Isotopes: Elements that have the same number of protons but a different number of neutrons

Stable isotopes: Naturally occurring, non-radioactive forms of elements.

Radioisotopes: Forms of an element undergoing radioactive decay. Possess isotope specific half-lives that characterize this radioactive decay.

Isotope Ratio Mass Spectrometer (IRMS): Specialized method used for stable isotope analysis. Measures the abundance and variations of the naturally occurring stable isotopes in a sample.

Stable Isotope Notation/ Delta (δ) Notation: Used to express stable isotopic composition, where a sample is described as a ratio relative to the ratio of an international standard.

Liquid Scintillation Counting (LSC): Instrument used in radioisotope analysis through the detection and quantification of the particles emitted during radioactive decay.

For further information on isotope analysis and notation, please visit the USGS website at: