K-Ar-Altersbestimmungen an Eisenmeteoriten—I Die Isotopenzusammensetzung des primären Kaliums

Abstract

The isotopic composition of primordial potassium has been determined in inclusions of five iron meteorites and in one stone meteorite and was compared with terrestrial standards. In iron meteorites with low spallation content, the same isotopic abundance has been found for K 40 as in terrestrial samples. In the Treysa meteorite spallation-produced K 40 could be detected. For the calculation of radiogenic ages of iron meteorites the same K 40 abundance of 0.012 per cent can be used as for terrestrial material. From the K 40 abundance one can estimate the maximal difference in proton irradiation of some 10 17 p/cm 2 between terrestrial and meteoritic matter during the early history of the solar system. Iron meteorites are especially interesting, since their origin might have been different from that of terrestrial matter and even from stone meteorites.