Cherenkov effect at the UMR's nuclear reactor (http://www.nuc.umr.edu/reactor/reactor.html)

Cherenkov radiation (also spelled Cerenkov) is electromagnetic radiation emitted when a charged particle passes through an insulator at a speed greater than that of light in the medium. The characteristic "blue glow" of nuclear reactors is due to Cherenkov radiation. It is named after Pavel Alekseyevich Cherenkov, the 1958 Nobel Prize winner who was the first to rigorously characterize it. Cerenkov effect image provided by and © the Nuclear Engineering Department of the University of Missouri-Rolla; used by kind permission of Dr. Akira T. Tokuhiro. ... Electromagnetic radiation or EM radiation is a combination (cross product) of oscillating electric and magnetic fields perpendicular to each other, moving through space as a wave, effectively transporting energy and momentum. ... Electric charge is a fundamental FATTY STASHEconserved property of some subatomic particles, which determines their electromagnetic interactions. ... Particles explode from the collision point of two relativistic velocity (100 GeV) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... Insulators are materials which prevent the flow of heat (thermal insulators) or electric charge (electrical insulators). ... Speed (symbol: v) is the rate of motion, or equivalently the rate of change of position, expressed as distance d moved per unit of time t. ... Cherenkov effect in a swimming pool nuclear reactor. ... Nuclear power station at Leibstadt, Switzerland. ... Pavel Alekseyevich Cherenkov (Russian Павел Алексеевич Черенков) (July 28, 1904 - January 6, 1990) was a Soviet physicist and Nobel Prize winner. ... 1958 was a common year starting on Wednesday (link will take you to calendar). ... List of Nobel Prize laureates in Physics from 1901 to the present day. ...

Physical origin

While relativity holds that the speed of light in a vacuum is a universal constant (c), the speed of light in a material may be significantly less than c. For example, the speed of light in water is only 0.75c. Matter can be accelerated beyond this speed during nuclear reactions and in particle accelerators. Cherenkov radiation results when a charged particle, most commonly an electron, exceeds the speed of light in a dielectric medium through which it passes. A simple introduction to this subject is provided in Special relativity for beginners Special relativity (SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein. ... The article on the vacuum cleaner is located elsewhere. ... In science, a physical constant is a physical quantity whose numerical value does not change. ... Water (from the Anglo-Saxon and Low German wæter) is a colourless, tasteless, and odourless substance that is essential to all known forms of life and is the most universal solvent. ... Matter is anything that has mass and occupies space. ... One of the early particle accelerators responsible for development of the atomic bomb. ... Properties The electron (sometimes called negatron; commonly represented as e−) is a subatomic particle. ... The electrons in the molecules shift toward the positively charged left plate. ...

Moreover, the velocity of light that must be exceeded is the phase velocity rather than the group velocity. The phase velocity can be altered dramatically by employing a periodic medium, and in that case one can even achieve Cherenkov radiation with no minimum particle velocity — a phenomenon known as the Smith-Purcell effect. In a more complex periodic medium, such as a photonic crystal, one can also obtain a variety of other anomalous Cherenkov effects, such as radiation in a backwards direction (whereas ordinary Cherenkov radiation forms an acute angle with the particle velocity). The phase velocity of a wave is the rate at which the phase of the wave propagates in space. ... The group velocity of a wave is the velocity with which the overall shape of the waves amplitude (known as the envelope of the wave) propagates through space. ... The Smith-Purcell effect was the precursor of the free electron laser (FEL). ... The opal in this bracelet contains a natural periodic microstructure responsible for its iridescent color. ...

As a charged particle travels, it disrupts the local electromagnetic field in its medium. Electrons in the atoms of the medium will be displaced and polarized by the passing EM field of a charged particle. Photons are emitted as an insulator's electrons restore themselves to equilibrium after the disruption has passed. (In a conductor, the EM disruption can be restored without emitting a photon.) In normal circumstances, these photons destructively interfere with each other and no radiation is detected. However, when the disruption travels faster than the photons themselves travel, the photons constructively interfere and intensify the observed radiation. An electromagnetic field is composed of two related vectorial fields, the electric field and the magnetic field. ... Properties For alternative meanings see atom (disambiguation). ... In physics, the photon (from Greek φοτος, meaning light) is a quantum of excitation of the quantised electromagnetic field and is one of the elementary particles studied by quantum electrodynamics (QED) which is the oldest part of the Standard Model of particle physics. ... For the 2002 science fiction movie see Equilibrium (2002 movie) Equilibrium or balance is any of a number of related phenomena in the natural and social sciences. ... En [ [ ciencia ] ] y [ [ ingeniería ] ], los conductores son los materiales de los cuales contenga las cargas movibles [ [ electricidad ] ]. Cuando una diferencia potencial eléctrica se impresiona a través de puntos separados en un conductor, las cargas móviles dentro del conductor se fuerzan para moverse, y una corriente eléctrica entre esos puntos aparece... Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...

A common analogy is the sonic boom of a supersonic aircraft or bullet. The sound waves generated by the supersonic body do not move fast enough to get out of the way of the body itself. Hence, the waves "stack up" and form a shock front. Similarly, a speed boat generates a large bow shock because it travels faster than waves can move on the surface of the water. When an aircraft breaks the sound barrier, an unusual cloud sometimes forms in its wake. ... Any speed over the speed of sound, which is approximately 343 m/s or 1,087 ft/s or 761 mph or 1,225 km/h at sea level, is said to be supersonic. ... A schematic representation of auditory signaling Sound is vibration, as perceived by the sense of hearing. ... For the vector animation platform, see Macromedia Shockwave. ...

In the same way, a superluminal charged particle generates a photonic shockwave as it travels through an insulator.

The geometry of the Cherenkov radiation.

In the figure, v is the velocity of the particle (red arrow), β is v/c, n is the refractive index of the medium. The blue arrows are photons. So: A fig for the Cherenkov effect. ... A fig for the Cherenkov effect. ... Cherenkov effect in a swimming pool nuclear reactor. ... The refractive index of a material is the factor by which electromagnetic radiation is slowed down (relative to vacuum) when it travels inside the material. ... In physics, the photon (from Greek φοτος, meaning light) is a quantum of excitation of the quantised electromagnetic field and is one of the elementary particles studied by quantum electrodynamics (QED) which is the oldest part of the Standard Model of particle physics. ...

Characteristics

Intuitively, the overall intensity of Cherenkov radiation is proportional to the velocity of the inciting charged particle and to the number of such particles. Unlike fluorescence or emission spectra that have characteristic spectral peaks, Cherenkov radiation is continuous. The relative intensity of one frequency is proportional to the frequency. That is, higher frequencies (shorter wavelengths) are more intense in Cherenkov radiation. This is why visible Cherenkov radiation is observed to be brilliant blue. In fact, most Cherenkov radiation is in the ultraviolet spectrum - it is only with sufficiently accelerated charges that it even becomes visible; the sensitivity of the human eye peaks at green, and is very low in the violet portion of the spectrum. Fluorescence induced by exposure to ultraviolet light in vials containing various sized cadmium selenide (CdSe) quantum dots. ... In optics, stimulated emission is the process by which, when perturbed by a photon, matter may lose energy resulting in the creation of another photon. ... The electromagnetic spectrum encompasses all possible wavelengths of electromagnetic radiation. ... The wavelength is the distance between repeating units of a wave pattern. ... Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region, but longer than that of soft X-rays. ...

As in sonic booms and bow shocks, the angle of the shock cone is inversely related to the velocity of the disruption. Hence, observed angles of incidence can be used to compute the direction and speed of a Cherenkov radiation producing charge. A cone is a basic geometrical shape: see cone (geometry). ...

Uses

Cherenkov radiation is used to detect high-energy charged particles. In pool-type nuclear reactors, the intensity of Cherenkov radiation is related to the frequency of the fission events that produce high-energy electrons, and hence is a measure of the intensity of the reaction. Cherenkov radiation is also used to characterize the remaining radioactivity of spent fuel rods. Sketch of induced nuclear fission, a neutron (n) strikes a uranium nucleus which splits into similar products (F. P.), and releases more neutrons to continue the process, and energy in the form of gamma and other radiation. ... Radioactive decay is the set of various processes by which unstable atomic nuclei (nuclides) emit subatomic particles. ...

When a high-energy cosmic ray impacts the Earth's atmosphere, it can produce an electron-positron pair with enormous velocities. The Cherenkov radiation from these charged particles is used to determine the source and intensity of the cosmic rays. Similar methods are used in very large neutrino detectors, such as the Super-Kamiokande. Cosmic rays can loosely be defined as energetic particles originating outside of the Earth. ... Earths atmosphere is the layer of gases surrounding the planet Earth and retained by the Earths gravity. ... A positron is the antiparticle of the electron. ... Pair production is a nuclear physics process which occurs where a high-energy photon, generally interacting with an atomic nucleus, produces a particle and an antiparticle. ... The neutrino is an elementary particle. ... Super-Kamiokande, or Super-K for short, is a neutrino observatory in Japan. ...

Notes

1. Cherenkov effect image provided by and © the Nuclear Engineering Department (http://www.nuc.umr.edu/index.html) of the University of Missouri-Rolla (http://www.umr.edu/); used by kind permission of Dr. Akira T. Tokuhiro. See http://www.nuc.umr.edu/reactor/reactor.html for the original context.

References

• L. D. Landau, E. M. Liftshitz, and L. P. Pitaevskii, Electrodynamics of Continuous Media (Pergamon: New York, 1984).
• J. V. Jelly, Cerenkov Radiation and Its Applications (Pergamon: London, 1958).
• S. J. Smith and E. M. Purcell, Phys. Rev. 92, 1069 (1953).
• Chiyan Luo, Mihai Ibanescu, Steven G. Johnson, and J. D. Joannopoulos, "Cerenkov Radiation in Photonic Crystals," Science 299, 368–371 (2003).