As oxygen-16 is also common in the atmosphere, the contribution to the beryllium-10 concentration from material deposited rather than created in situ must be taken into account. Each of these nuclides is produced at a different rate.
Both can be used individually to date how long the material has been exposed at the surface.
The excess relative to natural abundance of cosmogenic nuclides in a rock sample is usually measured by means of accelerator mass spectrometry.
Cosmogenic nuclides such as these are produced by chains of spallation reactions.
Surface exposure dating with a single cosmogenic nuclide relies on the assumption of simple constant exposure.
The production rate for a particular nuclide is a function of geomagnetic latitude, the amount of sky that can be seen from the point that is sampled, elevation, sample depth, and density of the material in which the sample is embedded.
Decay rates are given by the decay constants of the nuclides.
Cosmogenic isotopes are created when elements in the atmosphere or earth are bombarded by high energy particles (-mesons and protons, collectively known as cosmic rays) that penetrate into the atmosphere from outer space.
Some cosmic ray particles reach the surface of the earth and contribute to the natural background radiation environment.It was discovered about a decade ago that cosmic ray interaction with silica and oxygen in quartz produced measurable amounts of the isotopes Beryllium-10 and Aluminium-26.