Simultaneous determination of 226Ra and 210Pb in groundwater and soil samples by using the liquid scintillation counter-suspension gel method

The dynamics of the detection of 226Ra in water by scintillation counting in nonequilibrium conditions

The conventional methods for the ²²⁶Ra determination by liquid scintillation counting require to attain secular equilibrium between ²²⁶Ra and ²²²Rn prior to the counting. This study describes a method that allows the immediate counting of a sample after the dissolution of Ba(Ra)SO₄ in EDTA. This results from a detailed modelling of the activity of the parent ²²⁶Ra and its daughters in both the aqueous and organic scintillator phases. This methodology was tested on standard solutions of ²²⁶Ra showing promising results.

A new approach for the determination of 210Pb by liquid scintillation counting

A new approach to the calibration procedure is presented, as there is no need to discount bismuth from lead spectrum when constructing the efficiency curve. This work presents two calibration methods: one considering mostly lead spectrum contributions and other that considers both lead and bismuth contributions. Both methodologies provide consistent results when evaluated in an intercomparison program. Furthermore, this methodology allows simultaneous analysis of several samples and is suitable for any type of sample after proper digestion in liquid form.

A sequential determination of 90Sr and 210Po in food samples

The latest EU Council Regulation 2016/52/Euratom updates the emergency limits on radionuclides in foods including ²¹⁰Po and ⁹⁰Sr, two of the most important radionuclides for radiological dose from the ingestion pathway. A novel and straightforward method has been developed for sequential determination of ⁹⁰Sr and ²¹⁰Po in food samples using ultra low-level liquid scintillation counting and alpha-particle spectrometry. For ⁹⁰Sr analysis, the method makes use of stable strontium as yield tracer, and ²¹⁰Po is determined through self-deposition using ²⁰⁹Po as a yield tracer. The quantification limit for this method is 25.0 and 2.0Bqkg^-1 for ⁹⁰Sr and ²¹⁰Po, respectively. The proposed radiochemical separation can be completed within 2days for a batch of 12 samples. The radiochemical procedure was validated by its application for the measurement of IAEA certified reference materials, and through participation in a national intercomparison exercise. Results are also presented in seafood from the Mediterranean coast.

Determination of (226)Ra in produced water by liquid scintillation counting

It is proposed a method for the determination of (226)Ra in offshore platform liquid effluent samples (produced water). The method is based on a two-phase liquid scintillation counting system and allows for the direct and simple determination of (226)Ra content. Samples with high barium content may also have high (226)Ra concentration. Therefore, the sample volume is based on the barium concentration and ranges from 10 mL to 100 mL. Our new method was tested using multiple real samples and was compared with the BaSO4 precipitation method. The results based on the LSC were 30% higher than the precipitation method, which is attributed to the self-absorption of alpha particles in the BaSO4 precipitate. The determination of both (226)Ra and (228)Ra in the liquid effluent of offshore oil platforms is mandatory in Brazil. Thus, a second method of accurately assessing (228)Ra content remains necessary.

Lead: Radionuclides

Lead (Pb) is a highly toxic and radiogenic metal. It occurs naturally in the Earth, but is not very abundant. Even so, lead isotopes have been very useful ss tracers in glaciology, limnology, oceanography, and in atmospheric studies of global (transboundary) and local pollution. The dominant radioisotope of lead is 210 Pb, a very ubiquitous secondary radionuclide that is formed from 238 U decay via 222 Rn. 210 Pb originates from the Earth's crust, through the decay of 226 Ra. There are many factors that complicate the behavior of 210 Pb in soil, air, and water. Owing to these, a great deal of effort has been devoted to the quantitative determination of lead isotopes over the past few years. The separation and counting techniques for lead need to be rapid, convenient, and precise, and utilize very small amounts of material. Humans are exposed to lead through ingestion and inhalation, and it is stored for long periods of time mainly in bone and teeth. Thus, more studies on environmental exposures to lead need to be conducted, particularly for air monitoring, dust, water, and soil sampling, and lead‐based product sampling.

Simultaneous Determination of 226Ra and 228Ra in Water by Liquid Scintillation Spectrometry

Radium is a naturally occurring alkaline earth metal that is present in soils, water, plants, and foods in low concentrations. In the analysis of radium in trace amounts, co-precipitation is the favoured way of separating an element from its matrix. In this case, radium is co-precipitated with barium. The purity and yield of the extraction is controlled by adsorption onto the barium sulfate precipitate and pH manipulation controls the solubility of certain products. This technique enables the removal of interfering lead-210 to yield a purified radium source for analysis, which is done using liquid scintillation spectrometry. The analytical results of spiked water samples are in good agreement with the known activities of radium-226 and radium-228 standard reference materials. Minimum detectable limits for radium-226 and radium-228 are calculated to be 0.01 and 0.06 Bq L–1, respectively. The method provides a fast, reliable, and accurate alternative to traditional radium isotope analysis based on α and gamma spectrometry.

Deconvolution of liquid scintillation alpha spectra of mixtures of uranium and radium isotopes

A method for the determination of uranium and radium isotopes in water samples is proposed. Liquid scintillation techniques were used for collecting alpha spectra, which were then analyzed by fitting the alpha peaks with overlapping Gaussians. The analysis can quantify the observed isotopes with accuracy depending on the activity of each isotope. In order to simulate the peaks with Gaussian normal distribution functions, the centroid of each peak as well as the full width at half maximum (FWHM) are required, as they depend on the quenching of the sample. For this purpose, samples with known activities of 226Ra and its decay products and also of the uranium isotopes 238U and 234U, at various quenching levels, were used to establish the correlation of the peaks' shift with the quench effect. In addition, the correlation of the FWHM with the centroid of a peak was determined, using the same procedure. Following the above analysis technique, an average of 97+/-2% of detection efficiency and a lower limit of detection of 8.2 mBq kg(-1) for alpha isotopes were achieved.

Separation and subsequent determination of low radioactivity levels of radium by extraction scintillation

A method is developed for separation and subsequent determination of low (226)Ra levels based on its extraction efficiency by various organic extractants followed by direct interaction with mixed scintillation cocktail (SC) in toluene as the most suitable solvent. Three organic extractants including Tricaprylmethyleammonium chloride (Aliquat-336), triphenylphosphine sulphide (TPPS) and tri-n-octylphosphine oxide (TOPO) are individually embedded in 1-phenyl,4-phenyloxazole (PPO) as a primary scintillator and 1,4-di-2-(4-methyl, 5-phenyl oxazoyl) benzene (POPOP) as a second scintillator. Different parameters affecting the extraction process including shaking time, type and concentration of extractant, aqueous/organic volume ratio as well as various levels of (226)Ra are individually investigated. Based on the optimized condition, it was found that the extraction of (226)Ra by Aliquat-336 is highly selective with efficient separation capability from (133)Ba, which is necessary to determine the yield and recovery of (226)Ra in related measurements. The combination of extraction with direct scintillation processes is mainly elaborated to overcome the heterogeneity problem and hence the slow scintillation rate that often exists in conventional liquid scintillation counting especially with low radioactivity levels.

Simultaneous determination of 226Ra, 233U and 237Np by liquid scintillation spectrometry

A method has been developed for the simultaneous determination of 226Ra, 233U and 237Np by liquid-scintillation (LS) spectrometry. This method consists of the evaluation of the alpha-spectrum that is composed of the strongly overlapping peaks of 226Ra, 233U, 237Np, 222Rn and 218Po in the energy range of 4.60-6.00 MeV and the single 214Po peak at 7.69 MeV. The alpha-peaks are analysed by a special peak fit function that considers the deviation of the alpha-peak at the low energy side from the pure Gaussian shape. First 237Np is determined using its daughter 233Pa by analysing the beta-spectrum in the range 150-570 keV. 226Ra follows from the alpha-spectrum that is measured 6 weeks after sample preparation, i.e., 226Ra is determined from the radioactive equilibrium with its short-lived daughters 222Rn, 218Po and 214Po. Finally the 233U activity results from the fitted spectrum in the range of 4.4-4.8 MeV by subtracting the activity of 226Ra and 237Np. Knowing the exact energy position of the LS-peaks an alternative evaluation consists in the accurate deconvolution of the first three peaks that are formed by 226Ra and 233U (maximum of both at channel 700), 237Np (maxima at channels 700 and 725) and 222Rn (maximum at channel 737). In these two ways 226Ra, 233U and 237Np can be determined in mutual activity ratios of 1:50 with a relative standard deviation of less than 4% for the major activity and 9% for the minor activity.

Determination of 226Ra in aqueous solutions via sorption on thin films and α-spectrometry

An improved spectrometric method to determine the 226Ra activity in aqueous solutions is described. The method involves two stages, a preconcentration stage of 226Ra sorption onto a thin manganese layer and a measurement stage using alpha-spectrometry. Manganese oxide thin films were prepared and characterized with X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses. The thin films were found to follow the XRD patterns and chemical formula of the K-birnessite layered exchanger. The preconcentration of radium was studied relative to the initial radium concentration, pH and salt concentrations. The preconcentration kinetics was studied as a function of manganese surface, solution volume and salt concentration. Extensive Monte Carlo calculations were performed to optimise the detection of alpha-particles. In this way, the thin film preparation procedure as well as the radium sorption and the measurement conditions were optimised and detection limits lower than 0.5 mBq L(-1) were obtained for 2d of procedure completion. The method was validated with IAEA standards and it was applied for the determination of 226Ra in bottled waters and also wastewaters from the major thermoelectric plant in Greece. Moreover, the 226Ra distribution coefficients (K(d)) of two differently prepared powder manganese oxides, a crystalline silicotitanate and an aluminium-pillared montmorillonite were determined by gamma-spectrometry. 226Ra sorption experiments on silicotitanate thin films were performed and improvements in resolution and reduction of exposure time were observed.

Performance characteristics of sequential separation and quantification of lead-210 and polonium-210 by ion exchange chromatography and nuclear spectrometric measurements

A selective separation and quantitative determination procedure for 210Pb and 210Po in various environmental matrices from different sources such as IAEA-326 soil, phosphate rocks (PR), and phosphogypsum (PG) was developed. The tested samples were digested sequentially using concentrated mineral acids (HF, HNO3) by a programmable high-pressure microwave digestion system. The sample solution was loaded onto a preconditioned ion exchange column (Sr-resin) for chromatographic separation. Polonium-210 was eluted by 6 M HNO3 then spontaneously deposited onto polished silver discs to be measured using low-background alpha spectrometry. Lead-210 was sequentially eluted using 6 M HCl solution, precipitated as lead oxalate, dissolved in HNO3 solution, and mixed with scintillation cocktail to be measured by liquid scintillation counting (LSC). Performance of the developed procedure was tested using a reference soil (IAEA-326), with recommended isotope values, that was used as a quality control to assess separation and quantification efficiency (recovery %). The minimum detectable activities of 210Pb and 210Po were found to be 24 and 0.28 Bq kg(-1) for the measurements using LSC and alpha spectrometry, respectively. The recoveries (%) of 210Pb and 210Po were found to be 80 and 60%, respectively. To test the validity of the proposed LSC method, a comparative study was performed by measuring 210Pb activity concentration in test samples by nondestructive gamma-ray spectrometry.

Lead: Radionuclides

Lead (Pb) is a highly toxic and radiogenic metal. It occurs naturally in the Earth, but is not very abundant. Even so, lead isotopes have been very useful ss tracers in glaciology, limnology, oceanography, and in atmospheric studies of global (transboundary) and local pollution. The dominant radioisotope of lead is 210 Pb, a very ubiquitous secondary radionuclide that is formed from 238 U decay via 222 Rn. 210 Pb originates from the Earth's crust, through the decay of 226 Ra. There are many factors that complicate the behavior of 210 Pb in soil, air, and water. Owing to these, a great deal of effort has been devoted to the quantitative determination of lead isotopes over the past few years. The separation and counting techniques for lead need to be rapid, convenient, and precise, and utilize very small amounts of material. Humans are exposed to lead through ingestion and inhalation, and it is stored for long periods of time mainly in bone and teeth. Thus, more studies on environmental exposures to lead need to be conducted, particularly for air monitoring, dust, water, and soil sampling, and lead‐based product sampling.

A simple method for 210Pb determination in geological samples by liquid scintillation counting

A simple procedure for the determination of 210Pb in geological samples using liquid scintillation counting is presented. Following the acid digestion of the sample, the method uses sulphate precipitation for the radiochemical separation. Finally, lead oxalate is precipitated, and once re-dissolved, it is mixed with ULTIMA GOLD AB scintillator cocktail. The measurement is performed using a low-level LKB Quantulus 1220 spectrometer and the two-window technique. Calibration studies were performed to evaluate the interference of 210Bi in the 210Pb measurement. The method was tested on a geological reference sample, and gave satisfactory results and high reproducibility.