Rapid method for 226Ra and 228Ra analysis in water samples

Summary The measurement of radium isotopes in natural waters is important for oceanographic studies and for public health reasons. Radium-226 (T_1/2 = 1620 y) is one of the most toxic of the long-lived alpha-emitters present in the environment due to its long life and its tendency to concentrate in bones, which increases the internal radiation dose of individuals. The analysis of ²²⁶Ra and ²²⁸Ra in natural waters can be tedious and time-consuming. Different sample preparation methods are often required to prepare ²²⁶Ra and ²²⁸Ra for separate analyses. A rapid method has been developed at the Savannah River Environmental Laboratory that effectively separates both ²²⁶Ra and ²²⁸Ra (via ²²⁸Ac) for assay. This method uses MnO₂ Resin from Eichrom Technologies (Darien, IL, USA) to preconcentrate ²²⁶Ra and ²²⁸Ra rapidly from water samples, along with ¹³³Ba tracer. DGA Resin^ò (Eichrom) and Ln-Resin^ò (Eichrom) are employed in tandem to prepare ²²⁶Ra for assay by alpha-spectrometry and to determine ²²⁸Ra via the measurement of ²²⁸Ac by gas proportional counting. After preconcentration, the manganese dioxide is dissolved from the resin and passed through stacked Ln-Resin-DGA Resin cartridges that remove uranium and thorium interferences and retain ²²⁸Ac on DGA Resin. The eluate that passed through this column is evaporated, redissolved in a lower acidity and passed through Ln-Resin again to further remove interferences before performing a barium sulfate microprecipitation. The ²²⁸Ac is stripped from the resin, collected using cerium fluoride microprecipitation and counted by gas proportional counting. By using vacuum box cartridge technology with rapid flow rates, sample preparation time is minimized.     

Calibration and optimization of alpha-beta separation procedures for determination of radium/radon in single- and two-phase liquid scintillation systems

Liquid scintillation alpha beta discrimination technique based on pulse shape analysis (PSA) was evaluated for determination of ²²⁶Ra and ²²²Rn in water samples. In view of the significance of calibration, for the reliable and precise determination of ²²⁶Ra and ²²²Rn concentrations in water samples, calibration procedures were standardized for single and two phase systems using Quantulus 1220 liquid scintillation counter. PSA optimization and efficiency calibrations were performed using ²²⁶Ra standard rather than conventionally used pure alpha and beta standards and substantiated by measuring the activity concentrations of ²²⁶Ra and ²²²Rn in the spiked water samples.     

238U, 234U and 226Ra concentrations in mineral waters and their contribution to the annual committed effective dose in Turkey

Activity concentrations of ²³⁴U, ²³⁸U and ²²⁶Ra in mineral waters were determined on the basis of nine water bottling facilities using alpha particle spectrometry. The mineral water samples were collected from three geographic regions of Turkey. The radiochemical separation used in the uranium analysis is based on the isolation of uranium radioisotopes from other radionuclides such as Th, Am, Pu and Np using UTEVA resin. Alpha sources were prepared using electrodeposition method. The activity concentration of ²²⁶Ra was determined after deposition on a membrane using BaSO₄ co-precipitation method. The activity concentrations (mBq L^?1) of ²²⁶Ra, ²³⁸U and ²³⁴U ranged from <0.56 to 165, from <0.42 to 439 and from <0.42 to 464, respectively. The measured activity concentrations were used for the calculation of the average total annual effective ingestion doses for children and adults. The committed effective doses were calculated for three different scenarios according to mineral water consumption rate. In the most extreme scenario (for age group 12–17), all water samples except MW1 and MW2 cause annual committed effective doses below the reference level (0.1 mSv year^?1) recommended by World Health Organization (WHO).     

Determination and differentiation of <Superscript>226</Superscript>Ra and <Superscript>222</Superscript>Rn by gamma-ray spectrometry in drinking water

The analysis of ²²⁶Ra in natural waters can be tedious and time-consuming. For the determination and differentiation of activities of ²²⁶Ra and ²²²Rn in drinking water by γ-ray spectrometry a simple and fast method is presented. Activities of ²²⁶Ra > 0.5 Bq L⁻¹ can be determined according to stabilization of the sample without further procedures. For a more sensitive detection sample volumes of up to 5 litres are applicable by a rapid precipitation procedure without large expenditure. Further laborious enrichment methods are not necessary. Thus, detection limits of 0.1 Bq L⁻¹ can be obtained when using sample volumes of 5 litres. Therefore the method is suitable for the monitoring of radioactivity in drinking water samples in accordance with the legal guidance of the European Union.     

Application of a Liquid Scintillation Technique to the Measurement of 226Ra and 224Ra in Samples Affected by Non-Nuclear Industry Wastes

Experiment procedures have been developed for the determination of ²²⁶Ra and ²²⁴Ra activity concentration in solid and liquid samples collected around a non-nuclear industrial area, by liquid scintillation counting. The different radiochemical procedures developed in this work, have been adaptations of a radiochemical procedure previously used, for ²²⁶Ra and ²²⁴Ra determinations by LSC in drinking water, which was improved, refined up and adapted to the type of sample to be applied. These improved radiochemical methods have been applied to waste samples (phosphogypsum) produced by two factories which are engaged in phosphoric acid production, and to waters collected from the Odiel river, where during the sampling period a fraction of these wastes were released. ²²⁶Ra activity concentrations in the phosphogypsum ranged from 673 to 1178 Bq/kg dry weight, indicating that the wastes are particularly enriched in this radionuclide. Consequently, high ²²⁶Ra levels were easily found in the river waters analysed, especially in the neighbouring zones of the waste discharges.     

Direct determination of 226Ra in environmental matrices using collision cell inductively coupled plasma mass-spectrometry

Direct determination of ²²⁶Ra in complex environmental matrices (biological and uranium ore samples) by collision-cell inductively coupled plasma mass-spectrometry was investigated. Possible polyatomic interferences were studied and their effects on ²²⁶Ra measurements were determined. The instrumental conditions for optimal signal-to-noise ratio for ²²⁶Ra were found. Concentrations of ²²⁶Ra in certified reference samples were measured using both external calibration and standard addition approaches. The best precision was obtained by applying standard additions. The absolute detection limit for ²²⁶Ra was 1 fg with optimal gas flow rates for the collision cell of 7 ml^.min^-1 for helium and 4 ml^.min^-1 for hydrogen.     

Pulse time interval analysis (TIA) combined with liquid scintillation counting for the determination of environmental α-nuclides: Preparation and utilization of225Ra as a yield tracer

Time interval analysis (TIA), which has been verified to be suitable for the selective extraction of correlated successive α-decay events within a liquid scintillator, was further developed by combining pulse shape discrimination technique and simple chemical analysis. A β-emitter nuclide,²²⁵Ra, which is suitable for the use as a yield tracer belonging to Np-decay series, was also found to be detectable by the TIA-method after a certain standing period when the radium-extractant (RADAEX) was added small amounts of HDEHP [di (2-ethylhexyl) phosphoric acid], which was proved to keep the equilibrium state between Ra and its descendants. The present counting system (TIA analysis incorporated α-LSC/PSD) has been verified to be applicable to the simultaneous determination of three (including Th, Ac, and Np) decay series, if the chemical purification of radium fraction was applied to the environmental samples using an extractive scintillator in addition to utilization of an α-peak itself at lowest energy for the determination of²²⁶Ra in uranium decay series. This radioanalytical method was practically applied to the determination of natural radionuclides belonging to three decay series in environmental samples and compared to the alpha-spectrometric results using a Si-surface barrier detector (SSB).     

<Superscript>226</Superscript>Ra and <Superscript>228</Superscript>Ra determination in environmental samples by alpha-particle spectrometry

A complete methodology for ²²⁶Ra and ²²⁸Ra determination by alpha-particle spectrometry in environmental samples is being applied in our laboratory using ²²⁵Ra as an isotopic tracer. This methodology can be considered highly suitable for the determination of these nuclides when very low absolute limits of detection need to be achieved. The ²²⁶Ra determination can be performed at any time after the isolation of the radium isotopes from the analyzed samples while the ²²⁸Ra determination needs to be carried out at least six months later through the measurement of one of its grand-daughters. The method has been validated by its application to samples with known concentrations of these Ra nuclides, and by comparison with other radiometric methods.     

Using the 186-keV peak for 226Ra activity concentration determination in Hungarian coal-slag samples by gamma-ray spectroscopy

The uranium isotopic abundance and the ²³⁸U–²²⁶Ra secular equilibrium were determined in nine Hungarian coal slag samples. The ²²⁶Ra activity concentration was measured based on the radon decay products and also the ²²⁶Ra peak at 186 keV. Secular equilibrium existed in eight samples, whereas one sample showed a slight disequilibrium. The direct and fast measurement using only the 186 keV peak was validated which can be used after measuring the uranium isotopic ratio and verifying the ²³⁸U–²²⁶Ra secular equilibrium. This method can be used to measure the ²²⁶Ra content of high number of samples from the same geochemical background.     

Radium-224 in natural waters measured by γ-ray spectrometry

A method based on Ge(Li) γ-ray spectrométry is applied to the determination of ²²⁴Ra (t_{$\text{1}\text{2}$}= 3.64 days) in natural waters. The ²²⁴Ra is first removed from several hundred liters of water by preconcentration onto manganese dioxide-impregnated acrylic fibers. The fibers are leached, radium is coprecipitated with barium sulfate, and the γ-ray activity is counted so that activity ratios among ²²⁴Ra, ²²⁵Ra and ²²⁶Ra can be calculated. Concentrations are determined by using the ²²⁶Ra concentration determined on a small separate sample. Results from samples collected from ground water, estuarine, and continental shelf environments are presented.     

Natural radioactivity in bottled natural spring,mineral and therapeutic waters in Poland

Activities of ²³⁸U, ²³⁴U, ²²⁸Ra, ²²⁶Ra, and ²²⁴Ra as well as total α- and β-activities of 23 bottled spring, mineral and therapeutic waters produced and distributed in southern and central Poland are presented. The activities vary from a few tenth to a few mBq·L⁻¹ for uranium and to several hundred mBq·L⁻¹ for radium isotopes. The activities of ⁴⁰K were calculated from chemical analyses of potassium and checked for several mineral waters by gamma-spectrometer coupled with an HPGe detector. Positive correlation between water mineralization and activities of ⁴⁰K, ²²⁶Ra, as well as total alpha- and total beta-activities were observed. The radiological annual doses were calculated for all investigated waters and for different human age groups assuming the consumption of 1 liter of water per day. The calculated committed effective dose rate from uranium and radium isotopes resulting from consumption of the investigated waters exceeds the recommended value of 0.1 mSv per year in seventeen cases for infants and in one case for adults.     

Rapid determination of 226Ra in drinking water samples using dispersive liquid-liquid microextraction coupled with liquid scintillation counting

A new radioanalytical method was developed for rapid determination of ²²⁶Ra in drinking water samples. The method is based on extraction and preconcentration of ²²⁶Ra from a water sample to an organic solvent using a dispersive liquid-liquid microextraction (DLLME) technique followed by radiometric measurement using liquid scintillation counting. In DLLME for ²²⁶Ra, a mixture of an organic extractant (toluene doped with dibenzo-21-crown-7 and 2-theonyltrifluoroacetone) and a disperser solvent (acetonitrile) is rapidly injected into the water sample resulting in the formation of an emulsion. Within the emulsion, ²²⁶Ra reacts with dibenzo-21-crown-7 and 2-theonyltrifluoroacetone and partitions into the fine droplets of toluene. The water/toluene phases were separated by addition of acetonitrile as a de-emulsifier solvent. The toluene phase containing ²²⁶Ra was then measured by liquid scintillation counting. Several parameters were studied to optimize the extraction efficiency of ²²⁶Ra, including water immiscible organic solvent, disperser and de-emulsifier solvent type and their volume, chelating ligands for ²²⁶Ra and their concentrations, inorganic salt additive and its concentration, and equilibrium pH. With the optimized DLLME conditions, the accuracy (expressed as relative bias, B _r ) and method repeatability (expressed as relative precision, S _B ) were determined by spiking ²²⁶Ra at the maximum acceptable concentration level (0.5 Bq L⁻¹) according to the Guidelines for Canadian Drinking Water Quality. Accuracy and repeatability were found to be less than −5% (B _r ) and less than 6% (S _B ), respectively, for both tap water and bottled natural spring water samples. The minimum detectable activity and sample turnaround time for determination of ²²⁶Ra was 33 mBq L⁻¹ and less than 3 h, respectively. The DLLME technique is selective for extraction of ²²⁶Ra from its decay progenies.     

Determination of radium isotopes in mineral and environmental water samples by alpha-spectrometry

Summary A method for the determination of low-level radium isotopes in mineral and environmental water samples by alpha-spectrometry has been developed. Radium-225, which is in equilibrium with its mother ²²⁹Th, was used as a yield tracer. Radium were preconcentrated from water samples by coprecipitation with BaSO₄and iron (III) hydroxide at pH 8-9 using ammonia solution, then isolated from uranium, thorium and iron using a Microthene-TOPO chromatography column at 8M HCl, separated from barium in a cation-exchange resin column using 0.05M 1,2-cyclohexylenedinitrilotetraacetic acid monohydrate at pH 8.5 as an eluant, and finally electrodeposited on a stainless steel disc in a medium of 0.17M (NH₄)₂C₂O₄at pH 2.6 and current density of 400 mA^. cm^-2, and counted bya-spectrometry. Optimum experimental conditions for radium separation, purification and electrodeposition have been studied and discussed in the paper. The lower limits of detection of the method are 0.11 mBq^. l^-1for ²²⁶Ra, ²²⁸Ra and ²²⁴Ra, respectively, if 2 l of water are analyzed. The method has been checked with a certified reference material IAEA-Soil-6 supplied by the International Atomic Energy Agency and reliable results were obtained. Eighteen water samples collected in Italy have been analyzed with the method, the mean radiochemical yields for radium were 86.2±6.5%. The obtained radium concentrations were in the range of 0.50-60.8 mBq^. l^-1for ²²⁶Ra, of 0.10-25.7 mBq^. l^-1for ²²⁸Ra, and of￡LLD-7.97 mBq^. l^-1for ²²⁴Ra. The ²²⁸Ra/²²⁶Ra and ²²⁴Ra/²²⁶Ra ratios were in the range of 0.189-4.45 and￡LLD-0.941, respectively.     

Determination of radium isotopes in soil samples by alpha-spectrometry

A sensitive and accurate method for determination of radium isotopes in soil samples by α-spectrometry has been developed ²²⁵Ra, which is in equilibrium with its mother ²²⁹Th, was used as a yield tracer. Radium in soil samples was fused together with Na₂CO₃ and Na₂O₂ at 600 °C, leached with HNO₃, HCl and HF, preconcentrated by coprecipitation with BaSO₄, separated from uranium, thorium and iron using a Microthene-TOPO chromatographic column, isolated from barium in a cation-exchange resin column using 0.05M 1,2-cyclohexylene-dinitrilo-tetraacetic acid monohydrate as an eluant, electrodeposited on a stainless steel disc, and counted by α-spectrometry. The detection limit of the method is 0.43 Bq·kg⁻¹ for ²²⁶Ra, ²²⁸Ra and ²²⁴Ra if 0.50 g of soil sample are analyzed. The method was checked with two certified reference materials supplied by the IAEA, and reliable results were obtained Fourteen soil samples collected from the refractory industry in Italy were also analyzed. The mean radiochemical yields for radium were 85.7±4.3%, and the obtained radium concentrations in the soil samples were in the range of 8.08–3878 Bq·kg⁻¹ for ²²⁶Ra, of 1.60–678 Bq·kg⁻¹ for ²²⁸Ra and 1.25–550 Bq·kg⁻¹ for ²²⁴Ra, with ²²⁸Ra/²²⁶Ra and ²²⁴Ra/²²⁶Ra ratios ranged from 0.159–0.821 and from 0.142 to 0.525, respectively.     

Spatial distribution of radium in coastal marine waters of Tamil Nadu

An investigation on the distribution of radium activity levels in the entire south eastern coast of Tamil Nadu, India, from Chennai to Kanyakumari was carried out. Insitu preconcentration technique was adopted by passing 1,000?L of seawater through MnO₂ impregnated cartridge filters at all the locations. In the coastal waters, ²²⁶Ra and ²²⁸Ra concentration was observed to be in the range of 1 to 1.81 and 3.1 to 7.5?mBq/L, respectively with an average of 1.52 and 4.53?mBq/L. respectively, while the sediment samples showed ²²⁶Ra activity levels from 8.1 to 129.0?Bq/kg and ²²⁸Ra varied from 14.7 to 430.01?Bq/kg. The Kd values for ²²⁶Ra was observed to be from 5.3E03 to 3.5E05?L/kg and for ²²⁸Ra it was in the range of 2.3E03 to 5.9E04. It was observed that the concentration of ²²⁸Ra was more than ²²⁶Ra in all the locations. The spatial distribution of the activity with respect to location is discussed in the paper. The radioactive database obtained, represents reference values for coastal environment of Tamil Nadu.     

Natural radioactivity levels in mineral,therapeutic and spring waters in Tunisia

Radioactivity measurements were carried out in 26 groundwater samples from Tunisia. Activity concentrations of uranium were studied by radiochemical separation procedures followed by alpha spectrometry and that for radium isotopes by gamma-ray spectrometry.The results show that, the concentrations in water samples range from 1.2 to 69 mBq/L.1, 1.3 to 153.4 mBq/L, 2.0 to 1630.0 mBq/L and 2.0 to 1032.0 mBq/L for ²³⁸U, ²³⁴U, ²²⁶Ra and ²²⁸Ra, respectively. The U and Ra activity concentrations are low and similar to those published for other regions in the world. The natural radioactivity levels in the investigated samples are generally increased from mineral waters through therapeutic to the spring waters.The results show that a correlation between total dissolved solids (TDS) values and the ²²⁶Ra concentrations was found to be high indicating that ²⁶⁶Ra has a high affinity towards the majority of mineral elements dissolved in these waters. High correlation coefficients were also observed between ²²⁶Ra content and chloride ions for Cl^?–Na⁺ water types. This can be explained by the fact that radium forms a complex with chloride and in this form is more soluble.The isotopic ratio of ²³⁴U/²³⁸U and ²²⁶Ra/²³⁴U varies in the range from 0.8 to 2.6 and 0.6 to 360.8, respectively, in all investigated waters, which means that there is no radioactive equilibrium between the two members of the ²³⁸U series. The fractionation of isotopes of a given element may occur because of preferential leaching of one, or by the direct action of recoil during radioactive decay.The annual effective doses due to ingestion of the mineral waters have been estimated to be well below the 0.1 mSv/y reference dose level.     

Natural radionuclides in Austrian bottled mineral waters

All commercially available mineral waters of Austrian origin were investigated with regard to the natural radionuclides ²²⁸Ra, ²²⁶Ra, ²¹⁰Pb, ²¹⁰Po, ²³⁸U and ²³⁴U. From 1 to 1.5 L of sample the nuclides were extracted and measured sequentially: the radium isotopes as well as ²¹⁰Pb were measured by liquid scintillation counting after separation on a membrane loaded with element-selective particles (Empore Radium Disks), ²¹⁰Po was determined by α-particle spectroscopy after spontaneous deposition onto a copper planchette and uranium was determined also by α-particle spectroscopy after anion separation and microprecipitation with NdF₃. The calculated committed effective doses for adults, teens and babies were compared to the total indicative dose of 0.1 mSv/year given in the EC Drinking Water Directive. The dominant portion of the committed effective dose was due to ²²⁸Ra. Highly mineralised waters showed also higher ²²⁶Ra and ²²⁸Ra levels.     

Separation and determination of uranium and radium-226 in phosphorites and their industrial derivatives by extraction chromatography

An extraction chromatographic method based on microporous polyethylene (Microthene) supporting tri-n-octylphosphine oxide (TOPO) was used to separate uranium and²²⁶Ra from phosphorites and their industrial derivatives. Uranium was then determined by fluorimetry and by alpha-spectrometry after electroplating, and radium by precipitation as Ba(Ra)SO₄ and alpha counting with a ZnS(Ag) alpha detector. The method was checked by using an IAEA phosphorite sample having a certified uranium concentration. Some phosphorite, phosphoric acid and plaster samples supplied by an Italian industrial plant were analyzed; uranium isotopes always resulted in radioactive secular equilibrium.     

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.     

Determination of226Ra in environmental samples using high-resolution inductively coupled plasma mass spectrometry

A time-saving and accurate technique for determining²²⁶Ra in groundwater and soil was examined, using high-resolution inductively coupled plasma-mass spectrometry (HR-ICP-MS). The technique was applied to the determination of²²⁶Ra in groundwater and soil samples and compared with the conventional liquid scintillation counting method. This technique was capable of completing²²⁶Ra counting within 3 minutes, without the in-growth period to allow radon and its progeny to achieve secular equilibrium with the parent²²⁶Ra. The detection limits of HR-ICP-MS for²²⁶Ra in groundwater and soil were 0.19 mBq·1⁻¹ and 0.75 Bq·kg⁻¹, respectively, which were about 10 times lower than that of the liquid scintillation counter. The results obtained from HR-ICP-MS in groundwater and soil were in accordance with those of LSC within a relative error of about 13%.