Electronvolt

In physics, the electronvolt[1][2] (symbol eV, also written electron-volt and electron volt) is a unit of energy equal to approximately 1.6×10−19 joules (symbol J) in SI units.

Historically, 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; if q is quoted in integer units of the elementary charge and the potential in volts, one gets an energy in eV.

Like the elementary charge on which it is based, it is not an independent quantity but is equal to 1 J/C2hα / μ0c0. It is a common unit of energy within physics, widely used in solid state, atomic, nuclear, and particle physics. It is commonly used with the metric prefixes milli-, kilo-, mega-, giga-, tera-, peta- or exa- (meV, keV, MeV, GeV, TeV, PeV and EeV respectively). In some older documents, and in the name Bevatron, the symbol BeV is used, which stands for billion (109) electronvolts; it is equivalent to the GeV.

Measurement Unit SI value of unit
Energy eV 1.6021766208(98)×10−19 J
Mass eV/c2 1.782662×10−36 kg
Momentum eV/c 5.344286×10−28 kg⋅m/s
Temperature eV/kB 1.1604505(20)×104 K
Time ħ/eV 6.582119×10−16 s
Distance ħc/eV 1.97327×10−7 m

Definition

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(98)×10−19 C.[3] Therefore, one electronvolt is equal to 1.6021766208(98)×10−19 J.[4] 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 exactly, unlike the litre, the light-year and such other non-SI units.[5] Electronvolt (eV) is a unit of energy whereas volt (V) is the derived SI unit of electric potential. The SI unit for energy is joule (J). 1 eV is equal to 1.6021766208(98)×10−19 J.

Mass

By mass–energy equivalence, the electronvolt is also a unit of mass. It is common in particle physics, where units of mass and energy are often interchanged, to express mass in units of eV/c2, where c is the speed of light in vacuum (from E = mc2). It is common to simply express mass in terms of "eV" as a unit of mass, effectively using a system of natural units with c set to 1.[6] The mass equivalent of 1 eV/c2 is

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 (gigaelectronvolt) a convenient unit of mass for particle physics:

1 GeV/c2 = 1.783×10−27 kg.

The unified atomic mass unit (u), 1 gram divided by Avogadro's number, is almost the mass of a hydrogen atom, which is mostly the mass of the proton. To convert to megaelectronvolts, use the formula:

1 u = 931.4941 MeV/c2 = 0.9314941 GeV/c2.

Momentum

In high-energy physics, the electronvolt is often used as a unit of momentum. A potential difference of 1 volt causes an electron to gain an amount of energy (i.e., 1 eV). This gives rise to usage of eV (and keV, MeV, GeV or TeV) 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. Then, dividing the units of energy (such as eV) by a fundamental constant that has units of velocity (LT−1), 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.[7] [8]

The fundamental velocity constant c is often 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, then the conversion to MKS can be achieved by:

Distance

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 widely 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 mass–energy equivalence). In particular, particle scattering lengths are often presented in units of inverse particle masses.

Outside this system of units, the conversion factors between electronvolt, second, and nanometer are the following:

The above relations also allow expressing the mean lifetime τ of an unstable particle (in seconds) in terms of its decay width Γ (in eV) via Γ = ħ/τ. For example, the B0 meson has a lifetime of 1.530(9) picoseconds, mean decay length is = 459.7 μm, or a decay width of (4.302±25)×10−4 eV.

Conversely, the tiny meson mass differences responsible for meson oscillations are often expressed in the more convenient inverse picoseconds.

Energy in electronvolts is sometimes expressed through the wavelength of light with photons of the same energy: 1 eV = 8065.544005(49) cm−1.

Temperature

In certain fields, such as plasma physics, it is convenient to use the electronvolt as a unit of temperature. The conversion to the Kelvin scale is defined by using kB, the Boltzmann constant:

For example, a typical magnetic confinement fusion plasma is 15 keV, or 170 MK.

As an approximation: kBT is about 0.025 eV (≈ 290 K/11604 K/eV) at a temperature of 20 °C.

Properties

Colors in eV
Energy of photons in the visible spectrum in eV
EV to nm vis
Graph of wavelength (nm) to energy (eV)

The energy E, frequency v, and wavelength λ of a photon are related by

where h is the Planck constant, c is the speed of light. This reduces to

[9]

A photon with a wavelength of 532 nm (green light) would have an energy of approximately 2.33 eV. Similarly, 1 eV would correspond to an infrared photon of wavelength 1240 nm or frequency 241.8 THz.

Scattering experiments

In a low-energy nuclear scattering experiment, it is conventional to refer to the nuclear recoil energy in units of eVr, keVr, etc. This distinguishes the nuclear recoil energy from the "electron equivalent" recoil energy (eVee, keVee, etc.) measured by scintillation light. For example, the yield of a phototube is measured in phe/keVee (photoelectrons per keV electron-equivalent energy). The relationship between eV, eVr, and eVee depends on the medium the scattering takes place in, and must be established empirically for each material.

Energy comparisons

Light spectrum
Photon frequency vs. energy particle in electronvolts. The energy of a photon varies only with the frequency of the photon, related by speed of light constant. This contrasts with a massive particle of which the energy depends on its velocity and rest mass.[10][11][12] Legend
γ: Gamma rays MIR: Mid infrared HF: High freq.
HX: Hard X-rays FIR: Far infrared MF: Medium freq.
SX: Soft X-rays Radio waves LF: Low freq.
EUV: Extreme ultraviolet EHF: Extremely high freq. VLF: Very low freq.
NUV: Near ultraviolet SHF: Super high freq. VF/ULF: Voice freq.
Visible light UHF: Ultra high freq. SLF: Super low freq.
NIR: Near Infrared VHF: Very high freq. ELF: Extremely low freq.
Freq: Frequency
  • 5.25×1032 eV: total energy released from a 20 kt nuclear fission device
  • 1.22×1028 eV: the Planck energy
  • 10 YeV (1×1025 eV): the approximate grand unification energy
  • ~624 EeV (6.24×1020 eV): energy consumed by a single 100-watt light bulb in one second (100 W = 100 J/s6.24×1020 eV/s)
  • 300 EeV (3×1020 eV = ~50 J):[13] the so-called Oh-My-God particle (the most energetic cosmic ray particle ever observed)
  • 2 PeV: two petaelectronvolts, the most high-energetic neutrino detected by the IceCube neutrino telescope in Antarctica[14]
  • 14 TeV: the designed proton collision energy at the Large Hadron Collider (operated at about half of this energy since 30 March 2010, reached 13 TeV in May 2015)
  • 1 TeV: a trillion electronvolts, or 1.602×10−7 J, about the kinetic energy of a flying mosquito[15]
  • 125.1±0.2 GeV: the energy corresponding to the mass of the Higgs boson, as measured by two separate detectors at the LHC to a certainty better than 5 sigma[16]
  • 210 MeV: the average energy released in fission of one Pu-239 atom
  • 200 MeV: the average energy released in nuclear fission of one U-235 atom
  • 17.6 MeV: the average energy released in the fusion of deuterium and tritium to form He-4; this is 0.41 PJ per kilogram of product produced
  • 1 MeV (1.602×10−13 J): about twice the rest energy of an electron
  • 13.6 eV: the energy required to ionize atomic hydrogen; molecular bond energies are on the order of 1 eV to 10 eV per bond
  • 1.6 eV to 3.4 eV: the photon energy of visible light
  • 1.1 eV: the energy EG required to break a covalent bond in silicon
  • 720 meV: the energy EG required to break a covalent bond in germanium
  • 25 meV: the thermal energy kBT at room temperature; one air molecule has an average kinetic energy 38 meV
  • 230 µeV: the thermal energy kBT of the cosmic microwave background

Per mole

One mole of particles given 1 eV of energy has approximately 96.5 kJ of energy – this corresponds to the Faraday constant (F96485 C mol−1) where the energy in joules of N moles of particles each with energy X eV is X·F·N.

See also

Notes and references

  1. ^ IUPAC Gold Book Archived 2009-01-03 at the Wayback Machine, p. 75
  2. ^ SI brochure, Sec. 4.1 Table 7 Archived July 16, 2012, at the Wayback Machine
  3. ^ "CODATA Value: elementary charge". The NIST Reference on Constants, Units, and Uncertainty. US National Institute of Standards and Technology. June 2015. Retrieved 2015-09-22. 2014 CODATA recommended values
  4. ^ "CODATA Value: electron volt". The NIST Reference on Constants, Units, and Uncertainty. US National Institute of Standards and Technology. June 2015. Retrieved 2015-09-22. 2014 CODATA recommended values
  5. ^ "Definitions of the SI units: Non-SI units". The NIST Reference on Constants, Units, and Uncertainty. National Institute of Standards and Technology. Retrieved 2018-07-01.
  6. ^ Barrow, J. D. "Natural Units Before Planck." Quarterly Journal of the Royal Astronomical Society 24 (1983): 24.
  7. ^ "Units in particle physics". Associate Teacher Institute Toolkit. Fermilab. 22 March 2002. Archived from the original on 14 May 2011. Retrieved 13 February 2011.
  8. ^ "Special Relativity". Virtual Visitor Center. SLAC. 15 June 2009. Retrieved 13 February 2011.
  9. ^ "CODATA Value: Planck constant in eV s". Archived from the original on 22 January 2015. Retrieved 30 March 2015.
  10. ^ What is Light? Archived December 5, 2013, at the Wayback MachineUC Davis lecture slides
  11. ^ Elert, Glenn. "Electromagnetic Spectrum, The Physics Hypertextbook". hypertextbook.com. Archived from the original on 2016-07-29. Retrieved 2016-07-30.
  12. ^ "Definition of frequency bands on". Vlf.it. Archived from the original on 2010-04-30. Retrieved 2010-10-16.
  13. ^ Open Questions in Physics. Archived 2014-08-08 at the Wayback Machine German Electron-Synchrotron. A Research Centre of the Helmholtz Association. Updated March 2006 by JCB. Original by John Baez.
  14. ^ "A growing astrophysical neutrino signal in IceCube now features a 2-PeV neutrino". Archived from the original on 2015-03-19.
  15. ^ Glossary Archived 2014-09-15 at the Wayback Machine - CMS Collaboration, CERN
  16. ^ ATLAS; CMS (26 March 2015). "Combined Measurement of the Higgs Boson Mass in pp Collisions at √s=7 and 8 TeV with the ATLAS and CMS Experiments". Physical Review Letters. 114 (19): 191803. arXiv:1503.07589. Bibcode:2015PhRvL.114s1803A. doi:10.1103/PhysRevLett.114.191803. PMID 26024162.

External links

Bev

Bev may refer to:

Bev (given name), a list of people and fictional characters with the unisex given name

Bevs, slang for beverages, generally implying beer or other alcoholic drinksBEV may stand for:

Battery electric vehicle

Beam's eye view, an imaging technique used in radiation therapy

Black English Vernacular, a form of English commonly spoken by some African-Americans in the United States

Blacksburg Electronic Village

British Electric Vehicles Ltd, Southport, Lancashire, an early manufacturer of electric road and rail vehicles

Bundesamt für Eich- und Vermessungswesen, the Austrian agency for national mapping and metronomy

Billion-electronvolt (BeV), equivalent to the SI term GeV (gigaelectronvolt)

Binary collision approximation

The binary collision approximation (BCA) signifies a method used in ion irradiation physics to enable efficient computer simulation of the penetration depth and

defect production by energetic (with kinetic energies in the kilo-electronvolt (keV) range or higher) ions in solids. In the method, the ion is approximated to travel through a material by experiencing a sequence of independent binary collisions with sample atoms (nuclei). Between the collisions, the ion is assumed to travel in a straight path, experiencing electronic stopping power, but losing no energy in collisions with nuclei.

Electron temperature

Temperature is a statistical quantity. The formal definition is T = dU/dS, the change in internal energy with respect to entropy, holding volume and particle number constant. A practical definition comes from the fact that the atoms, molecules, or whatever particles in a system have an average kinetic energy. The average means to average over the kinetic energy of all the particles in a system.

If the velocities of a group of electrons, e.g., in a plasma, follow a Maxwell–Boltzmann distribution, then the electron temperature is defined as the temperature of that distribution. For other distributions, not assumed to be in equilibrium or have a temperature, two-thirds of the average energy is often referred to as the temperature, since for a Maxwell–Boltzmann distribution with three degrees of freedom, .

The SI unit of temperature is the kelvin (K), but using the above relation the electron temperature is often expressed in terms of the energy unit electronvolt (eV). Each kelvin (1 K) corresponds to 8.6173324(78)×10−5 eV; this factor is the ratio of the Boltzmann constant to the elementary charge. Each eV is equivalent to 11,605 kelvins. It can be calculated by the relation .

The electron temperature of a plasma can be several orders of magnitude higher than the temperature of the neutral species or of the ions. This is a result of two facts. Firstly, many plasma sources heat the electrons more strongly than the ions. Secondly, atoms and ions are much heavier than electrons, and energy transfer in a two-body collision is much more efficient if the masses are similar. Therefore, equilibration of the temperature happens very slowly, and is not achieved during the time range of the observation.

FLASH

FLASH, acronym of Free Electron LASer in Hamburg, a particle accelerator-based soft X-ray laser located at the DESY accelerator facilities in Hamburg, Germany. It can generate very powerful, ultrashort pulses (~10−14 s) of coherent radiation in the energy range 10 eV (electronvolt) to 200 eV. It started operation for external users in the year 2005 and is used for surface, molecular and atomic physics experiments. Intended applications are also the imaging of single biological complex molecules with time resolution.

Hartree

The hartree (symbol: Eh or Ha), also known as the Hartree energy, is the atomic unit of energy, named after the British physicist Douglas Hartree. It is defined as

2R∞hc, where R∞ is the Rydberg constant, h is the Planck constant and c is the speed of light.

The 2014 CODATA recommended value is Eh = 4.359 744 650(54)×10−18 J = 27.211 386 02(17) eV.The hartree energy is approximately the electric potential energy of the hydrogen atom in its ground state and, by the virial theorem, approximately twice its ionization energy; the relationships are not exact because of the finite mass of the nucleus of the hydrogen atom and relativistic corrections.

The hartree is usually used as a unit of energy in atomic physics and computational chemistry: for experimental measurements at the atomic scale, the electronvolt (eV) or the reciprocal centimetre (cm−1) are much more widely used.

High Energy Stereoscopic System

High Energy Stereoscopic System (H.E.S.S.) is a system of Imaging Atmospheric Cherenkov Telescopes (IACT) for the investigation of cosmic gamma rays in the photon energy range of 0.03 to 100 TeV. The acronym was chosen in honour of Victor Hess, who was the first to observe cosmic rays.

The name also emphasizes two main features of the installation, namely the simultaneous observation of air showers with several telescopes, under different viewing angles, and the combination of telescopes to a large system to increase the effective detection area for gamma rays. H.E.S.S. permits the exploration of gamma-ray sources with intensities at a level of a few thousandth parts of the flux of the Crab Nebula.

H.E.S.S. has five telescopes, four with a mirror just under 12 m in diameter, arranged 120 m apart from each other in a square, and one larger telescope with a 28 m mirror, constructed in the centre of the array. This current system, called H.E.S.S. II, saw its first light at 0:43 a.m. on 26 July 2012.As with other gamma-ray telescopes, H.E.S.S. observes high energy processes in the universe. Gamma-ray producing sources include supernova remnants, active galactic nuclei and pulsar wind nebulae. It also actively tests unproven theories in physics such as looking for the predicted gamma-ray annihilation signal from WIMP dark matter particles and testing Lorentz invariance predictions of loop quantum gravity.

H.E.S.S. is located on the Cranz family farm, Göllschau, in Namibia, near the Gamsberg, an area well known for its excellent optical quality. The first of the four telescopes of Phase I of the H.E.S.S. project went into operation in Summer 2002; all four were operational in December 2003.

In 2004 H.E.S.S. was the first IACT experiment to spatially resolve a source of cosmic gamma rays.

In 2005, it was announced that H.E.S.S. had detected eight new high-energy gamma ray sources, doubling the known number of such sources. As of 2014, more than 90 sources of Tera-Electronvolt gamma-rays were discovered by H.E.S.S.In 2016, HESS collaboration reported deep gamma ray observations which show the presence of petaelectronvolt protons originate from the supermassive black hole at central of Milky Way, and therefore should be considered as a viable alternative to supernova remnants as a source of petaelectronvolt Galactic cosmic rays.

Joule per mole

The joule per mole (symbol: J·mole−1 or J/mol) is an SI derived unit of energy per amount of material. Energy is measured in joules, and the amount of material is measured in moles. For example, Gibbs free energy is quantified as joules per mole.

Since 1 mole = 6.02214179×1023 particles (atoms, molecules, ions etc.), 1 Joule per mole is equal to 1 Joule divided by 6.02214179×1023 particles, or (6.022×10^23 particles/mole), 1.66054×10−24 Joule per particle. This very small amount of energy is often expressed in terms of a smaller unit such as the electronvolt (eV, see below).

Physical quantities measured in J·mol−1 usually describe quantities of energy transferred during phase transformations or chemical reactions. Division by the number of moles facilitates comparison between processes involving different quantities of material and between similar processes involving different types of materials. The meaning of such a quantity is always context-dependent and, particularly for chemical reactions, is dependent on the (possibly arbitrary) definition of a 'mole' for a particular process.

For convenience and due to the range of magnitudes involved these quantities are almost always reported in kJ·mol−1 rather than in J·mol−1. For example, heats of fusion and vaporization are usually of the order of 10 kJ·mol−1, bond energies are of the order of 100 kJ·mol−1, and ionization energies of the order of 1000 kJ·mol−1.

1 kJ·mol−1 is equal to 0.239 kcal·mol−1 or 1.04×10−2 eV per particle. At room temperature (25 °C, 77 °F, or 298.15 K) 1 kJ·mol−1 is equal to 0.4034  k B T {\displaystyle k_{B}T} .

Kratos MS 50

The Kratos MS 50, or EI 50, is a tool for electron ionization (EI). The EI 50, used for relatively small molecules (as opposed to methods like MALDI), ionizes molecules via electron ionization (normally under 70 electronvolt conditions) and then accelerates them through an electric potential. The spectroscopy is done by analyzing the different displacements by a magnet. For equal charge, these displacements depend only on velocity, thus for the EI 50's constant kinetic energy conditions, these displacements are uniquely determined by a particle's mass.

List of mass spectrometry acronyms

This is a compilation of initialisms and acronyms commonly used in mass spectrometry.

List of unusual units of measurement

An unusual unit of measurement is a unit of measurement that does not form part of a coherent system of measurement; especially in that its exact quantity may not be well known or that it may be an inconvenient multiple or fraction of base units in such systems. This definition is deliberately not exact since it might seem to encompass units such as the week or the light-year which are quite "usual" in the sense they are often used; if they are used out of context, they may be "unusual", as demonstrated by the Furlong/Firkin/Fortnight (FFF) system of units. Many of the unusual units of measurements listed here are colloquial measurements, units devised to compare a measurement to common and familiar objects.

Microprobe

A microprobe is an instrument that applies a stable and well-focused beam of charged particles (electrons or ions) to a sample.

Non-SI units mentioned in the SI

This is a list of units that are not defined as part of the International System of Units (SI), but are otherwise mentioned in the SI, because either the General Conference on Weights and Measures (CGPM) accepts their use as being multiples or submultiples of SI-units, they have important contemporary application worldwide, or are otherwise commonly encountered worldwide.

Photon energy

Photon energy is the energy carried by a single photon. The amount of energy is directly proportional to the photon's electromagnetic frequency and inversely proportional to the wavelength. The higher the photon's frequency, the higher its energy. Equivalently, the longer the photon's wavelength, the lower its energy.

Photon energy is solely a function of the photon's wavelength. Other factors, such as the intensity of the radiation, do not affect photon energy. In other words, two photons of light with the same color and therefore, same frequency, will have the same photon energy, even if one was emitted from a wax candle and the other from the Sun.

Photon energy can be represented by any unit of energy. Among the units commonly used to denote photon energy are the electronvolt (eV) and the joule (as well as its multiples, such as the microjoule). As one joule equals 6.24 × 1018 eV, the larger units may be more useful in denoting the energy of photons with higher frequency and higher energy, such as gamma rays, as opposed to lower energy photons, such as those in the radiofrequency region of the electromagnetic spectrum.

Superconducting camera

The superconducting camera, SCAM, is an ultra-fast photon-counting camera developed by the European Space Agency. It is cooled to just 0.3 K (three-tenths of a degree above absolute zero). This enables its sensitive electronic detectors, known as superconducting tunnel junction detectors, to register almost every photon of light that falls into it.

Its advantage over a CCD (charge-coupled device) is that it can measure both the brightness (rate) of the incoming photon stream and the colour (wavelength or energy) of each individual photon.

The number of free primary electrons generated per photon event is proportional to the photon energy and amounts to ~18,000 per electronvolt, and therefore if the device is operated in single-photon count mode the energy of each captured photon can be calculated in the visible-light range, where photons have energies of a few electronvolts, each generating >20,000 electrons. In a normal CCD, only one primary electron is generated per photon, except for very energetic photons, like X-rays, where a normal CCD can operate in a similar way to a SCAM.

Ultra-high-energy cosmic ray

In astroparticle physics, an ultra-high-energy cosmic ray (UHECR) is a cosmic ray with an energy greater than 1 EeV (1018 electronvolts, approximately 0.16 joules), far beyond both the rest mass and energies typical of other cosmic ray particles.

An extreme-energy cosmic ray (EECR) is an UHECR with energy exceeding 5×1019 eV (about 8 joule), the so-called Greisen–Zatsepin–Kuzmin limit (GZK limit). This limit should be the maximum energy of cosmic ray protons that have traveled long distances (about 160 million light years), since higher-energy protons would have lost energy over that distance due to scattering from photons in the cosmic microwave background (CMB). It follows that EECR could not be survivors from the early universe, but are cosmologically "young", emitted somewhere in the Local Supercluster by some unknown physical process. If an EECR is not a proton, but a nucleus with nucleons, then the GZK limit applies to its nucleons, which carry only a fraction of the total energy of the nucleus. For an iron nucleus, the corresponding limit would be 2.8×1021 eV. However, nuclear physics processes lead to limits for iron nuclei similar to that of protons. Other abundant nuclei have even much lower limits.

These particles are extremely rare; between 2004 and 2007, the initial runs of the Pierre Auger Observatory (PAO) detected 27 events with estimated arrival energies above 5.7×1019 eV, i.e., about one such event every four weeks in the 3000 km2 area surveyed by the observatory.

There is evidence that these highest-energy cosmic rays might be iron nuclei, rather than the protons that make up most cosmic rays.

The postulated (hypothetical) sources of EECR are known as Zevatrons, named in analogy to Lawrence Berkeley National Laboratory's Bevatron and Fermilab's Tevatron, and therefore capable of accelerating particles to 1 ZeV (1021 eV, zetta-electronvolt). In 2004 there was a consideration of the possibility of galactic jets acting as Zevatrons, due to diffusive acceleration of particles caused by shock waves inside the jets. In particular, models suggested that shock waves from the nearby M87 galactic jet could accelerate an iron nucleus to ZeV ranges. In 2007, the Pierre Auge Observatory oberved a correlation of EECR with extragalactic supermassive black holes at the center of nearby galaxies called active galactic nuclei (AGN). However, the strength of the correlation became weaker while continuing observations. Extremely high energies might be explained also by the Centrifugal mechanism of acceleration in the magnetospheres of AGN. Although newer results indicate that fewer than 40% of these cosmic rays seemed to be coming from the AGN, a much weaker correlation than previously reported. A more speculative suggestion by Grib and Pavlov (2007, 2008) envisages the decay of superheavy dark matter by means of the Penrose process.

Ultraviolet photoelectron spectroscopy

Ultraviolet photoelectron spectroscopy (UPS) refers to the measurement of kinetic energy spectra of photoelectrons emitted by molecules which have absorbed ultraviolet photons, in order to determine molecular orbital energies in the valence region.

Units of energy

Because energy is defined via work, the SI unit for energy is the same as the unit of work – the joule (J), named in honor of James Prescott Joule and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1 joule is equal to 1 newton metre and, in terms of SI base units

An energy unit that is used in atomic physics, particle physics and high energy physics is the electronvolt (eV). One eV is equivalent to 1.60217653×10−19 J.

In spectroscopy the unit cm−1 = 0.000123986 eV is used to represent energy since energy is inversely proportional to wavelength from the equation .

In discussions of energy production and consumption, the units barrel of oil equivalent and ton of oil equivalent are often used. Cubic mile of oil is sometimes used as a unit of energy in discussions of global scale energy economics.

When discussing amounts of energy released in explosions or bolide impact events, the TNT equivalent unit is often used.

Wide-bandgap semiconductor

Wide-bandgap semiconductors (also known as WBG semiconductors or WBGSs) are semiconductor materials which have a relatively large band gap compared to conventional semiconductors. Conventional semiconductors like silicon have a bandgap in the range of 1 - 1.5 electronvolt (eV), whereas wide-bandgap materials have bandgaps in the range of 2 - 4 eV. Generally, wide-bandgap semiconductors have electronic properties which fall in between those of conventional semiconductors and insulators.

Wide-bandgap semiconductors permit devices to operate at much higher voltages, frequencies and temperatures than conventional semiconductor materials like silicon and gallium arsenide. They are the key component used to make green and blue LEDs and lasers, and are also used in certain radio frequency applications, notably military radars. Their intrinsic qualities make them suitable for a wide range of other applications, and they are one of the leading contenders for next-generation devices for general semiconductor use.

The wider bandgap is particularly important for allowing devices that use them to operate at much higher temperatures, on the order of 300 °C. This makes them highly attractive for military applications, where they have seen a fair amount of use. The high temperature tolerance also means that these devices can be operated at much higher power levels under normal conditions. Additionally, most wide bandgap materials also have a much higher critical electrical field density, on the order of ten times that of conventional semiconductors. Combined, these properties allow them to operate at much higher voltages and currents, which makes them highly valuable in military, radio and energy conversion settings. The US Department of Energy believes they will be a foundational technology in new electrical grid and alternative energy devices, as well as the robust and efficient power components used in high energy vehicles from electric trains to plug-in electric vehicles. Most wide-bandgap materials also have high free-electron velocities, which allows them to work at higher switching speeds, which adds to their value in radio applications. A single WBG device can be used to make a complete radio system, eliminating the need for separate signal and radio frequency components, while operating at higher frequencies and power levels.

Research and development of wide-bandgap materials lags behind that of conventional semiconductors, which have received massive investment since the 1970s. However, their clear inherent advantages in many applications, combined with some unique properties not found in conventional semiconductors, has led to increasing interest in their use in everyday electronic devices to replace silicon. Their ability of handle higher energy densities is particularly attractive for attempts to continue obeying Moore's law, as conventional technologies appear to be reaching a density plateau.

Base units
Derived units
with special names
Other accepted units
See also

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