Uranium and Thorium Disequilibrium in Zeolitically Altered Rock

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Abstract
Extensive studies conducted during the past two decades regarding the behavior of 238U and its decay products in the geologic environment have shown that radioactive disequilibrium in the 238U decay series is a common phenomenon. The daughter products 234U and 230Th are especially useful as indicators of processes affecting uranium migration because of their relatively long half-lives and contrasting chemical behavior. A striking variability in 234U/238U ratios occurs in zeolitically altered volcanic tuff investigated in this study. Results indicate that initial preferential emplacement of 234U by adsorption-alpha recoil mechanisms gradually was overwhelmed by preferential displacement of 234U by leaching-alpha recoil mechanisms. The data provide guidelines for predicting the behavior of chemically analogous members of the 237Np decay series (233U, 229Th) in the natural environment following geologic disposal of radioactive wastes.