Isotopic Fractionation
The unequal distribution of isotopes between substances during chemical or physical processes, causing one form to concentrate more than another.
The preferential separation of isotopes during chemical reactions, phase changes, or physical processes. Lighter isotopes typically move or react faster than heavier ones, causing them to accumulate unevenly in different products or reservoirs. Scientists measure isotopic ratios to trace origins, temperatures, and reaction pathways in geology, astronomy, and biology.
What this means in real life
When water evaporates from the ocean, lighter water molecules (containing lighter oxygen isotopes) escape to the air slightly faster than heavier ones, leaving seawater enriched in heavier isotopes—a pattern scientists use to reconstruct ancient climates.
What it isn’t
It is not the radioactive decay of unstable isotopes. Radioactive decay is a nuclear process; isotopic fractionation is a chemical or physical sorting that does not change the nucleus or release radiation.
Commonly misused online
Often conflated with 'isotope enrichment' (deliberate industrial concentration of specific isotopes) or used loosely to mean 'any difference in isotope ratios,' ignoring the mechanism of preferential separation.