Radiation age

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The irradiation age referred to in the meteorite research the period of time during which a meteoroid of cosmic rays has been exposed before the meteorite fell to earth.

In the simplest case, the single-stage irradiation, the irradiation age corresponds to the time from the breakdown of the meteoroid from the mother body until it hits the earth. A meteoroid can, however, also have a more complex radiation history behind it. Some meteoroids have already been lying close to the surface on their mother body and have been exposed there to cosmic rays that penetrate about a meter deep into solid material. This is particularly true of lunar meteorites , because surface material on the moon can remain on the surface for a very long time due to the relatively large force of gravity compared to asteroids.

To determine the radiation age, use is made of the fact that cosmic radiation forms new daughter nuclei through nuclear reactions (mainly spallation ) with the atomic nuclei of a meteoroid. The radiation age can then be determined by measuring the frequency of these daughter nuclei. The nuclear reactions not only form stable daughter nuclei, but also unstable radionuclides . The radiation age can be calculated both with the help of stable daughter nuclei, mostly noble gas isotopes , and with the help of radionuclides. If the irradiation ages, which were determined on stable and unstable nuclei, match, a single-level irradiation history can be assumed, otherwise a multi-level irradiation history is probable.

literature

• Ebert KH and Waenke H .: About the effect of cosmic radiation on iron meteorites. In: Journal of Nature Research A . 12, 1957, pp. 766-773 ( PDF , free full text).