hafnium178m2

Hafnium-178m2, often written as 178Hf m2, is a nuclear isomer of hafnium-178 (Z = 72). It is a metastable excited state with unusually long lifetime and a high angular momentum. The isomer lies about 2.4 MeV above the ground state and has a half-life of roughly 31 years. Its spin-parity is assigned as 16+, and the decay to the ground state occurs mainly by gamma emission, a transition that is strongly hindered by the large spin difference, which accounts for the extended lifetime.

Production and occurrence: 178m2Hf is formed in nuclear reactions that produce hafnium-178 in excited configurations, typically in nuclear reactors or accelerator facilities. Target irradiation of hafnium or neighboring isotopes can yield hafnium-178 in metastable states, which are identified through gamma-ray spectroscopy. Isolation and study of the isomer require radiochemical separation and careful characterisation of its decay scheme.

Applications and research: The long-lived isomer is of interest in studies of nuclear structure and high-spin states. It has also attracted speculative attention as a potential medium for energy storage, based on the idea of releasing stored nuclear energy by triggering the isomer to decay. To date, there is no practical, reliable method demonstrated to trigger energy release on demand, and claims of such triggering remain controversial and unproven.

See also: Nuclear isomer, Hafnium, 178Hf.