Activity Ratios of Ra and Th Isotopes Leached from Euxenite

Abstract

The activity ratios of ²²⁴Ra/²²⁸Ra and ²²⁸Th/²³²Th in leachate from euxenite increased with increasing pH, while the activity ratio of ²³⁰Th/²³²Th decreased. The leaching behavior of ²²⁴Ra which is formed through four decay processes of²³²Th, was different from that of ²²⁸Ra which is formed by a single decay of ²³²Th. Thorium-228, decay products of²³²Th, was also leached more effectively than ²³²Th. However, ²³⁰Th which is formed through four decay processes of ²³⁸U showed different leaching behavior from ²²⁴Ra and ²²⁸Th. Variation in the activity ratio of ²²⁸Ra/²²⁶Ra in leachate from euxenite sample in metamict state with pH of the solution in contact showed no apparent tendency and was observed to be almost as same as that in the euxenite sample partly because of so small activity ratio in the sample. The leaching efficiency of Ra isotopes and ²²⁸Th was estimated to be mainly dependent on the difference in the history of decay processes which have formed the nuclides. This estimation was consistent with the observation with the monazite sample reported previously.