TABLE OF CONTENTS Accelerator Mass Spectrometry (AMS) is an analytical technique that uses an ion accelerator as an ultrasensitive mass spectrometer to ultimately count individual atoms. AMS was first introduced in 1977 and constitutes a highly sensitive method for detecting very low concentrations of long-lived radioisotopes or stable isotopes in a wide range of samples.
AMS separates rare radioisotopes from stable ones and measures their relative ratio with high sensitivity and precision. It is commonly used in radiocarbon dating experiments, where carbon-based materials are converted to graphite, and the amount of 14C they contain is measured. This provides a measure of the age of the item based on the half-life of the 14C isotope of 5568 years. Meteorites from space, air trapped in Antarctic ice, and the Turin shroud are some of the sources of samples to which AMS has been applied. Other applications include studying radiolabelled tracers in biological systems.
In the AMS technique, the element of interest is chemically separated from the original sample and loaded as a target in the sputter ion source of the tandem accelerator (Figure 10.1). Samples are pulverised, treated with acid and alkali and freeze-dried. In the case of carbon-based compounds, the sample is converted to either graphite or carbon dioxide. After ionisation of the samples and the separation of ions using a magnet, negative ions containing the radioisotope of interest are accelerated through a potential of several million volts (MV). Negative ions are used to distinguish 14C...
