Article

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

06/2012;
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: "The investigation into the possible effects of cosmic rays on living organisms will also offer great interest." - Victor F. Hess, Nobel Lecture, December 12, 1936 High-energy radiation bursts are commonplace in our Universe. From nearby solar flares to distant gamma ray bursts, a variety of physical processes accelerate charged particles to a wide range of energies, which subsequently reach the Earth. Such particles contribute to a number of physical processes occurring in the Earth system. A large fraction of the energy of charged particles gets deposited in the atmosphere, ionizing the atmosphere, causing changes in its chemistry and affecting the global electric circuit. Remaining secondary particles contribute to the background dose of cosmic rays on the surface and parts of the subsurface region. Life has evolved over the past ~ 3 billion years in presence of this background radiation, which itself has varied considerably during the period. As demonstrated by the Miller-Urey experiment, lightning plays a very important role in the formation of complex organic molecules, which are the building blocks of more complex structures forming life. There is growing evidence of increase in the lightning rate with increasing flux of charged particles. Is there a connection between enhanced rate of cosmic rays and the origin of life? Cosmic ray secondaries are also known to damage DNA and cause mutations, leading to cancer and other diseases. It is now possible to compute radiation doses from secondary particles, in particular muons and neutrons. Have the variations in cosmic ray flux affected the evolution of life on earth? We describe the mechanisms of cosmic rays affecting terrestrial life and review the potential implications of the variation of high-energy astrophysical radiation on the history of life on earth.
    11/2012;

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