Cosmic-ray-induced radioactivities in meteorites--II Al 26 , Be 10 and Co 60 , aerolites, siderites and tektites

Details Cosmic-ray-induced radioactivities in meteorites--II Al 26 , Be 10 and Co 60 , aerolites, siderites and tektites Cosmic-ray-induced radioactivities in meteorites--II Al 26 , Be 10 and Co 60 , aerolites, siderites and tektites

Oct 1958

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1958gecoa..14..364e&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 14, Issue 4, pp.364-379

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4

Scientific paper

The long-lived radionuclides Al 26 and Be 10 and the 5 year Co 60 have been detected in stone and iron meteorites. The highest levels observed, in disintegrations per minute per gram of specimen were: in stone, Al 26 , 0.063; Be 10 , 0.0051; Co 60 , 0.0018; in iron, Al 26 , 0.0055; Be 10 , 0.00070; Co 60 , 0.033. The Al 26 and Be 10 were evidently produced by cosmic-ray bombardment of the meteorites before fall. The Co 60 seems to have been produced principally by neutron capture in ordinary cobalt in recent years while the specimens were on earth, although disintegration of the long-lived Fe 60 may contribute some Co 60 . The Be 10 : Al 26 ratio is definitely lower in the Plainview chondrite than in the Richardton chondrite, suggesting that the former may have existed as a small body for only about a million years. The presence of both activities in the Odessa siderite indicates that it and its associated craters are probably less than about a million years old. The absence of these activities in the Canyon Diablo siderite is probably ascribable to a shielded position of the specimen inside the large meteoroid. Al 26 is definitely and Be 10 fairly certainly present in australites, indicating that tektites are glass meteorites and have spent at least a million years or so in space. Both activities are also present in Libyan Desert silica-glass, indicating that it is a variety of tektite. From the Al 26 and Be 10 levels or limits, in comparison with the levels in chondrites, the following approximate terrestrial ages or limits, in millions of years, are calculated: australites, <0.5; Libyan Desert silica-glass, 3.5; bediasites, >1.2; moldavites, >3. Measurements of these and other nuclides can give valuable information on the pre-fall and post-fall histories of meteorites and on the past intensity of the cosmic radiation. The average cosmic-ray flux over the past several million years appears not to have been grossly different from the present value. nergy

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