New Light on Blue Light

Today is the birthday of Igor Yevgenyevich Tamm, a physicist born in Vladivostok, Russia, in 1895 who helped explain the weak, bluish light observed in water shielding some nuclear reactors.

In 1934, Soviet physicist Pavel Cherenkov discovered that light is emitted when charged particles pass through a liquid medium. But the glow of "Cherenkov radiation" was not understood until Tamm and Ilya Frank explained it in 1937. The two proposed that the glow is caused by electrons traveling faster than the speed of light in water. These energetic electrons displace electrons in some of the water atoms along their path; the electromagnetic radiation emitted by the displaced atomic electrons combines to form a light wave, similar to a bow wave generated by a speedboat traveling faster than water waves.

Tamm, Frank, and Cherenkov shared the Nobel Prize in physics in 1958. Tamm died in 1971.

[Source: Britannica Online]