Exposure of Allan Hills 84001 and other achondrites on the Antarctic ice.
The enrichment of F on Antarctic meteorites is the result of their exposure to the atmosphere, and its measurement allows a subdivision of the terrestrial age into a duration of exposure on the ice and the time a meteorite was enclosed by the ice. In many cases, the periods of surface exposure are only small fractions of the terrestrial ages of meteorites collected in Antarctica. The enrichment of F on the surfaces of Antarctic achondrites was investigated by means of nuclear reaction analysis (NRA): scanning proton beams with an energy of 2.7 and 3.4 MeV were used to induce the reactions 19F(p, alpha gamma)16O and 19F(p,p gamma)19F, respectively. Gamma signals proportional to the F content were measured. The following Antarctic achondrites were investigated: Martian meteorite ALH 84001; diogenite ALHA77256; the eucrites ALHA81011 and ALHA78132; and in addition, the H5 chondrite ALHA79025. For ALH 84001, our data indicate a period of exposure on the ice of <500 years. Thus, this specimen was enclosed in the ice >95% of its terrestrial age of 13 000 years.
Krahenbuhl
U
U
Department of Chemistry and Biochemistry, University of Bern, Switzerland. kraehenbuehl@iac.unibe.ch
Noll
K
K
Dobeli
M
M
Grambole
D
D
Herrmann
F
F
Tobler
L
L
D000864:Antarctic Regions; D004781:Environmental Exposure; D005461:Fluorine / Q000032:analysis*; D007053:Ice; D019110:Meteoroids; D009686:Nuclear Physics; D010100:Oxygen; D013997:Time Factors
D007053:Ice; D005461:Fluorine; D010100:Oxygen