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#12.     The Radiation Belts

  (Files in red–history)


10. Trapped Motion

    10H. Einstein, 1910

10a. Particle Drift

11. Explorers 1/3

  11a. Geiger Counter

12. Rad. Belts

    12H. Argus 1958

12a. Inner Belt

12b. Outer Belt

13. Fast Particles

14. Synch. Orbit

15. Energy

        The Earth actually has two radiation belts of different origins. The inner belt, the one discovered by Van Allen's Geiger counter, occupies a compact region above the equator (see drawing, which also includes the trajectories of two space probes) and is a by-product of cosmic radiation. It is populated by protons of energies in the 10-100 Mev range, which readily penetrate spacecraft and which can, on prolonged exposure, damage instruments and be a hazard to astronauts. Both manned and unmanned spaceflights tend to stay out of this region.

      Cross-section of the two radiation
      belts, together with the orbits of
      Pioneers 3 and 4 which contributed
      early observations of them.
        The outer radiation belt 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 that plasma population, e.g. ions of about 1 Mev of energy (see energy units). 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.

Questions from Users:
  ***     What is a "REM"?
      ***   Apollo Astronauts and radiation
                ***       The Ozone Hole and the Magnetic Field (1)
                        ***       Ozone and the Magnetic Field (2): The "ozone hole"
                              ***       "Radiation Remediation"?
                                    ***       Radiation Belts and Manned Space Flight
                                          ***       Radiation Hazards to Air Crews

Next Stop: #12H.  The Radiation Belts--History

Author and Curator:   Dr. David P. Stern
     Mail to Dr.Stern:   education("at" symbol)phy6.org

Co-author: Dr. Mauricio Peredo

Spanish translation by J. Méndez

Last updated 25 November 2001
Re-formatted 9-28-2004

Above is background material for archival reference only.

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