Accelerator mass spectrometry: A nuclear analytical technique for ultra-trace isotopic analysis

The development of the nuclear analytical technique of accelerator mass spectrometry (AMS) has revolutionized the ability to detect rare isotopes, achieving previously unattainable detection limits. This has opened new avenues of research in a number of scientific disciplines. The AMS technique combines the ion selection principles of regular mass spectrometry with elemental identification through the nuclear stopping processes of high energy ions in a medium. This permits selection of the ion of interest by atomic mass and charge. For example, it is possible to detect a 36Cl to stable chloride ratio (36Cl/Cl) of 1 x 10-15, even in the presence of natural 36S. This technique is particularly appropriate for study of the long-lived cosmogenic isotopes. Perhaps the best known of these is 14C (t1/2 = 5730 y). Measurements via AMS permit dating of very old samples and dating of very small samples. Other nuclides with a broad range of geological, hydrological and oceanographic applications include 10Be (t1/2 = 1.6 x 106 y), 26Al (t1/2 = 7.3 x 106 y), 36Cl (t1/2 = 3.0 x 105 y), 41Ca (t1/2 = 1.0 x 105), and 129I (t1/2 = 1.6 x 107 y). One of the most recent areas of research is in biomedical applications of AMS, where 14C, 26Al, and 41Ca are showing great promise. A number of facilities dedicated to AMS measurements in the US and abroad are making these techniques available to the entire scientific community