New Half-Life Measurement of 182Hf: Improved Chronometer for the Early Solar System

The decay of ¹⁸²Hf, now extinct, into stable ¹⁸²W has developed into an important chronometer for studying early solar system processes such as the accretion and differentiation of planetesimals and the formation of the Earth and the Moon. The only ¹⁸²Hf half-life measurements available were performed 40years ago and resulted in an imprecise half-life of (9±2)×10⁶ yr. We redetermined the half-life by measuring the specific activity of ¹⁸²Hf based on two independent methods, resulting in a value of t_1/2(¹⁸²Hf)=(8.90±0.09)×10⁶ yr, in good agreement with the previous value, but with a 20 times smaller uncertainty. The greatly improved precision of this half-life now permits very precise intercalibration of the ¹⁸²Hf ¹⁸²W isotopic system with other chronometers.