Ultra-Sensitive Elemental Analysis Using Plasmas 6.Age Determination of Meteorites Using Radioactive Nuclides

Abstract

Recently, the precise isotope ratios of some refractory elements in meteorites have been reported using inductively coupled plasma mass spectrometry. The in situ decay of ¹⁸²Hf (T_1/2=9 Myr), which was produced at the latest nucleosynthesis, is recognized in many meteorites as isotopic anomalies of its daughter isotope, ¹⁸²W. The degrees of relative ¹⁸²W isotopic deviation in extra-terrestrial and terrestrial silicate samples vary from +0.3 % to ?-?0 % related to the size of their parent bodies. One ready interpretation of its correlation is the difference in timing of metal-silicate separation in the parent bodies. Between the earth and meteorite parent bodies, the difference is calculated to be about four times of the half-life of¹⁸²Hf, equivalent to 36 Myr.