temperature also affect the isotopic exchange. Studies made with radioactive tracers of 14 different elements show contamination of < 1% for most elements. The high contamination with (95)Zr-(95)Nb can be reduced considerably by adding carrier. The simple procedure can be carried out in about 13 min and does not require any special equipment.     

Radiochemical separation of strontium by isotopic exchange

Isotopic exchange has been used for the rapid separation of minute quantities of radio-strontium. A number of variables such as agitation time, concentration of strontium in both phases, mode of preparation and aging of the precipitates, were studied and optimized. With an optimized procedure, exchange yields of 96% and 94% respectively were obtained when strontium sulphate and strontium oxalate precipitates were used for the exchange. Decontamination studies made with radioactive tracers of 15 elements showed that the sulphate precipitate is more selective than the oxalate, most of the elements showing <1 % contamination except (140)Ba-(140)La and (110)Ag which show high contamination. This simple procedure has also been applied for the determination of radioactive strontium in rain-water samples.     

Round robin for uranium isotopic measurements by mass spectrometry

A round-robin for uranium isotopic analysis in two solutions with different concentrations prepared and certified by the Institute for Reference Materials and Measurements (IRMM, Geel, Belgium) was organized by CETAMA, a division of the Commissariat à l’énergie Atomique (CEA: French Atomic Energy Commission Fourteen laboratories took part in the program using twenty-five different instruments (ICP-QMS, ICP-SFMS and TIMS). For each solution and each isotopic ratio, a statistical analysis based on standard ISO 5725 was carried out to calculate the mean, the repeatability and reproducibility standard deviations, the z-score and zeta-score, the bias with respect to the target values, and to compare their precision. The mean measurement results for the ²³⁴U/²³⁸U and ²³⁵U/²³⁸U isotopic ratios show no significant biases compared with the target values, whatever is the analytical technique. The results were much less satisfactory for the ²³⁶U/²³⁸U isotopic ratio, for which only the laboratories specialized in traces analyses and/or precise isotopic analyses submitted results in good agreement with the target values. A detailed discussion is given in this article.     

Determination of uranium in natural waters after anion-exchange separation

A method is described for the determination of uranium by fluorimetry and spectrophotometry in samples of natural non-saline waters. After acidification with hydrochloric acid, the water sample is filtered and, following the addition of ascorbic acid and potassium thiocyanate, passed through a column of the strongly basic anion-exchange resin Dowex 1-X8 (thiocyanate form). On this exchanger uranium is adsorbed as an anionic thiocyanate complex. After removal of iron and other coadsorbed elements by washing first with a mixture consisting of 50 vol.% tetrahydrofuran, 40 vol.% methyl glycol and 10 vol.% 6 M hydrochloric acid, and then with pure aqueous 6 M hydrochloric acid, the uranium is eluted with 1 M hydrochloric acid. In the eluate, uranium is determined fluorimetrically or by means of the spectrophotometric arsenazo III method. The procedure was used for the routine determination of uranium in water samples collected in Austria.     

A particulate isotopic standard of uranium and plutonium in an aluminosilicate matrix

Mixed-actinide microstandard particles have been produced for calibration and performance testing of isotope-ratio mass spectrometers and ion and electron microprobe instruments. The spherical micrometer-size particles consist of an aluminosilicate matrix loaded with 2.2% by weight of isotopically certified uranium and 0.11% by weight of isotopically certified plutonium. The uranium and plutonium isotopic compositions have been verified by both thermal ionization mass spectrometry and secondary ionization mass spectrometry (SIMS). The elemental composition of the microspheres has been determined by both electron microprobe and SIMS analysis.     

A sequential radiochemical procedure for isotopic analysis of uranium and thorium in soil

A sequential radiochemical procedure for isotopic analysis of uranium and thorium in soil has been developed. Analysis involves total dissolution of the samples to allow equilibration of the natural isotopes with added tracers, followed by radiochemical separation using anion exchange chromatography (BioRad AG 1–X8). Further separation and purification is performed employing solvent extraction techniques. Finally, the U and Th fractions are co-precipitated with lanthanum and cerium fluoride, respectively, and quantified by alpha-particle spectrometry. Overall chemical yields range from 60 to 90%. Under normal operating conditions and present counting set up, the minimum detectable concentration (MDC) is approximately 2 Bq/kg for soil samples. This is based on one gram aliquot of sample, 80% chemical yield, and 1000 minute counting with a detector having about 15% counting efficiency. The procedure has been successfully tested with Standard Reference Materials. Various soil samples were analyzed with high chemical yields and fine quality of alpha-spectra. Decontamination factor studies were performed to determine the extent of the carry over of²¹⁰Po,²²⁵Ac,²²⁶Ra, and²²⁹Th into U fraction and²¹⁰Po,²²⁵Ac,²²⁶Ra, and²³²U into Th fraction.     

Study of uranium isotopic composition in groundwater and deviation from secular equilibrium condition

Uranium concentration in groundwater reflect both redox conditions and uranium content in host rock. In the present study an attempt has been made to study the uranium concentration and activity ratios of uranium isotopes to present the geochemical conditions of the groundwater in Malwa region of Punjab state, India and the reason for high uranium levels and variation of activity ratios from secular equilibrium conditions. Uranium concentration in groundwater samples was found to be in the range of 13.9 ± 1.2 to 172.8 ± 12.3 μg/l with an average value of 72.9 μg/l which is higher than the national and international guideline values. On the basis of uranium concentration, the groundwater of the study region may be classified as oxidized aquifer on normal uranium content strata (20 %) or oxidized aquifer on enhanced uranium content strata (80 %). The ²³⁸U, ²³⁵U and ²³⁴U isotopic concentration in groundwater samples was found to be in the range of 89.2–1534.5, 4.4–68.5, and 76.4–1386.2 mBq/l, respectively. Activity ratios of ²³⁴U/²³⁸U varies from 0.94 to 1.85 with a mean value of 1.11 which is close to unity that shows secular equilibrium condition. High value of ²³⁴U isotope than ²³⁸U may be due to alpha recoil phenomenon. The plot of AR of ²³⁴U/²³⁸U against the total uranium content in log scale reveals that the groundwaters of the study region either belongs to stable accumulation or normal oxidized aquifer.