Gamma-spectrometric analysis of high salinity fluids - how to analyze radionuclides of the thorium decay chain far from radioactive equilibrium?

► Highly saline brines of geothermal plants are far from radioactive equilibrium. ► General mathematical formulation for the coupled radionuclide activities within one decay series was established. ► Model was applied to the system Ra-228-Pb-212 and tested on real fluid samples from Neustadt-Glewe, Germany. ► Method allows the calculation of radionuclide concentrations at the moment of sampling in systems with radioactive disequilibria.