Radiation Belt

On July 9, 1962, at 0900 UT (Universal Time) a nuclear device of 1.4-megatons yield was detonated at 400 km above Johnston Island in the Pacific Ocean. Since the explosion took place in the trapping region of the magnetosphere, an artificial radiation belt of considerable intensity was produced. The possible sources of the radiation belt were: (I ) beta-decay electrons from the fission fragments created in the explosion; (2) protons and electrons from the decay of neutrons produced in the explosion; and (3) a largescale redistribution in space of naturally-occurring trapped particles. Of these possible sources, only the fission fragment electrons contributed significantly to the most intense part of the artificial radiation belt. There is some evidence for a redistribution of mirror points of naturally-occurring electrons in the outer radiation zone, probably the result of a hydromagnetic disturbance propagated outward from the explosion, while the neutron decay products are spread over an immense region of space and can be shown to produce fluxes smaller than the natural ones. The fission fragments themselves form a relatively localized source function from a geophysical point of view. Their decay electrons are trapped by the earth's magnetic field; they spiral around the field lines, oscillate between northern and southern