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The Cosmic Ray Increases At 35 and 60 Kyr BP

Published online by Cambridge University Press:  18 July 2016

V Florinski ,
W I Axford  and
G P Zank
V Florinski*
Affiliation:
Institute of Geophysics and Planetary Physics, University of California, Riverside, California 92521, USA.
W I Axford*
Affiliation:
Institute of Geophysics and Planetary Physics, University of California, Riverside, California 92521, USA.
G P Zank*
Affiliation:
Institute of Geophysics and Planetary Physics, University of California, Riverside, California 92521, USA.
*
Corresponding author. Email: vflorins@citrus.ucr.edu.
Email: ian@axford.org.
Email: zank@ucrac1.ucr.edu.
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Abstract

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Concentrations of 10Be in ice cores and marine sediments exhibit 2 peaks with significant enhancements at 35,000 and 60,000 BP. This radioisotope is produced in the upper atmosphere by spallation of cosmic-ray protons and secondary neutrons on atmospheric nitrogen and oxygen. Previously suggested explanations for the increases include geomagnetic field reversals, a decrease in solar activity, and a supernova explosion. We propose an alternative explanation which involves a change in the galactic environment of the solar system. The structure of the heliosphere is investigated for a period when the Sun enters a cold, dense, unmagnetized interstellar cloud. Under these conditions, the heliosphere contracts to 25% its present size, significantly affecting galactic cosmic ray modulation and increasing anomalous cosmic ray fluxes. A tenfold increase in anomalous cosmic ray flux and a twofold increase in galactic cosmic ray intensity at Earth are possible in this high-density case if heliosheath modulation is reduced. We show that this increase in galactic cosmic ray intensity could be responsible for the peaks in 10Be records.

Type
Part II
Information
Radiocarbon , Volume 46 , Issue 2: Proceedings of the 18th International Radiocarbon Conference (Part 2 of 2), Conference Editors: Nancy Beavan Athfield, Rodger J Sparks , 2004 , pp. 683 - 690
Copyright
Copyright © The Arizona Board of Regents on behalf of the University of Arizona 

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