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Q. Is there still radiation in Hiroshima and Nagasaki?

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The radiation in Hiroshima and Nagasaki today is on a par with the extremely low levels of background radiation (natural radioactivity) present anywhere on Earth. It has no effect on human bodies.

Atomic bombs differ from conventional bombs in emitting explosive energy on an entirely different order of magnitude and radiation. Of the emitted energy, 5% was initial radiation and 10% was residual radiation.

The initial radiation emitted at the moment of detonation inflicted great damage to human bodies. Most of those exposed to direct radiation within a one-kilometer radius died. Residual radiation was emitted later. Roughly 80% of all residual radiation was emitted within 24 hours. Research has indicated that 24 hours after the bombing the quantity of residual radiation a person would receive at the hypocenter would be 1/1000th of the quantity received immediately following the explosion. A week later, it would be 1/1,000,000th. Thus, residual radiation declined rapidly. 

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