Production

The atmospheric production of  ¹⁴C is by interactions of secondary neutrons  (from interactions with cosmic rays) with ¹⁴N. It oxidizes to carbon dioxide and becomes part of the carbon cycle. During its residence time of about 5 years in the atmosphere it mixes with the carbon dioxide  resulting in an equilibrium ratio of ¹⁴C over ¹²C corresponding to 1.18 x 10^-12.

This equilibrium in the carbon cycle makes the ¹⁴C the special absolute dating tool. Also, there is in situ production at the surface of the earth by spallation reactions of fast neutrons and muons with ¹⁶O. The production rate of this reaction is about a thousand times smaller than the atmospheric production rate so that it does not interfere with the atmospheric production (and hence in most cases not in dating analysis) . However, in regions of high altitude and latitude, with higher cosmic rays intensity, there is  in situ production observed as in surface rock or in Antarctic ice.

The atmospheric production of ¹⁰Be is by spallation reactions of cosmic rays with ¹⁴N and ¹⁶O. It oxidizes quickly to ¹⁰BeO, which attaches to aerosols. It precipitates within 2 years and enters soil, surface water, oceans and sediments. ¹⁰Be is also produced in situ in surface rock where it accumulates.

The atmospheric production of  ²⁶Al is produced is mainly from interactions with argon, and is very small. In surface rocks in situ production with silicon as target element takes place and accumulates.