Massenspektrometrische Isotopenhäufigkeitsmessungen an Kalium aus Eisenmeteoriten und das Problem der Bestimmung der 41K- 40K-Strahlungsalter

Abstract

In 11 iron meteorites the isotopic abundances of potassium have been measured. For some meteorites we obtained mass spectra of essentially cosmogenic potassium. For example, we obtained from Aroos 39K 42.0%, 40K 18.9%, 41K 39.1%. In other meteorites (e. g. Lombard 39K 88.0%, 40K 2.1%, 41K 9.9%) the primordial potassium predominates. From the isotopic abundances, the radiation ages of the iron meteorites were calculated from two different approaches: in the first case under the assumption that the potassium isotopes were produced in the same proportion in all meteorites; in the second case it was assumed that the energy spectrum of the radiation and hence the production ratios of the potassium isotopes differed from meteorite to meteorite. The He/Ne-ratios in the meteorites were taken to be characteristic of the nature of the energy spectrum. Since the relationship between the He/Neratio and the production ratios for the potassium isotopes is not yet well known the calculated radiation ages are probably only approximately correct. They vary between 1400 · 106 years (Clark County) and 200 · 106 years (Lombard).