strontium87

Strontium-87, denoted as 87Sr, is a stable isotope of the element strontium with mass number 87. It accounts for about 7% of natural strontium and has 38 protons and 49 neutrons. Like the other stable isotopes of strontium, it does not undergo radioactive decay under ordinary conditions.

87Sr is one of four stable isotopes of strontium, the others being 84Sr, 86Sr, and 88Sr. Its stability means that its natural abundance remains constant over geological timescales, aside from fractionation during geological processes.

In geology and geochemistry, the ratio of 87Sr to 86Sr is a valuable tracer. The 87Sr/86Sr ratio in rocks and minerals changes over time because rubidium-87 (Rb-87) slowly decays to 87Sr. Since 87Sr is stable, the amount of 87Sr increases as Rb-87 decays, providing a natural clock for dating rocks and minerals. Interpreting this ratio typically involves isochron methods to separate age effects from initial isotopic composition.

Applications of 87Sr/86Sr dating and tracing include studying crustal formation and differentiation, mantle processes, sediment provenance, and archaeological materials. The strontium isotopic system complements other radiometric dating methods and chemical tracers, helping researchers reconstruct geological histories and past environmental conditions.