Natural hafnium (72Hf) consists of five stable isotopes (176Hf, 177Hf, 178Hf, 179Hf, and 180Hf) and one very long-lived radioisotope, 174Hf, with a half-life of years. In addition, there are 30 known synthetic radioisotopes, the most stable of which is 182Hf with a half-life of years. This extinct radionuclide is used in hafnium–tungsten dating to study the chronology of planetary differentiation.
