[meteorite-list] Space Drifters
From: Starbits_at_aol.com <Starbits_at_meteoritecentral.com>
Date: Thu Apr 22 09:48:13 2004
<I was wondering how the loss of ablated material on a meteorite would effect its cosmic ray exposure age. Could the "young" CRE ages obtained for meteorites be a result of the more "tracked" outer "skin" of a meteoroid
being lost as the body travels through the atmosphere? The article states that cosmic rays only effect the outer centimeter or so of the meteoroid so if a significant portion of this outer layer were lost, wouldn't a "young" cosmic ray age be the result?>
There are actually different cosmic rays. Those from the sun have energies less than 2x10^8 eV and would penetrate about 1 to 2 cm. There are also glactic cosmic rays (GCR) that can have energies as high as 10^20 eV and these will penetrate several meters. I expect it is the GCR tracks that are being measured.
This is not the only method of determining transit times though. When the GCRs hit an atom they have enough energy to cause nuclear interactions, and among other things they produce various noble gas isotopes. It has been shown that the neon isotope ratios are affected by the depth a sample is buried. By using the neon numbers a depth correction can then be applied to the other noble gases to determine the correct exposure age.
Received on Fri 19 Oct 2001 05:42:06 PM PDT