Piper:
Sounds like a density gauge, and those are fairly common all over the country. They use them to measure concrete density.
They are radioactive, and some of the hum pretty good. The NRC licenses them and regulates them.
This sounds like the same kind of device that was tossed from a car last week Tuesday in Chicago that caused evacuations. I'd also like to know who was driving.
~exhaling
Thanks JM