Introduction to Cosmic Rays

What are Cosmic Rays?

 The term "Cosmic Rays" refers to elementary particles, nuclei, and electro-magnetic radiation of extra-terrestrial origin. These may include exotic, short-lived particles such as muons, pi-mesons or lambda baryons.

In the energy range of 10¹²-10¹⁵ eV (electron-volts*), cosmic rays arriving at the edge of the Earth's atmosphere have been measured to consist of approximately:

• 50% protons
• 25% alpha particles
• 13% C/N/O nuclei
• <1% electrons
• < 0.1% gammas

*An electron-volt is a microscopic unit corresponding to the energy gained or lost by an electron in crossing a potential gap of 1 V(volt). A typical battery (e.g. a AA-cell used in remote control units for television sets) has a voltage difference of 1.5 V. For comparison: a 40 W(watt) reading-light uses about 10²⁴ eV of energy in one hour.