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

Accelerator mass spectrometry (AMS) was used to measure the activity vs. de pth profiles of C-14 produced by both solar cosmic rays (SCR) and galactic cosmic rays (GCR) in Apollo 15 lunar cores 15001-6 and 15008, Apollo 17 cor e 76001, and lunar rock 68815. Calculated GCR production rates are in good agreement with C-14 measurements at depths below similar to 10 cm. Carbon-1 4 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 C-14 were observed in the Apollo 17 core 76001. New cross sections for production of 14C by proton spallatio n on O, Si, Al, Mg, Fe, and Ni were measured using AMS. These cross section s are essential for the analysis of the measured C-14 depth profiles. The b est fit to the activity-depth profiles for solar-proton-produced C-14 measu red in the tops of both the Apollo 15 cores and 68815 was obtained for an e xponential rigidity spectral shape R-0, of 110-115 MV and a 4 pi 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 Be-10, Al-26, and Mn-53 measurements. Copyright (C) 1 998 Elsevier Science Ltd.