81Kr in meteorites and lunar rocks as a clue for the cosmic-ray exposure history of solar system material

Cosmic-ray produced Kr isotopes, including the radioisotope 81Kr, in meteorites and lunar rocks are used to derive the duration of the exposure to cosmic rays. For many meteorites cosmic-ray exposure ages and terrestrial ages have been calculated. Of particular interest are the meteorites which were ejected from the Moon by large impacts and which were later captured by Earth and collected in Antarctica. From cosmic-ray produced Kr in lunar rocks sampled on the ejecta blanket of lunar craters the crater formation ages can be derived. Mass spectroscopy with an electron bombardment ion source was used to measure isotope ratios. (author)