176Hf

176Hf, or hafnium-176, is a stable isotope of the element hafnium (atomic number 72) with a mass number of 176. It is one of the naturally occurring hafnium isotopes and does not undergo radioactive decay under normal conditions.

In the cosmos, hafnium isotopes including 176Hf are produced by neutron capture processes in stars. On Earth, 176Hf is the stable daughter product of the long-lived radioactive decay of 176Lu, which beta-decays with a half-life of about 37.8 billion years. Because 176Lu decays to 176Hf over geological timescales, the isotopic composition of hafnium records radiogenic ingrowth that is used in geochronology and cosmochemistry.

The most important practical use of 176Hf lies in the Lu–Hf isotopic system (176Lu decays to 176Hf) for dating and tracing geological processes. By comparing the amount of 176Hf to other hafnium isotopes in rocks and minerals, scientists can infer mantle differentiation, crustal formation, and the timing of geological events. This approach is widely applied to study the formation and evolution of continental crust and to understand the early differentiation of planetary materials.

Because 176Hf is isobaric with other isotopes such as 176Yb, measurements of 176Hf require high-resolution mass spectrometry and appropriate corrections to account for interferences and for ongoing decay from 176Lu. Despite these complexities, 176Hf remains a central component of isotopic studies in geoscience and planetary science.