An equilibrium study for Uranium isotopes in soil samples

The Uranium (238U), Thorium (232Th) and Actinium (235U) natural series are composed of radioactive nuclides with different physical and chemical properties and with half lives varying from a few second to more than 109 y. When the series decay occurs in a closed system for physical and chemical exchange with environment, the series tends to reach, with time, the state of secular equilibrium. In this state, the activities of all series members are equal to the activity of its first nuclide. In nature, however many processes lead to geological environments open to element exchanges. Such processes can occur continuously in time as slow soil matrix dissolution by surface and ground water, mineral precipitation, adsorption on mineral surfaces, dissociation and the recoil following alpha decay. In recent years, the methods based on radioactive disequilibria have been applied to the study of different geological processes such as sedimentation in marine and continental environments soil formation and evolution, ground water dynamics etc. Since the natural radioactive series have several alpha emitting radionuclides, alpha spectrometry is one of the methods used to determine the isotope activity ratio. There are many published methods describing both the chemical separation and source preparation for alpha particle measurements. In the case of uranium and thorium, solvent extraction and ion exchange chromatography are usual techniques for chemical separation and purification. There are also many methods for alpha particle spectrometry source preparation but electrodeposition carried out from aqueous solution seem to be the most frequent used technique for actinides