Origin of radioactivity at Niue Island

Abstract

Abstract A high content of radioactivity in sediments, when sea water is the source of the radioactive elements, depends on the slow rate of sedimentary deposition. The radioactive content of the Niuean soils is comparable with that found in deep-sea sediments, but the rate of sedimentation in deep-sea areas is unlikely to have been as rapid as in the now dry lagoon at Niue. Hence a sea-water origin for the abnormally high radioactivity at Niue is unlikely. A separation from uranium of the daughter products, ionium and radium-226 (the main elements at Niue), takes place in hydrothermal solutions as well as in sea water. The latter could have come from the volcanic substructure at Niue, which could have been phonolite—often one of the most radioactive igneous rocks. The anomalous distribution of radioactive soil values at Niue favours a volcanic origin rather than a sea-water origin. Evidence is also presented that shows radioactivity in the limestone has been derived from ground water and not percolating ...