Uranium-series disequilibrium studies in the Tono uranium deposit, Japan

We have studied the behaviour of uranium-series nuclides in a natural environment, by analyzing rock specimens collected from boreholes and a gallery in the Tono sandstone-type uranium deposit. Chemical analyses and α and γ spectrometry were carried out. The activity ratios of 234Z/238U, 230Th/234U and 226Ra/230Th are discussed on the basis of chemical properties and decay constants of the nuclides. The following conclusions were obtained. (1) In the matrix of sedimentary rocks, reducing conditions have been maintained for the past one million years. (2) While some migration of uranium along faults and fractures is observed, the largest motion of uranium has been through the rock matrix over a distance of less than 1 m during the past one million years. (3) Radium has been mobilized during the past several thousand years in the Tono deposit. (orig.)