Accelerator mass spectrometry (AMS) is an experimental method for detecting the presence of rare isotopes of exceedingly small concentration within a macroscopic-sized sample of material. The method of measurement takes advantage of well-known techniques of charged particle identification developed in the long history of experimental nuclear physics. There are three essential ingredients within an AMS facility:

• An ion source, that ionizes the atoms within the sample material into a beam of charged partilcles
• An accelerator that receives the charged particles and accelerates them to high kinetic energy
• A charged particle detector that detects, counts and uniquely identifies each charged particle it receives from the accelerator

The radioisotopes sought in AMS measurements are typically those that have sufficiently long half lives to be of use for archaeological, geophysical, and astrophysical significance.  If a natural process creates enough quantity of an isotope of sufficiently long half life, then dating of geological events and processes that occurred millions of years ago is possible.