Lasers could become an important tool for detecting radioactive materials, such as those in covert nuclear weapons, from a greater distance than ever before.

Conventional radioactivity sensing techniques involve waiting for particles produced during radioactive decay to hit a detector. The method can sense these particles from tens of metres away – but not much further. Howard Milchberg at the University of Maryland and his colleagues have now shown that a laser-based method could be effective from as far…