Simulation of the Production of Shortlived Cosmogenic Nuclides and of 26Al in Meteoroids by Galactic Protons

Details Simulation of the Production of Shortlived Cosmogenic Nuclides and of 26Al in Meteoroids by Galactic Protons Simulation of the Production of Shortlived Cosmogenic Nuclides and of 26Al in Meteoroids by Galactic Protons

Jul 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27..314r&link_type=abstract

Meteoritics, vol. 27, no. 3, volume 27, page 314

Computer Science

1

Scientific paper

In order to simulate the production of cosmogenic nuclides by galactic protons in meteoroids, an artificial meteoroid with a diameter of 50 cm made out of gabbro was isotropically irradiated with 1.6 GeV protons at the Saturne cyclotron of the Laboratoire National Saturne/CEN Saclay (1). The artificial meteoroid contained more than 1400 individual targets consisting of pure elements, suitable chemical compounds, natural minerals and degassed meteoritic materials in two perpendicular bores, thus allowing the measurement of the elemental production rates from all target elements relevant in extraterrestrial matter. Up to now, more than 400 depth profiles for the production of radionuclides have been measured. Here, we report the results for ^26Al and for the short-lived cosmogenic radionuclides, e.g., ^7Be, ^22Na, ^46Sc, ^48V, ^51Cr, and ^54Mn. The experimental data were analyzed by model calculations derived from depth-dependent spectra of primary and secondary particles in the artificial meteoroid, calculated by Monte Carlo techniques using the HERMES code system (2), and from experimental and theoretical thin target cross sections of the underlying nuclear reactions. The model calculations excellently describe the production depth profiles in the artificial meteorite, if reliable cross sections are available. Cases of disagreement between the experimental and theoretical depth profiles point to still existing shortcomings in the theoretical cross sections for medium-energy neutron-induced reactions. Here, the results of the simulation experiment can be used to improve these cross sections by fitting the theoretical production rates to the experimental ones. The resulting cross sections can then be applied to model calcula- tions of the respective cosmogenic nuclide in extraterrestrial matter, as it was successfully demonstrated for the production of Be (3). Based on this analysis, we present model calculations for the production of ^26Al and of short-lived cosmogenic nuclides in stony meteoroids by galactic protons. The model calculations are compared with meteorite data. The elemental production rates of ^26Al and the dependence of the production rates on the solar modulation of the galactic proton spectra, in particular production rate ratios such as ^22Na/^26Al and ^54Mn/^26Al, are discussed in detail. Acknowledgement: This work was supported by the Deutsche Forschungsgemeinschaft and by the Swiss National Science Foundation. References: (1) Michel R. et al. (1991) Meteoritics (abstract) 26, 372a. (2) Cloth P. et al. (1988) Juel-2203. (3) Herpers U. et al. (1991) Meteoritics (abstract) 26, 344a.

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