Cosmogenic isotopes
Rare isotopes that are created when a high-energy cosmic ray interacts with the nucleus of an in situ atom. They are often used as indications of solar magnetic activity (which can shield cosmic rays) or as tracers of atmospheric transport, and are also called cosmogenic nuclides.
Definition courtesy of IPCC AR4.
All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.