Chapter 1Introduction

1.1 Basic Knowledge on Terrestrial Secondary Particles

Cosmic rays, which have extremely high energies, come from the galactic core and the sun to the atmosphere of the Earth. Primary cosmic rays in outer space consist mainly of protons (about 90%). Since cosmic rays are charged particles they twine around lines of geomagnetic or heliomagnetic forces as illustrated in Figure 1.1. Some of them are trapped by geomagnetic force to form the Van Allen radiation belts. Cosmic rays with energies less than the geomagnetic rigidity cutoff are deflected before entering the geomagnetic field. On the other hand, some are attracted into geomagnetic poles along with lines of geomagnetic force sometimes accompanied by the aurora borealis or australis. Cosmic rays are deflected more strongly near the equator since the lines of geomagnetic force are parallel to the surface of the Earth. Therefore, the strength of cosmic rays that reach the atmosphere differs depending on the geomagnetic latitude of the Earth.


Figure 1.1 Overall scheme of terrestrial radiation-induced single event effects

When the energetic protons enter the atmosphere (troposphere and stratosphere) of the Earth, some protons undergo nuclear spallation reaction with nuclei (mainly nitrogen and oxygen nuclei) in the atmosphere to produce a number of light particles including neutrinos, photons, electrons, ...

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