Computer Science
Scientific paper
Feb 1974
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1974gecoa..38..217h&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 38, Issue 2, pp.217-234
Computer Science
2
Scientific paper
An investigation on the low energy cosmic ray products 26 Al and 53 Mn in 18 chondrites encompassed several side aspects in meteoritics. The ratio of observed to calculated specific activity of 26 Al in 13 chondrites with recovered masses ranging from ~ 3 to 2000 kg remains constant within ±15 per cent of a mean of 0.93. This is consistent with Fuse and Anders' observation of invariance of the 26 Al-production rate with depth and size. A plot of the 53 Mn specific production rate (dpm/kg Fe) versus recovered meteorite mass revealed that the compensation by the secondaries for the absorption of the primaries is also effective in the case of 53 Mn. Thus, the 53 Mn production rate remains rather constant within ±15 per cent of a mean of 520 dpm/kg Fe for most of the stones. Applying this information to two chondrites, Ladder Creek and Scurry, of known relatively short exposure and terrestrial ages, the 53 Mn half-life ( T 53 ), computed from their 53 Mn obs / 26 Al obs ratios, is found to be 3.85 ± 0.4 m.y. which agrees very well with the currently accepted value of T 53 = 3.8 ± 0.6 m.y. From the observed 53 Mn/ 54 Mn activity ratio in Allende, relative to the production rate ratio of 0.98, an exposure age of t R = 4.2 m.y. is derived, in concordance with literature data. The result strongly suggests that this isotope pair holds promise as an index of absolute radiation ages of fresh falls.
Heimann Martin
Herr W.
Parekh P. P.
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