Modeling high-energy cosmic ray induced terrestrial and atmospheric neutron flux: A lookup table

06/2012; DOI: 10.1002/jgra.50377
Source: arXiv

ABSTRACT Under current conditions, the cosmic ray spectrum incident on the Earth is
dominated by particles with energies < 1 GeV. Astrophysical sources including
high energy solar flares, supernovae and gamma ray bursts produce high energy
cosmic rays (HECRs) with drastically higher energies. The Earth is likely
episodically exposed to a greatly increased HECR flux from such events, some of
which lasting thousands to millions of years. The air showers produced by HECRs
ionize the atmosphere and produce harmful secondary particles such as muons and
neutrons. Neutrons currently contribute a significant radiation dose at
commercial passenger airplane altitude. With higher cosmic ray energies, these
effects will be propagated to ground level. This work shows the results of
Monte Carlo simulations quantifying the neutron flux due to high energy cosmic
rays at various primary energies and altitudes. We provide here lookup tables
that can be used to determine neutron fluxes from primaries with total energies
1 GeV - 1 PeV. By convolution, one can compute the neutron flux for any
arbitrary CR spectrum. Our results demonstrate that deducing the nature of
primaries from ground level neutron enhancements would be very difficult.

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    ABSTRACT: A ~ 62 My periodicity in fossil biodiversity has been observed in independent studies of paleontology databases over ~0.5Gy. The period and phase of this biodiversity cycle coincides with the oscillation of our solar system normal to the galactic disk with an amplitude ~70 parsecs and a period ~64 My. Our Galaxy is falling toward the Virgo cluster, forming a galactic shock at the north end of our galaxy due to this motion, capable of accelerating particles and exposing our galaxy's northern side to a higher flux of cosmic rays. These high-energy particles strike the Earth's atmosphere initiating extensive air showers, ionizing the atmosphere by producing charged secondary particles. Secondary particles such as muons produced as a result of nuclear interactions are able to reach the ground and enhance the biological radiation dose. Using a Monte Carlo simulation package CORSIKA, we compute the biological dose resulting from enhanced muon exposure from cosmic rays and discuss their implications for terrestrial biodiversity variations.
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