Word: thickest
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Dates: during 1960-1969
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...hazard is cosmic radiation. The U.S.'s interplanetary probe, Pioneer V, reported a sinister, unpredictable enemy lurking in space: wide-ranging "storms" of deadly proton particles, spewed forth by the sun, of such energy (up to 20 billion electron volts per particle) that they will easily penetrate the thickest protective shield...