Other
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27q.256m&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 256
Other
Scientific paper
In the interplanetary space, meteoroids are continuously irradiated by high-energy cosmic ray particles that induce nuclear reactions leading to the production of cosmogenic nuclides. The bulk chemical composition of a meteorite influences final cosmogenic nuclide production in two ways: (1) nuclide production is a concentration-weighted sum of individual production rates describing the production from each target element, and (2) the shape of differential fluxes of primary and secondary nucleons and their total fluxes. These particle fluxes strongly depend on the multiplicities for production of secondary particles, which are functions of mass number. The transport phenomena are also dependent on the bulk composition of the meteorite. In stony meteorites, the average atomic and mass numbers vary by less than 15%. A substantial difference in inter- and intranuclear cascade development is expected for iron meteorites. The range of production rates for neon and argon isotopes in stones and irons discussed by Begemann and Schultz (1988) were attributed to an enhanced flux of low- energy secondary particles, especially neutrons. In this paper we present a simulation of nucleon fields developed inside meteorites with various bulk chemical compositions. The calculations based on Los Alamos LAHET Code System (Prael and Lichtenstein, 1989), which is a system of coupled Monte Carlo computer codes that treats the physical phenomena relevant in computer simulations in particle production and transport. A homogeneous and isotopic GCR irradiation, corresponding to an averaged GCR primary proton spectrum of spheres with chemical composition equivalent to L-, H-, Cl-chondrites, aubrites, and irons was simulated, very similar to calculations done by Michel et al. (1990). To avoid effects due to size, the spheres had the same radii of r=65 g/cm^2. Production and equilibrium particle fluxes were calculated for concentric shells with thickness of 0.1 r. The results of our simulations confirm the importance of bulk chemical composition on nucleon fluxes development inside a meteorite. All neutron spectra show a steep decrease with increase of energy that is dependent on chemical composition and size of the irradiated body. As a measure of differences among various meteorite classes, the ratio R of differential fluxes between L-chondrites and other specimens was calculated. For L- and H-chondrites the value of R is restricted within an interval 0.98-1.02. For aubrites, with lower Fe contents than L-chondrites, the increase of R with decrease of neutron energy is visible with maximum value of R=1.15 below 10 MeV. A similar trend is evident for L/Cl-chondrites but with maximum value of R=1.1. The L/iron-meteorite ratio has an opposite trend. The decrease is observable on the entire energy interval with a minimum value of R=0.65 for energies 2-15 MeV. Even at 300 MeV, the value of R is approximately 0.9. The common feature of all proton spectra is broad maximum around 80-150 MeV and a flat decrease toward lower energies due to Coulomb stopping. For energies below 400 MeV, neutrons become the dominant particle. The differences in shape of fluxes of protons and secondary neutrons and the differences in total fluxes can be substantial and emphasizes the importance of effects caused by bulk chemical composition. Our flux ratios for irons versus chondrites are consistent with the trends observed by Begemann and Schultz (1988) for ^38Ar in metal and stone phases of various meteorites and the lower ^22Ne/^21Ne ratio in metal- rich meteorites relative to stones. We are working on combining our calculated particle fluxes with cross sections to get production rates to more quantitatively compare our calculations with observed trends for cosmogenic nuclides in meteorites with different bulk compositions. References: Begemann F. and Schultz L. (1988) Lunar Planet. Sci. (abstract) 19, 386. Michel R., Dragovitsch P. and Filges D. (1990) Meteoritics (abstract) 25, 386. Prael R.E. and Lichtenstein H. (1989) Los Alamos report LA-UR-89-3014.
Masarik Jozef
Reedy Robert C.
No associations
LandOfFree
Effects of Bulk Chemical Composition on Particle Fluxes in Meteorites does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Effects of Bulk Chemical Composition on Particle Fluxes in Meteorites, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Effects of Bulk Chemical Composition on Particle Fluxes in Meteorites will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1209554