Natural hafnium (72Hf) consists of five observationally stable isotopes (176Hf, 177Hf, 178Hf, 179Hf, and 180Hf) and one very long-lived radioisotope, 174Hf, with a half-life of 3.8×1016 years.
[2] In addition, there are 34 known synthetic radioisotopes, the most stable of which is 182Hf with a half-life of 8.9×106 years.
This extinct radionuclide is used in hafnium–tungsten dating to study the chronology of planetary differentiation.
There are also at least 27 nuclear isomers, the most stable of which is 178m2Hf with a half-life of 31 years.
All isotopes of hafnium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.