Electronvolt
Encyclopedia
In physics
, the electron volt (symbol eV; also written electronvolt) is a unit of energy
equal to approximately joule
(symbol J). By definition, it is equal to the amount of kinetic energy
gained by a single unbound
electron
when it accelerates
through an electric
potential difference of one volt
. Thus it is 1 volt
(1 joule per coulomb, 1 J/C) multiplied by the electron charge
(1 e, or ). Therefore, one electron volt is equal to . Historically, the electron volt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences because a particle with 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 terminal bias in volts, one gets an energy in eV.
The electron volt is not an SI unit
and its value must be obtained experimentally. Like the elementary charge
on which it is based, it is not an independent quantity but is equal to (1 J/C)(2 h
α / μ_{0} c_{0}
)^{0.5} 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 SI prefix
es milli, kilo, mega, giga, tera, or peta (meV, keV, MeV, GeV, TeV and PeV respectively). Thus meV stands for millielectron volt.
In chemistry
, it is often useful to have the molar equivalent, that is the kinetic energy that would be gained by one mole
of electrons passing through a potential difference of one volt. This is equal to . Atomic properties like the ionization energy
are often quoted in electron volts.
expressed in coulombs). (per atom) is .
For comparison:: Total energy released from a 20 kT Nuclear Fission Device.
In some older documents, and in the name Bevatron
, the symbol BeV is used, which stands for billion electron volts; it is equivalent to the GeV.
. A potential difference of 1 volt causes an electron to gain a discrete 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 M^{ 1 } L ^{ 1 } T ^{ 1 }. The dimensions of energy units are M ^{ 1 } L ^{ 2 } T ^{ 2 }. Then, dividing the units of energy (such as eV) by a fundamental constant that has units of velocity (M ^{ 0 } L ^{ 1 } T ^{ 1 }), facilitates the required conversion of using energy units to describe momentum. In the field of highenergy particle physics, the fundamental velocity unit is the speed of light c. Thus, dividing energy in eV by the speed of light in vacuum, one can describe the momentum of an electron as eV/c.
The fundamental velocity constant c can be 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:
, the electron volt is also a unit of mass. It is common in particle physics
, where mass
and energy are often interchanged, to use eV/c^{2}, where c is the speed of light
in a vacuum (from E = mc^{2}
). Even more common is to use a system of natural units
with c set to 1 (hence, E = m), and simply use eV as a unit of mass.
For example, an electron and a positron
, each with a mass of 0.511 MeV/c^{2}, can annihilate to yield 1.022 MeV of energy. The proton
has a mass of 0.938 GeV
/c^{2} (and, in general, the masses of all hadron
s are of the order of 1 GeV/c^{2}), which makes the GeV (gigaelectronvolt) a very convenient unit of mass for particle physics
:
The atomic mass unit
, 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:
, a system of units in which the speed of light in a vacuum c and the reduced Planck constant
ħ are dimensionless and equal to unity is widely used: . 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 B^{0} meson
has a lifetime of 1.530(9) picosecond
s, mean decay length is , or a decay width of .
Conversely, the tiny meson mass mass differences responsible for meson oscillations are often expressed in the more convenient inverse picoseconds.
s (symbol: uppercase K) is defined by using k_{B}, the Boltzmann constant:
For example, a typical magnetic confinement fusion
plasma is 15 keV, or 170 megakelvins.
where h is the Planck constant
, c is the speed of light
. For quick calculations, this reduces to
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, and so on.
light. For example, the yield of a phototube
is measured in phe/keVee (photoelectrons per keV electronequivalent 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.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, the electron volt (symbol eV; also written electronvolt) is a unit of energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
equal to approximately joule
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
(symbol J). By definition, it is equal to the amount of kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
gained by a single unbound
Bound state
In physics, a bound state describes a system where a particle is subject to a potential such that the particle has a tendency to remain localised in one or more regions of space...
electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
when it accelerates
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...
through an electric
Electric potential
In classical electromagnetism, the electric potential at a point within a defined space is equal to the electric potential energy at that location divided by the charge there...
potential difference of one volt
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery. Definition :A single volt is defined as the...
. Thus it is 1 volt
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery. Definition :A single volt is defined as the...
(1 joule per coulomb, 1 J/C) multiplied by the electron charge
Elementary charge
The elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...
(1 e, or ). Therefore, one electron volt is equal to . Historically, the electron volt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences because a particle with charge q has an energy E=qV after passing through the potential V; if q is quoted in integer units of the elementary charge
Elementary charge
The elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...
and the terminal bias in volts, one gets an energy in eV.
The electron volt is not an SI unit
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...
and its value must be obtained experimentally. Like the elementary charge
Elementary charge
The elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...
on which it is based, it is not an independent quantity but is equal to (1 J/C)(2 h
Planck constant
The Planck constant , also called Planck's constant, is a physical constant reflecting the sizes of energy quanta in quantum mechanics. It is named after Max Planck, one of the founders of quantum theory, who discovered it in 1899...
α / μ_{0} c_{0}
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
)^{0.5} It is a common unit of energy within physics, widely used in solid state
Solidstate physics
Solidstate physics is the study of rigid matter, or solids, through methods such as quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solidstate physics studies how the largescale properties of solid materials result from...
, atomic
Atomic physics
Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and...
, nuclear
Nuclear physics
Nuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...
, and particle physics
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
. It is commonly used with the SI prefix
SI prefix
The International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...
es milli, kilo, mega, giga, tera, or peta (meV, keV, MeV, GeV, TeV and PeV respectively). Thus meV stands for millielectron volt.
In chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, it is often useful to have the molar equivalent, that is the kinetic energy that would be gained by one mole
Mole (unit)
The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon12 , the isotope of carbon with atomic weight 12. This corresponds to a value...
of electrons passing through a potential difference of one volt. This is equal to . Atomic properties like the ionization energy
Ionization energy
The ionization energy of a chemical species, i.e. an atom or molecule, is the energy required to remove an electron from the species to a practically infinite distance. Large atoms or molecules have a low ionization energy, while small molecules tend to have higher ionization energies.The property...
are often quoted in electron volts.
Energy
Conversion factors: = (the conversion factor is numerically equal to the elementary chargeElementary charge
The elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...
expressed in coulombs). (per atom) is .
For comparison:: Total energy released from a 20 kT Nuclear Fission Device.
 ~624 E
eV : energy needed to power a single 100 watt light bulb for one second. (100W = 100J/s = ~).  300 E
eV = (50 JJouleThe joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
) : the socalled OhMyGod particleUltrahighenergy cosmic rayIn astroparticle physics, an ultrahighenergy cosmic ray or extremeenergy cosmic ray is a cosmic ray with an extreme kinetic energy, far beyond both its rest mass and energies typical of other cosmic rays....
(the most energetic cosmic ray particle ever observed).  14 TeV: the designed proton collision energy at the Large Hadron ColliderLarge Hadron ColliderThe Large Hadron Collider is the world's largest and highestenergy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature....
(which has operated at half of this energy ).  1 TeV: A trillion electronvolts, or , about the kinetic energy of a flying mosquitoMosquitoMosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
.  210 MeV: The average energy released in fission of one Pu239Plutonium239Plutonium239 is an isotope of plutonium. Plutonium239 is the primary fissile isotope used for the production of nuclear weapons, although uranium235 has also been used and is currently the secondary isotope. Plutonium239 is also one of the three main isotopes demonstrated usable as fuel in...
atom.  200 MeV: The average energy released in nuclear fissionNuclear fissionIn nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
of one U235Uranium235 References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. External links:* * * one of the earliest articles on U235 for the...
atom .  17.6 MeV: The average energy released in the fusionNuclear fusionNuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
of deuteriumDeuteriumDeuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...
and tritiumTritiumTritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...
to form He4Helium4Helium4 is a nonradioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...
; this is per kilogram of product produced.  1 MeV: Or, , about twice the rest massenergy of an electron.
 13.6 eV: The energy required to ionIonAn ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
ize atomic hydrogenHydrogen atomA hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positivelycharged proton and a single negativelycharged electron bound to the nucleus by the Coulomb force...
. Molecular bond energiesBond energyIn chemistry, bond energy is the measure of bond strength in a chemical bond. It is the heat required to break one Mole of molecules into their individual atoms. For example, the carbonhydrogen bond energy in methane E is the enthalpy change involved with breaking up one molecule of methane into...
are on the order of one eV per molecule.  1.6 to 3.4 eV: the photon energy of visible light.
 1/40 eV: The thermal energyThermal energyThermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....
at room temperature. A single molecule in the air has an average kinetic energy 3/80 eV.
In some older documents, and in the name Bevatron
Bevatron
The Bevatron was a historic particle accelerator — specifically, a weakfocusing proton synchrotron — at Lawrence Berkeley National Laboratory, U.S.A., which began operating in 1954. The antiproton was discovered there in 1955, resulting in the 1959 Nobel Prize in physics for Emilio...
, the symbol BeV is used, which stands for billion electron volts; it is equivalent to the GeV.
Momentum
In highenergy physics, electronvolt is often used as a unit of momentumMomentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
. A potential difference of 1 volt causes an electron to gain a discrete 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 M^{ 1 } L ^{ 1 } T ^{ 1 }. The dimensions of energy units are M ^{ 1 } L ^{ 2 } T ^{ 2 }. Then, dividing the units of energy (such as eV) by a fundamental constant that has units of velocity (M ^{ 0 } L ^{ 1 } T ^{ 1 }), facilitates the required conversion of using energy units to describe momentum. In the field of highenergy particle physics, the fundamental velocity unit is the speed of light c. Thus, dividing energy in eV by the speed of light in vacuum, one can describe the momentum of an electron as eV/c.
The fundamental velocity constant c can be 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:
Mass
By massenergy equivalenceMassenergy equivalence
In physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. In this concept, mass is a property of all energy, and energy is a property of all mass, and the two properties are connected by a constant...
, the electron volt is also a unit of mass. It is common in particle physics
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
, where mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
and energy are often interchanged, to use eV/c^{2}, where c is the speed of light
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
in a vacuum (from E = mc^{2}
Massenergy equivalence
In physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. In this concept, mass is a property of all energy, and energy is a property of all mass, and the two properties are connected by a constant...
). Even more common is to use a system of natural units
Natural units
In physics, natural units are physical units of measurement based only on universal physical constants. For example the elementary charge e is a natural unit of electric charge, or the speed of light c is a natural unit of speed...
with c set to 1 (hence, E = m), and simply use eV as a unit of mass.
For example, an electron and a positron
Positron
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...
, each with a mass of 0.511 MeV/c^{2}, can annihilate to yield 1.022 MeV of energy. The proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
has a mass of 0.938 GeV
GEV
GEV or GeV may stand for:*GeV or gigaelectronvolt, a unit of energy equal to billion electron volts*GEV or Grid Enabled Vehicle that is fully or partially powered by the electric grid, see plugin electric vehicle...
/c^{2} (and, in general, the masses of all hadron
Hadron
In particle physics, a hadron is a composite particle made of quarks held together by the strong force...
s are of the order of 1 GeV/c^{2}), which makes the GeV (gigaelectronvolt) a very convenient unit of mass for particle physics
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
:

 1 GeV/c^{2} = 1.783 kg
The atomic mass unit
Atomic mass unit
The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon12 in its nuclear and electronic ground state, and has a value of...
, 1 gram divided by Avogadro's number
Avogadro's number
In chemistry and physics, the Avogadro constant is defined as the ratio of the number of constituent particles N in a sample to the amount of substance n through the relationship NA = N/n. Thus, it is the proportionality factor that relates the molar mass of an entity, i.e...
, is almost the mass of a hydrogen atom
Hydrogen atom
A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positivelycharged proton and a single negativelycharged electron bound to the nucleus by the Coulomb force...
, which is mostly the mass of the proton. To convert to megaelectronvolts, use the formula:

 1 amuAtomic mass unitThe unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon12 in its nuclear and electronic ground state, and has a value of...
= 931.46 MeV/c^{2} = 0.93146 GeV/c^{2}  1 MeV/c^{2} = 1.074 amu
 1 amu
Distance
In particle physicsParticle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
, a system of units in which the speed of light in a vacuum c and the reduced Planck constant
Planck constant
The Planck constant , also called Planck's constant, is a physical constant reflecting the sizes of energy quanta in quantum mechanics. It is named after Max Planck, one of the founders of quantum theory, who discovered it in 1899...
ħ are dimensionless and equal to unity is widely used: . 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 B^{0} meson
B meson
B mesons are mesons composed of a bottom quark or bottom antiquark and either an up , down , strange or charm quark . The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark's short lifetime...
has a lifetime of 1.530(9) picosecond
Picosecond
A picosecond is 10−12 of a second. That is one trillionth, or one millionth of one millionth of a second, or 0.000 000 000 001 seconds. A picosecond is to one second as one second is to 31,700 years....
s, mean decay length is , or a decay width of .
Conversely, the tiny meson mass mass differences responsible for meson oscillations are often expressed in the more convenient inverse picoseconds.
Temperature
In certain fields, such as plasma physics, it is convenient to use the electronvolt as a unit of temperature. The conversion to kelvinKelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
s (symbol: uppercase K) is defined by using k_{B}, the Boltzmann constant:
For example, a typical magnetic confinement fusion
Magnetic confinement fusion
Magnetic confinement fusion is an approach to generating fusion power that uses magnetic fields to confine the hot fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of fusion energy research, the other being inertial confinement fusion. The magnetic approach is...
plasma is 15 keV, or 170 megakelvins.
Properties
The energy E, frequency v, and wavelength λ of a photon are related bywhere h is the Planck constant
Planck constant
The Planck constant , also called Planck's constant, is a physical constant reflecting the sizes of energy quanta in quantum mechanics. It is named after Max Planck, one of the founders of quantum theory, who discovered it in 1899...
, c is the speed of light
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
. For quick calculations, this reduces to
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, and so on.
Scattering experiments
In a lowenergy 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 scintillationScintillation (physics)
Scintillation is a flash of light produced in a transparent material by an ionization event. See scintillator and scintillation counter for practical applications.Overview:...
light. For example, the yield of a phototube
Phototube
A phototube is a type of gasfilled or vacuum tube that is extremely sensitive to light in the ultraviolet, visible, and nearinfrared ranges of the electromagnetic spectrum.Operating principles:...
is measured in phe/keVee (photoelectrons per keV electronequivalent 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.
External links
 BIPM's definition of the electronvolt
 http://physics.nist.gov/cuu/Constants physical constants reference; CODATA data