Procedure for Simultaneous Determination of 223,224,226,228Ra by Alpha and Gamma Spectrometry

Reduction of natural radioactivity in groundwater with different salinity through adsorption of uranium and radium in filter materials

In many small communities in the Mediterranean area, groundwater is usually the only water body available. Depending mainly on the surrounding geology, their concentration of naturally occurring radionuclides may pose a radiological hazard. Removal of uranium and radium from drinking water is the best way to avoid it, i.e., reverse osmosis (RO), but consuming a lot of energy. Thus, two modified drinking water treatment plants (DWTPs) using zeolites coated with manganese dioxide as adsorbent material were analyzed as an alternative to RO. Groundwater salinity can negatively affect this process. Radium removal decreased as water salinity increased; but it had a major impact on uranium, rendering the adsorption effectless in one DWTP. Waste management and how to avoid it from becoming radioactive are of major concern. Radium and uranium were associated to the reducible fraction in the filter material and also to the carbonate fraction in the case of uranium. Regeneration of the filter material using KCl solutions was able to remove 81% and 63% of uranium and radium, respectively.

Improvements in the radiochemical method for separating 226Ra in solid samples through coprecipitation with BaSO4

The aim of this work was to improve the commonly used method for ²²⁶Ra determination in water and to establish its application in solid samples. This method is based on the coprecipitation of Ra with BaSO₄ and gross alpha counting of the precipitate. An exhaustive study of the coprecipitation behaviour of the most abundant cations present in solid samples was performed to avoid incorrect radiochemical yields. As a result, it was considered necessary to introduce two new purification steps into the conventional method. Likewise, two nuclides, ²⁴¹Am and ²²⁶Ra, were compared to obtain the mass efficiency curve given their different behaviour in the coprecipitation process. While Ra behaves similarly to Ba, Am coprecipitates, forming mixed crystals that may behave differently in the self-absorption process. The influence of the cations on the chemical yield with no precipitate purification was: Sr²⁺≫Fe³⁺>Mg²⁺≈Ca²⁺>K⁺≈Na⁺. The method was successfully applied to soil, sediment, and plant ash samples.

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.

Modification of natural radionuclide uptake by wheat using a NORM by-product as soil amendment

Drinking Water Treatment Plants (DWTPs) can be optimised for removal of natural radionuclides, thus meeting EU legislation. Removed radionuclides (^234,238U, ²²⁶Ra and ²¹⁰Po) go into sludges. What would happen if these sludges were used in agriculture? Wheat plantlets were cultivated in original and sludge-amended soils under laboratory controlled conditions. Soil-to plant transfer was significantly increased in factors ranging 1.2-3.7, 2.0-5.6, and 1.6-2.4 for ^234,238U, ²²⁶Ra and ²¹⁰Po, respectively. The additional input was preferentially accumulated in roots.

Removal of radium in a working drinking water treatment plant: Radiological hazard assessment and waste management

Occurrence of radium in drinking water may pose a radiological hazard. It is one of the most radiotoxic radionuclides and a major contributor to the Indicative Dose (ID), regulated parameter in UE. Its removal at Drinking Water Treatment Plants (DWTPs) can be considered a preventive action, as it cannot reach the final consumer nor be accumulated in distribution pipes. A filtration system based on greensand designed for radium removal was tested in an actual DWTP. Removal effectiveness depended on the spatial velocity water passed through the filter, range 65-100%. The lower the spatial velocity, the greater contact time, and the longer high removal percentages were achieved. The radium removed from the water was mainly associated to easily reducible fraction in greensand. So radium accumulation in the filter may pose a radiological hazard for the workers in the DWTP. Dose rate was assessed in the worst case scenario for this case study, being about 0.22 mSv/y, significantly lower than reference value 1 mSv/y. Radium accumulated in the greensand filter can be extracted in order to ease waste management, and subsequently, the filtration system can be regenerated showing similar capacity to extract radium as a new one.

Speciation of naturally occurring radionuclides in Mediterranean soils: bioavailabilty assessment

Knowledge of soil-to-plant transfer processes is a key element that can have a significant health impact. Much effort has been taken to characterize the speciation of anthropogenic radionuclides released into the environment. However, the information about naturally occurring radionuclides is scarce. This work evaluate the potential risks of transference, that is, the bioavailability of the ^234,238U, ²²⁶Ra, ^228,230,232Th, and ²¹⁰Po in three different soils collected in Mediterranean ecosystems. Chemical speciation of these radionuclides was carried out according to two different methods, Pavlotskaya and a modification of Tessier's protocol. Most of these radionuclides were associated to fractions strongly bound to soil particles and not able to be transferred. Increasing concentrations of U and Th extracted with increasing volume of NH₄OAc 1 M were observed, until it reached saturation. Readily bioavailable fraction in both methods (either exchangeable or water soluble + exchangeable) decreased in the following order: ²²⁶Ra > ^234,238 U > ^228,230,232Th > ²¹⁰Po. It was found that < 3% of the natural radionuclide concentration in soil are readily bioavailable for plant uptake in this region of Spain, and the resulting human health risk is negligible from natural radionuclide ingestion.

Radionuclides as natural tracers of the interaction between groundwater and surface water in the River Andarax, Spain

The identification of specific aquifers that supply water to river systems is fundamental to understanding the dynamics of the rivers' hydrochemistry, particularly in arid and semiarid environments where river flow may be discontinuous. There are multiple methods to identify the source of river water. In this study of the River Andarax, in the Southeast of Spain, an analysis of natural tracers (physico-chemical parameters, uranium, radium and radon) in surface water and groundwater indicates that chemical parameters and uranium clearly identify the areas where there is groundwater-surface water interaction. The concentration of uranium found in the river defines two areas: the headwaters with U concentrations of 2 μg L^-1 and the lower reaches, with U of 6 μg L^-1. Furthermore, variation in the ²³⁴U/²³⁸U isotopic ratio allowed us to detect the influence that groundwater from the carbonate aquifer has on surface water in the headwaters of the river, where the saline content is lower and the water has a calcium bicarbonate facies. The concentration of ²²⁶Ra and ²²²Rn are low in the surface waters: <1.6 × 10^-6 μg L^-1 and <5.1 × 10^-12 μg L^-1, respectively. There is a slight increase in the lower reaches where the water has a permanent flow, greater salinity and a calcium-magnesium-sulphate facies. All this is favoured by the influence of groundwater from the detritic aquifer on the surface waters. The results of this study indicate the utility in the use of physico-chemical and radiological data conjointly as tracers of groundwater-surface water interaction in semiarid areas where the lithology of aquifers is diverse (carbonate and detritic) and where evaporitic rocks are present.

Removal naturally occurring radionuclides from drinking water using a filter specifically designed for Drinking Water Treatment Plants

The occurrence of naturally occurring radionuclides in drinking water can pose health hazards in some populations, especially taking into account that routine procedures in Drinking Water Treatment Plants (DWTPs) are normally unable to remove them efficiently from drinking water. In fact, these procedures are practically transparent to them, and in particular to radium. In this paper, the characterization and capabilities of a patented filter designed to remove radium from drinking water with high efficiency is described. This filter is based on a sandwich structure of silica and green sand, with a natural high content manganese oxide. Both sands are authorized by Spanish authorities to be used in Drinking Water Treatment Plants. The Mn distribution in the green sand was found to be homogenous, thus providing a great number of adsorption sites for radium. Kinetic studies showed that the ²²⁶Ra adsorption on green sand was influenced by the content of major cations solved in the treated water, but the saturation level, about 96-99%, was not affected by it. The physico-chemical parameters of the treated water were unaltered by the filter. The efficiency of the filter for the removal of ²²⁶Ra remained unchanged with large water volumes passed through it, proving its potential use in DWTP. This filter was also able to remove initially the uranium content due to the presence of Fe₂O₃ particles in it, although it is saturated faster than radium.

Anthropogenic and naturally occurring radionuclide content in near surface air in Cáceres (Spain)

The anthropogenic (¹³⁷Cs, ⁹⁰Sr, ^239+240Pu and ²⁴¹Am) and naturally occurring radionuclide (⁴⁰K, ^234,238U, ^228,230,232Th, ²²⁶Ra and ²¹⁰Pb) content in near surface air present seasonal variations related to natural processes, such as soil erosion, resuspension of fine particles of soil and radon exhalation from soil (²¹⁰Pb). The objective is to analyze seasonal variations of their concentrations and compare with radiological events (Fukushima fallout and wild fire) in a location without any known source of anthropogenic radionuclides. The ²¹⁰Pb, ⁴⁰K, and ¹³⁷Cs presented annual variations, with maximum activity levels in summer. Solar radiation and rainfall were correlated with ²¹⁰Pb and ⁴⁰K. The ^234,238U, ^228,230,232Th, ²²⁶Ra, ¹³⁷Cs and ⁹⁰Sr presented positive correlation with monthly mean values of temperature. The ratio ⁹⁰Sr/¹³⁷Cs was within the range of those reported for soils in Spain. Finally, the maximal effective dose rate was estimated to be 37 and 88 μSv/y for infants and adults, respectively, well below 1 mSv/y reference level. The main contributor to effective dose was ²¹⁰Pb, about 92%, followed by: ²¹⁰Pb ≫ ^228,230,232Th > ²²⁶Ra, ^234,238U > ⁷Be, ^239+240Pu > ⁴⁰K, ⁹⁰Sr > ¹³⁷Cs > ²²Na.

Selection of the appropriate radionuclide source for the efficiency calibration in methods of determining gross alpha activity in water

Measuring the gross alpha activity in water samples is a rapid, straightforward way of determining whether the water might contain a radionuclide concentration whose consumption would imply a total indicative dose (TID) greater than some reference limit - currently set at 0.1 mSv/y in Europe. There are several methods used for such measurements. Two of them are desiccation with the salts being deposited on a planchet, and coprecipitation. The main advantage of these two methods is their ease of implementation and low cost of preparing the source to measure. However, there is considerable variability in the selection of the most suitable radioactive reference standard against which to calculate the water's gross alpha activity. The goal of this paper is to propose the most appropriate reference radionuclides to use as standards in determining gross alpha activities with these two methods, taking into account the natural radioactive characteristics of a wide range of waters collected at different points in Spain. Thus, the results will be consistent with each other and representative of the sum of alpha activities of all the alpha-emitters contained in a sample.

Assessment of radiological hazard of commercial granites from Extremadura (Spain)

The term "commercial granite" comprises different natural stones with different mineralogical components. In Extremadura, western Spain, "commercial granites" can be classified in three types: granite s.s. (sensus stricti), granodiorite, and diorite. The content of naturally occurring radionuclides depended of the mineralogy. Thus, the (40)K content increased as the relative content of alkaline feldspar increased but decreased as the plagioclase content increased. The radioactive content decreased in the following order: granite s.s. > granodiorite > diorite. In this work, the radiological hazard of these granites as building material was analyzed in terms of external irradiation and radon exposure. External irradiation was estimated based on the "I" index, ranged between 0.073 and 1.36. Therefore, these granites can be use as superficial building materials with no restriction. Radon exposure was estimated using the surface exhalation rates in polished granites. The exhalation rate in granites depends of their superficial finishes (different roughness). For distinct mechanical finishes of granite (polish, diamond sawed, bush-hammered and flamed), the surface exhalation rate increased with the roughness of the finishes. Thermal finish presented the highest exhalation rate, because the high temperatures applied to the granite may increase the number of fissures within it. The exhalation rates in polished granites varied from 0.013 to 10.4 Bq m(-2) h(-1).

Association of naturally occurring radionuclides in sludges from Drinking Water Treatment Plants previously optimized for their removal

The raw water used in Drinking Water Treatment Plants (DWTPs) can present high values of naturally occurring radionuclides. In order to reduce this content, the routine working conditions of DWTPs were successfully modified. This meant that those radionuclides were accumulated in the sludges generated, whose radioactive content was frequently above the exemption levels. It therefore becomes necessary to assess the association of naturally occurring radionuclides in the sludges for their potential use as agricultural fertilizers. Two approaches were studied: (a) the effect of different sequential extraction methods applied to a selected sludge; and (b) the effect of the different contents of inorganic complexes dissolved in the input water on the composition of the sludges generated by two DWTPs with different origins of their input water. Uranium and radium were mainly associated with the carbonated and reducible fractions, while (210)Po and (228)Th were associated with the residual fraction. There were differences between the two speciation methods, but the order of bioavailable radionuclides was roughly the same: (226)Ra≈(234,238)U>(228)Th>(210)Po. The major inorganic complexes content, mainly carbonate, in the raw water affected the radionuclide association. The greater the carbonate content in the raw water, the greater was the association of uranium and radium with the carbonated and easily reducible fractions.

A comparative experimental study of gross alpha methods in natural waters

The aim of the present work was to compare the results obtained with gross alpha methods such as evaporation, co-precipitation and total evaporation by liquid scintillation counting and to check whether these results are representative of the real total alpha activity concentration on the sample. The study was carried out on eight natural waters with very different radioactive characteristics. For all the samples uranium ((238)U, (235)U, and (234)U), radium ((226)Ra and (224)Ra), (210)Po, and (232)Th isotopes were also assayed by using radiochemical separation and alpha spectrometry in order to determine the sum of the activities of these alpha emitters. Precision (expressed as relative standard deviation) was below 28% for evaporation and below 18% for co-precipitation. In the case of total by liquid scintillation counting it was below 10% for samples with Total Alpha activity above 0.1 Bq/L (this value is about three times the MDA). Furthermore, for most of the studied waters, the Total Alpha activity and the gross alpha activity determined by the three methods were comparable. The obtained bias by the evaporation, co-precipitation, and total evaporation by liquid scintillation counting methods was lower than 40%, 25% and 20%, respectively. The ANOVA test was applied to find out if there was significant variability among the methods. For the samples with the most common radiochemical characteristics there were no significant differences among the three studied methods. However differences were detected for samples with a high saline content or with a very low activity level.

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.

Enhancement of natural radionuclides in the surroundings of the four largest coal-fired power plants in Spain

The production of electricity in coal-fired power plants (CFPP) is considered a NORM (Naturally Occurring Radioactive Materials) activity because the coals they burn can present relatively high contents of the naturally occurring radionuclides. In this study, the main radiological impact pathways into the surrounding environments of the four largest coal-fired power plants in Spain were analyzed. These pathways are, first, atmospheric evacuations and wind resuspension and, second, effluent evacuations to nearby rivers or directly to the sea. The atmospheric releases of radionuclides were evaluated by the analyses of soil profiles in the vicinities of the CFPPs. No significant enhancement of radionuclides in the surface soil was observed at the points of maximum deposition of combustion gases, located from 4.3 to 13 km away depending on the considered CFPP. However, an increase of (40)K, (226)Ra, and (232)Th in the surface soils was observed in the first kilometre from the chimney for two CFPPs. This suggested that these radionuclides were released in particulate form. There was also a net influence of the climate in which the CFPPs were located. This was observed in the two CFPPs that were in dry environments, while no increase was observed in the other two, located in more humid environments. The liquid effluents released usually presented an enhancement of dissolved chemical species regarding the initial intake water. Enrichments of the (234,238)U and (226)Ra contents in the water used in the plants' routine procedures were observed, and of (210)Po in the wastewater of just one of the plants. In any case, this enhancement was below the parametric value for the Total Indicative Dose for the hypothetical human consumption of the released waters. As a consequence of these releases of radionuclides, local products destined for human consumption produced in the vicinity of the facilities might incorporate natural radionuclides by these pathways, finding no significant enhancement of the natural radionuclide contents due to the CFPPs.

Analysis of the different source terms of natural radionuclides in a river affected by NORM (Naturally Occurring Radioactive Materials) activities

The present work studied the radioacitivity impact of a coal-fired power plant (CFPP), a NORM industry, on the water of the Regallo river which the plant uses for cooling. Downstream, this river passes through an important irrigated farming area, and it is a tributary of the Ebro, one of Spain's largest rivers. Although no alteration of the (210)Po or (232)Th content was detected, the (234,238)U and (226)Ra contents of the water were significantly greater immediately below CFPP's discharge point. The (226)Ra concentration decreased progressively downstream from the discharge point, but the uranium content increased significantly again at two sampling points 8 km downstream from the CFPP's effluent. This suggested the presence of another, unexpected uranium source term different from the CFPP. The input from this second uranium source term was even greater than that from the CFPP. Different hypotheses were tested (a reservoir used for irrigation, remobilization from sediments, and the effect of fertilizers used in the area), with it finally being demonstrated that the source was the fertilizers used in the adjacent farming areas.

Antlers of Cervus elaphus as biomonitors of ⁹⁰Sr in the environment

Adequate radioprotection of the environment requires the identification of biomonitors sensitive to the variation of its radionuclide content. Due to the chemical similarities between calcium and strontium, calcified tissues of mammals are considered to be good ⁹⁰Sr biomonitors. This work considered Cervus elaphus antlers which, being shed annually, can give information about the importance of radiostrontium contamination in an ecosystem in the time period required for the growth of the antler. The samples were collected at various points of W and SW Spain. The mean value of their ⁹⁰Sr content was (70 ± 43 (S.D.)) Bq/kg d.w., range (16-218) Bq/kg d.w., and the radionuclide was evenly distributed in the different parts of the antler. There was a good correlation between the antlers' ⁹⁰Sr content and the ⁹⁰Sr deposited in the soil. The antlers' content of ²²⁶Ra (from the natural uranium series) and the contents of some stable elements (Ca, Mg, Sr, and K) were also determined. The values for these stable elements were practically constant in the analyzed samples, and the concentrations measured decreased in the following order: Ca » Mg > K > Sr » ⁹⁰Sr > ²²⁶Ra.

210Pb and stable lead content in fungi: its transfer from soil

The uptake and transfer of natural radionuclides, other than (40)K, from soil to mushrooms has been somewhat overlooked in the literature. Their contribution to the dose due to the consumption of mushrooms was considered negligible. But the contribution of (210)Pb in areas unaffected by any recent radioactive fallout has been found to be significant, up to 35% of the annual dose commitment in Spain. More than 30 species of mushrooms were analyzed, and the (210)Pb detected was in the range of 0.75-202 Bq/kg d.w. A slight difference was observed between species with different nutritional mechanisms (saprophytes > or = mycorrhizae). The (210)Pb content was correlated with the stable lead content, but not with its predecessor in the uranium radioactive series, (226)Ra. This suggested that (210)Pb was taken up from the soil by the same pathway as stable lead. The bioavailability of (210)Pb in soil was determined by means of a sequential extraction procedure (NH(4)OAc, 1M HCl, 6M HCl, and residue). About 30% of the (210)Pb present in the soil was available for transfer to mushrooms, more than other natural radionuclides in the same ecosystem. Lycoperdon perlatum, Hebeloma cylindrosporum, and Amanita curtipes presented the highest values of the available transfer factor, ATF. As reflected in their ATF values, the transfer from soil to mushroom of some natural and anthropogenic radionuclides was in the following order:

Determining factors in the elimination of uranium and radium from groundwaters during a standard potabilization process

We studied the physico-chemical and radioactive characteristics of four waters of subsurface origin. They were chosen for having the highest natural radioactivity levels of waters for human consumption in the Autonomous Community of Extremadura, Spain Their activity levels for alpha emitting radionuclides are between 120 and 19300 mBq L(-1), all exceeding the 100 mBq L(-1) threshold established in the European Union above which radioactive isotopes that are present in water should be investigated to determine which corrective action, if any, is needed. These waters were used to compare the efficiency in eliminating their uranium and radium content of two potabilization processes - one the standard chlorination-only process used by their respective municipalities, and the other a procedure consisting of coagulation, flocculation, settling, filtration, and chlorination stages, specifically designed to maximize the elimination of their natural radioactive content. The results showed the uranium and radium elimination efficiencies to depend strongly on the water's hydrogencarbonate, calcium, and magnesium ion concentrations. In particular, with increasing concentrations of any of these ions, the uranium elimination efficiency fell from 90% to 60% at its optimal working pH, pH=6, while the radium elimination efficiency rose from 50% to 90% at its optimal working pH, pH=10.

Distribution of radionuclides in different parts of a mushroom: influence of the degree of maturity

Mushrooms are known to be bioaccumulators of radionuclides, but little is known about their distribution within the fruiting bodies or the influence of the degree of maturity on uptake. We carried out a series of cultures of the species Pleurotus eryngii under controlled laboratory conditions to analyze these variables. The maximal uptake of 134Cs and 85Sr was found to occur in mature fruiting bodies, and with the growth of the mushroom the distribution of radionuclides within the fruiting bodies became inhomogeneous. In particular, there was an exponential increase in the percentage of the total activity of 134Cs, 85Sr, and 60Co in the cap+gills as the fruiting bodies matured, accompanied by a complementary decrease in the stem. Radiocaesium, potassium, calcium, (239+240)Pu, (234,238)U, (228,230,232)Th, and 226Ra were assayed in the cap, gills, and stem of fruiting bodies of Tricholoma equestre collected in a natural ecosystem and cultured P. eryngii. Potassium and radiocaesium were mainly located in the cap+gills, and 226Ra in the gills. There was a disequilibrium between (230,232)Th and 228Th in the different parts of the fungi, probably due to uptake of 228Ra and subsequent decay to 228Th. Finally, the distribution pattern of (239+240)Pu, (234,238)U, and (230,232)Th seemed to be species dependent.

Soil-fungi transfer coefficients: Importance of the location of mycelium in soil and of the differential availability of radionuclides in soil fractions

Soil-fungus transfer coefficients are usually defined as the ratio between the content of the fruiting bodies and that of the soil. Since, however, the methodology of how to determine the soil content is not firmly established, there exist a variety of definitions in the literature. We analyzed the 137Cs, 90Sr, 40K, and 226Ra content of mushroom and soil samples from two pine-wood ecosystems in Spain. The location of the mycelium in the soil profiles of these ecosystems was determined by means of the ergosterol concentration. The results showed the mycelium to generally be localized in the surface layer of soil (0-5 cm). We also carried out a speciation procedure for this layer of soil to determine the different degrees of association of the radionuclides in the soil. The results led us to propose some variations to the traditional definition used in quantifying radionuclide transfer. With these modifications, we were able to analyze Cs-K competition in several species of mycorrhizal and saprophytic fungi.

Fast methods for determination of antropogenic actinides and U/Th-series isotopes in aqueous samples

Rapid and simple methods are applied at the PSI radioanalytical laboratory for determining anthropogenic actinides in waste and nuclear reactor waters (U, Pu, Am, Cm) as well as for analysis of naturally occurring alpha-emitters in continental river and ground water. Anion exchange chromatography followed by alpha-spectrometry as well as alpha/beta-LSC is applied for the reactor coolant waters. To avoid alpha-spectrum interference between 238Pu and 241Am at 5.5 MeV, the Pu-fraction is purified using anion exchange resin. Prior to the separation of the Pu-fraction, all actinides (U, Pu, Am, Cm) are adsorbed batch-wise under stirring onto Actinide Resin and subsequent decomposition of the reagent. The residue is then re-dissolved in a sulfate buffer solution for electrolytic deposition. In tabular water samples isotopes of Ra and Po are analyzed additionally via sorption onto manganese coated discs (Ra) and deposition on silver discs (Po). For counting times of 1 day and use of 0.1-1l sample aliquots, detection limits of a few mBql(-1) can be obtained easily.

Preconcentration of radium isotopes from natural waters using MnO2 Resin

We have characterized "MnO2 Resin," a new resin developed by the PG Research Foundation, for radium adsorption over wide ranges of pH, reaction times and salt concentrations. We show that the sorption of 133Ba (used as a proxy for Ra) is highly dependent on pH with the most useful range from pH 4 to 8. The surface layers of the Mn oxides apparently become more positively charged under acidic conditions (below pH 4), which prevents diffusion of positively charged alkaline earth species (e.g. Ba2+, Ra2+) into the sorption sites. Adsorption at higher pH is thought to be inhibited because of carbonate complexation. We found that the sorption characteristics for radium onto MnO2 Resin are especially favorable for low-salinity waters but the sorption is still very satisfactory for highly salted solutions (KD=2.8x10(4) in both cases) but with slower kinetics. For analytical purposes, both column and pump experiments showed high recoveries with no measurable discrimination between Ra and Ba regardless of flow rates in fresh water. Seawater tests showed that recoveries of Ra and Ba are lower than fresh water at elevated flow rates with Ra adsorption higher than Ba at flow rates above 10 ml/min.

Measurement of 224Ra and 225Ra activities in natural waters using a radon-in-air monitor

We report a simple new technique for measuring low-level radium isotopes (224Ra and 226Ra) in natural waters. The radium present in natural waters is first preconcentrated onto MnO2-coated acrylic fiber (Mn fiber) in a column mode. The radon produced from the adsorbed radium is then circulated through a closed air-loop connected to a commercial radon-in-air monitor. The monitor counts alpha decays of radon daughters (polonium isotopes) which are electrostatically collected onto a silicon semiconductor detector. Count data are collected in energy-specific windows, which eliminate interference and maintain very low backgrounds. Radium-224 is measured immediately after sampling via 220Rn (216Po), and 226Ra is measured via 222Rn 218Po) after a few days of ingrowth of 222Rn. This technique is rapid, simple, and accurate for measurements of low-level 224Ra and 226Ra activities without requiring any wet chemistry. Rapid measurements of short-lived 222Rn and 224Ra, along with long-lived 226Ra, may thus be made in natural waters using a single portable system for environmental monitoring of radioactivity as well as tracing of various geochemical and geophysical processes. The technique could be especially useful for the on-site rapid determination of 224Ra which has recently been found to occur at elevated activities in some groundwater wells.

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.

Determination of 228Ra, 226Ra and 224Ra in natural water via adsorption on MnO2-coated discs

A fast procedure based on sorption of Ra on MnO2 coated polyamide discs is presented for determination of radium isotopes (i.e. 228Ra, 226Ra, 224Ra) in aqueous samples. The sample discs can be used directly for low-level alpha-spectrometry without the need for further separation and preparation methods to produce planar sample sources. While the activity of alpha-emitting 224Ra and 226Ra can be determined during a first measurement, beta-emitting 228Ra is obtained via ingrowth of the progeny 228Th on the same sample disc after a standing time of about six months. Calculations are presented for optimizing the analytical accuracy as well as for predicting the sorption yield or chemical recovery of radium on the sample disc as a function of exposure time because the sorption uptake proceeds with first-order kinetics. The analyses can be carried out on small samples of 0.5-11 and, for long counting times of one week and use of high-purity silicon surface barrier detectors, a detection limit of 0.15 mBq l-1 is obtained for 226Ra. Since the half-life of 224Ra is only 3.7 d and since 228Th (as a measure for 228Ra) is built up only partially on the sample disc, a slightly higher detection limit of 0.24 mBq l-1 results for the latter isotopes. The procedure is therefore sufficiently sensitive to allow the investigation of Ra isotope relationships in aquifers at typical environmental levels.