Cherenkov radiation is produced when charged particles move through water faster than the speed at which light travels through water. Water molecules are excited by this process, and when the excited molecules return to their ground state, they release photons that produce the blue light seen in the figure above. One of the places where this type of situation commonly occurs is inside nuclear reactors. Water is used to cool the rods containing radioactive material in nuclear reactors, which use emissions from radioisotopes to produce heat that can drive a turbine and generate electricity.
Nuclear power plants are used in many countries around the world. As of 2013, there are 434 operational nuclear plants around the world, over 100 of which are found in the U.S. In 2012, nuclear power accounted for 19% of the total U.S. production of electricity. Radioactivity is poorly understood by the general public. Images of nuclear bombs and runaway power plant incidents are of great concern to many. However, there are many useful applications, including medical imaging and treatment using radioisotopes. In this chapter, we will explore basic ideas about radioactivity and see how we can use this phenomenon for constructive purposes.