Cherenkov, Pavel Alekseyevich (1904-1990), a Russian physicist, made important contributions to the field of nuclear physics with his discovery of Cherenkov radiation. Cherenkov shared the 1958 Nobel Prize in physics with Russian scientists Ilya M. Frank and Igor Yevgenevich Tamm. The three men were the first Russian scientists to win a Nobel Prize in physics.
In the early 1930's, Cherenkov observed that a bottle of water bombarded with gamma rays emitted a faint blue glow. Other scientists had also noted the light but thought it was a form of fluorescence. Through a series of painstaking experiments, Cherenkov demonstrated that the glow was a totally new phenomenon but could not identify its cause. In 1937, Frank and Tamm proved that the light was created by charged particles moving through liquid faster than the speed of light. This finding led to the development of a Cherenkov counter, which detects Cherenkov radiation. The device counts and measures elementary particles and has proven useful in the study of cosmic rays, which travel through outer space. Because the counter provides information about the mass and energy of a particle, it helped scientists discover the antiproton. Cherenkov attended Voronezh State University, earning a bachelor's degree in mathematics and physics in 1928. He spent two years teaching high school before moving to Leningrad for graduate studies at the Institute of Physics and Mathematics of the Soviet Academy of Sciences. After receiving an advanced degree, he transferred to Moscow to work at the institute, which had relocated and changed its name to the P. N. Lebedev Physical Institute of the Soviet Academy of Sciences. He was later promoted to senior scientific officer and ultimately served as head of the high-energy physics department until his death.
At graduate school, Cherenkov worked under the supervision of Sergei I. Vavilov, who suggested that Cherenkov study what happens when high-energy particles penetrate a liquid. Cherenkov showed that, in most cases, fluorescence was responsible for the light produced by a liquid. As the liquid absorbs the high-energy radiation, the incoming energy excites the atoms and causes them to reach a higher energy state. The atoms quickly return to a lower energy state, however, and the difference between the higher and lower state is emitted as electromagnetic radiation in some cases appearing as light.
When Cherenkov tried the procedure with gamma rays from radium, he observed a blue glow that he did not readily understand. To discover the underlying cause, he conducted a series of experiments to test the light under a variety of conditions. He had to rely on his eyesight to measure the light because he lacked high-energy radiation detectors. Since he had only weak sources of radium, he had to sensitize his eyes to see the fleeting blue glow and thus started his workday by sitting in a totally darkened room for an hour.
To investigate all possibilities, Cherenkov used a number of different liquids but, in each case, the blue glow was unaffected. He then added chemicals, such as potassium iodide, to the liquid. If the light were created by fluorescence, the addition of chemicals would dim the brightness. Once again, however, the blue glow remained the same. Cherenkov also noted that the glow's polarization did not run in the same direction as that of fluorescent light. It was this last discovery that helped Frank and Tamm figure out the true nature of the luminescence.
Frank and Tamm theorized that molecular action was responsible for the glow. Gamma rays have a much higher energy level than other radiation sources, such as X rays, and are capable of ejecting an electron liberated from an atom in the liquid. When this happens, the electron is propelled at such a high velocity that it moves faster than the speed of light. Although one of the principles of Albert Einstein 's theory of relatively is that particles cannot move faster than the speed of light, this situation is only true in a vacuum. Light moves more slowly in a liquid, and the blue light produced when the particle exceeds the speed of light is analogous to the sonic boom created when an airplane exceeds the speed of sound. For their discovery and interpretation of this effect, Cherenkov, Frank, and Tamm won the Nobel Prize.
In 1940, Cherenkov received a doctorate degree and went on to teach physics at the Moscow Power Engineering Institute and the Moscow Institute of Physical Engineers. He received the State Prize from the Soviet government three times and was a member of the Soviet Academy of Sciences.