Natural hafnium (72 Hf) consists of five observationally stable isotopes (176 Hf, 177 Hf, 178 Hf, 179 Hf, and 180 Hf) and one very long-lived radioisotope , 174 Hf, with a half-life of 7.0× 1016 years.[ 2] In addition, there are 34 known synthetic radioisotopes , the most stable of which is 182 Hf 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 .[ 5]
No other radioisotope has a half-life over 1.87 years. Most isotopes have half-lives under 1 minute. There are also at least 27 nuclear isomers , the most stable of which is 178m2 Hf 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.
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