Every radioisotope has a characteristic rate of decay, called its half-life . After one half-life period, one half of the original number of radioactive atoms remains. After two half-life periods, only one quarter of the atoms remain. While an organism is alive, the radioisotope carbon-14 is present within it in a fixed ratio. The decay begins when a living organism dies and carbon-14 is no longer absorbed.
Students can use exponents and their reciprocals to calculate half-life.
Scientists must extract the radioisotopes from the artifacts in order to measure their weight. They ionize the sample and pass the ions through an instrument called a mass spectrometer . In the spectrometer, the ions pass between the poles of a magnet, which deflects them into a curved path. For ions with the same charge, the angle of deflection depends on mass, so that the ions are automatically sorted by isotope, according to their masses. Students can explore the paths of isotopes as they are sorted in a simulated mass spectrometer in the Physics Explorer activity, The Mass Spectrometer .