The earth is apparently ringed by two radiation belts, not just one. At a Washington meeting of the American Astronautical Society last week, Cosmic Ray Expert James Van Allen of State University of Iowa reported what the Army’s Pioneer III moon probe discovered about the high-speed electrons (or protons) that gyrate in the earth’s magnetic field. The probe’s two tiny Geiger counters worked fine all the way out to the 63,000-mile peak and back again, traversing two distinct, doughnut-shaped radiation belts. The inner belt begins 1,400 miles above the surface and extends to 3,400 miles. The outer belt begins at 8,000 miles and goes to 12,000 miles.
The center of either belt would make tough orbiting ground for the crew of a manned satellite. The radiation intensity there is the equivalent of at least 10 roentgens per hour, which would give a lethal dose to an unshielded man in about 45 hours. Between the belts, the radiation is only 0.3 roentgens per hour. A space ship staying between the two belts could remain in orbit for several weeks before its crew absorbed a deadly dose.
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