ABSTRACT
The indicative dose (ID) is one of the parameters established in the current European directive for water intended for human consumption. To determine the ID, it is necessary to know the activity concentration of: 238U, 234U, 226Ra, 210Po, 239,240Pu and 241Am. The existing methods to determine these radionuclides involve complex radiochemical separations (ionic exchange columns, extraction chromatography, etc.), followed by measurements with a semiconductor detector, laboratory procedures that are time-consuming and costly. As a lower cost alternative that reduces measuring and preparation times, avoids the need for a self-absorption correction and the use of tracers, and above all that can be used in any laboratory, methods based on liquid-liquid extraction and selective co-precipitation were developed. These methodologies offer high separation recovery and selectivity, and the measurements are made using a gas proportional counter or a solid ZnS(Ag) scintillation counter. The separation factor ranged between 91.4% and 100.0% for all alpha-emitting radionuclides across the different methods. The activity concentration for each method was computed through linear equations that represent the relationship between the activity and selectivity of the different alpha-emitting radionuclides. This mathematical procedure simplifies the radiochemical separations and provides more accurate activity concentrations. The results of the internal and external validation studies proved that the proposed method is suitable for determining 241Am, 226Ra, uranium, plutonium, thorium and 210Po in water samples.
ABSTRACT
The [Ba+Fe]-coprecipitation method is applied to measure gross alpha activity for radiological examination of drinking water in the laboratory. This method collects all the alpha-emitting radionuclides of interest (natural alpha emitters and transuranium elements) in a precipitate on a filter. This paper describes an investigation of sample pretreatment of the precipitate collected by the [Ba+Fe]-coprecipitation method for gross alpha activity determination. The aim of this preliminary work is to be a starting point to develop simple and rapid radiochemical procedures for specific alpha emitters (polonium, radium, thorium, uranium, plutonium and americium), in contrast to the sophisticated, expensive and time-consuming alpha spectrometry method. The sample pretreatment aspects considered include quantitative [Ba+Fe]-coprecipitation, two methods for precipitate treatment (leaching and complete destruction of the filter), and the determination of the alpha-emitting proportions present in the barium sulfate precipitate and acid solution obtained after precipitate treatment. Furthermore, a radiochemical procedure for (226)Ra determination was performed and finally, the sample pretreatment proposed in this work was summarized.
ABSTRACT
Two methods were used to apply self-absorption corrections for the determination of beta radioactivity in water samples (either for an identified radionuclide or for monitoring trends). One method was performed by estimating the absorption coefficient by assuming an exponential behaviour of absorption using external absorbers, while the other method was performed by preparing empirical curves using standards of different mass. In the first method, a relationship between absorption coefficient and maximum beta energy was also derived. In the second method, self-absorption curves for 90Sr/90Y standard were prepared with several sodium salts (carbonate, nitrate and sulphate salts) and, for 40K standard using a potassium salt. Both beta emitters are usually necessary to calibrate detectors for beta radioactivity measurements. This study showed that, for 90Sr/90Y, results using standards of different mass were more accurate than using external absorbers. Furthermore, it is highly recommended to melt sodium nitrate salts in order to perform a self-absorption curve for 90Sr/90Y because standards were stable in time and homogeneously distributed. For 40K, a self-absorption curve may be easily derived using paper absorbers of different thickness, instead of performing a time consuming self-absorption curve using a set of varying thickness of 40K standards. In order to test the two methods, the gross beta activity of several environmental water samples was analysed.
