Thorium-234 Electrodeposition Using Ionic and Aqueous Uranyl Solutions

Abstract

Electrodeposition process of natural uranyl many has several deposit possibilities, since the process variables and uranium natural isotopes and secular equilibrium may induce the formation of several uranium compounds. One of these deposit possibilities is the strong beta-emitter thorium-234. The present work showed that pulsed polarization and 2-propanol natural uranyl solution (50 mM [U]) induced the formation of intense beta-emission in the samples, with activity beta-alpha ratio reaching levels of 300, which is much higher than the secular equilibrium ratio around 1. The natural decay of the deposited samples showed that the beta-emitter as most probable element to be thorium-234 within a pertinent regression exponential decay curve adjustment (R 2 =0.998) giving a typical experimentation value for half-life as 22.88 days. This value was found lower than the typical 24.10 days for thorium-234 (specific activity of 85.69x10 13 Bq/g), probably due to activity contribution of uranium-235 daughter, thorium-231 (specific activity of 19.67x10 15 Bq/g), which beta-decays having half-life of 25.6 h. Further experimentation with pulsed polarization of the cathode (0 to -15V; 12.5 Hz – duty time = 87.5% and process time varying until 3600s) also showed that thorium-234 depends on solution acidity, solution usage and deposition time. XRD spectra suggests that the deposit would be probably a combined structure of uranium-thorium hydride, which decomposes with time.