Measurement of Geologic Time by the Rubidium-Strontium Method

Abstract

The natural radioactivity of rubidium was first reported by J. J. T Homson in 1905 and later confirmed by Campbell and Wood (1906). However, the radioactive isotope of rubidium in nature was not positively identified until 1937. In that year Hahn, Strassman, and Walling (1937) separated strontium from a specimen of lepidolite from the Silver Leaf Mine in Manitoba, and Mattauch (1937) showed by mass spectroscopy that 99.7 percent of this strontium was ⁸⁷Sr. Since rubidium was known to emit negatively-charged beta particles, it was clear that the ⁸⁷Sr in this lepidolite had formed by decay of ⁸⁷Rb. This conclusion was confirmed by Hemmendinger and Smythe (1937), who demonstrated that ⁸⁷Rb was the only naturally-occurring radioactive isotope of rubidium.