Tsar Bomba's Fallout-Reducing Lead Tamper

On October 30, 1961, the Soviet Union detonated Tsar Bomba over Novaya Zemlya in the largest human-made explosion ever recorded. Its designers replaced a planned uranium tamper with lead to prevent additional fission and reduce radioactive fallout. The change cut the bomb's potential yield from about 100 megatons to 50 megatons. Fusion supplied roughly 97% of the blast's energy, leaving the test with unusually low fallout relative to its size.

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