Stableisotope

Stable isotopes are non-radioactive isotopes of chemical elements whose nuclei are stable on geological timescales. Most elements have at least one stable isotope, and some have several. Common examples include carbon-12 and carbon-13, nitrogen-14 and nitrogen-15, and the oxygen isotopes oxygen-16, oxygen-17, and oxygen-18, as well as hydrogen-1 (protium) and deuterium (hydrogen-2). The natural abundances of these isotopes vary by element and source, giving each element a characteristic isotopic composition.

In measurements and notation, isotopic ratios are typically expressed using delta values (δ) relative to international standards. Isotope ratio mass spectrometry (IRMS) is a primary method for precise determinations of these ratios. For elements with multiple stable isotopes, the standard atomic weight reflects the weighted average of natural abundances; some elements exhibit variability in standard atomic weights depending on material source, reflecting different isotopic compositions.

Applications of stable isotopes span many disciplines. In earth and environmental sciences, stable isotopes are used to study hydrological cycles, paleoclimate, and biogeochemical processes. In archaeology and anthropology, carbon and nitrogen isotopes help reconstruct ancient diets and migration patterns. In biology and medicine, stable isotopes serve as tracers to follow metabolic pathways, nutrient fluxes, and drug delivery, while enriched isotopes assist in calibration and imaging. They are preferred in many contexts because they are non-radioactive and do not pose radiological hazards.

Notes: stable isotopes can be fractionated—enriched or depleted—in natural and experimental processes, producing characteristic isotopic signatures. The study of these signatures relies on careful calibration, standardization, and interpretation within the context of the element and system under study.