Science: Not-So-Clean Fallout

"Clean" thermonuclear bombs, like clean small boys, do not necessarily stay clean for long. The most familiar kind of radioactive fallout comes from the fission of plutonium or uranium 235, and from the so-called clean bombs that the U.S. Government has announced contain only small amounts of these troublemaking substances. The bulk of the bomb's bang comes from fusion of hydrogen, which creates no fission products.

But a bomb can be clean in one way and dirty in another. In Science, William H. Shipman and other scientists from the Naval Radiological Defense Laboratory, San Francisco, tell how they found large quantities of...

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