Radiation Exposure and Dating

Abstract

Produced in the terrestrial environment during nuclear reactions between primary and secondary energetic cosmic‐ray particles and the atoms of the Earth's environment, cosmogenic radionuclides such as beryllium‐10 ( 10 Be, T ½ ∼ 1.4 Ma), aluminum‐26 ( 26 Al, T ½ ∼ 0.7 Ma), and chlorine‐36 ( 36 Cl, T ½ ∼ 0.3 Ma) enable use of the fraction produced in the atmosphere to date possibly over the last 10 Ma the sedimentary deposits in which they have accumulated over the last 10 Ma. The fraction produced in the crust (in‐situ production) that accumulates over time in specific mineral species allows, through the measurement of its concentration (a function of both the duration of exposure to cosmic radiation and the stability of the studied surface), dating of artifacts over a time span of 0.2–5 Ma. To achieve such dating, a dedicated method able to separate the very rare cosmogenic radionuclides from their abundant isobaric interferences had to be developed: the accelerator mass spectrometry (AMS) technique.