Applications of AMS

Common radioisotope elements measured with AMS and their applications are shown in Table 1, below. Because ¹⁴C analysis is by far the most popular application of AMS, the methods discussed below are all techniques used involving ¹⁴C.

Radiocarbon dating is an analytical method based on the rate of decay of ¹⁴C, a radioactive carbon isotope formed in the atmosphere by the reaction between neutrons from cosmic rays and ¹⁴N (neutron + ¹⁴N = ¹⁴C + proton).^[2] Resultant ¹⁴C atoms are taken up by plants in the form of ¹⁴CO₂, then transferred to animals though the food chain. When animals and plants die, they cease to uptake ¹⁴C, and a steady decay of ¹⁴C continues in their tissues over time. ¹⁴C atoms decay via electron emission (β radiation) to form ¹⁴N, a process which has a half life of 5,730 years.  Radiocarbon levels in the atmosphere change according to complex patterns which are affected by a variety of fluctuations ranging from the sun’s solar activity and the earth’s magnetic field, to ocean ventilation rate and climate. ¹⁴C analysis of tree rings, corals, lake sediments, ice cores, and other sources has led to a detailed record of ¹⁴C variations through time, allowing researchers to establish an official radiocarbon calibration curve (also referred to as a radiocarbon clock) dating back 26,000 calendar years. In the 1960s, nuclear weapons testing released large amounts of neutrons into the atmosphere, nearly doubling ¹⁴C activity.  Samples taken after this time period can be radiocarbon dated using a ¹⁴C bomb curve like the peak shown below in Figure 3, can retrieve very precise dates (within 1 year at the steepest part of the curve).

Figure 1. The New Zealand curve (red) is representative of atmospheric ¹⁴C in the Southern Hemisphere, and the Austrian curve is representative of the Northern Hemisphere.

¹⁴C analysis provides valuable information in the radiocarbon dating of the world’s most priceless artifacts. One such example of the monumental impact of ¹⁴C AMS is the radiocarbon dating of the Dead Sea Scrolls to dates from 300 BC to AD 61 by labs in Zurich and Arizona. AMS has also contributed greatly to environmental and atmospheric studies by providing information regarding particle composition and origin. In the biochemical field, synthesized ¹⁴C labeled compounds can be administered as a tracer dose for in-vivo human metabolic and drug studies which require AMS analysis of graphitized biological samples.

AMS is a highly sensitive method for isotopic analysis that has numerous key applications that are only growing with advances in technology. High costs and technical complexities that arise with the use of a particle accelerator are the only limits to the widespread use of AMS. Recent times have seen the emergence of commercially available compact accelerators that use as low as 200 kV for radiocarbon dating and biomedical applications, and as particle accelerators become more commonplace, modifications to the instrument have also broadened the number of isotopes the instrument can measure.