Uranium is a chemical element with symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 electrons, of which 6 are valence electrons. Uranium is weakly radioactive because all isotopes of uranium are unstable, with half-lives varying between 159,200 years and 4.5 billion years. The most common isotopes in natural uranium are uranium-238 and uranium-235. Uranium has the highest atomic weight of the primordially occurring elements, its density is about 70% higher than that of lead, lower than that of gold or tungsten. It occurs in low concentrations of a few parts per million in soil and water, is commercially extracted from uranium-bearing minerals such as uraninite. In nature, uranium is found as uranium-238, uranium-235, a small amount of uranium-234. Uranium decays by emitting an alpha particle; the half-life of uranium-238 is about 4.47 billion years and that of uranium-235 is 704 million years, making them useful in dating the age of the Earth.
Many contemporary uses of uranium exploit its unique nuclear properties. Uranium-235 is the only occurring fissile isotope, which makes it used in nuclear power plants and nuclear weapons. However, because of the tiny amounts found in nature, uranium needs to undergo enrichment so that enough uranium-235 is present. Uranium-238 is fissionable by fast neutrons, is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor. Another fissile isotope, uranium-233, can be produced from natural thorium and is important in nuclear technology. Uranium-238 has a small probability for spontaneous fission or induced fission with fast neutrons. In sufficient concentration, these isotopes maintain a sustained nuclear chain reaction; this generates the heat in nuclear power reactors, produces the fissile material for nuclear weapons. Depleted uranium is used in kinetic energy penetrators and armor plating. Uranium is used as a colorant in uranium glass. Uranium glass fluoresces green in ultraviolet light.
It was used for tinting and shading in early photography. The 1789 discovery of uranium in the mineral pitchblende is credited to Martin Heinrich Klaproth, who named the new element after the discovered planet Uranus. Eugène-Melchior Péligot was the first person to isolate the metal and its radioactive properties were discovered in 1896 by Henri Becquerel. Research by Otto Hahn, Lise Meitner, Enrico Fermi and others, such as J. Robert Oppenheimer starting in 1934 led to its use as a fuel in the nuclear power industry and in Little Boy, the first nuclear weapon used in war. An ensuing arms race during the Cold War between the United States and the Soviet Union produced tens of thousands of nuclear weapons that used uranium metal and uranium-derived plutonium-239; the security of those weapons and their fissile material following the breakup of the Soviet Union in 1991 is an ongoing concern for public health and safety. See Nuclear proliferation; when refined, uranium is a weakly radioactive metal.
It has a Mohs hardness of 6, sufficient to scratch glass and equal to that of titanium, rhodium and niobium. It is malleable, ductile paramagnetic electropositive and a poor electrical conductor. Uranium metal has a high density of 19.1 g/cm3, denser than lead, but less dense than tungsten and gold. Uranium metal reacts with all non-metal elements and their compounds, with reactivity increasing with temperature. Hydrochloric and nitric acids dissolve uranium, but non-oxidizing acids other than hydrochloric acid attack the element slowly; when finely divided, it can react with cold water. Uranium in ores is extracted chemically and converted into uranium dioxide or other chemical forms usable in industry. Uranium-235 was the first isotope, found to be fissile. Other occurring isotopes are fissionable, but not fissile. On bombardment with slow neutrons, its uranium-235 isotope will most of the time divide into two smaller nuclei, releasing nuclear binding energy and more neutrons. If too many of these neutrons are absorbed by other uranium-235 nuclei, a nuclear chain reaction occurs that results in a burst of heat or an explosion.
In a nuclear reactor, such a chain reaction is slowed and controlled by a neutron poison, absorbing some of the free neutrons. Such neutron absorbent materials are part of reactor control rods; as little as 15 lb of uranium-235 can be used to make an atomic bomb. The first nuclear bomb used in war, Little Boy, relied on uranium fission, but the first nuclear explosive and the bomb that destroyed Nagasaki were both plutonium bombs. Uranium metal has three allotropic forms: α stable up to 668 °C. Orthorhombic, space group No. 63, lattice parameters a = 285.4 pm, b = 587 pm, c = 495.5 pm. Β stable from 668 °C to 775 °C. Tetragonal, space group P42/mnm, P42nm, or P4n2, lattice parameters a = 565.6 pm, b = c = 1075.9 pm. Γ from 775 °C to melting point—this is the most malleable and ductile state. Body-centered cubic, lattice parameter a = 352.4 pm. The major application of uranium in the military sector is
Large Hadron Collider
The Large Hadron Collider is the world's largest and most powerful particle collider and the largest machine in the world. It was built by the European Organization for Nuclear Research between 1998 and 2008 in collaboration with over 10,000 scientists and hundreds of universities and laboratories, as well as more than 100 countries, it lies in a tunnel 27 kilometres in circumference and as deep as 175 metres beneath the France–Switzerland border near Geneva. First collisions were achieved in 2010 at an energy of 3.5 teraelectronvolts per beam, about four times the previous world record. After upgrades it reached 6.5 TeV per beam. At the end of 2018, it entered a two-year shutdown period for further upgrades; the collider has four crossing points, around which are positioned seven detectors, each designed for certain kinds of research. The LHC collides proton beams, but it can use beams of heavy ions: Lead–lead collisions and proton-lead collisions are done for one month per year; the aim of the LHC's detectors is to allow physicists to test the predictions of different theories of particle physics, including measuring the properties of the Higgs boson and searching for the large family of new particles predicted by supersymmetric theories, as well as other unsolved questions of physics.
The term hadron refers to composite particles composed of quarks held together by the strong force. The best-known hadrons are the baryons such as neutrons. A collider is a type of a particle accelerator with two directed beams of particles. In particle physics, colliders are used as a research tool: they accelerate particles to high kinetic energies and let them impact other particles. Analysis of the byproducts of these collisions gives scientists good evidence of the structure of the subatomic world and the laws of nature governing it. Many of these byproducts are produced only by high-energy collisions, they decay after short periods of time, thus many of them are nearly impossible to study in other ways. Physicists hope that the Large Hadron Collider will help answer some of the fundamental open questions in physics, concerning the basic laws governing the interactions and forces among the elementary objects, the deep structure of space and time, in particular the interrelation between quantum mechanics and general relativity.
Data are needed from high-energy particle experiments to suggest which versions of current scientific models are more to be correct – in particular to choose between the Standard Model and Higgsless model and to validate their predictions and allow further theoretical development. Many theorists expect new physics beyond the Standard Model to emerge at the TeV energy level, as the Standard Model appears to be unsatisfactory. Issues explored by LHC collisions include: is the mass of elementary particles being generated by the Higgs mechanism via electroweak symmetry breaking? It was expected that the collider experiments will either demonstrate or rule out the existence of the elusive Higgs boson, thereby allowing physicists to consider whether the Standard Model or its Higgsless alternatives are more to be correct. Is supersymmetry, an extension of the Standard Model and Poincaré symmetry, realized in nature, implying that all known particles have supersymmetric partners? Are there extra dimensions, as predicted by various models based on string theory, can we detect them?
What is the nature of the dark matter that appears to account for 27% of the mass-energy of the universe? Other open questions that may be explored using high-energy particle collisions: It is known that electromagnetism and the weak nuclear force are different manifestations of a single force called the electroweak force; the LHC may clarify whether the electroweak force and the strong nuclear force are just different manifestations of one universal unified force, as predicted by various Grand Unification Theories. Why is the fourth fundamental force so many orders of magnitude weaker than the other three fundamental forces? See Hierarchy problem. Are there additional sources of quark flavour mixing, beyond those present within the Standard Model? Why are there apparent violations of the symmetry between matter and antimatter? See CP violation. What are the nature and properties of quark–gluon plasma, thought to have existed in the early universe and in certain compact and strange astronomical objects today?
This will be investigated by heavy ion collisions in ALICE, but in CMS, ATLAS and LHCb. First observed in 2010, findings published in 2012 confirmed the phenomenon of jet quenching in heavy-ion collisions; the LHC is the world's largest and highest-energy particle accelerator. The collider is contained in a circular tunnel, with a circumference of 26.7 kilometres, at a depth ranging from 50 to 175 metres underground. The 3.8-metre wide concrete-lined tunnel, constructed between 1983 and 1988, was used to house the Large Electron–Positron Collider. It crosses the border between Switzerland and France with most of it in France. Surface buildings hold ancillary equipment such as compressors, ventilation equipment, control electronics and refrigeration plants; the collider tunnel contains two adjacent parallel beamlines each containing a beam, which travel in opposite directions around the ring. The beams intersect at four points around the ring, where the particle collisio
Nuclear magnetic resonance
Nuclear magnetic resonance is a physical phenomenon in which nuclei in a strong static magnetic field are perturbed by a weak oscillating magnetic field and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at the nucleus. This process occurs near resonance, when the oscillation frequency matches the intrinsic frequency of the nuclei, which depends on the strength of the static magnetic field, the chemical environment, the magnetic properties of the isotope involved. NMR results from specific magnetic properties of certain atomic nuclei. Nuclear magnetic resonance spectroscopy is used to determine the structure of organic molecules in solution and study molecular physics, crystals as well as non-crystalline materials. NMR is routinely used in advanced medical imaging techniques, such as in magnetic resonance imaging. All isotopes that contain an odd number of protons and/or neutrons have an intrinsic nuclear magnetic moment and angular momentum, in other words a nonzero nuclear spin, while all nuclides with numbers of both have a total spin of zero.
The most used nuclei are 1H and 13C, although isotopes of many other elements can be studied by high-field NMR spectroscopy as well. A key feature of NMR is that the resonance frequency of a particular simple substance is directly proportional to the strength of the applied magnetic field, it is this feature, exploited in imaging techniques. Since the resolution of the imaging technique depends on the magnitude of the magnetic field gradient, many efforts are made to develop increased gradient field strength; the principle of NMR involves three sequential steps: The alignment of the magnetic nuclear spins in an applied, constant magnetic field B0. The perturbation of this alignment of the nuclear spins by a weak oscillating magnetic field referred to as a radio-frequency pulse; the oscillation frequency required for significant perturbation is dependent upon the static magnetic field and the nuclei of observation. The detection of the NMR signal during or after the RF pulse, due to the voltage induced in a detection coil by precession of the nuclear spins around B0.
After an RF pulse, precession occurs with the nuclei's intrinsic Larmor frequency and, in itself, does not involve transitions between spin states or energy levels. The two magnetic fields are chosen to be perpendicular to each other as this maximizes the NMR signal strength; the frequencies of the time-signal response by the total magnetization of the nuclear spins are analyzed in NMR spectroscopy and magnetic resonance imaging. Both use applied magnetic fields of great strength produced by large currents in superconducting coils, in order to achieve dispersion of response frequencies and of high homogeneity and stability in order to deliver spectral resolution, the details of which are described by chemical shifts, the Zeeman effect, Knight shifts; the information provided by NMR can be increased using hyperpolarization, and/or using two-dimensional, three-dimensional and higher-dimensional techniques. NMR phenomena are utilized in low-field NMR, NMR spectroscopy and MRI in the Earth's magnetic field, in several types of magnetometers.
Nuclear magnetic resonance was first described and measured in molecular beams by Isidor Rabi in 1938, by extending the Stern–Gerlach experiment, in 1944, Rabi was awarded the Nobel Prize in Physics for this work. In 1946, Felix Bloch and Edward Mills Purcell expanded the technique for use on liquids and solids, for which they shared the Nobel Prize in Physics in 1952. Yevgeny Zavoisky observed nuclear magnetic resonance in 1941, well before Felix Bloch and Edward Mills Purcell, but dismissed the results as not reproducible. Russell H. Varian filed the "Method and means for correlating nuclear properties of atoms and magnetic fields", U. S. Patent 2,561,490 on July 24, 1951. Varian Associates developed the first NMR unit called NMR HR-30 in 1952. Purcell had worked on the development of radar during World War II at the Massachusetts Institute of Technology's Radiation Laboratory, his work during that project on the production and detection of radio frequency power and on the absorption of such RF power by matter laid the foundation for his discovery of NMR in bulk matter.
Rabi and Purcell observed that magnetic nuclei, like 1H and 31P, could absorb RF energy when placed in a magnetic field and when the RF was of a frequency specific to the identity of the nuclei. When this absorption occurs, the nucleus is described as being in resonance. Different atomic nuclei within a molecule resonate at different frequencies for the same magnetic field strength; the observation of such magnetic resonance frequencies of the nuclei present in a molecule allows any trained user to discover essential chemical and structural information about the molecule. The development of NMR as a technique in analytical chemistry and biochemistry parallels the development of electromagnetic technology and advanced electronics and their introduction into civilian use. All nucleons, neutrons and protons, composing any atomic nucleus, have the intrinsic quantum property of spin, an intrinsic angular momentum analogous to the classical angular momentum of a spinning sphere; the overall spin of the nucleus is determined b
Compact Muon Solenoid
The Compact Muon Solenoid experiment is one of two large general-purpose particle physics detectors built on the Large Hadron Collider at CERN in Switzerland and France. The goal of CMS experiment is to investigate a wide range of physics, including the search for the Higgs boson, extra dimensions, particles that could make up dark matter. CMS is 21.6 metres long, 15 m in diameter, weighs about 14,000 tonnes. 3,800 people, representing 199 scientific institutes and 43 countries, form the CMS collaboration who built and now operate the detector. It is located in an underground cavern at Cessy in France, just across the border from Geneva. In July 2012, along with ATLAS, CMS tentatively discovered the Higgs boson.. By March 2013 its existence was confirmed. Recent collider experiments such as the now-dismantled Large Electron-Positron Collider and the newly renovated Large Hadron Collider at CERN, as well as the closed Tevatron at Fermilab have provided remarkable insights into, precision tests of, the Standard Model of Particle Physics.
A principle achievement of these experiments is the discovery of a particle consistent with the Standard Model Higgs boson, the particle resulting from the Higgs mechanism, which provides an explanation for the masses of elementary particles. However, there are still many questions; these include uncertainties in the mathematical behaviour of the Standard Model at high energies, tests of proposed theories of dark matter, the reasons for the imbalance of matter and antimatter observed in the Universe. The main goals of the experiment are: to explore physics at the TeV scale to further study the properties of the Higgs boson discovered by CMS and ATLAS to look for evidence of physics beyond the standard model, such as supersymmetry, or extra dimensions to study aspects of heavy ion collisions; the ATLAS experiment, at the other side of the LHC ring is designed with similar goals in mind, the two experiments are designed to complement each other both to extend reach and to provide corroboration of findings.
CMS and ATLAS uses different technical solutions and design of its detector magnet system to achieve the goals. CMS is designed as a general-purpose detector, capable of studying many aspects of proton collisions at 0.9-13 TeV, the center-of-mass energy of the LHC particle accelerator. The CMS detector is built around a huge solenoid magnet; this takes the form of a cylindrical coil of superconducting cable that generates a magnetic field of 4 teslas, about 100 000 times that of the Earth. The magnetic field is confined by a steel'yoke' that forms the bulk of the detector's weight of 12 500 tonnes. An unusual feature of the CMS detector is that instead of being built in-situ underground, like the other giant detectors of the LHC experiments, it was constructed on the surface, before being lowered underground in 15 sections and reassembled, it contains subsystems which are designed to measure the energy and momentum of photons, electrons and other products of the collisions. The innermost layer is a silicon-based tracker.
Surrounding it is a scintillating crystal electromagnetic calorimeter, itself surrounded with a sampling calorimeter for hadrons. The tracker and the calorimetry are compact enough to fit inside the CMS Solenoid which generates a powerful magnetic field of 3.8 T. Outside the magnet are the large muon detectors, which are inside the return yoke of the magnet. For full technical details about the CMS detector, please see the Technical Design Report; this is the point in the centre of the detector at which proton-proton collisions occur between the two counter-rotating beams of the LHC. At each end of the detector magnets focus the beams into the interaction point. At collision each beam has a radius of 17 μm and the crossing angle between the beams is 285 μrad. At full design luminosity each of the two LHC beams will contain 2,808 bunches of 1.15×1011 protons. The interval between crossings is 25 ns, although the number of collisions per second is only 31.6 million due to gaps in the beam as injector magnets are activated and deactivated.
At full luminosity each collision will produce an average of 20 proton-proton interactions. The collisions occur at a centre of mass energy of 8 TeV. But, it is worth noting that for studies of physics at the electroweak scale, the scattering events are initiated by a single quark or gluon from each proton, so the actual energy involved in each collision will be lower as the total centre of mass energy is shared by these quarks and gluons; the first test which ran in September 2008 was expected to operate at a lower collision energy of 10 TeV but this was prevented by the 19 September 2008 shutdown. When at this target level, the LHC will have a reduced luminosity, due to both fewer proton bunches in each beam and fewer protons per bunch; the reduced bunch frequency does allow the crossing angle to be reduced to zero however, as bunches are far enough spaced to prevent secondary collisions in the experimental beampipe. Momentum of particles is crucial in helping us to build up a picture of events at the heart of the collision.
One method to calculate the momentum of a particle is to track its path through a magnetic field. The CMS tracker records the paths taken by charged particles by finding their positions at a number of key points; the tracker can reconstruct the paths of high-energy muons and hadrons as well as see tracks coming from the decay of short-lived particles such as beauty or “b quarks” that will be used to
Leland Stanford Junior University is a private research university in Stanford, California. Stanford is known for its academic strength, proximity to Silicon Valley, ranking as one of the world's top universities; the university was founded in 1885 by Leland and Jane Stanford in memory of their only child, Leland Stanford Jr. who had died of typhoid fever at age 15 the previous year. Stanford was a U. S. Senator and former Governor of California who made his fortune as a railroad tycoon; the school admitted its first students on October 1, 1891, as a coeducational and non-denominational institution. Stanford University struggled financially after the death of Leland Stanford in 1893 and again after much of the campus was damaged by the 1906 San Francisco earthquake. Following World War II, Provost Frederick Terman supported faculty and graduates' entrepreneurialism to build self-sufficient local industry in what would be known as Silicon Valley; the university is one of the top fundraising institutions in the country, becoming the first school to raise more than a billion dollars in a year.
The university is organized around three traditional schools consisting of 40 academic departments at the undergraduate and graduate level and four professional schools that focus on graduate programs in Law, Medicine and Business. Stanford's undergraduate program is the most selective in the United States by acceptance rate. Students compete in 36 varsity sports, the university is one of two private institutions in the Division I FBS Pac-12 Conference, it has gained the most for a university. Stanford athletes have won 512 individual championships, Stanford has won the NACDA Directors' Cup for 24 consecutive years, beginning in 1994–1995. In addition, Stanford students and alumni have won 270 Olympic medals including 139 gold medals; as of October 2018, 83 Nobel laureates, 27 Turing Award laureates, 8 Fields Medalists have been affiliated with Stanford as students, faculty or staff. In addition, Stanford University is noted for its entrepreneurship and is one of the most successful universities in attracting funding for start-ups.
Stanford alumni have founded a large number of companies, which combined produce more than $2.7 trillion in annual revenue and have created 5.4 million jobs as of 2011 equivalent to the 10th largest economy in the world. Stanford is the alma mater of 30 living billionaires and 17 astronauts, is one of the leading producers of members of the United States Congress. Stanford University was founded in 1885 by Leland and Jane Stanford, dedicated to Leland Stanford Jr, their only child; the institution opened in 1891 on Stanford's previous Palo Alto farm. Despite being impacted by earthquakes in both 1906 and 1989, the campus was rebuilt each time. In 1919, The Hoover Institution on War and Peace was started by Herbert Hoover to preserve artifacts related to World War I; the Stanford Medical Center, completed in 1959, is a teaching hospital with over 800 beds. The SLAC National Accelerator Laboratory, established in 1962, performs research in particle physics. Jane and Leland Stanford modeled their university after the great eastern universities, most Cornell University and Harvard University.
Stanford opened being called the "Cornell of the West" in 1891 due to faculty being former Cornell affiliates including its first president, David Starr Jordan. Both Cornell and Stanford were among the first to have higher education be accessible and open to women as well as to men. Cornell is credited as one of the first American universities to adopt this radical departure from traditional education, Stanford became an early adopter as well. Most of Stanford University is on one of the largest in the United States, it is located on the San Francisco Peninsula, in the northwest part of the Santa Clara Valley 37 miles southeast of San Francisco and 20 miles northwest of San Jose. In 2008, 60% of this land remained undeveloped. Stanford's main campus includes a census-designated place within unincorporated Santa Clara County, although some of the university land is within the city limits of Palo Alto; the campus includes much land in unincorporated San Mateo County, as well as in the city limits of Menlo Park and Portola Valley.
The academic central campus is adjacent to Palo Alto, bounded by El Camino Real, Stanford Avenue, Junipero Serra Boulevard, Sand Hill Road. The United States Postal Service has assigned it two ZIP Codes: 94305 for campus mail and 94309 for P. O. box mail. It lies within area code 650. Stanford operates or intends to operate in various locations outside of its central campus. On the founding grant: Jasper Ridge Biological Preserve is a 1,200-acre natural reserve south of the central campus owned by the university and used by wildlife biologists for research. SLAC National Accelerator Laboratory is a facility west of the central campus operated by the university for the Department of Energy, it contains the longest linear particle accelerator in the world, 2 miles on 426 acres of land. Golf course and a seasonal lake: The university has its own golf course and a seasonal lake, both home to the vulnerable California tiger salamander; as of 2012 Lake Laguni
International System of Units
The International System of Units is the modern form of the metric system, is the most used system of measurement. It comprises a coherent system of units of measurement built on seven base units, which are the ampere, second, kilogram, mole, a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units; the system specifies names for 22 derived units, such as lumen and watt, for other common physical quantities. The base units are derived from invariant constants of nature, such as the speed of light in vacuum and the triple point of water, which can be observed and measured with great accuracy, one physical artefact; the artefact is the international prototype kilogram, certified in 1889, consisting of a cylinder of platinum-iridium, which nominally has the same mass as one litre of water at the freezing point. Its stability has been a matter of significant concern, culminating in a revision of the definition of the base units in terms of constants of nature, scheduled to be put into effect on 20 May 2019.
Derived units may be defined in terms of other derived units. They are adopted to facilitate measurement of diverse quantities; the SI is intended to be an evolving system. The most recent derived unit, the katal, was defined in 1999; the reliability of the SI depends not only on the precise measurement of standards for the base units in terms of various physical constants of nature, but on precise definition of those constants. The set of underlying constants is modified as more stable constants are found, or may be more measured. For example, in 1983 the metre was redefined as the distance that light propagates in vacuum in a given fraction of a second, thus making the value of the speed of light in terms of the defined units exact; the motivation for the development of the SI was the diversity of units that had sprung up within the centimetre–gram–second systems and the lack of coordination between the various disciplines that used them. The General Conference on Weights and Measures, established by the Metre Convention of 1875, brought together many international organisations to establish the definitions and standards of a new system and standardise the rules for writing and presenting measurements.
The system was published in 1960 as a result of an initiative that began in 1948. It is based on the metre–kilogram–second system of units rather than any variant of the CGS. Since the SI has been adopted by all countries except the United States and Myanmar; the International System of Units consists of a set of base units, derived units, a set of decimal-based multipliers that are used as prefixes. The units, excluding prefixed units, form a coherent system of units, based on a system of quantities in such a way that the equations between the numerical values expressed in coherent units have the same form, including numerical factors, as the corresponding equations between the quantities. For example, 1 N = 1 kg × 1 m/s2 says that one newton is the force required to accelerate a mass of one kilogram at one metre per second squared, as related through the principle of coherence to the equation relating the corresponding quantities: F = m × a. Derived units apply to derived quantities, which may by definition be expressed in terms of base quantities, thus are not independent.
Other useful derived quantities can be specified in terms of the SI base and derived units that have no named units in the SI system, such as acceleration, defined in SI units as m/s2. The SI base units are the building blocks of the system and all the other units are derived from them; when Maxwell first introduced the concept of a coherent system, he identified three quantities that could be used as base units: mass and time. Giorgi identified the need for an electrical base unit, for which the unit of electric current was chosen for SI. Another three base units were added later; the early metric systems defined a unit of weight as a base unit, while the SI defines an analogous unit of mass. In everyday use, these are interchangeable, but in scientific contexts the difference matters. Mass the inertial mass, represents a quantity of matter, it relates the acceleration of a body to the applied force via Newton's law, F = m × a: force equals mass times acceleration. A force of 1 N applied to a mass of 1 kg will accelerate it at 1 m/s2.
This is true whether the object is floating in space or in a gravity field e.g. at the Earth's surface. Weight is the force exerted on a body by a gravitational field, hence its weight depends on the strength of the gravitational field. Weight of a 1 kg mass at the Earth's surface is m × g. Since the acceleration due to gravity is local and varies by location and altitude on the Earth, weight is unsuitable for precision
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