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A brilliant blue glow engulfs the Missouri S&T reactor core when it is operating at a high power. This effect is known as Cherenkov radiation, named after the Russian scientist who developed the theory explaining the phenomena.
At full power (200 kW), the reactor core produces approximately 6.4E+15 fissions per second. Each fission event liberates a tremendous amount of energy. Part of this energy is carried away by fission products, which decay, producing high- energy beta particles. Often, beta particles are emitted with such high kinetic energies that their velocities exceed the speed of light in water. When this occurs, blue light is emitted and the reactor core "glows blue".
While no particle can exceed the speed of light in a vacuum (3.0E+8 m/sec), it is possible for a particle to travel faster than light in certain mediums, such as water. The speed of light in a particular medium is related to the speed of light in a vacuum and by the index of refraction. Water has an index of refraction of 1.3; thus the speed of light in water is 2.3E+8 m/s. Beta particles with kinetic energies in excess of 0.26 MeV travel at speeds in excess of 2.3E+8 m/s.
When the charged beta particle moves through water it tends to "polarize" (or orient) the water molecules in a direction adjacent to its path, thus "distorting" the local electric charge distribution. After the beta particle has passed, the molecules realign themselves in their original, random charge distribution. A pulse of electromagnetic radiation in the form of blue light is emitted as a result of this "reorientation." When the speed of the beta particle is less than the speed of the light, the pulses tend to "cancel" themselves by destructive interference; however, when the speed of the beta particle is greater than the speed of light then the light pulses are "amplified" through constructive interference. The phenomenon is analogous to the acoustic "sonic boom" observed when an object exceeds the speed of sound in air.
The intensity of the blue glow is directly proportional to the number of fissions occurring and the reactor power level. This property is utilized in Cherenkov detectors that measure the magnitude of Cherenkov radiation produced in a detector made of Lucite.
Cherenkov radiation becomes visible in the Missouri S&T Reactor core at a power of about 6 kW. At 200 kW the core glows brilliantly with a soft blue glow. The blue glow continues for some time after the reactor has been shut down due to the decay of fission products.