Determination of 226Ra in mineral drinking waters by alpha liquid scintillation with rejection of beta-gamma emitters

Applications of PERALS-Alpha Spectrometry for the Investigation of Radionuclides in Water Samples

In this paper, experiences of the last 20 years with the PERALS-technique are described. PERALS stands for photo electron-rejecting alpha liquid scintillation. This liquid scintillation technique was developed by Jack McDowell in the 1970s and is a powerful technique for the analyses of many natural alpha nuclides and also the beta nuclide ⁹⁰Sr. The principle is based on a selective extraction of the radionuclide from the water phase by means of a complexing or ion pair reagent. The extractant contains also a cocktail suitable for scintillation counting. Therefore, the extract can be analyzed directly after the extraction step. After removing quenchers, such as oxygen, and the proper setting of a pulse shape discriminator, alpha pulses can be counted with a photomultiplier. This paper describes the development of robust analysis schemes for the determination of traces of polonium, thorium, uranium and other actinides in water samples (groundwater, rain water, river water, drinking water, mineral water, sea water). For radon and radium, the enrichment in the extract is poor. Therefore, PERALS methods are not suitable for trace analyses of these analytes. In addition, the extraction of the beta-emitter ⁹⁰Sr with a PERALS cocktail is discussed, even though its beta spectrum is not analyzed with a PERALS counter. Results from the survey of drinking water and mineral water in Switzerland are presented for every radio element.

Optimal methods for preparation, separation, and determination of radium isotopes in environmental and biological samples

In recent years, radium has attracted considerable attention primarily because of the rapid increase in unconventional (fracking) drilling technology in the United States and around the world. One of the major radionuclides of interest in unconventional drilling wastes is radium isotopes (²²⁴Ra, ²²⁶Ra, ²²⁸Ra). To access long-term risks associated with radium isotopes entering into the environment, accurate measurements of radium isotopes in environmental and biological samples are crucial. This article reviews many aspects of radium chemistry, which includes recent developments in radiochemical separations methods, advancements in analytical techniques followed by a more detailed discussion on the recent trends in radium determination.

Radon-222 and radium-226 occurrence in water: a review

A total of 2143 dissolved radon-222 and radium-226 activity concentrations measured together in water samples was compiled from the literature. To date, the use of such a large database is the first attempt to establish a relationship for the 226Ra–222Rn couple. Over the whole dataset, radon and radium concentrations range over more than nine and six orders of magnitude, respectively. Geometric means yield 9.82±0.73 Bq l−1 for radon and 54.6±2.7 mBq l−1 for radium. Only a few waters are in 226Ra–222Rn radioactive equilibrium, with most of them being far from equilibrium; the geometric mean of the radium concentration in water/radon concentration in water (CRa/CRn) ratio is estimated to be 0.0056±0.0004. Significant differences in radon and radium concentrations are observed between groundwaters and surface waters, on the one hand, and between hot springs and cold springs, on the other. Within water types, typical ranges of radon and radium concentrations can be associated with subgroups of waters. While the radium concentration characterizes the geochemistry of the groundwater–rock interaction, the radon concentration, in most cases, is a signal of non-mobile radium embedded in the encasing rocks. Thus, the 226Ra–222Rn couple can be a useful tool for the characterization of water and for the identification of water source rocks, shedding light on the various water–rock interaction processes taking place in the environment.

Optimized measurement of radium-226 concentration in liquid samples with radon-222 emanation

Measuring radium-226 concentration in liquid samples using radon-222 emanation remains competitive with techniques such as liquid scintillation, alpha or mass spectrometry. Indeed, we show that high-precision can be obtained without air circulation, using an optimal air to liquid volume ratio and moderate heating. Cost-effective and efficient measurement of radon concentration is achieved by scintillation flasks and sufficiently long counting times for signal and background. More than 400 such measurements were performed, including 39 dilution experiments, a successful blind measurement of six reference test solutions, and more than 110 repeated measurements. Under optimal conditions, uncertainties reach 5% for an activity concentration of 100 mBq L(-1) and 10% for 10 mBq L(-1). While the theoretical detection limit predicted by Monte Carlo simulation is around 3 mBq L(-1), a conservative experimental estimate is rather 5 mBq L(-1), corresponding to 0.14 fg g(-1). The method was applied to 47 natural waters, 51 commercial waters, and 17 wine samples, illustrating that it could be an option for liquids that cannot be easily measured by other methods. Counting of scintillation flasks can be done in remote locations in absence of electricity supply, using a solar panel. Thus, this portable method, which has demonstrated sufficient accuracy for numerous natural liquids, could be useful in geological and environmental problems, with the additional benefit that it can be applied in isolated locations and in circumstances when samples cannot be transported.

Continuous online determination of 226Ra in liquid effluents using automated column chromatography-ICP-MS

A measurement system capable of continuous on-line matrix removal, pre-concentration and analysis of 226Ra using pre-packed columns coupled to a flow injection system and an ICP-MS was developed. Full instrumental control of both the ICP-MS and the flow injection system provided automatic integration of the transient signals. The flow injection system was programmed to control column conditioning, sample loading, column rinsing, analyte elution and column cleaning operations employing appropriate solutions. The application of this system to the 226Ra analysis of an industrial liquid effluent was demonstrated. Using this particular instrument together with pre-concentration and matrix removal procedures, a limit of detection of 5.4 fg L−1 (2 mBq L−1) and a method detection limit of 16.2 fg L−1 (6 mBq L−1) were achieved for the measurement of 226Ra using a 25 mL sample volume. Total time for sample handling and analysis is approximately 10 minutes. The concentration of 226Ra in a discharged effluent sample was 0.73 pg L−1 (27 mBq L−1), which is in good agreement with the value of 0.81 pg L−1 (30 mBq L−1) measured using conventional alpha counting techniques.

Application of PERALS™ alpha spectrometry and gamma spectrometry for analysis and investigation of environmental spills at ISL uranium mining projects

Radiation protection and environmental monitoring in mining requires effective and reliable radionuclide analysis at all stages of the mine project-prior to mining, during operation and through to remediation and decommissioning. The approach presented in this paper was specially developed for the monitoring of radioactive waste resulting from spills during mining and mineral processing operations and uses a combination of high resolution gamma spectrometry, and PERALS™ alpha spectrometry to identify and reliably quantify the activity of the major members of the U-238 decay chain at activities down to 10 mBq g(-1) by direct radionuclide counting and by assessment of the activity of their decay products. This approach has reduced sample preparation and analysis time while providing effective analysis and quantification of naturally occurring radionuclides in environmental samples. It has been successfully applied to several in situ leach (ISL) mining-related projects involving investigations of process material spill impacts and also to routine environmental monitoring.

Determination of radium isotopes in environmental samples by gamma spectrometry, liquid scintillation counting and alpha spectrometry: a review of analytical methodology

Radium (Ra) isotopes are important from the viewpoints of radiation protection and environmental protection. Their high toxicity has stimulated the continuing interest in methodology research for determination of Ra isotopes in various media. In this paper, the three most routinely used analytical techniques for Ra isotope determination in biological and environmental samples, i.e. low-background γ-spectrometry, liquid scintillation counting and α-spectrometry, were reviewed, with emphasis on new methodological developments in sample preparation, preconcentration, separation, purification, source preparation and measurement techniques. The accuracy, selectivity, traceability, applicability and minimum detectable activity (MDA) of the three techniques were discussed. It was concluded that the MDA (0.1mBqL(-1)) of the α-spectrometry technique coupled with chemical separation is about two orders of magnitude lower than that of low-background HPGe γ-spectrometry and LSC techniques. Therefore, when maximum sensitivity is required, the α-spectrometry technique remains the first choice.

Deconvolution of alpha liquid scintillation spectra for quantitative analysis of actinide elements in water samples

The reliability and accuracy of actinide measurement in environmental samples strongly depend on the α-spectrum deconvolution process used to identify all radionuclides present in the sample, and the necessity to take into account internal conversion is demonstrated. In this process, all actinides can be resolved as the sum of three peaks: the main alpha transition and two sum peaks for which the additional α ray is merged with the internal conversion on L-shell peak and with all other conversions on M-shell, N-shell, etc.

The intensity of the internal conversions for thorium, uranium, plutonium and americium have been calculated and normalised to the intensity of the main alpha transition. These data can be used to determine the activity of any above-mentioned actinide by alpha liquid scintillation with alpha/beta discrimination. The quantitative analysis and the isotopic ratio determination of several certified solutions of actinides demonstrate the validity of this approach.

Understanding the peak asymmetry in alpha liquid scintillation with β/γ discrimination

The peak evaluation in alpha liquid scintillation is known to be easy, mostly due to the gaussian shape of the peaks. However, we often observed a high-energy tail in addition to a pure gaussian function. This effect is only detectable with a high resolution α liquid scintillation spectrometer such as the PERALS® system. Indeed, its intrinsic resolution (180 keV for a 4 MeV α particle) is better than that obtained for conventional LSC spectrometers. The peak asymmetry was quantified using the Fisher´s coefficient γ1 (symmetry factor). We show that the main effect responsible for the asymmetry is internal conversion. Indeed, most of the even-even nuclides have low α intensity transitions leading to excited levels of their daughter nuclides. The internal conversion is almost equal to 100% and consequently produces a sum peak at higher energy. No generalization is possible for odd-even nuclides, but the knowledge of their disintegration scheme allows to explain the experimental values obtained and the differences observed (e.g. between 241Am and 243Am). The experimental determinations of γ1 are given for polonium, radon, radium, thorium, uranium, plutonium, americium, and curium isotopes. We show the necessity to take into account the L and M shell contributions for few nuclides like thorium isotopes to get a maximum accuracy in the activity measurements.

Determination of radium-226 in aqueous solutions by alpha-spectrometry

The new European legislation imposes a lower threshold for radioactivity in drinking water. This requires the development of more sensitive and reliable analytical methods. This work presents an improved alpha-spectrometric technique to determine the radium-226 activity in aqueous solution relying on the radium adsorption onto a thin manganese oxide layer followed by alpha-measurement. The preparation of the MnO2 deposit has been optimized as well as the radium adsorption conditions. Detection threshold and limit of 5 and 10 mBq x L(-1), respectively, with a 10% (95% confidence) uncertainty are currently reached. This paper reports on the overall technique and on its application to assess the radium-226 activity in 28 French mineral waters. In addition, the gross alpha- and beta-activities have been evaluated using proportional counting while the uranium concentrations were derived from ICPMS.

Comparison and improvement of the determinations of actinide low activities using several alpha liquid scintillation spectrometers

We applied three procedures using two a liquid scintillation spectrometers (PERALS and TRI-CARB) and two scintillation cocktails (Alphaex and Ultima Gold LLT) for the determination of alpha-emitter low activities. For each procedure, the limit of detection, the resolution, the separation factor, and the Fischer coefficient were determined in order to perform 232U-234U-238U isotopic measurements. The deconvolution usually performed is clean when the PERALS spectrometer is used. This is not possible for the TRI-CARB spectrometer using the Ultima Gold LLT scintillation cocktail. This problem was solved by combining the advantages of both techniques using the Alphaex scintillation cocktail in the TRI-CARB spectrometer. Under these conditions, the limit of detection was improved, the resolution decreased from 500-800 to 420-590 keV, and the separation factor increased from 0.9 to 1.1-1.2. This third procedure was applied with success for 232U-234U-238U isotopic experiments.