COSMIC-RAY-INDUCED RADIOACTIVITIES IN METEORITES. II. Al$sup 26$, Be$sup 10$ AND Co$sup 60$, AEROLITES, SIDERITES AND TEKTITES

Journal Article · Wed Oct 01 04:00:00 EDT 1958 · Geochim. et Cosmochim. Acta

DOI:https://doi.org/10.1016/0016-7037(58)90075-9· OSTI ID:4324334

Ehmann, W D; Kohman, T P

The long-lived radionuclides Al/sup 26/ and Be/sup 10/and the 5 year Co/ sup 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/ sup 26/ 0.063; Be/sup 10/ 0.0051; Co/sup 60/ 0.0018; in iron, Al/sup 26/ 0.0055; Be/sup 10/ 0.00070; Co/sup 60/ 0 033. The Al/sup 26/ and Be/sup 10/ were evidently produced by cosmic-ray bombardment of the meteorites before fall. The Co/sup 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/sup 60/ may contribute some Co/sup 60/ The Be/sup 10/: Al/ sup 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/sup 26/ is definitely and Be/sup 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-giass, indicating that it is a variety of tektite. From the Al/sup 26/ and Be/sup 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. (auth)

• Research Organization: Carnegie Inst. of Tech., Pittsburgh
• NSA Number: NSA-13-001980
• OSTI ID: 4324334
• Journal Information: Geochim. et Cosmochim. Acta, Journal Name: Geochim. et Cosmochim. Acta Vol. Vol: 14
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

CHEMISTRY
METEORITES
MOLDAVITES
TEKTITES