Helium- und Neonisotope in Eisenmeteoriten und der Tritiumverlust in Hexaedriten

Abstract

The He- and Ne-contents as well as their isotopic composition have been measured of 40 iron meteorites, including 12 hexahedrites. These hexahedrites were of particular interest because many of them showed a definite 3He-deficiency which we explain by a loss of tritium. This effect was already found by us previously for the hexahedrite Braunau. The tritium loss depends on the temperature the meteorites were exposed to, hence, on their orbital elements. Some of the hexahedrites have lost practically all their tritium produced during their exposure to the cosmic rays, indicating that they always had been in the vicinity of the Earth or even closer to the Sun. Two octahedrites, Anoka and Staunton, suffered an appreciable loss of tritium too. From the rare gas data of meteorites with a nearly complete loss of tritium the cross-section ratios of the direct production of tritium, 3He, and 4He by the cosmic rays in iron meteorites could be calculated. In the ataxite Washington County a portion of the rare gas content was identified to be of primordial origin.