{sup 14}C depth profiles in Apollo 15 and 17 cores and lunar rock 68815
- Univ. of Arizona, Tucson, AZ (United States). NSF Arizona AMS Facility
- Harvard Univ., Cambridge, MA (United States). Harvard Cyclotron Lab.
- Los Alamos National Lab., NM (United States)
- Comenius Univ., Bratislava (Slovakia). Dept. of Nuclear Physics
Accelerator mass spectrometry (AMS) was used to measure the activity vs. depth profiles of {sup 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 {sup 14}C measurements at depths below {approximately}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 {sup 14}C were observed in the Apollo 17 core 76001. New cross sections for production of {sup 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 {sup 14}C depth profiles. The best fit to the activity-depth profiles for solar-proton-produced {sup 14}C measured in the tops of both the Apollo 15 cores and 68815 was obtained for an exponential rigidity spectral shape R{sub 0} of 110--115 MV and a 4 {pi} flux (J{sub 10}, Ep > 10 MeV) of 103--108 protons/cm{sup 2}/s. These values of R{sub 0} are higher, indicating a harder rigidity, and the solar-proton fluxes are higher than those determined from {sup 10}Be, {sup 26}Al, and {sup 53}Mn measurements.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- OSTI ID:
- 329211
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 62, Issue 17; Other Information: PBD: Sep 1998
- Country of Publication:
- United States
- Language:
- English
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