Natural iron (26Fe) consists of four stable isotopes: 5.845% 54Fe (possibly radioactive with half-life >4.4×1020 years),[4] 91.754% 56Fe, 2.119% 57Fe and 0.286% 58Fe.
Much of the past work on measuring the isotopic composition of iron has centered on determining 60Fe variations due to processes accompanying nucleosynthesis (i.e., meteorite studies) and ore formation.
In the last decade however, advances in mass spectrometry technology have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the stable isotopes of iron.
Much of this work has been driven by the Earth and planetary science communities, though applications to biological and industrial systems are beginning to emerge.
54Fe is observationally stable, but theoretically can decay to 54Cr, with a half-life of more than 4.4×1020 years via double electron capture (εε).
[7] However, because of the details of how nucleosynthesis works, 56Fe is a more common endpoint of fusion chains inside supernovae, where it is mostly produced as 56Ni.
Thus, 56Ni is more common in the universe, relative to other metals, including 62Ni, 58Fe and 60Ni, all of which have a very high binding energy.
Therefore it is among the heaviest elements formed in stellar nucleosynthesis reactions in massive stars.
[8] The transition was famously used to make the first definitive measurement of gravitational redshift, in the 1960 Pound–Rebka experiment.
[9] Iron-58 can be used to combat anemia and low iron absorption, to metabolically track iron-controlling human genes, and for tracing elements in nature.
In phases of the meteorites Semarkona and Chervony Kut, a correlation between the concentration of 60Ni, the granddaughter isotope of 60Fe, and the abundance of the stable iron isotopes could be found, which is evidence for the existence of 60Fe at the time of formation of the Solar System.
The abundance of 60Ni in extraterrestrial material may also provide further insight into the origin of the Solar System and its early history.
Iron-60 found in fossilized bacteria in sea floor sediments suggest there was a supernova near the Solar System about 2 million years ago.
Assuming that the material ejected in a supernova expands uniformly out from its origin as a sphere with surface area 4πr2.
The fraction of the material intercepted by the Earth is dependent on its cross-sectional area (πR2Earth) as it passes through the expanding debris.
The number of 60Fe atoms per unit area found on Earth can be estimated if the typical amount of 60Fe ejected from a supernova is known.
This calculation uses speculative values for terrestrial 60Fe atom surface density (N60 ≈ 4 × 1011 atoms/m2) and a rough estimate of the mass of 60Fe ejected by a supernova (10-5 M☉).
More sophisticated analyses have been reported that take into consideration the flux and deposition of 60Fe as well as possible interfering background sources.
The signal traces the Galactic plane, showing that 60Fe synthesis is ongoing in our Galaxy, and probing element production in massive stars.