86Sr

86Sr is a stable isotope of the element strontium (Sr) with a mass number of 86. It contains 38 protons and 48 neutrons. In nature, 86Sr accounts for about 9.86% of natural strontium.

Strontium has four stable isotopes: 84Sr, 86Sr, 87Sr, and 88Sr. Their approximate natural abundances are 84Sr ≈ 0.56%, 86Sr ≈ 9.86%, 87Sr ≈ 7.0%, and 88Sr ≈ 82.6%. Because 86Sr is stable, it is not used for radiometric dating on its own; instead, the ratio 87Sr/86Sr is central to rubidium-strontium dating and to tracing geological and archaeological materials. The 87Sr component arises from the radiogenic decay of 87Rb.

Analytically, 86Sr is measured using mass spectrometry methods such as TIMS (thermal ionization mass spectrometry) or MC-ICP-MS (multi-collector inductively coupled plasma mass spectrometry). Measurements often require correction for isobaric interferences (notably Kr-86) and for instrumental mass bias. Isotopic dilution and standard-sample bracketing are common techniques to improve accuracy.

Applications of 86Sr and its isotopic systematics include geochemical provenance studies, hydrology and archaeology, and the broader field of Sr isotope geochemistry. Variations in the 87Sr/86Sr ratio in rocks, soils, waters, and biogenic materials provide a fingerprint of geological formation, weathering, and migration processes. In laboratory work, 86Sr is frequently used as a reference or normalization isotope in isotope ratio measurements.