Computer Science
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28..391m&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 391
Computer Science
2
Cosmic Rays, Cosmogenic Nuclides, Lunar Rock 68815, Nuclides
Scientific paper
The determination of the flux and spectral shape of solar-cosmic-ray (SCR) particles from measurements of cosmogenic nuclides in lunar samples requires many pieces of information. An important part of the analysis is the correction of the measured nuclide concentration for the contribution by galactic-cosmic-ray (GCR) particles in the surface layers, where SCR production is important. Usually the GCR contribution is inferred from the concentration of the nuclide measured at a depth where SCR production is negligible and using a GCR production profile to extrapolate back to the surface. The shapes of these GCR profiles were found to be important for neon and argon [1] and ^10Be [2] in lunar rock 68815. Better determination of this near-surface GCR production profile would improve this important correction. As almost all nuclides have some production by SCR particles, it is hard to determine experimentally this GCR profile. The GCR production profile in the top of lunar rock 68815 was calculated using the Los Alamos Monte Carlo LAHET Code System (LCS). LCS has yielded calculated production rates that almost always are in good agreement with cosmogenic- nuclide measurements in meteorites [3,4]. The fluxes of protons and neutrons in rock 68815 was calculated for 1 g/cm^2 layers down to a depth of 25 g/cm^2 and with a coarser depth mesh to a depth of 500 g/cm^2 with LCS. These fluxes for each layer were then multiplied by the relevant cross sections and integrated over energy for eight nuclides: ^10Be, ^14C, ^21Ne, ^22Ne, ^26Al, ^36Cl, ^38Ar, and ^53Mn. The calculated production profiles below about 30 g/cm^2 agree well with lunar core measurements. All the cosmogenic nuclides studied have GCR production profiles that increase from the surface of the Moon to a maximum at depths of ~20-50 g/cm^2 and then decrease with increasing depth. The amount of this increase varies considerably, with products made by higher-energy particles and by protons having less increase in production rate with depth. The amount of the increase from the surface to depths of 10 or 20 g/cm^2 correlates with the depth of the peak production rate. The highest-energy product in this study, ^10Be, has a peak production rate near ~20 g/cm^2 and has ratios of the production rate at 0-1 g/cm^2 to those at 9-10 and 19-20 g/cm^2 of 0.965 and 0.940 respectively. With typical lunar saturation activities of ~12 dpm/kg, the surface has a ^10Be activity due only to GCR particles that is ~1 dpm/kg less than that near the production peak. The flat ^10Be activities measured in lunar samples [2] would thus imply a SCR contribution about equal to this small GCR difference, restricting the spectral shapes of solar protons that made ^10Be to those with few high-energy particles. For the composition of lunar rock 68815, the nuclides with the steepest GCR profiles were ^26Al and ^38Ar, with ratios of production rates at 0-1 g/cm^2 to those at 9-10 and 19-20 g/cm^2 of about 0.79 and 0.71 respectively, and with peak production rates near ~50 g/cm^2. The production ratios for these depths were, respectively, about 0.82 and 0.74 for ^53Mn and ^14C, about 0.84 and 0.76 for ^36Cl, and 0.88 and 0.84 for ^21Ne and ^22Ne. These calculations for the production of nuclides in the top layers of lunar rocks by GCR particles show that there are increases with depth down to ~20-50 g/cm^2 and that the amount of the increase varies with the nuclear reactions making the nuclide. Experimental confirmation of these calculated GCR production profiles should be made, possibly with 35-day ^37Ar in lunar rocks from a mission like Apollo 16 that had few solar particle events prior to it. This work was supported by NASA and done under the auspices of the U.S. Department of Energy. References: [1] Garrison D. G. et al. (1993) LPS XXIV, 521. [2] Nishiizumi K. et al. (1988) Proc. LSPC 18th, 79. [3] Masarik J. and Reedy R. C. (1993) LPS XXIV, 937. [4] Reedy R. C. et al. (1993) LPS XXIV, 1195.
Masarik Jozef
Reedy Robert C.
No associations
LandOfFree
Production Profiles of Nuclides by Galactic-Cosmic-Ray Particles in the Tops of Lunar Rocks 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 Production Profiles of Nuclides by Galactic-Cosmic-Ray Particles in the Tops of Lunar Rocks, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Production Profiles of Nuclides by Galactic-Cosmic-Ray Particles in the Tops of Lunar Rocks will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1072372