Accelerator mass spectrometry (AMS) differs from other forms of mass spectrometry in that it accelerates ions to extraordinarily high kinetic energies before mass analysis. The special strength of AMS among the mass spectrometric methods is its power to separate a rare isotope from an abundant neighboring mass ("abundance sensitivity", e.g. ¹⁴C from ¹²C). The method suppresses molecular isobars completely and in many cases can separate atomic isobars (e.g. ¹⁴N from ¹⁴C) also. This makes possible the detection of naturally occurring, long-lived radio-isotopes such as ¹⁰Be, ³⁶Cl, ²⁶Al and ¹⁴C. Their typical isotopic abundance ranges from 10^-12 to 10^-18. AMS can outperform the competing technique of decay counting for all isotopes where the half-life is long enough.