Determination of U in environmental samples by single extraction chromatography coupled to triple-quadrupole inductively coupled plasma-mass spectrometry

In order to measure trace ²³⁶U and ²³⁶U/²³⁸U in environmental samples with a high matrix effect, a novel and simple method was developed that makes the digestion and purification procedures compatible with advanced triple-quadrupole inductively coupled plasma-mass spectrometry. A total dissolution of sample with HF + HNO₃ + HClO₄ was followed by chromatographic separation with a single resin column containing normal type DGA resin (N,N,N′,N’-tetra-n-octyldiglycolamide) as the extractant system. The analytical accuracy and precision of ²³⁶U/²³⁸U ratios, measured as ²³⁶U¹⁶O⁺/²³⁸U¹⁶O⁺, were examined by using the reference materials IAEA-135, IAEA-385, IAEA-447, and JSAC 0471. The low method detection limit (3.50 × 10⁻⁶ Bq kg⁻¹) makes it possible to perform routine monitoring of environmental ²³⁶U due to global fallout combined with the Fukushima Daiichi Nuclear Power Plant accident fallout (>10⁻⁵ Bq kg⁻¹). Finally, the developed method was successfully applied to measure ²³⁶U/²³⁸U ratios and ²³⁶U activities in soil samples contaminated by the accident. The low ²³⁶U/²³⁸U atom ratios ((1.50–13.5) × 10⁻⁸) and ²³⁶U activities ((2.25–14.1) × 10⁻² mBq kg⁻¹) indicate ²³⁶U contamination was mainly derived from global fallout in the examined samples.     

Radiological characterization of drinking waters in Central Italy

Due to the importance of water in human life, its quality must be strictly controlled; for this purpose, simple and reliable analytical methods must be available. In this study, a monitoring of radioactivity content was performed in tap waters collected in a region of Central Italy to check the compliance with recent European and Italian regulations. Gross alpha and beta activities, ²³⁸U, ²³⁴U, ²²⁶Ra, ²²²Rn, and ³H concentrations were measured. Gross alpha and beta activities were determined by standard ISO 9696 and ISO 9697; for ²²⁶Ra, ²²²Rn and ³H determination, liquid scintillation was used. ²³⁸U and ²³⁴U concentrations were determined by alpha spectrometry after separation from the matrix by extraction chromatography and electroplating. The results revealed that the tritium concentration was always lower than 6.75 Bq l^− 1. The concentrations (mBq l^− 1) of ²²⁶Ra, ²²²Rn, ²³⁸U, and ²³⁴U ranged from < 1.70 to 15.31, from 0.69 to 20.3, from 0.65 to 48.77, and from 0.78 to 51.50, respectively.²³⁴U/²³⁸U ratios were higher than 1 in most cases. The results obtained revealed that, in most samples, gross alpha and gross beta were lower than the parameter value indicated in the international regulations. An attempt was also made to find a correlation between these results and the chemical parameters of waters.     

A combined method of neutron activation analysis and radiometric measurements for <Superscript>234</Superscript>U and <Superscript>238</Superscript>U determination in soil samples of low uranium concentration

A method that combines the use of non-destructive neutron activation analysis and high-resolution α spectrometry has been developed for determination of the activities of ²³⁴U and ²³⁸U in geological samples of low uranium content. The ²³⁸U content is determined by k₀-based neutron activation analysis, whereas the ²³⁴U/²³⁸U relationship is measured by α spectrometry after isolation and electrodeposition of the uranium extracted from a lixiviation with 6 M HCl. The main advantage of the method is the simplicity of the chemical operations, including the fact that the steps destined to assure similar chemical state for the tracer and the uranium species present in the sample are not necessary. The method was applied to soil samples from sites of the North Peru Coast. Uranium concentration range 3–40 mg/kg and the isotopic composition correspond to natural uranium, with about 10% uncertainty.     

Isotopic concentration of uranium from alpha spectrum of electrodeposited source on 4H-SiC detector at 500 °C

4H-SiC alpha detectors were fabricated with a 21-μm thick depletion depth and were packaged into a stainless-steel casing with a mineral insulation cable and a standard BNC connector. The packaged detectors had a resolution of 0.624% FWHM at 5.486 MeV prior to salt immersion. The detectors were then immersed in a LiCl–KCl–UCl₃ molten salt at 500 °C, from which a thin layer of depleted uranium was electrodeposited onto the detectors. Alpha particle emission spectra were collected from the electrodeposited source. The energy resolution of the surviving detector was 2.29% FWHM at 4.198 MeV and was sufficient to separate the ²³⁴U from ²³⁸U alpha emissions (577 keV difference). The ²³⁴U/²³⁸U activity ratio and the isotopic concentrations of ²³⁴U and ²³⁸U were determined and are representative of the uranium source used in the electrodeposition.

     

Determination of U/U atom ratio in uranium samples using liquid scintillation counting (LSC)

A correlation has been developed for the determination of ²³⁵U/²³⁸U atom ratio in uranium samples using liquid scintillation counting (LSC). The ²³⁵U/²³⁸U atom ratio determined by thermal ionization mass spectrometry (TIMS) was correlated to the ratio of (i) α-count rate and (ii) Cerenkov count rate due to ^234mPa in the sample; both measured by LSC. This correlation is linear over the range of ²³⁵U/²³⁸U atom ratio encountered in the nuclear fuel samples, i.e. the low enriched uranium (LEU) samples with ²³⁵U < 20 atom%. The methodology based on this correlation will be useful for the quick determination and verification of ²³⁵U/²³⁸U atom ratios in fuel samples using cost effective technique of LSC.     

Radiochemical characterization of spring waters in Balaton Upland, Hungary, estimation of radiation dose to members of public

Hungary is rich in spring waters. A survey studying the naturally occurring alpha emitter radionuclides in 30 frequently visited and regularly consumed spring waters was conducted out in the Balaton Upland region of Hungary.²²⁶Ra, ²²⁴Ra, ²³⁴U, ²³⁸U and ²¹⁰Po activity concentrations were determined by using alpha spectrometry after separation from matrix elements. Average concentration (mBq L^{− 1}) of ²²⁶Ra, ²²⁴Ra, ²³⁴U, ²³⁸U and ²¹⁰Po in the spring waters is varied from 2.1 to 601, from < 1.1 to 65.4, from 3.9 to 741.9, from < 0.44 to 274.3 and from 2 to 15.2 respectively. In most cases radioactive disequilibrium was observed between uranium and radium isotopes. The doses for the analyzed samples of spring water are in the range 3.59–166.73 μSv y^{− 1} with an average 18.2 μSv y^{− 1} .This is well below the 100 μSv y^{− 1} reference level of the committed effective dose recommended by WHO. Only one water sample had a dose higher than 100 μSv y^{− 1}, mainly due to the contribution from radium (²²⁶Ra, ²²⁴Ra) and ²¹⁰Po isotopes. This study provides important information for consumers and authorities about their internal radiological exposure risk from spring water intake.     

Particle isolation for analysis of uranium minor isotopes in individual particles by secondary ion mass spectrometry

A new technique to measure ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope ratios for individual particles in environmental samples was developed, which was a combination of particle isolation under scanning electron microscope (SEM) and secondary ion mass spectrometry (SIMS). The technique was verified by measuring ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope ratios in individual particles in a simulated environmental sample containing uranium standard (NBL CRM U010) and Pb metal particles. When the uranium particles were not isolated, the relative deviations of the measured isotope ratios from the reference values increased with increasing the signal intensity ratio of ²⁰⁸Pb to ²³⁸U, which was due to the molecular ion interferences by the Pb particles co-existing in the sputtered area. By the isolation of individual uranium particles, the interferences were eliminated and the measured isotope ratios were in good agreement with the reference values. The maximum relative deviations among 20 particles were 8.9% for ²³⁴U/²³⁸U and 13.1% for ²³⁶U/²³⁸U isotope ratios, respectively. The technique was also successfully applied to the analysis of a real swipe sample containing various kinds of elements.     

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%.     

Determination of 234U/238U isotope ratios in environmental waters by quadrupole ICP-MS after U stripping from alpha-spectrometry counting sources

The ²³⁴U/²³⁸U isotope ratio has been widely used as a tracer for geochemical processes in underground aquifers. Quadrupole-based inductively coupled plasma mass spectrometry (ICP-MS) equipped with a high-efficiency nebulizer and a membrane desolvator was employed for the determination of ²³⁴U/²³⁸U isotope ratios in natural water samples. The instrumental limit of detection for ²³⁴U was at the low pg L⁻¹ level with very low sample consumption. Measurement precision (²³⁴U/²³⁸U) was 3–5% for bottled mineral water with elevated uranium concentration (>1 μg L⁻¹). For the analysis of groundwater samples from the Almonte-Marisma underground aquifer (Huelva, Spain), uranium was stripped from stainless steel planchets that had previously been used as radiometric counting sources for alpha-particle spectrometry. Potential spectral interferences from other metals introduced during the dissolution were investigated. Matrix-matched blank solutions were needed to subtract the background on ²³⁴U due to the formation of platinum argides, and to allow for mass bias correction and background correction. The Pt appears to be an impurity present in the stainless steel, either as a minor component by itself or after extraction from the anode and a subsequent uranium electrodeposition. The ²³⁴U/²³⁸U isotope ratio data were in very good agreement with those of alpha spectrometry, while precision was improved by a factor of up to 10 and counting time was reduced down to ~20 min (10 replicate measurements).     

Uranium isotopes as a tracer of groundwater transport studies

The activity concentrations of ²³⁴U and ²³⁸U in thermal groundwater, deep well water and river water samples from Central Poland were determined. Concentration of ²³⁴U and ²³⁸U in the examined waters varied from <0.013 (LLD) to 16.8 mBq/dm³ and from <0.013 (LLD) to 45.5 mBq/dm³ respectively. The highest uranium activity concentrations were measured in the thermal groundwater from Mszczonow and Cieplice, while the lowest were observed in thermal ground water from Uniejow and Poddebice. In thermal groundwater from Skierniewice, uranium activity concentrations were below lower limit of detection (0.013 mBq/dm³). The ²³⁴U/²³⁸U activity ratio varied from 0.37 (Cieplice) to 1.30 (Poddebice well water).     

Application of laser ablation inductively coupled plasma mass spectrometry for the isotopic analysis of single uranium particles

The paper describes the application of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for the isotopic analysis of individual uranium-oxide particles. The procedure developed is suitable for the accurate measurement of ²³⁴U, ²³⁵U, ²³⁶U and ²³⁸U isotopes in single actinide particles with lateral dimensions down to 10 μm. The ²³⁵U/²³⁸U isotope ratios can be obtained with a precision of a few percent relative standard deviation using a single collector ICP-MS instrument. The precision could be improved by the use of slow ablation and by taking several LA-ICP-MS replicate spectra on the same particle investigated. For the minor isotopes use of higher mass resolution (R = 4000) was necessary in some cases to avoid spectral interferences. The technique developed offers a rapid and accurate possibility for the isotopic composition determination of uranium-containing individual particles in environmental and safeguards samples.     

Evaluation and application of Diffusive Gradients in Thin Films (DGT) technique using Chelex-100, Metsorb™ and Diphonix binding phases in uranium mining environments

A new resin- Diphonix^® in Diffusive Gradients in Thin Films (DGT) technique for the determination of uranium was investigated and compared with previously used binding phases for uranium, Chelex^®-100 and Metsorb™. The DGT gel preparation and the elution procedure were optimized for the new resin. The U uptake on Diphonix^® resin gel was 97.4 ± 1.5% (batch method; [U] = 20 μg L⁻¹; 0.01 M NaNO₃; pH = 7.0 ± 0.2). The optimal eluent was found to be 1 M 1-hydroxyethane-1, 1-diphosphonic acid (HEDPA) with an elution efficiency of 80 ± 4.2%. Laboratory DGT study on U accumulation using a DGT samplers with Diphonix^® resin showed a very good performance across a wide range of pH (3–9) and ionic strength (0.001–0.7 M NaNO₃). Diffusion coefficients of uranium at different pH were determined using both, a diffusion cell and the DGT time-series, demonstrating the necessity of the implementation of the effective diffusion coefficients into U-DGT calculations. Diphonix^® resin gel exhibits greater U capacity than Chelex^®-100 and Metsorb™ binding phase gels (a Diphonix^® gel disc is not saturated, even with loading of 10.5 μmol U). Possible interferences with Ca²⁺ (up to 1.33 × 10⁻² M), PO₄³⁻${{\text{PO}}_4}^{3\mathrm{-}}$ (up to 1.72 × 10⁻⁴ M), SO₄²⁻${{\text{SO}}_4}^{2\mathrm{-}}$ (up to 4.44 × 10⁻³ M) and −HCO₃${{\text{HCO}}_3}^{\mathrm{-}}$ (up to 8.20 × 10⁻³ M) on U-DGT uptake ([U] = 20 μg L⁻¹) were investigated. No effect or minor effect of Ca²⁺, PO₄³⁻${{\text{PO}}_4}^{3\mathrm{-}}$, SO₄²⁻${{\text{SO}}_4}^{2\mathrm{-}}$, and −HCO₃${{\text{HCO}}_3}^{\mathrm{-}}$ on the quantitative measurement of U by Diphonix^®-DGT was observed. The results of this study demonstrated the DGT technique with Diphonix^® resin is a reliable and robust method for the measurement of labile uranium species under laboratory conditions.     

Comparison of AMS,TIMS, and SIMS techniques for determining uranium isotope ratios in individual particles

The determination of isotope ratios in individual uranium particles is very important for nuclear safeguards. In this work, accelerator mass spectrometry (AMS), thermal ionization mass spectrometry (TIMS), and secondary ion mass spectrometry (SIMS) were applied to isotope ratio analysis of individual uranium particles and compared in terms of background, measurement accuracy, and efficiency. Several individual uranium particles (1–7 μm) from certified reference materials were used as samples. The results show that the average values of blank counting rate of ²³⁵U for AMS, FT-TIMS (FT: fission track), SEM-TIMS (SEM: scanning electron microscope), and SIMS were 7.3, 7.8, 2.7 and 2.2 cps, respectively. The relative error of ²³⁴U/²³⁵U and ²³⁴U/²³⁶U isotope ratios of the particles from U200 for AMS were within 10% and 20%, whereas the results of FT-TIMS and SIMS were within 5% and 10%, respectively. The relative error and external precision of ²³⁴U/²³⁸U and ²³⁵U/²³⁸U of the particles from U850 for the method of AMS, SEM-TIMS, and SIMS were within 10% and 5%, respectively. For ²³⁶U/²³⁸U, the average values of the relative error and external precision measured by AMS were within 5%, which measured by SEM-TIMS and SIMS were all within 10%. AMS has advantages in measuring ²³⁶U/²³⁸U. The measurement time of AMS and SEM-TIMS was shorter than that of FT-TIMS and longer than that of SIMS. It is considered that AMS and SEM-TIMS have a certain development prospect, and it is necessary to research deeply.     

Improvement in precision of extremely low <Superscript>236</Superscript>U/<Superscript>238</Superscript>U isotope ratio determination by using mass spectrometer with narrow dynamic range

The precision in measurement of trace level uranium isotopic ratio, i.e., ²³⁶U/²³⁸U or ²³⁴U/²³⁸U, on single Faraday detector with narrow dynamic range is very hard to achieve. this is mainly due to the narrow dynamic range of a single detector systems. A significant improvement in mass spectrometric determination of ²³⁶U/²³⁸U ratio has been achieved by employing an alternate method using a single Faraday detector of narrow dynamic range. The method makes use of the precise measurements of the ²³⁶U/²³⁴U ratio, ²³⁴U/²³⁵U ratio and ²³⁵U/²³⁸U ratio, which are used to calculate the ²³⁶U/²³⁸U ratio using the equation ²³⁶U/²³⁸U=²³⁶U/²³⁴Uײ³⁴U/²³⁵Uײ³⁵U/²³⁸U. Despite the fact that correlation of the data tends to increase the uncertainty in the result, our results show a significant improvement, i.e., more than 8 times better precision in measuring the ²³⁶U/²³⁸U ratio with this method (σ=3.98×10⁻⁰⁸) as compared to direct measurement of ²³⁶U/²³⁸U (σ=3.104×10⁻⁰⁷). The method widens the applicability of the single collector system with narrow dynamic range and it will potentially be helpful to improve the precision in the case of the static multi-collector system also. The objective of the present study was to compare the results of the same sample analyzed with the present alternate method and the direct method for precision.     

Recovery and pre-concentration of americium (III) from dilute acid solutions using an emulsion liquid membrane containing di-2-ethylhexyl phosphoric acid (D2EHPA) as extractant

Radiochemical results of U isotopes (²³⁴U, ²³⁵U and ²³⁸U) and their activity ratios are reported for well waters as local sources of drinking waters collected from the ten settlements around the Semipalatinsk Nuclear Test Site (SNTS), Kazakhstan. The results show that ²³⁸U varies widely from 3.6 to 356 mBq/L (0.3–28.7 μg/L), with a factor of about 100. The ²³⁸U concentrations in some water samples from Dolon, Tailan, Sarzhal and Karaul settlements are comparable to or higher than the World Health Organization’s restrictive proposed guideline of 15 μg (U)/L. The ²³⁴U/²³⁸U activity ratios in the measured water samples are higher than 1, and vary between 1.1 and 7.9, being mostly from 1.5 to 3. The measured ²³⁵U/²³⁸U activity ratios are around 0.046, indicating that U in these well waters is of natural origin. It is probable that the elevated concentration of ²³⁸U found in some settlements around the SNTS is not due to the close-in fallout from nuclear explosions at the SNTS, but rather to the intensive weathering of rocks including U there. The calculated effective doses to adults resulting from consumption of the investigated waters are in the range 1.0–18.7 μSv/y. Those doses are lower than WHO and IAEA reference value (100 μSv/y) for drinking water.     

Separation of neptunium, plutonium, americium and curium from uranium with di-(2-ethylhexyl)-phosphoric acid (HDEHP) for radiometric and ICP-MS analysis

The possibility of using di-(2-ethylhexyl)-phosphoric acid (HDEHP) in solvent extraction for the separation of neptunium, plutonium, americium and curium from large amounts of uranium was studied. Neptunium, plutonium, americium and curium (as well as uranium) were extracted from HNO₃, whereafter americium and curium were back-extracted with 5M HNO₃. Thereafter was neptunium back-extracted in 1M HNO₃ containing hydroxylamine hydronitrate. Finally, plutonium was back-extracted in 3M HCl containing Ti(III). The method separates²³⁸Pu from²⁴¹Am for α-spectroscopy. For ICP-MS analysis, the interferences from²³⁸U are eliminated: tailing from²³⁸U, for analysis of²³⁷Np, and the interference of²³⁸UH⁺ for analysis of²³⁹Pu. The method has been used for the analysis of actinides in samples from a spent nuclear fuel leaching and radionuclide transport experiment.     

Uranium determination in water samples with elevated salinity from Southern Poland by micro coprecipitation using alpha spectrometry

Due to the importance of water in human life, its quality must be strictly controlled; so simple and reliable analytical methods must be available. For this purpose a rapid procedure for the determination of uranium isotopes in natural water samples with elevated salinity was adopted. It was tested in 16 water samples from Upper and Lower Silesia Regions in Poland. Water samples had salinity in a range of 290–26,925 mg l^{− 1}.In water samples the concentrations of ²³⁴U and ²³⁸U ranged from 2.07 to 52.08 mBq l^{– 1} and from 2.18 to 43.38 mBq l^{– 1} respectively, while ²³⁵U level was below MDA (0.7 mBq l^{− 1}).The isotopic ratio of ²³⁴U/²³⁸U varies in the range from 0.949 to 3.344 in all investigated waters which means that there is usually no radioactive equilibrium between the parent nuclide ²³⁸U and its daughter product ²³⁴U.These results do not show a correlation between total dissolved solids (TDS) values and concentration of dissolved uranium isotopes.Committed effective dose for adults due to uranium intake as a result of drinking water usage was in range of 0.15–3.29 µSv y^{− 1} with an average value of 1.09 µSv y^{− 1} far below the 100 µSv y^{− 1} WHO recommendation.     

Determination of the isotope ratio234U/238U with a scintillation α-spectrometer

A method has been developed for the determination of the isotope ratio²³⁴U/²³⁸U. The preparation of the radiation source and a procedure based on the scintillation measurement of the α-spectrum are described. The results obtained are compared with data of the α-β method used earlier. By way of example, a few isotope ratios obtained in the examination of natural waters are presented for comparison. The results show the advantages of the application of the simple scintillation α-spectrometer and the justification of its use for²³⁴U/²³⁸U serial measurements.     

Anomalously high 234U/238U activity ratios of Tatsunokuchi hot spring waters, Ishikawa Prefecture, Japan

Uranium concentration and the ²³⁴U/²³⁸U activity ratio have been measured for the Tatsunokuchi hot spring waters of Ishikawa Prefecture in Japan, collected periodically over a long period (1977-2000). The concentration of ²³⁸U varied drastically between 0.045 and 1.02 mBq/l (a factor of about 20), while the ²³⁴U concentration was almost unchanged, ranging from 2.30 to 3.07 mBq/l. Resultant ²³⁴U/²³⁸U activity ratios showed a wide range from 2.7 to 51. Equilibrium calculation by using the geochemical code showed that U for one end-member representing low uranium contents and very high ²³⁴U/²³⁸U ratios was expected to exist as UO₂(CO₃)₂ ^2-. By using the U isotopic and ¹⁴C dating methods, the age of this water was roughly estimated to be in the range of 10⁴-10⁵ years.     

Uranium isotope anomaly in minerals

A series of leaching experiments with HF, HCl, HNO₃ were carried out on samples of uranium minerals (uraninite and carnotite samples). Anomalously high²³⁴U/²³⁸U ratios were observed in some uranium fractions. The observed²³⁴U/²³⁸U activity ratios varied between the values of 1.019±0.155 and 6.210±0.504 (Ci/Ci), while the bulk carnotite sample had an activity ratio of 1.010±0.005 (Ci/Ci). These results are interpreted as due to alpha-recoil effect and changes in oxidation state of uranium.