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Numerical Simulation of Neutron Capture Production of Cosmogenic Nuclides in Stony Meteorites
| Content Provider | Semantic Scholar |
|---|---|
| Author | Kollár, Daniel Michel, Rolf Masarik, Jozef |
| Copyright Year | 2003 |
| Abstract | Introduction: A purely physical model for the simulation of cosmic-ray-particle interactions with matter was used to investigate the effects of bulk composition on production of neutron-capture produced cosmogenic nuclides in meteoroids. Calculational Model: The numerical simulation of interactions of primary and secondary cosmic-ray particles was done with the LAHET Code System (LCS) [1] which uses MCNP [2] for transport of low-energy neutrons. The investigated objects were spheres with various radii that were divided into spherical layers. We used the spectrum of the galactic-cosmic-ray particles corresponding to solar modulation parameter Φ = 650 MeV. The statistical errors of the LCS calculated fluxes were ~3–5%. The production rates were calculated using the excitation functions from evaluated neutron data files ENDF/B-VI [3] and JEF-2.2 [4]. Results and Discussion: There are significant differences between production rate depth profiles in ordinary chondrites and Cchondrites caused by the presence of hydrogen which is a strong neutron moderator. We found that there are also differences between capture rates in individual subclasses of ordinary chondrites. Generally, higher iron and lower oxygen content results in lower fluxes of thermal neutrons and therefore also lower capture rates and vice versa. The relative differences depend on excitation function of particular (n,γ) reaction. The capture rate of Cl in LL-chondrites relative to that in L-chondrites is shown in FIG. 1. For meteorite sizes with radii greater than 50 cm the ratio is constant with depth and radius for all investigated isotopes. The situation is similar for H-/L-chondrite ratio when the difference in bulk densities is considered. The mean GCR particle flux at 1 AU determined by comparing calculated depth profiles to measured Ca data from Apollo 15 drill core [3] was 2.86 cm s which is ≈1.6 times less than the values obtained in model calculations of spallation production [5, 6]. References: [1] Prael R. E. and Lichtenstein H. (1989) LA-UR89-3014. [2] Briesmeister J. F. (1993) LA-12625-M. [3] McLane V. E. et al. (1991) BNL-NCS-17541. [4] Rowlands J. (2000) JEFF report 17 [5] Reedy R. C. and Masarik J (1994) LPCS 25, 1119. [6] Leya I. et al. (2001) M&PS 36, 1547. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://www.lpi.usra.edu/meetings/metsoc2003/pdf/5163.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
