Autor: Jull, A. J. T.; Cloudt, S.; Donahue, D. J.; Sisterson, J. M.; Reedy, R. C.; Masarik, J.
Názov: ¹⁴C depth profiles in Apollo 15 and 17 cores and lunar rock 68815
Typ: publication
Dátum: 1998
Jazyk: en
Poznámka:
Abstrakt:
Accelerator mass spectrometry (AMS) was used to measure the activity vs. depth profiles of ¹⁴C
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 ¹⁴C 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 ¹⁴C were observed in the Apollo 17 core 76001. New
cross sections for production of ¹⁴C 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 ¹⁴C depth profiles. The best fit to the
activity-depth profiles for solar-proton-produced ¹⁴C measured in the tops of both the Apollo 15 cores and
68815 was obtained for an exponential rigidity spectral shape R₀ of 110-115 MV and a 4π flux (J₁₀ ,Ep>10
MeV) of 103-108 protons/cm²/s. These values of R₀ are higher, indicating a harder rigidity, and the
solar-proton fluxes are higher than those determined from ¹⁰Be, ²⁶Al, and ⁵³Mn measurements.
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