Measurement and Modeling of the Production of He, Ne, and AR from Mg, Al, Si, Fe, and NI in an Artificial Iron Meteoroid Irradiated Isotropically with 1.6 GeV Protons

Details Measurement and Modeling of the Production of He, Ne, and AR from Mg, Al, Si, Fe, and NI in an Artificial Iron Meteoroid Irradiated Isotropically with 1.6 GeV Protons Measurement and Modeling of the Production of He, Ne, and AR from Mg, Al, Si, Fe, and NI in an Artificial Iron Meteoroid Irradiated Isotropically with 1.6 GeV Protons

Sep 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30r.494b&link_type=abstract

Meteoritics, vol. 30, no. 5, page 494

Other

2

Cosmic Rays, Simulation, Galactic Cosmic Rays, Isotopes, Cosmogenic, Production Rates, Meteoroids, Iron, Noble Gases

Scientific paper

The production by GCR protons of He, Ne and Ar isotopes from their main target elements was investigated in a simulation experiment [1] by irradiating a 20-cm diameter iron sphere isotropically with 1.6 GeV protons. The model-meteoroid contained, among other targets, pure Mg, Al, Si, Fe, and Ni foils at various depths in central bores. Radionuclide production in these targets was measured by gamma-spectrometry. Stable He, Ne, and Ar isotopes were measured by mass spectrometry. These latter results and the ^22Na data are reported here. As in our earlier simulation with a 50-cm diameter gabbro sphere irradiated with 1.6 GeV protons [2], the present experiment simulates the exposure of meteoroids to galactic protons in space within about 20%, if normalized to the same number of particles. Some systematic deviations are attributed to differences between the monoenergetic irradiation and the exposure to the GCR spectrum and to resulting differences between the secondary particle fields. A comparison of the new production rates with those obtained in the gabbro sphere [2] clearly exhibits the influence of bulk chemical composition on production rates which was discovered earlier by Begemann and Schultz [3] in stony irons. Model calculations of the production of He, Ne, Ar, and ^22Na were performed for all artificial iron and stony meteoroids irradiated by our collaboration [2, 4, 5, this work]. Production rates were calculated from depth-dependent p- and n-spectra derived by Monte Carlo techniques using the HERMES code system [6] and from cross sections for the relevant nuclear reactions. For p-induced reactions all available experimental thin-target cross sections were used [2]. Cross sections for n-induced reactions were calculated by the new AREL code [7] which is a relativistic version of the hybrid model of preequilibrium reactions [8]. In addition to these a priori calculations a posteriori model calculations were performed. Theoretical cross sections for n-induced reactions were improved by a least square fitting procedure adjusting the calculated production rates to all experimental ones from the simulation experiments. The simultanous interpretation of rare gas production rates measured in artificial meteoroids of different radii and bulk chemical composition irradiated by 600 MeV and 1.6 GeV protons results in an improved set of neutron cross sections. The new experimental production rates provide a basis for validation of model calculations of rare gas production in all types of extraterrestrial matter. In particular, they allow to validate model calculations of the matrix effect [9, 10] on the basis of laboratory data obtained under controlled conditions. Production rates in stony and iron meteoroids are consistently described by a physical model without free parameters. Acknowledgments: This work was supported by the Swiss National Science Foundation. References: [1] Michel R. et al. (1993) Meteoritics, 28, 399-400. [2] Wieler R. et al. (1992) Meteoritics, 27, 315-316. [3] Begemann F. and Schultz L. (1988) LPS XIX, 51-52. [4] Michel R. et al. (1986) Nucl. Instr. Meth. Phys. Res., B16, 61-82. [5] Michel R. et al. (1989) Nucl. Instr. Meth. Phys. Res., B42, 76-100. [6] Cloth P. et al. (1988) Juel 2203. [7] Blann M. (1994) personal communication. [8] Blann M. (1972) Phys. Rev. Lett., 28, 757-759. [9] Michel et al. (1990) Meteoritics, 25, 386-387. [10] Masarik J. et al. (1994) GCA, 58, 5307-5317.

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