3he cosmogenic nuclide age dating
The parent isotopes are the most abundant of these elements, and are common in crustal material, whereas the radioactive daughter nuclei are not commonly produced by other processes.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.
The excess relative to natural abundance of cosmogenic nuclides in a rock sample is usually measured by means of accelerator mass spectrometry.In rock and other materials of similar density, most of the cosmic ray flux is absorbed within the first meter of exposed material in reactions that produce new isotopes called cosmogenic nuclides.At Earth's surface most of these nuclides are produced by neutron spallation.By the time the cosmic ray cascade reaches the surface of Earth it is primarily composed of neutrons.When one of these particles strikes an atom it can dislodge one or more protons and/or neutrons from that atom, producing a different element or a different isotope of the original element.The cumulative flux of cosmic rays at a particular location can be affected by several factors, including elevation, geomagnetic latitude, the varying intensity of the Earth's magnetic field, solar winds, and atmospheric shielding due to air pressure variations.
Rates of nuclide production must be estimated in order to date a rock sample.
It is most useful for rocks which have been exposed for between 10 years and 30,000,000 years.
The most common of these dating techniques is Cosmogenic radionuclide dating.
Both can be used individually to date how long the material has been exposed at the surface.
Because there are two radionuclides decaying, the ratio of concentrations of these two nuclides can be used without any other knowledge to determine an age at which the sample was buried past the production depth (typically 2–10 meters).
Earth is constantly bombarded with primary cosmic rays, high energy charged particles — mostly protons and alpha particles.