The alpha particles radiated by radioactive material will excite zinc sulfide crystals, causing them to emit a weak, bluish glow.
A British company (British Instrument Consultants) is developing night vision goggles specially tuned to enhance that specific wavelength of light emitted by this reaction.
By spraying zinc sulfide crystals around an area where a radiation leak is suspected, and then by studying the area through such goggles, the radiated areas stand out remarkably well.