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Radioactive fall-out after the surface detonation of nuclear weapons has been known since the Trinity detonation at Alamogordo, N. Mex., in 1945. The harmful effects from this fall-out were noted by the discovery of radiation damage to some cattle grazing in a canyon about 20 miles from the detonation. However, the possibility of widespread hazard to humans was discounted and remained so until the accidental exposure in 1954 of personnel who inhabited some islands 150 to 200 miles from Bikini Atoll. None of the native population, or the American service men who were exposed, died from the radiation. However, much study of the problem has been made since that time, to learn more about the hazard which exists and to find the best way of protecting personnel from the dangers of radiation from the fall-out.
The effects of nuclear weapons are due to the fission of material (uranium-235 or plutonium-239)