Liquid hydrogen
Liquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found in the molecular H2 form. To exist as a liquid, H2 must be cooled below hydrogen's critical point of 33 K. However, for hydrogen to be in a liquid state without boiling at atmospheric pressure, it needs to be cooled to 20.28 K. One common method of obtaining liquid hydrogen involves a compressor resembling a jet engine in both appearance and principle. Liquid hydrogen is used as a concentrated form of hydrogen storage; as in any gas, storing it as liquid takes less space than storing it as a gas at normal temperature and pressure. However, the liquid density is low compared to other common fuels. Once liquefied, it can be maintained as a liquid in thermally insulated containers. There are two spin isomers of hydrogen. In 1885, Zygmunt Florenty Wróblewski published hydrogen's critical temperature as 33 K. Hydrogen was liquefied by James Dewar in 1898 by using regenerative cooling and his invention, the vacuum flask; the first synthesis of the stable isomer form of liquid hydrogen, was achieved by Paul Harteck and Karl Friedrich Bonhoeffer in 1929.
The two nuclei in a dihydrogen molecule can have two different spin states. Parahydrogen, in which the two nuclear spins are antiparallel, is more stable than orthohydrogen, in which the two are parallel. At room temperature, gaseous hydrogen is in the ortho isomeric form due to thermal energy, but an ortho-enriched mixture is only metastable when liquified at low temperature, it undergoes an exothermic reaction to become the para isomer, with enough energy released as heat to cause some of the liquid to boil. To prevent loss of the liquid during long-term storage, it is therefore intentionally converted to the para isomer as part of the production process using a catalyst such as iron oxide, activated carbon, platinized asbestos, rare earth metals, uranium compounds, chromium oxide, or some nickel compounds. Liquid hydrogen is a common liquid rocket fuel for rocketry applications — both NASA and the United States Air Force operate a large number of liquid hydrogen tanks with an individual capacity up to 3.8 million liters.
In most rocket engines fueled by liquid hydrogen, it first cools the nozzle and other parts before being mixed with the oxidizer — liquid oxygen — and burned to produce water with traces of ozone and hydrogen peroxide. Practical H2–O2 rocket engines run fuel-rich so that the exhaust contains some unburned hydrogen; this reduces nozzle erosion. It reduces the molecular weight of the exhaust, which can increase specific impulse, despite the incomplete combustion. Liquid hydrogen can be used as the fuel for an internal combustion fuel cell. Various submarines and concept hydrogen vehicles have been built using this form of hydrogen. Due to its similarity, builders can sometimes modify and share equipment with systems designed for liquefied natural gas. However, because of the lower volumetric energy, the hydrogen volumes needed for combustion are large. Unless direct injection is used, a severe gas-displacement effect hampers maximum breathing and increases pumping losses. Liquid hydrogen is used to cool neutrons to be used in neutron scattering.
Since neutrons and hydrogen nuclei have similar masses, kinetic energy exchange per interaction is maximum. Superheated liquid hydrogen was used in many bubble chamber experiments; the first thermonuclear bomb, Ivy Mike, used liquid deuterium, for nuclear fusion. The product of its combustion with oxygen alone is water vapor, which can be cooled with some of the liquid hydrogen. Since water is considered harmless to the environment, an engine burning it can be considered "zero emissions." In aviation, water vapor emitted in the atmosphere contributes to global warming. Liquid hydrogen has a much higher specific energy than gasoline, natural gas, or diesel; the density of liquid hydrogen is only 70.99 g/L, a relative density of just 0.07. Although the specific energy is more than twice that of other fuels, this gives it a remarkably low volumetric energy density, many fold lower. Liquid hydrogen requires cryogenic storage technology such as special thermally insulated containers and requires special handling common to all cryogenic fuels.
This is more severe than liquid oxygen. With thermally insulated containers it is difficult to keep such a low temperature, the hydrogen will leak away, it shares many of the same safety issues as other forms of hydrogen, as well as being cold enough to liquefy, or solidify atmospheric oxygen, which can be an explosion hazard. The triple point of hydrogen is at 13.81 K 7.042 kPa. Due to its cold temperatures, liquid hydrogen is a hazard for cold burns. Apart from that, elemental hydrogen as a liquid is biologically inert and its only human health hazard as a vapor is displacement of oxygen, resulting in asphyxiation; because of its flammability, liquid hydrogen should be kept away from heat or flame unless ignition is intended
Antiproton
The antiproton, p, is the antiparticle of the proton. Antiprotons are stable, but they are short-lived, since any collision with a proton will cause both particles to be annihilated in a burst of energy; the existence of the antiproton with −1 electric charge, opposite to the +1 electric charge of the proton, was predicted by Paul Dirac in his 1933 Nobel Prize lecture. Dirac received the Nobel Prize for his previous 1928 publication of his Dirac equation that predicted the existence of positive and negative solutions to the Energy Equation of Einstein and the existence of the positron, the antimatter analog to the electron, with positive charge and opposite spin; the antiproton was first experimentally confirmed in 1955 at the Bevatron particle accelerator by University of California, Berkeley physicists Emilio Segrè and Owen Chamberlain, for which they were awarded the 1959 Nobel Prize in Physics. In terms of valence quarks, an antiproton consists of two up one down antiquark; the properties of the antiproton that have been measured all match the corresponding properties of the proton, with the exception that the antiproton has electric charge and magnetic moment that are the opposites of those in the proton.
The questions of how matter is different from antimatter, the relevance of antimatter in explaining how our universe survived the Big Bang, remain open problems—open, in part, due to the relative scarcity of antimatter in today's universe. Antiprotons have been detected in cosmic rays for over 25 years, first by balloon-borne experiments and more by satellite-based detectors; the standard picture for their presence in cosmic rays is that they are produced in collisions of cosmic ray protons with nuclei in the interstellar medium, via the reaction, where A represents a nucleus: p + A → p + p + p + A The secondary antiprotons propagate through the galaxy, confined by the galactic magnetic fields. Their energy spectrum is modified by collisions with other atoms in the interstellar medium, antiprotons can be lost by "leaking out" of the galaxy; the antiproton cosmic ray energy spectrum is now measured reliably and is consistent with this standard picture of antiproton production by cosmic ray collisions.
These experimental measurements set upper limits on the number of antiprotons that could be produced in exotic ways, such as from annihilation of supersymmetric dark matter particles in the galaxy or from the Hawking radiation caused by the evaporation of primordial black holes. This provides a lower limit on the antiproton lifetime of about 1-10 million years. Since the galactic storage time of antiprotons is about 10 million years, an intrinsic decay lifetime would modify the galactic residence time and distort the spectrum of cosmic ray antiprotons; this is more stringent than the best laboratory measurements of the antiproton lifetime: LEAR collaboration at CERN: 0.08 years Antihydrogen Penning trap of Gabrielse et al.: 0.28 years APEX collaboration at Fermilab: 50000 years for p → μ− + anything APEX collaboration at Fermilab: 300000 years for p → e− + γThe magnitude of properties of the antiproton are predicted by CPT symmetry to be related to those of the proton. In particular, CPT symmetry predicts the mass and lifetime of the antiproton to be the same as those of the proton, the electric charge and magnetic moment of the antiproton to be opposite in sign and equal in magnitude to those of the proton.
CPT symmetry is a basic consequence of quantum field theory and no violations of it have been detected. BESS: balloon-borne experiment, flown in 1993, 1995, 1997, 2000, 2002, 2004 and 2007. CAPRICE: balloon-borne experiment, flown in 1994 and 1998. HEAT: balloon-borne experiment, flown in 2000. AMS: space-based experiment, prototype flown on the space shuttle in 1998, intended for the International Space Station, launched May 2011. PAMELA: satellite experiment to detect cosmic rays and antimatter from space, launched June 2006. Recent report discovered 28 antiprotons in the South Atlantic Anomaly. Antiprotons were produced at Fermilab for collider physics operations in the Tevatron, where they were collided with protons; the use of antiprotons allows for a higher average energy of collisions between quarks and antiquarks than would be possible in proton-proton collisions. This is because the valence quarks in the proton, the valence antiquarks in the antiproton, tend to carry the largest fraction of the proton or antiproton's momentum.
Their formation requires energy equivalent to a temperature of 10 trillion K and this does not tend to happen naturally. However, at CERN, protons are accelerated in the Proton Synchrotron to an energy of 26 GeV, smashed into an iridium rod; the protons bounce off the iridium nuclei with enough energy for matter to be created. A range of particles and antiparticles are formed, the antiprotons are separated off using magnets in vacuum. In July 2011, the ASACUSA experiment at CERN determined the mass of the antiproton to be 1836.1526736 times more massive than an electron. This is the same as the mass of a proton, within the level of certainty of the experiment. Antiprotons have been shown within laboratory experiments to have the potential to treat certain cancers, in a similar method used for ion therapy; the primary difference between antiproton therapy and proton therapy is that following ion energy deposition the antiproton annihilates depositing additional energy in the cancerous region. In October 2017, scientists working on the BASE experiment at CERN reported a measurement of the antiproton magnetic moment to a precision of 1.5 parts per billion.
It is consiste
Albert Ghiorso
Albert Ghiorso was an American nuclear scientist and co-discoverer of a record 12 chemical elements on the periodic table. His research career spanned six decades, from the early 1940s to the late 1990s. Ghiorso was born in California on July 1915, of Italian and Spanish ancestry, he grew up in California. As a teenager, he built radio circuitry and earned a reputation for establishing radio contacts at distances that outdid the military, he received his BS in electrical engineering from the University of California, Berkeley in 1937. After graduation, he worked for Reginald Tibbets, a prominent amateur radio operator who operated a business supplying radiation detectors to the government. Ghiorso's ability to develop and produce these instruments, as well as a variety of electronic tasks, brought him into contact with the nuclear scientists at the University of California Radiation Laboratory at Berkeley, in particular Glenn Seaborg. During a job in which he was to install an intercom at the lab, he met two secretaries, one of whom married Seaborg.
The other, Wilma Belt, became Albert's wife of 60+ years. Ghiorso was raised in a devout Christian family, but left the religion and became an atheist. However, he still identified with Christian ethics. In the early 1940s, Seaborg moved to Chicago to work on the Manhattan Project, he invited Ghiorso to join him, for the next four years Ghiorso developed sensitive instruments for detecting the radiation associated with nuclear decay, including spontaneous fission. One of Ghiorso's breakthrough instruments was a 48-channel pulse height analyzer, which enabled him to identify the energy, therefore the source, of the radiation. During this time they discovered two new elements, although publication was withheld until after the war. After the war and Ghiorso returned to Berkeley, where they and colleagues used the 60" Crocker cyclotron to produce elements of increasing atomic number by bombarding exotic targets with helium ions. In experiments during 1949-1950, they produced and identified elements 97 and 98.
In 1953, in a collaboration with Argonne Lab and collaborators sought and found elements 99 and 100, identified by their characteristic radiation in dust collected by airplanes from the first thermonuclear explosion. In 1955, the group used the cyclotron to produce 17 atoms of element 101, the first new element to be discovered atom-by-atom; the recoil technique invented by Ghiorso was crucial to obtaining an identifiable signal from individual atoms of the new element. In the mid-1950s it became clear that to extend the periodic chart any further, a new accelerator would be needed, the Berkeley Heavy Ion Linear Accelerator was built, with Ghiorso in charge; that machine was used in the discovery of elements 102-106, each produced and identified on the basis of only a few atoms. The discovery of each successive element was made possible by the development of innovative techniques in robotic target handling, fast chemistry, efficient radiation detectors, computer data processing; the 1972 upgrade of the HILAC to the superHILAC provided higher intensity ion beams, crucial to producing enough new atoms to enable detection of element 106.
With increasing atomic number, the experimental difficulties of producing and identifying a new element increase significantly. In the 1970s and 1980s, resources for new element research at Berkeley were diminishing, but the GSI laboratory at Darmstadt, under the leadership of Peter Armbruster and with considerable resources, was able to produce and identify elements 107-109. In the early 1990s, the Berkeley and Darmstadt groups made a collaborative attempt to create element 110. Experiments at Berkeley were unsuccessful, but elements 110-112 were identified at the Darmstadt laboratory. Subsequent work at the JINR laboratory at Dubna, led by Yuri Oganessian and a Russian-American team of scientists, was successful in identifying elements 113-118, thereby completing the seventh row of the periodic table of the elements. Ghiorso invented numerous techniques and machines for isolating and identifying heavy elements atom-by-atom, he is credited with implementing the multichannel analyzer and the technique of recoil to isolate reaction products, although both of these were significant extensions of understood concepts.
His concept for a new type of accelerator, the Omnitron, is acknowledged to have been a brilliant advance that would have enabled the Berkeley lab to discover numerous additional new elements, but the machine was never built, a victim of the evolving political landscape of the 1970s in the U. S. that de-emphasized basic nuclear research and expanded research on environmental and safety issues. As a result of the failure to build the Omnitron, Ghiorso conceived the joining of the HILAC and the Bevatron, which he called the Bevalac; this combination machine, an ungainly articulation across the steep slope at the Rad Lab, provided heavy ions at GeV energies, thereby enabling development of two new fields of research: "high-energy nuclear physics," meaning that the compound nucleus is sufficiently hot to exhibit collective dynamical effects, heavy ion therapy, in which high-energy ions are used to irradiate tumors in cancer patients. Both of these fields have expanded into acti
Strong focusing
In accelerator physics strong focusing or alternating-gradient focusing is the principle that the net effect on a particle beam of charged particles passing through alternating field gradients is to make the beam converge. By contrast, weak focusing is the principle that nearby circles, described by charged particles moving in a uniform magnetic field, only intersect once per revolution. Earnshaw's theorem shows. However, ridged poles of a cyclotron or two or more spaced quadrupole magnets alternately focus horizontally and vertically. Strong focusing was first conceived by Nicholas Christofilos in 1949 but not published, In 1952, the strong focusing principle was independently developed by Ernest Courant, M. Stanley Livingston, Hartland Snyder and J. Blewett at Brookhaven National Laboratory, who acknowledged the priority of Christofilos' idea; the advantages of strong focusing were quickly realised, deployed on the Alternating Gradient Synchrotron. Courant and Snyder found that the net effect of alternating the field gradient was that both the vertical and horizontal focusing of protons could be made strong at the same time, allowing tight control of proton paths in the machine.
This increased beam intensity while reducing the overall construction cost of a more powerful accelerator. The theory revolutionised cyclotron design and permitted high field strengths to be employed, while massively reducing the size of the magnets needed by minimising the size of the beam. Most particle accelerators today use the strong-focusing principle. Modern systems use multipole magnets, such as quadrupole and sextupole magnets, to focus the beam down, as magnets give a more powerful deflection effect than earlier electrostatic systems at high beam kinetic energies; the multipole magnets refocus the beam after each deflection section, as deflection sections have a defocusing effect that can be countered with a convergent magnet'lens'. This can be shown schematically as a sequence of convergent lenses; the quadrupoles are laid out in what are called FODO patterns. Following the beam particles in their trajectories through the focusing arrangement, an oscillating pattern would be seen; the action upon a set of charged particles by a set of linear magnets can be expressed as matrices which can be multiplied together to give their net effect, using ray transfer matrix analysis.
Higher-order terms such as sextupoles, octupoles etc. may be treated by a variety of methods, depending on the phenomena of interest. Electron gun – uses cylindrical symmetric fields such as provided by a Wehnelt cylinder to focus an electron beam Maglev – has been a suggested use of strong focusing Quadrupole magnet Sextupole magnet Nicholas Christofilos – the scientist who first conceived strong focusing Lawrence Berkeley National Laboratory: World of Beams
Emilio Segrè
Emilio Gino Segrè was an Italian-American physicist and Nobel laureate, who discovered the elements technetium and astatine, the antiproton, a subatomic antiparticle, for which he was awarded the Nobel Prize in Physics in 1959. From 1943 to 1946 he worked at the Los Alamos National Laboratory as a group leader for the Manhattan Project, he found in April 1944 that Thin Man, the proposed plutonium gun-type nuclear weapon, would not work because of the presence of plutonium-240 impurities. Born in Tivoli, near Rome, Segrè studied engineering at the University of Rome La Sapienza before taking up physics in 1927. Segrè was appointed assistant professor of physics at the University of Rome in 1932 and worked there until 1936, becoming one of the Via Panisperna boys. From 1936 to 1938 he was director of the Physics Laboratory at the University of Palermo. After a visit to Ernest O. Lawrence's Berkeley Radiation Laboratory, he was sent a molybdenum strip from the laboratory's cyclotron deflector in 1937, emitting anomalous forms of radioactivity.
After careful chemical and theoretical analysis, Segrè was able to prove that some of the radiation was being produced by a unknown element, named technetium, the first artificially synthesized chemical element that does not occur in nature. In 1938, Benito Mussolini's fascist government passed anti-Semitic laws barring Jews from university positions; as a Jew, Segrè was now rendered an indefinite émigré. At the Berkeley Radiation Lab, Lawrence offered him a job as a research assistant. While at Berkeley, Segrè helped discover the element astatine and the isotope plutonium-239, used to make the Fat Man nuclear bomb dropped on Nagasaki. In 1944, he became a naturalized citizen of the United States. On his return to Berkeley in 1946, he became a professor of physics and of history of science, serving until 1972. Segrè and Owen Chamberlain were co-heads of a research group at the Lawrence Radiation Laboratory that discovered the antiproton, for which the two shared the 1959 Nobel Prize in Physics.
Segrè was active as a photographer and took many photos documenting events and people in the history of modern science, which were donated to the American Institute of Physics after his death. The American Institute of Physics named its photographic archive of physics history in his honor. Emilio Gino Segrè was born into a Sephardic Jewish family in Tivoli, near Rome, on 1 February 1905, the son of Giuseppe Segrè, a businessman who owned a paper mill, Amelia Susanna Treves, he had two older brothers and Marco. His uncle, Gino Segrè, was a law professor, he was educated at the ginnasio in Tivoli and, after the family moved to Rome in 1917, the ginnasio and liceo in Rome. He graduated in July 1922 and enrolled in the University of Rome La Sapienza as an engineering student. In 1927, Segrè met Franco Rasetti; the two young physics professors were looking for talented students. They attended the Volta Conference at Como in September 1927, where Segrè heard lectures from notable physicists including Niels Bohr, Werner Heisenberg, Robert Millikan, Wolfgang Pauli, Max Planck and Ernest Rutherford.
Segrè joined Fermi and Rasetti at their laboratory in Rome. With the help of the director of the Institute of Physics, Orso Mario Corbino, Segrè was able to transfer to physics, studying under Fermi, earned his laurea degree in July 1928, with a thesis on "Anomalous Dispersion and Magnetic Rotation". After a stint in the Italian Army from 1928 to 1929, during which he was a commissioned as a second lieutenant in the antiaircraft artillery, Segrè returned to the laboratory on Via Panisperna, he published his first article, which summarised his thesis, "On anomalous dispersion in mercury and in lithium", jointly with Edoardo Amaldi in 1928, another article with him the following year on the Raman effect. In 1930, Segrè began studying the Zeeman effect in certain alkaline metals; when his progress stalled because the diffraction grating he required to continue was not available in Italy, he wrote to four laboratories elsewhere in Europe asking for assistance and received an invitation from Pieter Zeeman to finish his work at Zeeman's laboratory in Amsterdam.
Segrè was awarded a Rockefeller Foundation fellowship and, on Fermi's advice, elected to use it to study under Otto Stern in Hamburg. Working with Otto Frisch on space quantization produced results that did not agree with the current theory. Segrè was appointed assistant professor of physics at the University of Rome in 1932 and worked there until 1936, becoming one of the Via Panisperna boys. In 1934, he met Elfriede Spiro, a Jewish woman whose family had come from Ostrowo in West Prussia, but had fled to Breslau when that part of Prussia became part of Poland after World War I. After the Nazi Party came to power in Germany in 1933, she had emigrated to Italy, where she worked as a secretary and an interpreter. At first she did not speak Italian well, Segrè and Spiro conversed in German, in which he was fluent; the two were married at the Great Synagogue of Rome on 2 February 1936. He agreed with the rabbi to spend the minimal amount on the wedding, giving the balance of what would be spent on a luxury wedding to Jewish refugees from Germany.
The rabbi managed to give them many of the trappings of a luxury wedding anyway. The couple had three children: Claudio, born in 1937, Amelia Gertrude Allegra, born in 1937, Fausta Irene, born in 1945. After marrying, Segrè sought a stable job and became professor of physics and director of the Physics Institute at the University of Palermo, he found the equipment there primitive and the library bereft o
Proton
A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and a mass less than that of a neutron. Protons and neutrons, each with masses of one atomic mass unit, are collectively referred to as "nucleons". One or more protons are present in the nucleus of every atom; the number of protons in the nucleus is the defining property of an element, is referred to as the atomic number. Since each element has a unique number of protons, each element has its own unique atomic number; the word proton is Greek for "first", this name was given to the hydrogen nucleus by Ernest Rutherford in 1920. In previous years, Rutherford had discovered that the hydrogen nucleus could be extracted from the nuclei of nitrogen by atomic collisions. Protons were therefore a candidate to be a fundamental particle, hence a building block of nitrogen and all other heavier atomic nuclei. In the modern Standard Model of particle physics, protons are hadrons, like neutrons, the other nucleon, are composed of three quarks.
Although protons were considered fundamental or elementary particles, they are now known to be composed of three valence quarks: two up quarks of charge +2/3e and one down quark of charge –1/3e. The rest masses of quarks contribute only about 1% of a proton's mass, however; the remainder of a proton's mass is due to quantum chromodynamics binding energy, which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together. Because protons are not fundamental particles, they possess a physical size, though not a definite one. At sufficiently low temperatures, free protons will bind to electrons. However, the character of such bound protons does not change, they remain protons. A fast proton moving through matter will slow by interactions with electrons and nuclei, until it is captured by the electron cloud of an atom; the result is a protonated atom, a chemical compound of hydrogen. In vacuum, when free electrons are present, a sufficiently slow proton may pick up a single free electron, becoming a neutral hydrogen atom, chemically a free radical.
Such "free hydrogen atoms" tend to react chemically with many other types of atoms at sufficiently low energies. When free hydrogen atoms react with each other, they form neutral hydrogen molecules, which are the most common molecular component of molecular clouds in interstellar space. Protons are composed of three valence quarks, making them baryons; the two up quarks and one down quark of a proton are held together by the strong force, mediated by gluons. A modern perspective has a proton composed of the valence quarks, the gluons, transitory pairs of sea quarks. Protons have a positive charge distribution which decays exponentially, with a mean square radius of about 0.8 fm. Protons and neutrons are both nucleons, which may be bound together by the nuclear force to form atomic nuclei; the nucleus of the most common isotope of the hydrogen atom is a lone proton. The nuclei of the heavy hydrogen isotopes deuterium and tritium contain one proton bound to one and two neutrons, respectively. All other types of atomic nuclei are composed of two or more protons and various numbers of neutrons.
The concept of a hydrogen-like particle as a constituent of other atoms was developed over a long period. As early as 1815, William Prout proposed that all atoms are composed of hydrogen atoms, based on a simplistic interpretation of early values of atomic weights, disproved when more accurate values were measured. In 1886, Eugen Goldstein discovered canal rays and showed that they were positively charged particles produced from gases. However, since particles from different gases had different values of charge-to-mass ratio, they could not be identified with a single particle, unlike the negative electrons discovered by J. J. Thomson. Wilhelm Wien in 1898 identified the hydrogen ion as particle with highest charge-to-mass ratio in ionized gases. Following the discovery of the atomic nucleus by Ernest Rutherford in 1911, Antonius van den Broek proposed that the place of each element in the periodic table is equal to its nuclear charge; this was confirmed experimentally by Henry Moseley in 1913 using X-ray spectra.
In 1917, Rutherford proved that the hydrogen nucleus is present in other nuclei, a result described as the discovery of protons. Rutherford had earlier learned to produce hydrogen nuclei as a type of radiation produced as a product of the impact of alpha particles on nitrogen gas, recognize them by their unique penetration signature in air and their appearance in scintillation detectors; these experiments were begun when Rutherford had noticed that, when alpha particles were shot into air, his scintillation detectors showed the signatures of typical hydrogen nuclei as a product. After experimentation Rutherford traced the reaction to the nitrogen in air, found that when alphas were produced into pure nitrogen gas, the effect was larger. Rutherford determined that this hydrogen could have come only from the nitrogen, therefore nitrogen must contain hydrogen nuclei. One hydrogen nucleus was being knocked off by the impact of the alpha particle, producing oxygen-17 in the process; this was 14N + α → 17O + p.
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Electronvolt
In physics, the electronvolt is a unit of energy equal to 1.6×10−19 joules in SI units. The electronvolt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences, because a particle with electric charge q has an energy E = qV after passing through the potential V. Like the elementary charge on which it is based, it is not an independent quantity but is equal to 1 J/C √2hα / μ0c0, it is a common unit of energy within physics used in solid state, atomic and particle physics. It is used with the metric prefixes milli-, kilo-, mega-, giga-, tera-, peta- or exa-. In some older documents, in the name Bevatron, the symbol BeV is used, which stands for billion electronvolts. An electronvolt is the amount of kinetic energy gained or lost by a single electron accelerating from rest through an electric potential difference of one volt in vacuum. Hence, it has a value of one volt, 1 J/C, multiplied by the electron's elementary charge e, 1.6021766208×10−19 C.
Therefore, one electronvolt is equal to 1.6021766208×10−19 J. The electronvolt, as opposed to volt, is not an SI unit, its derivation is empirical, which means its value in SI units must be obtained by experiment and is therefore not known unlike the litre, the light-year and such other non-SI units. Electronvolt is a unit of energy; the SI unit for energy is joule. 1 eV is equal to 1.6021766208×10−19 J. By mass–energy equivalence, the electronvolt is a unit of mass, it is common in particle physics, where units of mass and energy are interchanged, to express mass in units of eV/c2, where c is the speed of light in vacuum. It is common to express mass in terms of "eV" as a unit of mass using a system of natural units with c set to 1; the mass equivalent of 1 eV/c2 is 1 eV / c 2 = ⋅ 1 V 2 = 1.783 × 10 − 36 kg. For example, an electron and a positron, each with a mass of 0.511 MeV/c2, can annihilate to yield 1.022 MeV of energy. The proton has a mass of 0.938 GeV/c2. In general, the masses of all hadrons are of the order of 1 GeV/c2, which makes the GeV a convenient unit of mass for particle physics: 1 GeV/c2 = 1.783×10−27 kg.
The unified atomic mass unit, 1 gram divided by Avogadro's number, is the mass of a hydrogen atom, the mass of the proton. To convert to megaelectronvolts, use the formula: 1 u = 931.4941 MeV/c2 = 0.9314941 GeV/c2. In high-energy physics, the electronvolt is used as a unit of momentum. A potential difference of 1 volt causes an electron to gain an amount of energy; this gives rise to usage of eV as units of momentum, for the energy supplied results in acceleration of the particle. The dimensions of momentum units are LMT−1; the dimensions of energy units are L2MT−2. Dividing the units of energy by a fundamental constant that has units of velocity, facilitates the required conversion of using energy units to describe momentum. In the field of high-energy particle physics, the fundamental velocity unit is the speed of light in vacuum c. By dividing energy in eV by the speed of light, one can describe the momentum of an electron in units of eV/c; the fundamental velocity constant c is dropped from the units of momentum by way of defining units of length such that the value of c is unity.
For example, if the momentum p of an electron is said to be 1 GeV the conversion to MKS can be achieved by: p = 1 GeV / c = ⋅ ⋅ = 5.344286 × 10 − 19 kg ⋅ m / s. In particle physics, a system of "natural units" in which the speed of light in vacuum c and the reduced Planck constant ħ are dimensionless and equal to unity is used: c = ħ = 1. In these units, both distances and times are expressed in inverse energy units (while energy and mass are expressed in the same units, see mas
