Fe57

Fe-57 is an isotope of iron with atomic number 26 and mass number 57. It is a stable isotope and accounts for about 2.1% of natural iron. The nucleus contains 26 protons and 31 neutrons (N = 31). The ground state has nuclear spin 1/2−, and the first excited state lies 14.4 keV above the ground state. This 14.4 keV transition decays to the ground state with a half-life of about 98 nanoseconds and is central to Mössbauer spectroscopy.

The 14.4 keV transition is notable because, in solids, it can occur with negligible recoil (the Mössbauer effect), enabling high-resolution measurements of hyperfine interactions. This makes Fe-57 the standard Mössbauer nucleus for iron-containing compounds. Natural Fe-57 is present in roughly 2 percent of iron, and the isotope is widely used as a probe in solid-state chemistry, metallurgy, and related fields.

Production and usage: In laboratory practice, the 14.4 keV gamma-ray source for Mössbauer spectroscopy is typically produced from the beta decay of cobalt-57, which decays to iron-57 in an excited state and subsequently emits the 14.4 keV gamma ray upon de-excitation. This gamma source, combined with Fe-57-containing samples, enables precise measurements of magnetic ordering, oxidation state, site symmetry, and crystal structure.

Applications: Fe-57 Mössbauer spectroscopy is employed to study steels and alloys, mineralogy, geochronology, catalysis, and various biological iron-containing systems, providing detailed information about electronic environments and phase transitions.