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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.