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Why Does Spent Nuclear Fuel Glow Blue?

Have you ever seen this eerie blue glow? Probably not unless you work in a nuclear reactor, but perhaps you’ve seen it on TV or in a movie such as X-Men: First Class.

The movies got the facts for this glow right, but why do nuclear reactors glow blue anyway?

The fascinating answer is roughly analogous to a light-based sonic boom. When nuclear energy is created, charged particles and light are emitted from the radioactive material. You may know that the speed of light in a vacuum is a constant at 186,000 miles per second. But nuclear reactors aren’t in vacuums; they’re surrounded by water to keep them cool. As such, the speed of light in water is only 75% of the speed of light in a vacuum.

The blue glow comes from the emitted particles of energy that move faster than light through the water! The electrons of the water get all excited and then, to restore an equilibrium, they emit energy in the form of photons which is the visible blue light. It’s blue because the properties of this radiation have shorter light wavelengths and the shorter the wavelength, the more blue the light will appear.

Russian Scientist Pavel Alekseyevich Cherenkov was the first to detect this energy phenomenon, and it’s named after him. The blue glow is called Cherenkov Radiation.

Article by Tim Agen, appearing courtesy Xcel Energy Blog.