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Revealing Histories of Exposure Using In Situ Produced 26Al and 10Be in Libyan Desert Glass

Published online by Cambridge University Press:  18 July 2016

Jeffrey Klein ,
Robert Giegengack ,
Roy Middleton ,
Pankaj Sharma ,
J R Underwood Jr  and
R A Weeks
Jeffrey Klein
Affiliation:
Department of Physics, University of Pennsylvania, Philadelphia, 19104
Robert Giegengack
Affiliation:
Department of Physics, University of Pennsylvania, Philadelphia, 19104 Department of Geology, University of Pennsylvania, Philadelphia
Roy Middleton
Affiliation:
Department of Physics, University of Pennsylvania, Philadelphia, 19104
Pankaj Sharma
Affiliation:
Department of Physics, University of Pennsylvania, Philadelphia, 19104
J R Underwood Jr
Affiliation:
Department of Physics, University of Pennsylvania, Philadelphia, 19104 Department of Geology, Kansas State University, Manhattan, Kansas 66506
R A Weeks
Affiliation:
Department of Physics, University of Pennsylvania, Philadelphia, 19104 Department of Mechanical and Materials Engineering, Vanderbilt University, Nashville, Tennessee 37235
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Abstract

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We present the results of measurements of 26Al and 10Be produced in situ in 12 samples of Libyan Desert Glass by cosmic rays during the last ten million years. Based on the variability of the concentrations of 10Be and of the 26Al/10Be ratios we measured, we conclude that individual fragments of glass have experienced different exposure histories, implying several major redistributions of the glass within the past 106 years. The 26Al and 10Be concentrations are inconsistent with the theoretical estimates of the rates of in situ production. We estimate minimum production rates of 70 atoms g-1 yr-1 and 10 atoms g-1 yr-1 for 26Al and 10Be, respectively, produced in quartz at sea level between 60–90° latitude. Despite the present uncertainty in the rates of production, we feel that these results show clearly the effectiveness of in situ produced 26Al and 10Be in studying earth-surface processes.

Type
IV. Methods and Applications
Information
Radiocarbon , Volume 28 , Issue 2A , 1986 , pp. 547 - 555
Copyright
Copyright © The American Journal of Science 

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