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In situ production of terrestrial cosmogenic helium and some applications to geochronologyThe concentrations of cosmogenic He-3 have been measured in a series of basaltic drill core samples from Hawaiian volcanoes Haleakala and Mauna Loa. The He-3 concentration in the surface of a radiocarbon dated Mauna Loa flow (20,000 years) gives reasonable agreement with a theoretical production rate of 140 atoms/g/yr, and suggests that the uncertainty in this rate is roughly 10 percent. The results illustrate the feasibility of using He-3 to measure exposure ages of young basaltic lava flows and for measuring erosion rates. Erosion rates calculated from the three Haleakala cores range from 7 to 11 meters/million years. The drill core data demonstrate that accurate depth control is crucial to the use and evaluation of cosmogenic helium. Depth profiles from several of the older cores display a nonexponential depth dependence of He-3(c) below 170 g/sq cm, which is attributed to the contribution from Li-6(n, alpha)T, where the neutrons are from stopped muons. This has important implications for depth dependence of cosmogenic He-3 because muons are weakly attenuated compared to the nucleonic component that produces spallation.
Document ID
19870043259
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Kurz, Mark D.
(Woods Hole Oceanographic Institution MA, United States)
Date Acquired
August 13, 2013
Publication Date
December 1, 1986
Publication Information
Publication: Geochimica et Cosmochimica Acta
Volume: 50
ISSN: 0016-7037
Subject Category
Geophysics
Accession Number
87A30533
Funding Number(s)
CONTRACT_GRANT: NAG9-69
CONTRACT_GRANT: NSF EAR-86-10611
CONTRACT_GRANT: NSF OCE-85-16082
Distribution Limits
Public
Copyright
Other

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