The half-life of 129I

Abstract The radionuclide 129 I is a long-lived fission product that decays to 129 Xe by beta-particle emission. It is an important tracer in geological and biological processes and is considered one of the most important radionuclides to be assessed in studies of global circulation. It is also one of the major contributors to radiation dose from nuclear waste in a deep geological repository. Its half-life has been obtained by a combination of activity and mass concentration measurements in the frame of a cooperation of 6 European metrology institutes. The value obtained for the half-life of 129 I is 16.14 (12) × 10 6 a, in good agreement with recommended data but with a significant improvement in the uncertainty.