Every see those vertical yellow gateways at border crossings and interstate weigh stations? Those are radiation scanners. Partially to keep terrorists at bay, but also to keep stuff like this at bay. In the 3rd world, this is sadly a frequent occurrence that these materials are used as scrap.

Example detector: http://ntl.bts.gov/lib/jpodocs/repts_te/14400_files/5_13.jpg