14 C depth profiles in Apollo 15 and 17 cores and lunar rock 68815

Details 14 C depth profiles in Apollo 15 and 17 cores and lunar rock 68815 14 C depth profiles in Apollo 15 and 17 cores and lunar rock 68815

Sep 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998gecoa..62.3025j&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 62, Issue 17, pp.3025-3036

Physics

17

Scientific paper

Accelerator mass spectrometry (AMS) was used to measure the activity vs. depth profiles of 14 C produced by both solar cosmic rays (SCR) and galactic cosmic rays (GCR) in Apollo 15 lunar cores 15001-6 and 15008, Apollo 17 core 76001, and lunar rock 68815. Calculated GCR production rates are in good agreement with 14 C measurements at depths below ~10 cm. Carbon-14 produced by solar protons was observed in the top few cm of the Apollo 15 cores and lunar rock 68815, with near-surface values as high as 66 dpm/kg in 68815. Only low levels of SCR-produced 14 C were observed in the Apollo 17 core 76001. New cross sections for production of 14 C by proton spallation on O, Si, Al, Mg, Fe, and Ni were measured using AMS. These cross sections are essential for the analysis of the measured 14 C depth profiles. The best fit to the activity-depth profiles for solar-proton-produced 14 C measured in the tops of both the Apollo 15 cores and 68815 was obtained for an exponential rigidity spectral shape R 0 of 110-115 MV and a 4 flux (J 10 , Ep > 10 MeV) of 103-108 protons/cm 2 /s. These values of R 0 are higher, indicating a harder rigidity, and the solar-proton fluxes are higher than those determined from 10 Be, 26 Al, and 53 Mn measurements.

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