Radiation Belts

The Earth has both an inner and outer radiation belt.

Inner Radiation Belt:

The inner radiation belt was discoverd by Explorers 1 and 3 (Van Allen's Geiger counter) and extends above the equator about 1 RE= 6371 km (about 4000 miles).

It is populated by very energetic protons in the 10-100 MeV range (by-product of collisions by cosmic rays with atoms of the atmosphere). The cosmic radiation has a rather low intensity (comparable to starlight) and only by accumulating particles over the span of years does the inner belt reach its high intensity.

These particles can readily penetrate spacecraft  and on prolonged exposure they can damage instruments and be a hazard to astonauts.

Outer Radiation Belt:

The space probes Pioneer 3 and 4 detected the outer radiation belt. It is nowadays seen as part of the plasma trapped in the magnetosphere. The name radiation belt is usually applied to the more energetic part of the plasma population (e.g ions of about 1 MeV of energy). The more numerous lower-energy particles are known as the "ring current", since they carry the current responsible for magnetic storms. Most of the ring current energy resides in the ions (typically with 0.05 MeV), but energetic electrons can also be found.

Monitoring of the radiation belts: 

• The Radiation Environment Monitor (REM) and
• ESA's Standard Radiation Environment Monitor (SREM)

See CHERBS paper on REM Results on  "Measurements of the Radiation Belts from MIR and STRV 1994-1997"

NEWS FLASH:
Earth's own magnetosphere and not the solar wind accelerates the particles of the radiation belts. (see ISTP press release)    
More introduction to Radiation Belts:

• Radiation Belts  GSFC/NASA
• The Radiation Belt -- History GSFC/NASA
• Radiation (van Allen) belts Space Physics - Oulu

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