This dime was briefly radioactive some time in the 1950's or 1960's. A museum operated in Oak Ridge used to have an exhibit, described here in detail, where visitors could have their dimes exposed to neutron radiation, which caused the silver in them to become radioactive for a few minutes. You might think the exhibit was closed due to safety or "what the hell do you think you're doing, are you crazy!?" kinds of reasons, but in fact it was forced to shut down in the mid 1960's when the US mint stopped making dimes out of silver. The neutron activation process used works only with real silver coins.
I suppose by now it probably would have been shut down anyway by namby pambies who think giving visitors radioactive souvenirs is somehow a bad idea, but of course you can still find these all over eBay (something like a million were done over the years). The radioactivity lasted only a few minutes (half-life 22 seconds), so today they are perfectly safe by anyone's definition.
Source: eBay seller danniken
Contributor: Theodore Gray
Acquired: 11 August, 2007
Text Updated: 11 August, 2007