TY - JOUR
T1 - 14C depth profiles in Apollo 15 and 17 cores and lunar rock 68815
AU - Jull, A. J.T.
AU - Cloudt, S.
AU - Donahue, D. J.
AU - Sisterson, J. M.
AU - Reedy, R. C.
AU - Masarik, J.
N1 - Funding Information:
We thank C. Meyer and staff at the Johnson Space Center who assisted in the cutting of lunar rock 68815. We are grateful to the following for assistance in cross-section sample preparations: A. M. Koehler, R. J. Schneider IV, both at Harvard Cyclotron Laboratory; K. Kim, A. Beverding, P. A. J. Englert, formerly at San Jose State University; J. Vincent, S. Yen, and A. Y. Zyuzin, TRIUMF, University of British Columbia; and C. Castaneda, Crocker Nuclear Laboratory, University of California, Davis. We also would like to thank L. J. Toolin, D. Biddulph, G. S. Burr, L. Hewitt, and A. L. Hatheway for technical assistance on the Arizona AMS. Some of the work of J. Masarik was done while he was a visiting scientist at EAWAG, Dübendorf, Switzerland. We thank G. F. Herzog, K. Nishiizumi and an anonymous reviewer for their useful comments. This work was supported over a number of years by NASA grants NAG 9-233, NAGW-3614 (Jull), NAGW-4609 (Sisterson) and NASA Order W-18,396 (Reedy). The work at NSF-Arizona AMS Facility was also partly supported by NSF grants EAR 88-22292, 92-03883, and 95-08413. S. Cloudt was also partly supported by the Arizona NASA Space Grant College Consortium.
PY - 1998/9
Y1 - 1998/9
N2 - 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 R(o) of 110-115 MV and a 4π flux (J10, Ep > 10 MeV) of 103-108 protons/cm2/s. These values of R(o) are higher, indicating a harder rigidity, and the solar-proton fluxes are higher than those determined from 10Be, 26Al, and 53Mn measurements.
AB - 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 R(o) of 110-115 MV and a 4π flux (J10, Ep > 10 MeV) of 103-108 protons/cm2/s. These values of R(o) 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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U2 - 10.1016/S0016-7037(98)00193-8
DO - 10.1016/S0016-7037(98)00193-8
M3 - Article
AN - SCOPUS:0032409285
SN - 0016-7037
VL - 62
SP - 3025
EP - 3036
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 17
ER -