Cosmogenic nuclides in eucrites

Abstract

The cosmogenic nuclides 10Be and 26Al were measured in a number of selected Antarctic and non-Antarctic eucrites by accelerator mass spectrometry. Whenever available, different samples from the same meteorite were analyzed, in order to get information on depth-dependent variations of activities of cosmogenic radionuclides. For 26Al, measurements by gamma-gammacoincidence techniques were also done. For the Antarctic meteorites stable He-, Ne- and Ar-isotopes were determined in the same samples by conventional mass spectrometry. A detailed mineralogical study of the meteorites analyzed allowed a classification or reclassification as monomict and polymict eucrites. In meteorite falls 10Be and 26Al are in saturation. Some 10Be and most 26Al data in Antarctic eucrites are lower than those in falls. For 26Al this is attributed to the long terrestrial residence times of Antarctic meteorites. For 10Be the lower concentrations are unlikely to be due to the decay during terrestrial residence. The experimental data are discussed together with rare gas measurements in the context of model calculations of the depth- and size-dependent production of cosmogenic nuclides in eucrites. In the case of four Antarctic Allan Hills eucrites a possible pairing is derived on the basis of cosmogenic radionuclides, stable rare gas isotopes and mineralogical similarity.