A mild wave of nervousness washed over the Philadelphia area last March, when police reported the theft of a soil-density gauge-a small, portable device that contains radioactive material-from a construction site. When a radiation detector at a nearby scrapyard sounded an alarm less than a day later-just after the missing device's case turned up nearby-the tension began to turn into panic. The yard shut down, and all sorts of officials descended upon it. Luckily, the gauge turned up in a nearby trash can, leaving just about everyone involved feeling relieved. That's because a radiation source no bigger than a thimble can spell disaster if it gets exposed in a scrapyard, fed into a shredder, or melted in a furnace, potentially releasing radiation into the environment.
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