Friday, September 3, 2021

Cherenkov Effect: Technically it is Faster than Light

The Science Loop Channel on Youtube has another interesting science video for you. It is about the Cherenkov Effect.

Technically, this is a photonic boom. Don't get excited here! This is called the Cherenkov effect. When a charged particle goes faster than the speed of light in a medium it creates this gorgeous blue light. In a medium Light travel a little bit slower than the vacuum. So other particles can go faster without violating relativity.

Particle physics (also known as high energy physics) is really a branch of physics that studies the nature of the particles that constitute matter and radiation.

The Cherenkov effect occurs when a particle carrying an electric charge travels through a transparent medium like water or air. If the particle travels faster than light in this medium, its passage causes a brief flash of light, a Cherenkov light. Very high speeds are impressive.

Cherenkov (Russian: Черенков) radiation  is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium at a speed greater than the phase velocity (speed of propagation of a wave in a medium) of light in that medium. Special relativity is not violated since light travels slower in materials with refractive index greater than one, and it is the speed of light in vacuum which cannot be exceeded (or reached) by particles with mass. A classic example of Cherenkov radiation is really the characteristic blue glow of an underwater nuclear reactor. Its cause is similar to the cause of a sonic boom, the sharp sound heard when faster-than-sound movement occurs. The phenomenon is named for Soviet physicist Pavel Cherenkov, who shared the 1958 Nobel Prize in Physics for its discovery.

The so-called Frank-Tamm formula yields the amount of Cherenkov radiation emitted on a given frequency as a charged particle moves through a medium at superluminal velocity. It is named for Russian physicists Ilya Frank and Igor Tamm who developed the theory of the Cherenkov effect in 1937, for which they were awarded a Nobel Prize in Physics in 1958.

When a so-called charged particle moves faster than the phase speed of light in a medium, electrons interacting with the particle can emit coherent photons while conserving energy and momentum. This process can be viewed as a decay. See Cherenkov radiation and nonradiation condition for an explanation of this effect.

The History of Radiation Discoveries is interesting. This is really one of various effects of radiation. This radiation effect is named after the Soviet scientist Pavel Cherenkov, the 1958 Nobel Prize winner, who was the first to detect it experimentally under the supervision of Sergey Vavilov at the Lebedev Institute in 1934. Therefore, it is also known as Vavilov-Cherenkov radiation. Cherenkov saw a faint bluish light around a radioactive preparation in water during experiments. His doctorate thesis was on luminescence of uranium salt solutions that were excited by gamma rays instead of less energetic visible light, as done commonly. He discovered the anisotropy of the radiation and came to the conclusion that the bluish glow was not a fluorescent phenomenon.

"Fluorescence" is the ability of certain chemicals to give off visible light after absorbing radiation which is not normally visible, such as ultraviolet light.

"Anisotropy" is the property of being directionally dependent, as opposed to isotropy, which means homogeneity in all directions. It can be defined as a difference in the physical property of a certain material when measured along different axes. Anisotropy in ultrasound examination is an angle-generated artifact.

Cherenkov Effect: a theory of this certain effect was later developed in 1937 within the framework of Einstein's special relativity theory by Cherenkov's colleagues Igor Tamm and Ilya Frank, who also shared the 1958 Nobel Prize.

Cherenkov radiation as conical wave front had been theoretically predicted by the English polymath Oliver Heaviside in papers published between 1888 and 1889 and by Arnold Sommerfeld in 1904, but both had been quickly forgotten following the relativity theory's restriction of super-c particles until the 1970s. Marie Curie observed a pale blue light in a highly concentrated radium solution in 1910, but did not investigate its source. In 1926, the French radiotherapist Lucien Mallet described the luminous radiation of radium irradiating water having a continuous spectrum.

In 2019, a team of researchers from Dartmouth’s and Dartmouth-Hitchcock's Norris Cotton Cancer Center discovered Cherenkov light being generated in the vitreous humor of patients undergoing radiotherapy. The light was observed using a camera imaging system called a CDose, which is specially designed to view light emissions from biological systems. For decades, patients had reported phenomena such as "flashes of bright or blue light" when receiving radiation treatments for brain cancer, but the effects had never been experimentally observed.

There is also something called "Reverse Cherenkov effect." A reverse Cherenkov effect can be experienced using materials called negative-index metamaterials (materials with a subwavelength microstructure that gives them an effective "average" property very different from their constituent materials, in this case having negative permittivity and negative permeability). This means that, when a charged particle (usually electrons) passes through a medium at a speed greater than the phase velocity of light in that medium, that particle emits trailing radiation from its progress through the medium rather than in front of it (as is the case in normal materials with, both permittivity and permeability positive). One can also obtain such reverse-cone Cherenkov radiation in non-metamaterial periodic media where the periodic structure is on the same scale as the wavelength, so it cannot be treated as an effectively homogeneous metamaterial.

Cherenkov radiation has many uses, such as:

Detection of labelled biomolecules
Medical imaging of radioisotopes and external beam radiotherapy
Nuclear reactors
Cherenkov radiation in a TRIGA reactor pool
Astrophysics experiments
Particle physics experiments

There are 2 kinds of radiation: non-ionizing radiation and ionizing radiation. Non-ionizing radiation has enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to remove electrons from atoms. Examples of this kind of radiation are radio waves, visible light and microwaves.

Radiation can also be put into these 7 types of radiation:

The electromagnetic spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared, optical, ultraviolet, X-rays, and gamma-rays.

Radiation is energy that comes from a source and travels through space and may be able to penetrate various materials. Light, radio, and microwaves are types of radiation that are called nonionizing. Gamma radiation and x rays are examples of electromagnetic radiation.

Exposure to very high levels of radiation, such as being close to an atomic blast, can cause acute health effects such as skin burns and acute radiation syndrome (radiation sickness). It can also result in long-term health effects such as cancer and cardiovascular disease.

All modern communication systems use forms of electromagnetic radiation. Variations in the intensity of the radiation represent changes in the sound, pictures, or other information being transmitted. For example, a human voice can be sent as a radio wave or microwave by making the wave vary to corresponding variations in the voice. Musicians have also experimented with gamma rays sonification, or using nuclear radiation, to produce sound and music.

Researchers use radioactive atoms to determine the age of materials that were once part of a living organism. The age of such materials can be estimated by measuring the amount of radioactive carbon they contain in a process called radiocarbon dating. Similarly, using other radioactive elements, the age of rocks and other geological features (even some man-made objects) can be determined; this is called Radiometric dating. Environmental scientists use radioactive atoms, known as tracer atoms, to identify the pathways taken by pollutants through the environment.

Radiation is used to determine the composition of materials in a process called neutron activation analysis. In this process, scientists bombard a sample of a substance with particles called neutrons. Some of the atoms in the sample absorb neutrons and become radioactive. The scientists can identify the elements in the sample by studying the emitted radiation.

Some other Radiation Effects:

Askaryan Effect

Bremsstrahlung (from bremsen "to brake" and Strahlung "radiation"; i.e., "braking radiation" or "deceleration radiation")

Radioluminescence is the phenomenon by which light is produced in a material by bombardment with ionizing radiation such as alpha particles, beta particles, or gamma rays.

A tachyon or tachyonic particle is a hypothetical particle that always travels faster than light.

Transition Radiation (TR) is a form of electromagnetic radiation emitted when a charged particle passes through inhomogeneous media, such as a boundary between 2 certain different media. This is in contrast to Cherenkov radiation, which occurs when a charged particle passes through a homogeneous dielectric medium at a speed greater than the phase velocity of electromagnetic waves in that medium.

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