title: Exposure of Allan Hills 84001 and other achondrites on the Antarctic ice.
abstract: 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.
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern, Switzerland. kraehenbuehl@iac.unibe.ch
authors.forename: U
authors.initials: U
authors.lastname: Krahenbuhl
authors.forename: K
authors.initials: K
authors.lastname: Noll
authors.forename: M
authors.initials: M
authors.lastname: Dobeli
authors.forename: D
authors.initials: D
authors.lastname: Grambole
authors.forename: F
authors.initials: F
authors.lastname: Herrmann
authors.forename: L
authors.initials: L
authors.lastname: Tobler
mesh_terms: D000864:Antarctic Regions; D004781:Environmental Exposure; D005461:Fluorine / Q000032:analysis*; D007053:Ice; D019110:Meteoroids; D009686:Nuclear Physics; D010100:Oxygen; D013997:Time Factors
chemical_list: D007053:Ice; D005461:Fluorine; D010100:Oxygen