Reusability of plastic scintillators used in beta emitter activity determination

Hybrid Nanoparticle Platform for Nanoscale Scintillation Proximity Assay

β-particle emitting radionuclides, such as 3H, 14C, 32P, 33P, and 35S, are important molecular labels due to their small size and the prevalence of these atoms in biomolecules but are challenging to selectively detect and quantify within aqueous biological samples and systems. Here, we present a core-shell nanoparticle-based scintillation proximity assay platform (nanoSPA) for the separation-free, selective detection of radiolabeled analytes. nanoSPA is prepared by incorporating scintillant fluorophores into polystyrene core particles and encapsulating the scintillant-doped cores within functionalized silica shells. The functionalized surface enables covalent attachment of specific binding moieties such as small molecules, proteins, or DNA that can be used for analyte-specific detection. nanoSPA was demonstrated for detection of 3H-labeled analytes, the most difficult biologically relevant β-emitter to measure due to the low energy β-particle emission, using three model assays that represent covalent and non-covalent binding systems that necessitate selectivity over competing 3H-labeled species. In each model, nmol quantities of target were detected directly in aqueous solution without separation from unbound 3H-labeled analyte. The nanoSPA platform facilitated measurement of 3H-labeled analytes directly in bulk aqueous samples without surfactants or other agents used to aid particle dispersal. Selectivity for bound 3H-analytes over unbound 3H analytes was enhanced up to 30-fold when the labeled species was covalently bound to nanoSPA, and 4- and 8-fold for two non-covalent binding assays using nanoSPA. The small size and enhanced selectivity of nanoSPA should enable new applications compared to the commonly used microSPA platform, including the potential for separation-free, analyte-specific cellular or intracellular detection.

Improved non-destructive method for 90Sr activity determination in aqueous solutions using Monte Carlo simulation

The development of new methods and improvements of existing methods for the specific activity determination of ⁹⁰Sr and other distinct beta emitters has been of considerable interest. The reason for this interest is that the notably small number of methods that are able to meet all the set criteria, such as reliability of the results, measurement uncertainty and time, and minimum production of radioactive waste, as well as applicability to various samples with reference to their nature, geometry and composition. In this paper, two methods for rapid ⁹⁰Sr activity determination based on Monte Carlo simulations are used, one for a Si semiconductor detector for beta spectrometric measurements and the other for the Geiger-Muller (GM) ionization probe. To improve the reliability of the measurement results, samples with high and low strontium activity solutions were prepared in the form of dry residues. The results of the proposed methodology were verified with a standard method using a liquid scintillation counter, and notably good agreements are achieved.

Plastic vs. liquid scintillation for 14C radiotracers determination in high salt matrices

The use of radiotracers is a common procedure for better understanding of the dynamics of oil reservoirs. Several molecules and radionuclides are implemented for this purpose; one of these is (14)C labelled thiocyanate. Samples taken from fluids in production wells require a pre-treatment step in order to purify and concentrate the activity of the radiotracer before measurement. Pre-treatment is based on ionic exchange and the solution eluted includes a high concentration of salt that can be a serious drawback for the development of a stable emulsion when the liquid sample and the scintillation cocktail are mixed for Liquid Scintillation (LS). The objective of this study is to evaluate the capability of Plastic Scintillation (PS) to determine the activity of radiotracers in salt matrices. For this purpose, an initial comparative study of the influence of salt and coloured matrices on the detection efficiency for PS and LS was performed. Results indicate that in both techniques colour quenching produces the same effects: efficiency decrease and spectra shift, whereas salt quenching produces different effects for PS and LS, ionization quenching for PS and chemical quenching for LS. As a result of this divergence, the calibration required for each counting method is different: two steps for PS and a single step for LS. After system study and procedure optimization, radiotracer activities in real samples taken from oil reservoirs have been determined. The results indicated that PS shows similar capability to the classical LS to determine the activity in these salt matrix samples with the additional advantages that no separation of the phase can appear and no mixed waste is produced after measurement.

First approach to radionuclide mixtures quantification by using plastic scintillators. Influence of the diameter of the plastic beads

Recent studies have evaluated the capability of plastic scintillation (PS) as an alternative to liquid scintillation (LS) in radionuclide activity determination without mixed waste production. In order to complete the comparison, we now assess the extent to which PS can be used to quantify mixtures of radionuclides and the influence of the diameter of the plastic scintillation beads in detection efficiency. The results show that the detection efficiency decreases and the spectrum shrink to lower energies when the size of the plastic scintillation beads increases, and that the lower the energy of the beta particle, the greater the variation takes place. Similar behaviour has been observed for beta-gamma and alpha emitters. Two scenarios for the quantification of mixtures are considered, one including two radionuclides (14C and 60Co) whose spectra do not overlap significantly, and the other including two radionuclides (137Cs and 90Sr/90Y), where the spectra of one the isotopes is totally overlapped by the other The calculation has been performed by using the conventional window selection procedure and a new approach in which the selected windows correspond to those with lower quantification errors. Relative errors obtained using the proposed approach (less than 10%) are lower than those of the conventional procedure, even when a radionuclide is completely overlapped, except for those samples with extreme activity ratios that were not included in the window optimization process.