Belts

The Van Allen Radiation Belt is a torus of energetic charged particles (plasma) around Earth, held in place by Earth's magnetic field. The Van Allen belts are closely related to the polar aurora where particles strike the upper atmosphere and fluoresce. more...

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The presence of a radiation belt had been theorized by Nicholas Christofilos prior to the Space Age and was confirmed by the Explorer I on January 31, 1958, and Explorer III missions, under Doctor James Van Allen. The trapped radiation was first mapped out by Sputnik 3, Explorer IV, Pioneer III and Luna 1. The release of fluorohydrocarbons in the upper atmosphere causes a selective absorption of alpha particles in that space. A conglomeration of such (invisible) clouds are called pseudo–Van Allen belts and are 1x10^-9 lower than the real Van Allen belts. Recently, the NSF funded 2 competing proposals to study these belts and their effect on the amount of radiation that enters the inner atmosphere of the earth.

Energetic electrons form two distinct radiation belts, while protons form a single belt. Within these belts are particles capable of penetrating about 1 g/cm² of shielding (e.g., 1 millimetre of lead).

The term Van Allen Belts refers specifically to the radiation belts surrounding Earth; however, similar radiation belts have been discovered around other planets. The Sun does not support long-term radiation belts. The Earth's atmosphere limits the belts' particles to regions above 200-1000 km, while the belts do not extend past 7 Earth radii R_E. The belts are confined to an area which extends about 65° from the celestial equator.

Outer belt

The large outer radiation belt extends from an altitude of about 13 000–65 000 km (2 to 10 Earth radii) above the Earths surface, and has its greatest intensity between 14,500 and 19,000 km. The outer belt consists mainly of high energy (0.1–10 MeV) electrons trapped by the Earth's magnetosphere. The gyroradii for energetic protons would be large enough to bring them into contact with the Earth's atmosphere. The electrons here have a high flux and at the outer edge (close to the magnetopause), where geomagnetic field lines open into the geomagnetic "tail", fluxes of energetic electrons can drop to the low interplanetary levels within about 100 km (a decrease by a factor of 1000).

The particle population of the outer belt is varied, containing electrons and various ions. Most of the ions are in the form of energetic protons, but a certain percentage are alpha particles and O+ oxygen ions, similar to those in the ionosphere but much more energetic. This mixture of ions suggests that ring current particles probably come from more than one source.

Read more at Wikipedia.org