Physics
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.399m&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 399
Physics
Cosmogenic Nuclides, Iron Meteorites, Production Rates, Simulation Experiments
Scientific paper
Isotropic irradiations of artificial meteoroids have been succesfully used [1- 5] to simulate the interactions of galactic protons with extraterrestrial matter and to validate a physical model [6] for the calculation of cosmogenic nuclide production rates in stony meteoroids and lunar surface materials. Since the production of secondary particles by high-energy protons depends on the mean mass number of the target materials, significant differences in cosmogenic nuclide production rates are to be expected between meteoroid classes such as stones, stony irons, and irons. Experimental evidence for this effect of bulk chemical composition was found by Begemann and Schultz [7]. Model calculations [8,9] support this interpretation. In order to simulate the interactions of galactic protons with iron meteoroids, an artificial iron meteoroid with a diameter of 20 cm was isotropically irradiated with 1.6-GeV protons at the Saturne cyclotron at Laboratoire National Saturne/CEN Saclay. The artificial iron meteoroid was made of steel (99% Fe). There were 3 perpendicular bores that were filled with 9 cylindrical iron boxes containing more than 900 individual targets. These targets covered all elements investigated in the earlier simulation experiments [1-5]. During a 133-hr irradiation the artificial iron meteoroid received a (preliminary) proton dose of 2.17 X 10^14 cm^-2, which is equivalent to a 2.3- Ma exposure of a meteoroid in space. After irradiation the individual targets inside the artificial meteoroid were distributed to the collaborating laboratories, where the residual product nuclides are investigated by X-ray and gamma ray spectrometry as well as by conventional and accelerator mass spectrometry. Up to now, more than 200 depth profiles have been measured. Measurements of stable and long-lived nuclides will begin after the targets have cooled sufficiently. The experimental data are interpreted by model calculations based on spectra of primary and secondary particles derived by Monte Carlo techniques and experimental and theoretical thin-target cross sections of the underlying nuclear reactions. The calculations allow us to distinguish the influence of bulk chemical composition onto cosmogenic nuclide production rates and to improve the modeling of production rates in iron meteoroids. Acknowledgment: This work was supported by the Swiss National Science Foundation. References: [1] Michel R. et al. (1985) Nucl. Instr. Meth. Phys. Res., B16, 61-82; (1989) ibid., B42, 76-100; (1993) J. Radioanal. Nucl. Chem., 169, 13- 25. [2] Herpers U. et al. (1991) Meteoritics, 26, 344. [3] Wieler R. et al. (1992) Meteoritics, 27, 315-316. [4] Weber H. W. and Begemann F. (1992) Meteoritics, 27, 305. [5] Gilabert E. et al. (1992) Meteoritics, 27, 223-224. [6] Michel R. et al. (1991) Meteoritics, 26, 221-242. [7] Begemann F. and Schultz L. (1988) LPS XIX, 51-52. [8] Michel R. et al. (1990) Meteoritics, 25, 386-387. [9] Masarik J. et al. (1993) LPS XXIV, 937-938.
Allègre Claude J.
Audouze Jean
Begemann Friedrich
Birck Jean-Louis
Cloth P.
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