Activity Ratios of Ra and Th Isotopes Leached from Granite

Abstract

The activity ratios of ²²⁸Ra/²²⁶Ra in the leachates from a granite sample with HCl, NaOH and NaCl aqueous solutions were observed to be smaller than that in the granite sample. The activity ratios of ²²⁴Ra/²²⁸Ra, ²³⁰Th/²³²Thand ²²⁸Th/²³²Thincreased with an increase in pH of the HClaqueous solution. The leaching behavior of ²²⁶Raand ²²⁴Ra which are formed through 5 decay processes of ²³⁸Uand through 4 decay processes of ²³²Th, respectively, was different from that of ²²⁸Rawhich is formed by a single decay of ²³²Th. Thorium isotopes, ²³⁰Th and ²²⁸Th, decay products of ²³⁸U and ²³²Th, respectively, were also leached more effectively than ²³²Th.The leaching efficiency of Ra and Thisotopes was estimated to be dependent on the difference in the history of decay processes which have formed the nuclides. This estimation was consistent with the observations with the radioactive mineral samples reported previously.