the longest-lived non-ground state nuclear isomer is the nuclide tantalum-180m (), which has a half-life in excess of 1,000 trillion years. this nuclide occurs primordially, and has never been observed to decay to the ground state. (in contrast, the ground state nuclide tantalum-180 does not occur primordially, since it decays with a half life of only 8 hours to hf (86%) or w (14%)).