Nuclear reactor radiation. This radiation (blue glow) is produced in the water surrounding nuclear reactors. This glow is produced by the Cherenkov effect, a phenomenon discovered in the 1930s by the Russian physicist Pavel Alexeyevich Cherenkov. Cherenkov concluded that the radiation was produced when high-speed charged particles pass through a material (here, water) at a speed that is greater than the speed of light in the material. The effect is similar to that of the sonic boom caused by an airplane when it travels through air faster than the sound wave it produces. Photographed in 2004 at the CEA (Centre of Atomic Energy) in Saclay, France.