Comparative study of $sup 26$Al and $sup 53$Mn in eighteen chondrites
An investigation on the low-energy cosmic-ray products /sup 26/Al and / sup 53/Mn in 18 chondrites encompassed several side aspects in meteoritics. The ratio of observed to calculated specific activity of /sup 26/Al in 13 chondrites with recovered masses ranging from approximates 3 to 2000 kg remains constant within plus or minus 15 per cent of a mean of 0.93, This is consistent with Fuse and Anders' observation (Geochim. Cosmochim. Acta; 33:653 to 670 (1969)) of invariance of the /sup 26/Alproduction rate with depth and size. A plot of the / sup 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 /sup 53/Mn. Thus, the /sup 53/Mn production rate remains rather constant within plus or minus 15 per cent of a mean of 520 dpm/kg Fe for moat of the stones. Applying this information to two chondrites, Ladder Creek and Scurry, of known relatively short exposure and terrestrial ages, the /sup 53/Mn half-life (T/sub 53/), computed from their /sup 53/Mn/sub obs//sup 26/aub obs/ r atios, is found to be 3.85 plus or minus 0.4 m.y. which agrees very well with the currently accepted value of T/sub 53/ = 3.8 plus or minus 0.8 m.y. From the observed /sup 53/Mn/ /sup 54/Mn activity ratio in Allende, relative to the production rate ratio of 0.98, an exposure age of t/ sub 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. (auth)
- Research Organization:
- Univ., Cologne
- NSA Number:
- NSA-29-019092
- OSTI ID:
- 4362500
- Journal Information:
- Geochim. Cosmochim. Acta, v. 38, no. 2, pp. 217-234, Journal Name: Geochim. Cosmochim. Acta, v. 38, no. 2, pp. 217-234; ISSN GCACA
- Country of Publication:
- United Kingdom
- Language:
- English
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