(Also air shower, cascade, extensive air shower, shower.) Multiple generations of secondary cosmic rays
produced when primary cosmic rays interact with atoms in the upper atmosphere
, yielding subatomic particles
and gamma rays
. The secondary cosmic rays in turn produce even more down through the atmosphere
Billions of these particles travel downward at nearly the speed of light
and at ground level may extend over several square kilometers (in which instance the shower may be termed an extensive air shower). The maximum flux of cosmic rays, both primary and secondary, is at an altitude
of 20 km, and below this the absorption
by the atmosphere reduces the flux
, though the rays are still readily detectable at sea level
. Intensity of cosmic ray showers has also been observed to vary with latitude, being more intense at the poles.
Friedlander, M. W. 1989. Cosmic Rays. pp. 13, 79.
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