AMS is most often employed to determine the concentration of 14C, e.g. by archaeologists for radiocarbon dating. An accelerator mass spectrometer is required over other forms of mass spectrometry (because of their insufficient abundance sensitivity) to resolve stable nitrogen-14 from radiocarbon. Due to the long half-life of 14C, decay counting requires significantly larger samples. 10Be, 26Al are used for surface exposure dating in geology and 129I is used as hydrological tracer. Accelerator mass spectrometry is widely used in biomedical research.