Electron Electron Experiments with Crookes tube first demonstrated the particle nature of electrons. In this illustration, the profile of the cross-shaped target is projected against the tube face at right by a beam of electrons.[1] Composition: Elementary particle[2] Family: Fermion Group: Lepton Generation: First Interaction: Gravity, Electromagnetic, Weak Antiparticle: Positron (also called antielectron) Theorized: Richard Laming (1838–51),[3] G. Johnstone Stoney (1874) and others.[4][5] Discovered: J. J. Thomson (1897)[6] Symbol(s): e−, β− Mass: 9.10938215(45)×10−31 kg[7] 5.4857990943(23)×10−4 u[7] [1822.88850204(77)]-1 u[note 1] 0.510998910(13) MeV/c2[7] Electric charge: −1 e[note 2] −1.602176487(40)×10−19 C[7] Magnetic moment: −1.00115965218111 μB[7] Spin: 1⁄2 The electron is a subatomic particle that carries a negative electric charge. It has no known substructure and is believed to be a point particle.[2] Electrons participate in gravitational, electromagnetic and weak in- teractions. Like its rest mass and elementary charge, the intrinsic angular momentum (or spin) of an electron has a constant value. In the collision of an electron and a positron, the electron’s antiparticle, both are annihil- ated. An electron–positron pair can be pro- duced from gamma ray photons with suffi- cient energy.[8] The concept of an indivisible amount of electric charge was theorized to explain the chemical properties of atoms, beginning in 1838 by British natural philosopher Richard Laming;[4] the name electron was introduced for this charge in 1894 by Irish physicist Ge- orge Johnstone Stoney. The electron was identified as a particle in 1897 by J. J. Thom- son and his team of British physicists.[6][9] Electrons are identical particles that belong to the first generation of the lepton particle family. Electrons have quantum mechanical properties of both a particle and a wave, so they can collide with other particles and be diffracted like light. Each electron occupies a quantum state that describes its random be- havior upon measuring a physical parameter, such as its energy or spin orientation. Be- cause an electron is a type of fermion, no two electrons can occupy the same quantum state; this property is known as the Pauli ex- clusion principle.[10] In many physical phenomena, such as electricity, magnetism, and thermal conduct- ivity, electrons play an essential role. An electron generates a magnetic field while moving, and it is deflected by external mag- netic fields. When an electron is accelerated, it can absorb or radiate energy in the form of photons. Electrons, together with atomic nuc- lei made of protons and neutrons, make up atoms. However, electrons contribute less than 0.06% to an atom’s total mass. The at- tractive Coulomb force between an electron and a proton causes electrons to be bound in- to atoms. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding.[11] Electrons were created by the Big Bang, and they can be annihilated during stellar nucleosynthesis. Electrons are produced by From Wikipedia, the free encyclopedia Electron 1 cosmic rays entering the atmosphere and are predicted to be created by Hawking radiation at the event horizon of a black hole. Radio- active isotopes can release an electron from an atomic nucleus as a result of negative beta decay. Laboratory instruments are capable of containing and observing individual elec- trons, while telescopes can detect electron plasma by its energy emission. Electron plasma has multiple applications, including welding, cathode ray tubes, electron micro- scopes, radiation therapy, lasers and particle accelerators. History The ancient Greeks noticed that amber, a gemstone that is formed from the hardened sap of trees, attracted small objects when rubbed with fur; apart from lightning, this phenomenon was man’s earliest experience of electricity.[12] In his 1600 treatise De Mag- nete, the English physician William Gilbert coined the New Latin term electricus, to refer to this property of attracting small ob- jects after being rubbed.[13] Both electric and electricity are derived from the Latin ēlec- trum, which came from the Greek word ēlektron (ήλεκτρον) for amber. During the period 1838–51, British natural philosopher Richard Laming conceived the idea that an atom is composed of a core of matter surrounded by subatomic particles that had unit electric charges.[3] Beginning in 1846, German physicist William Weber theor- ized that electricity was composed of posit- ively and negatively charged fluids, and their interaction was governed by the inverse square law. After studying the phenomenon of electrolysis in 1874, Irish physicist George Johnstone Stoney suggested that there exis- ted a "single definite quantity of electricity", the charge of a monovalent ion. He was able to estimate the value of this elementary charge e by means of Faraday’s laws of elec- trolysis.[14] However, Stoney believed these charges were permanently attached to atoms and could not be removed. In 1881, German physicist Hermann von Helmholtz argued that both positive and negative charges were divided into elementary parts, each of which "behaves like atoms of electricity".[4] In 1894, Stoney coined the term electron to represent these elementary charges, say- ing, "...an estimate was made of the actual amount of this most remarkable fundamental unit of electricity, for which I have since ven- tured to suggest the name electron."[15] The English name electron is a combination of the word electric and the suffix -on, with the lat- ter now used to designate a subatomic particle, such as a proton or neutron.[16][17] At the end of the nineteenth century, the various scientific concepts came together to form a unified theory based upon an electron as a fundamental component of matter.[5] Discovery A beam of electrons is being deflected in a circle by a magnetic field.[18] German physicist Johann Wilhelm Hittorf un- dertook the study of electrical conductivity in rarified gases. In 1869 he discovered a glow emitted from the cathode that increased in size with decrease in gas pressure. In 1876, German physicist Eugen Goldstein showed that the rays from this glow cast a shadow, and he dubbed them cathode rays.[19] During the 1870s, English chemist and physicist Sir William Crookes developed the first cathode ray tube to have a high vacuum inside.[20] He then showed that the luminescence rays ap- pearing within the tube carried energy and moved from the cathode to the anode. Fur- thermore, by applying a magnetic field, he was able to deflect the rays, thereby demon- strating that the beam behaved as though it were negatively charged.[21][22] In 1879, he proposed that these properties could be ex- plained by what he termed ’radiant matter’. He suggested that this was a fourth state of matter, consisting of negatively charged mo- lecules that were being projected with high velocity from the cathode.[23] The German-born British physicist Arthur Schuster expanded upon Crookes’ experi- ments by placing metal plates in parallel to the cathode rays and applying an electrical potential between the plates. The field From Wikipedia, the free encyclopedia Electron 2 deflected the rays toward the positive plate, providing further evidence that the rays car- ried negative charge. By measuring the amount of deflection for a given level of cur- rent, in 1890 Schuster was able to estimate the charge-to-mass ratio of the ray compon- ents. However, this produced such an unex- pectedly large value that little credence was given to his calculations at the time.[21] In 1896, British physicist J. J. Thomson, with his colleagues John S. Townsend and H. A. Wilson,[6] performed experiments indicat- ing that cathode rays really were unique particles, rather than waves, atoms or mo- lecules as was believed earlier. Thomson made good estimates of both the charge e and the mass m, finding that cathode ray particles, which he called "corpuscles," had perhaps one thousandth of the mass of the least massive ion known: hydrogen. He showed that their charge to mass ratio, e/m, was independent of cathode material. He fur- ther showed that the negatively charged particles produced by radioactive materials, by heated materials and by illuminated ma- terials were universal.[24] The name electron was again proposed for these particles by the Irish physicist George F. Fitzgerald, and it has since gained universal acceptance.[21] While studying naturally fluorescing min- erals in 1896, French physicist Henri Becquerel discovered that they emitted radi- ation without any exposure to an external en- ergy source. These radioactive materials be- came the subject of much interest by scient- ists, including New Zealand physicist Ernest Rutherford who discovered they emitted particles. He designated these particles alpha and beta, based on their ability to penetrate matter.[25] In 1900, Becquerel showed that the beta rays emitted by radium could be de- flected by an electric field, and that their mass-to-charge ratio was the same as for cathode rays.[26] This evidence strengthened the view that electrons existed as compon- ents of atoms.[27][28] The electron’s charge was more carefully measured by American physicist Robert Mil- likan in his oil-drop experiment of 1909, which was published in 1911. This experi- ment used an electric field to prevent a charged droplet of oil from falling as a result of gravity. This device could measure the electric charge from as few as 1–150 ions with an error margin of less than 0.3%. Com- parable experiments had been done earlier by Thomson’s team, using clouds of charged water droplets generated by electrolysis,[6] and in 1911 by Abram Ioffe, who independ- ently obtained the same result as Millikan us- ing charged microparticles of metals, then published his results in 1913.[29][30] However, oil drops were more stable than water drops due to their slower evaporation rate, and thus more suited to precise experi- mentation over longer periods of time.[31] Around the beginning of the twentieth century, it was found that under certain con- ditions a fast moving charged particle caused a condensation of supersaturated water va- por along its path. In 1911, Charles Wilson used this principle to devise his cloud cham- ber, allowing the tracks of charged particles, such as fast-moving electrons, to be photo- graphed. This and subsequent particle de- tectors allowed electrons to be studied indi- vidually, rather than in bulk as had been the case before.[32] Atomic theory The Bohr model of the atom, showing quant- ized states of electron orbital energy. An electron dropping to a lower orbit emits a photon equal to the energy difference between the orbits. By 1914, experiments by physicists Ernest Rutherford, Henry Moseley, James Franck and Gustav Hertz had largely established the structure of an atom as a dense nucleus of positive charge surrounded by lower-mass electrons.[33] In 1913, Danish physicist Niels Bohr postulated that electrons resided in From Wikipedia, the free encyclopedia Electron 3 quantized energy states, with the energy de- termined by the angular momentum of the electron’s orbits about the nucleus. The elec- trons could move between these states, or or- bits, by the emission or absorption of photons at specific frequencies. By means of these quantized orbits, he accurately explained the spectral lines of hydrogen that were formed when the gas is energized by heat or electri- city.[34] However, Bohr’s model failed to ac- count for the relative intensities of the spec- tral lines and it was unsuccessful in explain- ing the spectrum of more complex atoms.[33] Chemical bonds between atoms were ex- plained by Gilbert Newton Lewis, who in 1916 proposed that a covalent bond between two atoms is maintained by a pair of elec- trons shared by them.[35] Later, in 1923, Wal- ter Heitler and Fritz London gave the full ex- planation of the electron-pair formation and chemical bonding in terms of the then-re- cently developed quantum mechanics.[36] In 1919, the American chemist Irving Langmuir elaborated on the Lewis’ static model of the atom and suggested that all electrons were distributed in successive "concentric (nearly) spherical shells, all of equal thickness".[37] The shells were, in turn, divided by him in a number of cells each containing one pair of electrons. With this model Langmuir was able to qualitatively explain the chemical properties of all elements in the periodic table,[36] which were known to largely repeat themselves according to the periodic law.[38] In 1924, Austrian physicist Wolfgang Pauli observed that the shell-like structure of the atom could be explained by a set of four para- meters that defined every quantum energy state, as long as each state was inhabited by no more than a single electron. (This prohibi- tion against more than one electron occupy- ing the same quantum energy state became known as the Pauli exclusion principle.)[39] However, what physicists lacked was a phys- ical mechanism to explain the fourth para- meter, which had two possible values. This was provided by the Dutch physicists Abra- ham Goudsmith and George Uhlenbeck when they suggested that an electron, in addition to the angular momentum of its orbit, could possess an intrinsic angular mo- mentum.[33][40] This property became known as spin, and it explained the previously mys- terious splitting of spectral lines observed with a high-resolution spectrograph; this phenomenon is known as fine structure split- ting.[41] Quantum mechanics See also: History of quantum mechanics In his 1924 dissertation Recherches sur la théorie des quanta, French physicist Louis de Broglie hypothesized that all matter pos- sesses a wave–particle duality similar to light:[42] the de Broglie hypothesis. That is, under the appropriate conditions, electrons and other matter would show properties of either particles or waves. The corpuscular properties of a particle are demonstrated when it is shown to have a localized position in space at each moment in time and a tra- jectory that is subject to modification by ex- ternal forces.[43] The wave-like nature is ob- served, for example, when a beam of light is passed through parallel slits and creates in- terference patterns. In 1927, the interference effect was demonstrated with a beam of elec- trons by English physicist George Paget Thomson with a thin metal film and by Amer- ican physicists Clinton Davisson and Lester Germer using a crystal of nickel.[44] In quantum mechanics, the behavior of an electron in an atom is described by an orbit- al, which is a probability distribution rather than an orbit. In the figure, the shading at a point indicates the relative probability of the particle in the lowest-energy orbital being at that point. From Wikipedia, the free encyclopedia Electron 4 The success of de Broglie’s prediction led to the publication, by Erwin Schrödinger in 1926, of the equation named after him that successfully describes how electron waves propagated.[45] Rather than yielding a solu- tion that determines the location of an elec- tron over time, this wave equation can be used to predict the probability of finding an electron near a position. This approach was later called quantum mechanics, which provided an almost exact derivation to the energy states of an electron in a hydrogen atom.[46] Once spin and the interaction between multiple electrons were considered, the quantum mechanics allowed the configur- ation of electrons in atoms with higher atom- ic numbers than hydrogen to be successfully predicted. However, for atoms with multiple electrons, the exact solution to the wave equation is much more complicated, so ap- proximations are necessary.[47] In 1928, building on Wolfgang Pauli’s work, Paul Dirac formulated the Dirac equa- tion, which for the first time correctly de- scribed an electron moving at velocities close to the speed of light.[48] In order to resolve some problems with in his relativistic equa- tion, in 1930 Dirac developed a model of the vacuum as an infinite sea of particles having negative energy, which was dubbed the Dirac sea. This led him to predict the existence of a positron, the antimatter counterpart of the electron.[49] This particle was discovered in 1932 by Carl D. Anderson, who proposed calling standard electrons negatrons, and us- ing electron as a generic term to describe both the positively and negatively charged variants. This usage of the term ’negatron’ is still occasionally encountered today, and it may be shortened to ’negaton’.[50][51] The first experimental discrepancy in Dir- ac’s theory was discovered in 1947 by Willis Lamb, working in collaboration with gradu- ate student Robert Retherford. They found that certain quantum states of hydrogen atom, which should have the same energy, were shifted in relation to each other, the dif- ference being the Lamb shift. About the same time, Polykarp Kusch, working with Henry M. Foley, discovered the magnetic moment of the electron is slightly larger than predicted by Dirac’s theory. This small difference was later called anomalous magnetic dipole mo- ment of the electron. To resolve these issues, a refined version of the quantum electro- dynamics theory was developed by Sin-Itiro Tomonaga, Julian Schwinger and Richard P. Feynman.[52] Particle accelerators With the development of the particle acceler- ator during the first half of the twentieth cen- tury, physicists began to delve deeper into the properties of subatomic particles.[53] The first successful attempt to accelerate elec- trons using magnetic induction was made in 1942 by Donald Kerst. His initial betatron reached energies of 2.3 MeV (million electron volts), while subsequent betatrons achieved 300 MeV. In 1947, synchrotron radiation was discovered with a 70 MeV electron synchro- tron at General Electric. This radiation was caused by the acceleration of electrons, mov- ing near the speed of light, through a mag- netic field.[54] With a beam energy of 1.5 GeV, the first high-energy particle collider was ADONE, which began operations in 1968.[55] This device accelerated electrons and positrons—the antiparticles of electrons—in opposite directions, effectively doubling the energy of their collision when compared to striking a static target with an electron.[56] The Large Electron-Positron Collider (LEP) at CERN, which was operational from 1989 to 2000, achieved collision energies of 209 GeV and made important measurements for the Standard Model of particle physics.[57][58] Characteristics Classification In the Standard Model of particle physics, electrons belong to the group of subatomic particles called leptons, which are believed to be elementary or fundamental particles. Elec- trons have the lowest mass of any electrically charged lepton and belong to the first-generation of fundamental particles.[59] The electron is an analog of the two charged leptons of the second and third gen- erations, the muon and the tauon, respect- ively, which are identical in charge, spin, and interaction, but are more massive. All mem- bers of the lepton group belong to the family of fermions. This family includes all element- ary particles with half-odd integer spin; the electron has spin 1⁄2. Leptons differ from the other basic constituent of matter, the quarks, by their lack of strong interaction.[60] From Wikipedia, the free encyclopedia Electron 5 Standard model of elementary particles. The electron is at lower left. If the spin of the electron is oriented in the same direction as its momentum, it is called a right-handed spin; otherwise it is left-handed. Thus the same electron can have left- or right-handed spin, depending on its velocity with respect to an observer. The left- handed spin component of the electron forms a weak isospin doublet with the electron neutrino, which is an uncharged, first-gener- ation lepton with little or no mass.[61] The right-handed component of the electron spin is an isospin singlet.[62] Fundamental properties The mass of an electron is approximately 9.109 × 10−31 kilograms,[7] or 5.489 × 10−4 atomic mass units. Based on Einstein’s prin- ciple of mass–energy equivalence, this mass corresponds to a rest energy of 0.511 MeV. The ratio between the mass of a proton and that of an electron is about 1836.[63] This ra- tio is one of the fundamental constants of physics, and the Standard Model of particle physics assumes this and other constants are unchanging. Astronomical measurements show that the ratio has held the same value for at least half the age of the universe.[64] Electrons have an electric charge of −1.602 × 10−19 Coulomb,[7] which is used as a standard unit of elementary charge for sub- atomic particles. Within the limits of experi- mental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign.[65] As the symbol e is used for the constant of electric charge, the elec- tron is commonly symbolized by e−, where the minus sign indicates the negative charge. The positron is symbolized by e+ because it has the same properties as the electron but with a positive rather than negative charge.[7][60] The electron has no known substruc- ture.[2][66] Hence, it is defined or assumed to be a point charge with no spatial extent—a point particle.[10] Observation of a single electron in a Penning trap shows the upper limit of the particle’s radius is 10−22 meters.[67] The classical electron radi- us is 2.8179 × 10−15 m. This is the radius that is inferred from the electron’s electric charge, by assuming that its mass has exclus- ively electrostatic origin and using the clas- sical theory of electrodynamics alone, while ignoring quantum mechanics.[note 3] There are elementary particles that spon- taneously decay into different particles. An example is the muon, which decays into an electron, a neutrino and an antineutrino, with a half life of 2.2 × 10−6 seconds. However, the electron is thought to be stable on theor- etical grounds; an electron decaying into a neutrino and photon would mean that elec- tric charge is not conserved.[68] The experi- mental lower bound for the electron’s mean lifetime is 4.6 × 1026 years, with a 90% con- fidence interval.[69] Quantum properties As with all particles, electrons can act as waves. This is called the wave–particle dual- ity and can be demonstrated using the double-slit experiment. The wave-like nature of the electron allows it to pass through two parallel slits simultaneously, rather than just one slit as would be the case for a classical particle. In quantum mechanics, the wave- like property of an electron is described mathematically by a complex-valued function, the wave function, commonly denoted by the Greek letter psi (ψ). When the absolute value of this function is squared, it gives the prob- ability that an electron will be observed near a location—the electron density.[70] Electrons are identical particles because they can not be distinguished from each oth- er by their intrinsic physical properties. In the quantum mechanics, this means that a From Wikipedia, the free encyclopedia Electron 6 Example of an asymmetric wave function for a quantum state of two identical fermions in a box. If the particles swap position, the wave function inverts. pair of interacting electrons must be able to swap positions without an observable change to the state of the system. The wave function of fermions, including electrons, is antisym- metric, meaning that it changes sign when two electrons are swapped; that is, ψ(r1, r2) = −ψ(r2, r1), where the variables r1 and r2 correspond to the first and second electrons, respectively. Since the absolute value is not changed by a sign swap, this corresponds to equal probabilities. Bosons, such as the photon, have symmetric wave functions in- stead.[70] In the case of antisymmetry, solutions of the wave equation for interacting electrons result in a zero probability that each pair will occupy the same location or state. This is re- sponsible for the Pauli exclusion principle, which precludes any two electrons from oc- cupying the same quantum state. This prin- ciple explains many of the properties of elec- trons. For example, it causes groups of bound electrons to occupy different orbitals in an atom, rather than all overlapping each other in the same orbit.[70] Virtual particles Physicists believe that empty space may be continually creating pairs of virtual particles, such as a positron and electron, which rap- idly annihilate each other shortly there- after.[71] The net energy from this reaction is zero. The combination of the energy variation needed to create these particles, and the time during which they exist, fall under the threshold of detectability expressed by the Heisenberg uncertainty relation, ΔE•Δt ≥ ħ. In effect, the energy needed to create these virtual particles, ΔE, can be "borrowed" from the vacuum for a period of time, Δt, so that their product is no more than the reduced Planck constant, ħ ≈ 6.6 × 10−16 eV·s. Thus, for a virtual electron, Δt is at most 1.3 × 10−21 s.[72] Virtual electron-positron pairs appearing at random near an electron (at lower left) While an electron-positron virtual pair is in existence, the coulomb force from the am- bient electric field surrounding an electron causes a created positron to be attracted to the original electron, while a created elec- tron experiences a repulsion. This causes the two charged virtual particles to physically separate for a brief period before merging back together, and during this period they behave like an electric dipole. The combined effect of many such pair creations is to par- tially shield the charge of the electron, in a process called vacuum polarization. Thus the effective charge of an electron is actually smaller than its true value, and the charge in- creases with decreasing distance from the electron.[73][74] This polarization was con- firmed experimentally in 1997 using the Japanese TRISTAN particle accelerator.[75] A comparable shielding effect is seen for the mass of the electron. The equivalent rest energy consists of the mass-energy of the "bare" particle plus the energy of the sur- rounding electric field. In classical physics, the energy of the electric field is dependent upon the size of the charged object, which, for a dimensionless particle, results in an in- finite energy. Instead, because of vacuum fluctuations, allowance must be made for an electron–positron pair appearing in the elec- tric field and the positron annihilating the original electron, causing the virtual electron From Wikipedia, the free encyclopedia Electron 7 to become a real electron. This interaction creates a negative energy imbalance that counteracts the radius-dependency of the electric field.[76] The total mass is referred to as the renormalized mass, because a math- ematical technique called renormalization is used by physicists to relate the observed mass and bare mass of the electron. This method replaces the terms used to compute the mass with the actual mass found experi- mentally, thereby avoiding problems with di- vergences in the formulas.[77] The electron has an intrinsic angular mo- mentum or spin, which equals 1⁄2 in units of ħ, and an intrinsic magnetic moment along its spin axis.[7] The magnitude of the spin is √3⁄2ħ.[note 4] A projection of the spin on any axis can only be ±ħ⁄2; this property is usually stated by referring to the electron as a spin-1⁄2 particle. The magnetic moment associated with the orbital motion of an electron in an atom is ex- pressed in terms of the Bohr magneton,[note 5] which is a physical constant equal to 9.274 009 15(23) × 10−24 joules per tesla.[7] The intrinsic angular momentum of an electron is almost equal to one Bohr magneton, with the 0.1% difference (anomalous magnetic mo- ment) being explained by interaction with vir- tual particles and antiparticles.[78][79] The extraordinarily precise agreement of this pre- dicted difference with the experimentally de- termined value is viewed as one of the great achievements of the quantum electrodynam- ics.[80][81] In classical physics, the angular mo- mentum and magnetic moment of an object depend upon its physical dimensions. Hence, the concept of a dimensionless electron pos- sessing these properties is unclear. A pos- sible explanation lies in the formation of vir- tual photons in the electric field generated by the electron. These photons cause the elec- tron to shift about in a jittery fashion (known as zitterbewegung),[82] which results in a net circular motion with precession. This motion produces both the spin and the magnetic mo- ment of the electron.[10][83] In atoms, this creation of virtual photons explains the Lamb shift observed in spectral lines.[73] Interaction An electron generates an electric field that exerts an attractive force on a particle with a positive charge, such as the proton, and a repulsive force on a particle with a negative charge. The strength of this force is determ- ined by Coulomb’s inverse square law.[84] When an electron is in motion, it generates a magnetic field,[85] which is related to the mo- tion of electrons (the current) with respect to an observer by the Ampère-Maxwell law. It is this property of induction which supplies the magnetic field that drives an electric mo- tor.[86] The electromagnetic field of an arbit- rary moving charged particle is expressed by the Liénard–Wiechert potentials, which are valid even when the particle’s speed is close to that of light (or relativistic velocities). A charged particle q (at left) is moving with velocity v through a magnetic field B that is oriented perpendicular to the display. For an electron, q is negative so it follows a curved trajectory toward the top. When an electron is moving through a magnetic field, it is subject to the Lorentz force that exerts an influence in a direction perpendicular to the plane defined by the magnetic field and the electron velocity. This centripetal force causes the electron to fol- low a helical trajectory through the field at a radius equal to the gyroradius. The accelera- tion from this curving motion induces the electron to radiate energy in the form of syn- chrotron radiation.[87][88][note 6] The energy emission in turn causes a recoil of the elec- tron, known as the Abraham-Lorentz-Dirac force, which creates a friction that slows the electron. This force is caused by a back-reac- tion of the electron’s own field upon itself.[89] In the quantum electrodynamics the elec- tromagnetic interaction between particles is mediated by photons. An isolated electron that is not undergoing acceleration is unable to emit or absorb a real photon; doing so From Wikipedia, the free encyclopedia Electron 8 would violate conservation of energy and mo- mentum. Instead, virtual photons can trans- fer momentum between two charged particles. It is this exchange of virtual photons that, for example, generates the Coulomb force.[90] Energy emission can oc- cur when a moving electron is deflected by a charged particle, such as a proton. The accel- eration of the electron results in the emission of Bremsstrahlung radiation.[91] Here, Bremsstrahlung is produced by an electron e deflected by the electric field of an atomic nucleus. The energy change E2 − E1 determines the frequency f of the emitted photon. The relative strength of the electromag- netic interaction between two charged particles, such as an electron and a proton, is given by the fine-structure constant. This value is a dimensionless quantity formed by the ratio of two energies: the electrostatic energy of attraction (or repulsion) at a separ- ation of one Compton wavelength, and the rest energy of the charge. It is given by α ≈ 7.297353 × 10−3, which is approximately equal to 1⁄137.[7] The outcome of an elastic collision between a photon and a solitary electron is called Compton scattering. This collision res- ults in a transfer of momentum between the particles, which modifies the wavelength of the photon by an amount called the Compton shift.[note 7] The maximum magnitude of this wavelength shift is h/mc, which is known as the Compton wavelength.[92] For an electron, it has a value of 2.43 × 10−12 m.[7] When electrons and positrons collide, they annihilate each other, giving rise to two or more gamma ray photons emitted at roughly 180° to each other. If the electron and positron have negligible momentum, a positronium atom can form before annihila- tion results in two 0.511 MeV gamma ray photons.[93][94] On the other hand, high-en- ergy photons may transform into an electron and a positron by a process called pair pro- duction, but only in the presence of a nearby charged particle, such as a nucleus.[95][96] In the theory of electroweak interaction, the left-handed spin component of the elec- tron forms a weak isospin doublet with the electron neutrino. This means that during weak interactions, electron neutrinos behave like electrons. Either member of this doublet can undergo a charged current interaction by emitting or absorbing a W boson and be con- verted into the other member. Charge is con- served during this reaction because the W boson also carries a charge, cancelling out any net change during the transmutation. Charged current interactions are responsible for the phenomenon of beta decay in a radio- active atom. Both the electron and electron neutrino can undergo a neutral current inter- action via a Z0 boson exchange, and this is responsible for neutrino-electron elastic scat- tering.[61] Atoms and molecules An electron can be bound to the nucleus of an atom by the attractive Coulomb force. The wave-like behavior of a bound electron is de- scribed by a function called an atomic orbital. Each orbital has its own set of quantum num- bers such as energy, angular momentum and projection of angular momentum, and only a discrete set of these orbitals exist around the nucleus. Electrons can transfer between dif- ferent orbitals by the emission or absorption of photons with an energy that matches the difference in potential.[97] Other methods of orbital transfer include collisions with particles, such as electrons, and the Auger effect.[98] In order to escape the atom, the energy of the electron must be increased above its binding energy to the atom. This oc- curs, for example, with the photoelectric From Wikipedia, the free encyclopedia Electron 9 Probability densities for the first few hydro- gen atom orbitals, seen in cross-section. The energy level of a bound electron determines the orbital it occupies, and the color shows the probability that the electron will be seen near a position. effect, where an incident photon exceeding the atom’s ionization energy is absorbed by the electron.[99] The orbital angular momentum of elec- trons is quantized. Because the electron is charged, it produces a magnetic moment that is proportional to the angular momentum. The net magnetic moment of an atom is equal to the vector sum of all its component orbital and spin magnetic moments. Pairs of elec- trons in an atom align their spins in opposite directions, giving them different spin quantum numbers that satisfy the Pauli ex- clusion principle. Thus the magnetic mo- ments of an atom’s paired electrons cancel each other out. The nucleus contributes a magnetic moment, but this is negligible in comparison to the effect from the elec- trons.[100] The chemical bond between atoms occurs as a result of electromagnetic interactions, as described by the laws of quantum mechan- ics.[101] The strongest bonds are formed by the sharing or transfer of electrons between atoms, allowing the formation of mo- lecules.[102] Within a molecule, electrons move under the influence of several nuclei, and occupy molecular orbitals; much as they can occupy atomic orbitals in isolated atoms. [103] A fundamental factor in these molecular structures is the existence of electron pairs. These are electrons with opposed spins, allowing them to occupy the same molecular orbital without violating the Pauli exclusion principle (much like in atoms). Different mo- lecular orbitals have different spatial distri- bution of the electron density. For instance, in bonded pairs (i.e. in the pairs that actually bind atoms together) electrons can be found with the maximal probability in a relatively small volume between the nuclei. On the con- trary, in non-bonded pairs electrons are dis- tributed in a large volume around nuclei.[104] Conductivity Lightning is an example of the phenomena produced by triboelectricity.[105] If a body has more or fewer electrons than are required to balance the positive charge of the nuclei, then that object has an electric charge. (For a single atom or molecule, the object is termed an ion.) When there is an ex- cess of electrons, the object is said to be neg- atively charged. When there are fewer elec- trons than the number of protons in nuclei, the object is said to be positively charged. When the number of electrons and the num- ber of protons are equal, their charges cancel each other and the object is said to be elec- trically neutral. A macroscopic body can de- velop an electric charge through rubbing, by the triboelectric effect.[106] Independent electrons moving in vacuum or certain media are termed free electrons. When free electrons move, they produce a net flow of charge called an electric current, which generates a magnetic field. Likewise a From Wikipedia, the free encyclopedia Electron 10 current can be created by a changing mag- netic field. These interactions are described mathematically by Maxwell’s equations.[107] At a given temperature, each material has an electrical conductivity that determines the value of electric current when an electric po- tential is applied. Examples of good conduct- ors include metals such as copper and gold, whereas glass and Teflon are poor conduct- ors. In any dielectric material, the electrons remain bound to their respective atoms and the material behaves as an insulator. Any semiconductor has a variable level of con- ductivity that lies between the extremes of conduction and insulation.[108] On the other hand, metals have an electronic band struc- ture that allows for delocalized electrons. These electrons are not associated with spe- cific atoms, so when an electric field is ap- plied, they are free to move like a gas (called Fermi gas)[109] through the material much like free electrons. Because of collisions between electrons and atoms, the drift velocity of electrons in a conductor is on the order of millimetres per second. However, the speed at which a change of current at one point in the material causes changes in currents in other parts of the material, the velocity of propagation, is typically about 75% of light speed.[110] This occurs because electrical signals propagate as a wave, with the velocity dependent on the dielectric constant of the material.[111] Metals make relatively good conductors of heat, primarily because the delocalized elec- trons are free to transport thermal energy between atoms. However, unlike electrical conductivity, the thermal conductivity of a metal is nearly independent of temperature. This is expressed mathematically by the Wiedemann-Franz law,[109] which states that the ratio of thermal conductivity to the elec- trical conductivity is proportional to the tem- perature. The thermal disorder in the metal- lic lattice increases the electrical resistivity of the material, producing a temperature de- pendence for electrical current.[112] When cooled below a point called the crit- ical temperature, materials can undergo a phase transition in which they lose all res- istivity to electrical current, in a process known as superconductivity. In BCS theory, this behavior is modeled by pairs of electrons entering a quantum state known as a Bose–Einstein condensate. These Cooper pairs have their motion coupled to nearby matter via lattice vibrations called phonons, thereby avoiding the collisions with atoms that normally create electrical resist- ance.[113] (Cooper pairs have a radius of roughly 100 nm, so they can overlap each other.)[114] However, the mechanism by which higher temperature superconductors operate remains uncertain. Motion and energy According to Einstein’s theory of special re- lativity, as an electron’s speed approaches the speed of light, from an observer’s point of view its relativistic mass increases, thereby making it more and more difficult to acceler- ate it from within the observer’s frame of ref- erence. The speed of an electron can ap- proach, but never reach, the speed of light in a vacuum, c. However, when relativistic elec- trons—that is, electrons moving at a speed close to c—are injected into a dielectric medi- um such as water, where the local speed of light is significantly less than c, the electrons temporarily travel faster than light in the me- dium. As they interact with the medium, they generate a faint light called Cherenkov radi- ation.[115] Lorentz factor as a function of velocity. It starts at value 1 and goes to infinity as v ap- proaches c. The effects of special relativity are based on a quantity known as the Lorentz factor, defined as γ = 1/√1 − v2/c2 where v is the speed of the particle. The kinetic energy Ke of an electron moving with velocity v is: From Wikipedia, the free encyclopedia Electron 11 where me is the mass of electron. For ex- ample, the Stanford linear accelerator can accelerate an electron to roughly 51 GeV.[116] This gives a value of 100,000 for γ, since the mass of an electron is 0.51 MeV/c2. The relativistic momentum of this electron is 100,000 times the momentum that classical mechanics would predict for an electron at the same speed.[note 8] Since an electron behaves as a wave, at a given velocity it has a characteristic de Broglie wavelength. This is given by λe = h/p where h is Planck’s constant and p is the mo- mentum.[42] For the 51 GeV electron above, the wavelength is about 2.4×10−17 m, small enough to explore structures well below the size of an atomic nucleus.[117] Formation Pair production caused by the collision of a photon with an atomic nucleus The Big Bang theory is the most widely ac- cepted scientific theory to explain the early stages in the evolution of the Universe.[118] For the first millisecond of the Big Bang, the temperatures were over 10 billion kelvins and photons had mean energies over a mil- lion electron volts. These photons were suffi- ciently energetic that they could react with each other to form pairs of electrons and positrons, where γ is a photon, e+ is a positron and e− is an electron. Likewise, positron-electron pairs annihilated each other and emitted en- ergetic photons. An equilibrium between electrons, positrons and protons was main- tained during this phase of the evolution of the Universe. After 15 seconds had passed, however, the temperature of the universe dropped below the threshold where electron- positron formation could occur. Most of the surviving electrons and positrons annihilated each other, releasing gamma radiation that briefly reheated the universe.[119] For reasons that remain uncertain, during the process of leptogenesis there was an ex- cess in the number of electrons over positrons.[120] Hence, about one electron in every billion survived the annihilation pro- cess. This excess matched the excess of pro- tons over anti-protons, in a condition known as baryon asymmetry, resulting in a net charge of zero for the universe.[121][122] The surviving protons and neutrons began to par- ticipate in reactions with each other—in the process known as nucleosynthesis, forming isotopes of hydrogen and helium, with trace amounts of lithium. This process peaked after about five minutes.[123] Any leftover neutrons underwent negative beta decay with a half- life of about a thousand seconds, releasing a proton and electron in the process, where n is a neutron, p is a proton and νe is an electron antineutrino. For about the next 300,000–400,000 years, the excess electrons remained too energetic to bind with atomic nuclei.[124] What followed is a period known as recombination, when neutral atoms were formed and the expanding universe became transparent to radiation.[125] Roughly one million years after the big bang, the first generation of stars began to form.[125] Within a star, stellar nucleosyn- thesis results in the production of positrons from the fusion of atomic nuclei. These anti- matter particles immediately annihilate with electrons, releasing gamma rays. The net res- ult is a steady reduction in the number of electrons, and a matching increase in the number of neutrons. However, the process of stellar evolution can result in the synthesis of radioactive isotopes. Selected isotopes can subsequently undergo negative beta decay, emitting an electron and antineutrino from the nucleus.[126] An example is the cobalt-60 (60Co) isotope, which decays to form nick- el-60 (60Ni).[127] From Wikipedia, the free encyclopedia Electron 12 An extended air shower generated by an en- ergetic cosmic ray striking the Earth’s atmosphere At the end of their lifetime, a star with more than about 20 solar masses can under- go gravitational collapse to form a black hole.[128] According to classical physics, these massive stellar objects exert a gravita- tional attraction that is strong enough to pre- vent anything, even radiation, from escaping past the Schwarzschild radius. However, it is believed that quantum mechanical effects may allow Hawking radiation to be emitted at this distance. Electrons (and positrons) are thought to be created at the event horizon of these stellar remnants. When pairs of virtual particles (such as an electron and positron) are created in the vi- cinity of the event horizon, the random spa- cial distribution of these particles may permit one of them to appear on the exterior; this process is called quantum tunneling. The gravitational potential of the black hole can then supply the energy that transforms this virtual particle into a real particle, allowing it to radiate away into space.[129] In exchange, the other member of the pair is given negat- ive energy, which results in a net loss of mass-energy by the black hole. The rate of Hawking radiation increases with decreasing mass, eventually causing the black hole to evaporate away until, finally, it explodes.[130] Cosmic rays are particles travelling through space with high energies. Energy events as high as 3.0 × 1020 eV have been re- corded.[131] When these particles collide with nucleons in the Earth’s atmosphere, a shower of particles is generated, including pions.[132] More than half of the cosmic radiation ob- served from the Earth’s surface consists of muons. The particle called a muon is a lepton which is produced in the upper atmosphere by the decay of a pion. A muon, in turn, can decay to form an electron or positron. Thus, for the negatively charged pion π−,[133] where μ− is a muon and νμ is a muon neutrino. Observation Aurorae are typically caused by energetic electrons precipitating into the atmo- sphere.[134] Remote observation of electrons requires the detection of their radiated energy. For ex- ample, in high-energy environments such as the corona of a star, free electrons form a plasma that radiates energy due to Bremsstrahlung. Electron gas can undergo plasma oscillation, which is waves caused by synchronized variations in electron density, and these produce energy emissions that can be detected by the use of radio tele- scopes.[135] The frequency of a photon is proportional to its energy. As a bound electron transitions between different energy levels of an atom, it will absorb or emit photons at characteristic frequencies called absorption and emission lines, respectively. For instance, when atoms are irradiated by a source with a broad spec- trum, distinct absorption lines will appear in the spectrum of transmitted radiation. Each element or molecule displays a characteristic set of spectral lines, such as the hydrogen spectral series. Spectroscopic measurements of the strength and width of these lines allow the composition and physical properties of a substance to be determined.[136][137] From Wikipedia, the free encyclopedia Electron 13 In laboratory conditions, the interactions of individual electrons can be observed by means of particle detectors, which allow measurement of specific properties such as energy, spin and charge.[99] The develop- ment of the Paul trap and Penning trap al- lows charged particles to be contained within a small region for long durations. This en- ables very precise measurements of the particle properties. For example, in one in- stance the Penning trap was used to contain a single electron for a period of 10 months.[81] Measurements allowed the mag- netic moment of the electron to be measured to a precision of eleven digits, which, in 1980, was a greater accuracy than for any other physical constant.[138] The first video images of an electron’s en- ergy distribution were captured by a team at Lund University in Sweden, February 2008. To capture this phenomenon, the scientists used extremely short flashes of light, called attosecond pulses, which allowed the team at the university’s Faculty of Engineering to capture the electron’s motion for the first time.[139][140] The distribution of the electrons in solid materials can be visualized by angle resolved photoemission spectroscopy (ARPES). This technique uses the photoelectric effect to measure the reciprocal space, a mathematic- al representation of periodic structures, used to infer the original structure. ARPES can be used to determine the direction, speed and scattering of electrons within the materi- al.[141] Plasma applications Particle beams Electron beams are used in welding[143] and lithography.[144] Electron beam processing is used to irradiate materials in order to change their material properties or sterilize medical and food products.[145] In radiation therapy, electron beams are generated by linear ac- celerators for treatment of superficial tu- mors. Because an electron beam only penet- rates to a limited depth before being ab- sorbed, typically up to 5 cm for beams in the range 5–20 MeV, electron therapy is useful for treating skin lesions such as basal cell carcinomas. An electron beam can be used to supplement the treatment of areas that have been irradiated by X-rays.[146][147] During a NASA wind tunnel test, a model of the Space Shuttle is targeted by a beam of electrons, simulating the effect of ionizing gases during re-entry.[142] Particle accelerators use electric fields to propel electrons and their antiparticles to high energies. As these particles pass through magnetic fields, they emit synchro- tron radiation. The intensity of this radiation is spin dependent, which causes polarization of the electron beam—a process known as the Sokolov-Ternov effect.[note 9] The polar- ized electron beams can be useful for various experiments. Synchrotron radiation can also be used for cooling the electron beams, which reduces the momentum spread of the particles. Once the particles have accelerated to the required energies, separate electron and positron beams are brought into colli- sion. The resulting energy emissions are ob- served with particle detectors and used to study particle physics.[148] Imaging Low-energy electron diffraction (LEED) is a method of bombarding a crystalline material with a collimated beam of electrons, then ob- serving the resulting diffraction patterns to determine the structure of the material. The required energy of the electrons is typically in the range of 20–200–eV.[149] The reflection high energy electron diffraction (RHEED) technique uses the reflection of a beam of electrons fired at various low angles to char- acterize the surface of crystalline materials. The beam energy is typically in the range of 8–20 keV and the grazing angle is 1–4°.[150][151] The electron microscope directs a focused beam of electrons at a specimen. As the From Wikipedia, the free encyclopedia Electron 14 beam interacts with the material, the elec- trons are scattered and lose energy. By re- cording the changes in the electron beam, in- vestigators can produce an image of the ma- terial.[152] In blue light, conventional optical microscopes have a diffraction-limited resolu- tion of about 100 nm. By comparison, elec- tron microscopes are limited by the de Broglie wavelength of the electron. This is equal to 0.0037 nm for electrons accelerated across a 100,000-volt potential.[153] For ex- ample, the TEAM electron microscope is cap- able of 0.05 nm resolution: small enough to resolve individual atoms.[154] This makes the electron microscope a useful laboratory in- strument for high resolution imaging. However, electron microscopes are expens- ive instruments that are costly to maintain. The high vacuum required to operate an elec- tron microscope also prevents them from be- ing used to observe living organisms.[155] There exist two main types of electron mi- croscopes: transmission and scanning. Trans- mission electron microscopes function in a manner similar to optical microscopes, with a beam of electrons passing through a materi- al. The magnifications range from 1,000× to 1,000,000× or better. Quantum effects of electrons are used in the scanning tunneling microscope to study features on solid sur- faces with lateral resolution at the atomic scale of around 0.2 nm.[155][156] Other In the free electron laser (FEL), a relativistic electron beam is passed through a pair of un- dulators containing arrays of dipole magnets, whose fields are oriented in alternating direc- tions. The electrons emit synchrotron radi- ation, which, in turn, coherently interacts with the electrons. This leads to the strong amplification of the radiation field at the res- onance frequency. FEL can emit a coherent high-brilliance electromagnetic radiation with a wide range of frequencies, from mi- crowaves to soft X-rays. These devices can be used in the future for manufacturing, commu- nication and various medical applications, such as soft tissue surgery.[157] Electrons are at the heart of cathode ray tubes, which are used extensively as display devices in laboratory instruments, computer monitors and television sets.[158] In a pho- tomultiplier tube, one photon strikes the pho- tocathode, initiating an avalanche of electrons that produces a detectable cur- rent.[159] Vacuum tubes used the flow of electrons in a near vacuum to manipulate electrical signals, and they played a critical role in the development of electronics tech- nology. However, vacuum tubes have been largely supplanted by solid-state devices such as the transistor.[160] See also • Covalent bonding • Electron bubble • Exoelectron emission • G-factor • One-electron universe • Spintronics • Stern–Gerlach experiment Notes [1] The fractional version’s denominator is the inverse of the decimal value (along with its relative standard uncertainty of 4.2×10−10). [2] The electron’s charge is the negative of elementary charge, which is a positive value for the proton. [3] From electrostatics theory, the potential energy of a sphere with radius r and charge e is given by: where ε0 is the vacuum permittivity. For an electron with rest mass m0, the rest energy is equal to: where c is the speed of light in a vacuum. Setting them equal and solving for r gives the classical electron radius. See: Haken, Hermann; Wolf, Hans Christoph; Brewer, W. D. (2005). The Physics of Atoms and Quanta: Introduction to Experiments and Theory. Springer. p. 70. ISBN 3540208070. [4] This magnitude is given by the spin angular momentum, for quantum number s = 1⁄2. See: Gupta, M. C. (2001). Atomic and Molecular Spectroscopy. New Age Publishers. p. 81. ISBN 8122413005. [5] Bohr magneton From Wikipedia, the free encyclopedia Electron 15 [6] Radiation from non-relativistic electrons is sometimes termed cyclotron radiation. [7] The change in wavelength, Δλ, depends on the angle of the recoil, θ, as follows, where c is the speed of light in a vacuum and m is the electron mass. See Zombeck (2007:393,396). [8] Solving for the velocity of the electron, and using an approximation for large γ, gives: [9] The polarization of an electron beam means that the spins of all electrons point into one direction. In other words, the projections of the spins of all eldctrons onto the their momentum vector have the same sign. References [1] Dahl, Per F. (1997). Flash of the Cathode Rays: A History of J J Thomson’s Electron. CRC Press. p. 72. ISBN 0750304537. [2] ^ Eichten, Estia J.; Lane, Kenneth D.; Peskin, Michael E. (1983). "New Tests for Quark and Lepton Substructure". Physical Review Letters 50: 030802(1–4). doi:10.1103/ PhysRevLett.97.030802. [3] ^ Farrar, W. V. (1969). "Richard Laming and the Coal-Gas Industry, with His Views on the Structure of Matter". Annals of Science 25: 243–254. doi:10.1080/00033796900200141. [4] ^ Arabatzis, Theodore (2006). Representing Electrons: A Biographical Approach to Theoretical Entities. University of Chicago Press. pp. 70–74. ISBN 0226024210. [5] ^ Buchwald, Jed Z.; Warwick, Andrew (2001). Histories of the Electron: The Birth of Microphysics. MIT Press. pp. 195–203. ISBN 0262524244. [6] ^ Dahl (1997:122–185). [7] ^ The original source for CODATA is: Mohr, Peter J.; Taylor, Barry N.; Newell, David B. (2006-06-06). "CODATA recommended values of the fundamental physical constants". Reviews of Modern Physics 80: 633–730. doi:10.1103/ RevModPhys.80.633. Individual physical constants from the CODATA are available at: "The NIST Reference on Constants, Units and Uncertainty". National Institute of Standards and Technology. http://physics.nist.gov/ cuu/. Retrieved on 2009-01-15. [8] Anastopoulos, Charis (2008). Particle Or Wave: The Evolution of the Concept of Matter in Modern Physics. Princeton University Press. pp. 236–237. ISBN 0691135126. [9] Wilson, Robert (1997). Astronomy Through the Ages: The Story of the Human Attempt to Understand the Universe. CRC Press. p. 138. ISBN 0748407480. [10]^ Curtis, Lorenzo J. (2003). Atomic Structure and Lifetimes: A Conceptual Approach. Cambridge University Press. p. 74. ISBN 0521536359. [11]Pauling, Linus C. (1960), The Nature of the Chemical Bond and the Structure of Molecules and Crystals (3rd ed.), Cornell University Press, pp. 4–5, ISBN 0801403332, http://books.google.co.uk/ books?id=L-1K9HmKmUUC [12]Shipley, Joseph T. (1945). Dictionary of Word Origins. New York, N. Y.: The Philosophical Library. p. 133. [13]Baigrie, Brian (2006). Electricity and Magnetism: A Historical Perspective. Greenwood Press. pp. 7–8. ISBN 0-3133-3358-0. [14]Barrow, J. D. (1983). "Natural Units Before Planck". Royal Astronomical Society Quarterly Journal 24: 24–26. http://adsabs.harvard.edu/abs/ 1983QJRAS..24...24B. Retrieved on 2008-08-30. [15]Stoney, George Johnstone (October 1894). "Of the "Electron," or Atom of Electricity". Philosophical Magazine 38 (5): 418–420. [16]Soukhanov, Anne H. ed. (1986). Word Mysteries & Histories. Boston, MA: Houghton Mifflin Company. p. 73. ISBN 0-395-40265-4. [17]Guralnik, David B. ed. (1970). Webster’s New World Dictionary. Englewood Cliffs, From Wikipedia, the free encyclopedia Electron 16 N. J.: Prentice-Hall, Incorporated. p. 450. [18]Born, Max; Blin-Stoyle, Roger John; Radcliffe, J. M. (1989). Atomic Physics. Courier Dover Publications. p. 26. ISBN 0486659844. [19]Dahl (1997:55–58). [20]DeKosky, Robert (1983). "William Crookes and the quest for absolute vacuum in the 1870s". Annals of Science 40 (1): 1–18. doi:10.1080/ 00033798300200101. [21]^ Leicester, Henry M. (1971). The Historical Background of Chemistry. Courier Dover Publications. pp. 221–222. ISBN 0486610535. [22]Dahl (1997:64–78). [23]Zekman, P. (1907). "Sir William Crookes, F.R.S.". Nature 77 (1984): 1–3. doi:10.1038/077001a0. http://books.google.com/ books?id=UtYRAAAAYAAJ. Retrieved on 2008-08-25. [24]Thomson, J. J. (1906-12-11). "Lecture, The Nobel Prize in Physics 1906". The Nobel Foundation. http://nobelprize.org/ nobel_prizes/physics/laureates/1906/ thomson-lecture.html. Retrieved on 2008-08-25. [25]Trenn, Thaddeus J. (March 1976). "Rutherford on the Alpha-Beta-Gamma Classification of Radioactive Rays". Isis 67 (1): 61–75. doi:10.1086/351545. http://www.jstor.org/pss/231134. Retrieved on 2008-09-04. [26]Becquerel, Henri (1900). "Déviation du Rayonnement du Radium dans un Champ Électrique" (in French). Comptes Rendus de l’Académie des Sciences 130: 809–815. [27]Buchwald and Warwick (2001:90-91). [28]Myers, William G. (1976-07-01). "Becquerel’s Discovery of Radioactivity in 1896". Journal of Nuclear Medicine 17 (7): 579–582. PMID 775027. http://jnm.snmjournals.org/cgi/content/ abstract/17/7/579. Retrieved on 2008-09-04. [29]Kikoin, I. K.; Sominskiĭ, M. S. (1961). "Abram Fedorovich Ioffe (on his eightieth birthday)". Soviet Physics Uspekhi 3: 798–809. doi:10.1070/ PU1961v003n05ABEH005812. [30]Kizilova, Anna. "Abram Ioffe (biography". Russia-InfoCentre. http://www.russia- ic.com/people/education_science/i/261/. Retrieved on 2006-09-22. [31]Millikan, R. A. (1911). "The Isolation of an Ion, a Precision Measurement of its Charge, and the Correction of Stokes’s Law". Physical Review 32 (2): 349–397. doi:10.1103/PhysRevSeriesI.32.349. [32]Das Gupta, N. N.; Ghosh, S. K. (1999). "A Report on the Wilson Cloud Chamber and Its Applications in Physics". Reviews of Modern Physics 18: 225–290. doi:10.1103/RevModPhys.18.225. [33]^ Smirnov, Boris M. (2003). Physics of Atoms and Ions. Springer. pp. 14–21. ISBN 038795550X. [34]Bohr, Niels (1922-12-11). "Nobel Lecture: The Structure of the Atom". The Nobel Foundation. http://nobelprize.org/ nobel_prizes/physics/laureates/1922/ bohr-lecture.html. Retrieved on 2008-12-03. [35]Lewis, Gilbert N. (April 1916). "The Atom and the Molecule". Journal of the American Chemical Society 38 (4): 762–786. doi:10.1021/ja02261a002. [36]^ Arabatzis, Theodore; Gavroglu, Kostas (1997). "The chemists’ electron". European Journal of Physics 18: 150–163. doi:10.1088/0143-0807/18/3/ 005. http://www.iop.org/EJ/abstract/ 0143-0807/18/3/005. [37]Langmuir, Irving (1919). "The Arrangement of Electrons in Atoms and Molecules". Journal of the American Chemical Society 41 (6): 868–934. doi:10.1021/ja02227a002. [38]Scerri, Eric R. (2007). The Periodic Table. Oxford University Press US. pp. 205–226. ISBN 0195305736. [39]Massimi, Michela (2005). Pauli’s Exclusion Principle, The Origin and Validation of a Scientific Principle. Cambridge University Press. pp. 7–8. ISBN 0521839114. [40]Uhlenbeck, G. E.; Goudsmith, S. (1925). "Ersetzung der Hypothese vom unmechanischen Zwang durch eine Forderung bezüglich des inneren Verhaltens jedes einzelnen Elektrons" (in German). Die Naturwissenschaften 13 (47). http://adsabs.harvard.edu/abs/ 1925NW.....13..953E. Retrieved on 2008-09-02. [41]W., Pauli (1923). "Über die Gesetzmäßigkeiten des anomalen Zeemaneffektes" (in German). Zeitschrift From Wikipedia, the free encyclopedia Electron 17 für Physik 16 (1): 155–164. doi:10.1007/ BF01327386. http://adsabs.harvard.edu/ abs/1923ZPhy...16..155P. Retrieved on 2008-09-02. [42]^ de Broglie, Louis (1929-12-12). "Lecture, The Nobel Prize in Physics 1929". Nobel Foundation. http://nobelprize.org/nobel_prizes/ physics/laureates/1929/broglie- lecture.html. Retrieved on 2008-08-30. [43]Falkenburg, Brigitte (2007). Particle Metaphysics: A Critical Account of Subatomic Reality. Springer. p. 85. ISBN 3540337318. [44]Davisson, Clinton (1937-12-13). "Lecture, The Nobel Prize in Physics 1937". Nobel Foundation. http://nobelprize.org/ nobel_prizes/physics/laureates/1937/ davisson-lecture.html. Retrieved on 2008-08-30. [45]Schrödinger, Erwin (1926). "Quantisierung als Eigenwertproblem" (in German). Annalen der Physik 385 (13): 437–490. doi:10.1002/ andp.19263851302. http://adsabs.harvard.edu/abs/ 1926AnP...385..437S. Retrieved on 2008-08-31. [46]Rigden, John S. (2003). Hydrogen. Harvard University Press. pp. 59–86. ISBN 0674012526. [47]Reed, Bruce Cameron (2007). Quantum Mechanics. Jones & Bartlett Publishers. pp. 275–350. ISBN 0763744514. [48]Dirac, P. A. M. (1928-02-01). "The Quantum Theory of the Electron". Proceedings of the Royal Society of London. Series A 117 (778): 610–624. doi:10.1098/rspa.1928.0023. [49]Dirac, Paul A. M. (1933-12-12). "Theory of Electrons and Positrons". The Nobel Foundation. http://nobelprize.org/ nobel_prizes/physics/laureates/1933/ dirac-lecture.html. Retrieved on 2008-11-01. [50]Kragh, Helge (2002). Quantum Generations: A History of Physics in the Twentieth Century. Princeton University Press. p. 132. ISBN 0691095523. [51]Gaynor, Frank (1950). Concise Encyclopedia of Atomic Energy. New York: Philosophical Library. pp. 117. [52] "The Nobel Prize in Physics 1965". The Nobel Foundation. http://nobelprize.org/ nobel_prizes/physics/laureates/1965/. Retrieved on 2008-11-04. [53]Panofsky, Wolfgang K. H. (1997). "The Evolution of Particle Accelerators & Colliders" (PDF). Stanford University. http://www.slac.stanford.edu/pubs/ beamline/27/1/27-1-panofsky.pdf. Retrieved on 2008-09-15. [54]Elder, F. R.; Gurewitsch, A. M.; Langmuir, R. V.; Pollock, H. C. (1947). "Radiation from Electrons in a Synchrotron". Physical Review 71 (11): 829–830. doi:10.1103/PhysRev.71.829.5. [55]Hoddeson, Lillian; Brown, Laurie; Riordan, Michael; Dresden, Max (1997). The Rise of the Standard Model: Particle Physics in the 1960s and 1970s. Cambridge University Press. pp. 25–26. ISBN 0521578167. [56]Bernardini, Carlo (2004). "AdA:The First Electron-Positron Collider". Physics in Perspective 6 (2): 156–183. doi:10.1007/ s00016-003-0202-y. http://ads.ari.uni- heidelberg.de/abs/2004PhP.....6..156B. Retrieved on 2008-09-15. [57]Staff (2008). "Testing the Standard Model: The LEP experiments". CERN. http://public.web.cern.ch/PUBLIC/en/ Research/LEPExp-en.html. Retrieved on 2008-09-15. [58]Staff (2000-12-01). "LEP reaps a final harvest". CERN Courier. http://cerncourier.com/cws/article/cern/ 28335. Retrieved on 2008-11-01. [59]Frampton, Paul H.; Hung, P. Q.; Sher, Marc (June 2000). "Quarks and Leptons Beyond the Third Generation". Physics Reports 330: 263–3485. doi:10.1016/ S0370-1573(99)00095-2. [60]^ Raith, Wilhelm; Mulvey, Thomas (2001). Constituents of Matter: Atoms, Molecules, Nuclei and Particles. CRC Press. pp. 777–781. ISBN 0849312027. [61]^ Quigg, Chris (June 4–30, 2000). "The Electroweak Theory". TASI 2000: Flavor Physics for the Millennium: 80, Boulder, Colorado: arXiv. Retrieved on 2008-09-21. [62]Rosen, S. P. (1978). "Universality and the weak isospin of leptons, nucleons, and quarks". Physical Review D 17: 2471–2474. doi:10.1103/ PhysRevD.17.2471. [63]Zombeck, Martin V. (2007). Handbook of Space Astronomy and Astrophysics (Third ed.). Cambridge University Press. p. 14. ISBN 0521782422. From Wikipedia, the free encyclopedia Electron 18 [64]Murphy, Michael T.; Flambaum, Victor V.; Muller, Sébastien; Henkel, Christian (2008-06-20). "Strong Limit on a Variable Proton-to-Electron Mass Ratio from Molecules in the Distant Universe". Science 320 (5883): 1611–1613. doi:10.1126/science.1156352. PMID 18566280. http://www.sciencemag.org/ cgi/content/abstract/320/5883/1611. Retrieved on 2008-09-03. [65]Zorn, Jens C.; Chamberlain, George E.; Hughes, Vernon W. (1963). "Experimental Limits for the Electron- Proton Charge Difference and for the Charge of the Neutron". Physical Review 129 (6): 2566–2576. doi:10.1103/ PhysRev.129.2566. [66]Gabrielse, G.; Hanneke, D.; Kinoshita, T.; Nio, M.; Odom, B. (2006). "New Determination of the Fine Structure Constant from the Electron g Value and QED". Physical Review Letters 97: 811–814. doi:10.1103/ PhysRevLett.50.811. [67]Dehmelt, Hans (1988). "A Single Atomic Particle Forever Floating at Rest in Free Space: New Value for Electron Radius". Physica Scripta T22: 102–110. doi:10.1088/0031-8949/1988/T22/016. [68]Steinberg, R. I.; Kwiatkowski, K.; Maenhaut, W.; Wall, N. S. (1999). "Experimental test of charge conservation and the stability of the electron". Physical Review D 61 (2): 2582–2586. doi:10.1103/ PhysRevD.12.2582. [69]Yao, W.-M.; Particle Data Group (July 2006). "Review of Particle Physics". Journal of Physics G: Nuclear and Particle Physics 33 (1): 77–115. doi:10.1088/0954-3899/33/1/001. [70]^ Munowitz, Michael (2005). Knowing, The Nature of Physical Law. Oxford University Press. pp. 162–218. ISBN 0195167376. [71]Kane, Gordon (2006-10-09). "Are virtual particles really constantly popping in and out of existence? Or are they merely a mathematical bookkeeping device for quantum mechanics?". Scientific American. http://www.sciam.com/ article.cfm?id=are-virtual-particles- rea&topicID=13. Retrieved on 2008-09-19. [72]Taylor, John (1989). Davies, Paul. ed. The New Physics. Cambridge University Press. p. 464. ISBN 0521438314. [73]^ Genz, Henning (2001). Nothingness: The Science of Empty Space. Da Capo Press. pp. 241–243, 245–247. ISBN 0738206105. [74]Gribbin, John (1997-01-25). "More to electrons than meets the eye". New Scientist. http://www.newscientist.com/ article/mg15320662.300-science--more- to-electrons-than-meets-the-eye.html. Retrieved on 2008-09-17. [75]Levine, I.; TOPAZ Collaboration (1997). "Measurement of the Electromagnetic Coupling at Large Momentum Transfer". Physical Review Letters 78: 424–427. doi:10.1103/PhysRevLett.78.424. [76]Murayama, Hitoshi (March 10–17, 2006). "Supersymmetry Breaking Made Easy, Viable and Generic". Proceedings of the XLIInd Rencontres de Moriond on Electroweak Interactions and Unified Theories. Retrieved on 2008-09-30. —lists a 9% mass difference for an electron that is the size of the Planck distance. [77]Modanese, Giovanni (2003). "Inertial Mass and Vacuum Fluctuations in Quantum Field Theory". Foundations of Physics Letters 16: 135–141. doi:10.1023/A:1024118627357. http://arxiv.org/abs/hep-th/0009046. Retrieved on 2008-09-30. [78]Schwinger, Julian (1948). "On Quantum- Electrodynamics and the Magnetic Moment of the Electron". Physical Review 73 (4): 416–417. doi:10.1103/ PhysRev.73.416. [79]Odom, B.; Hanneke, D.; D’Urso, B.; Gabrielse, G. (2006). "New Measurement of the Electron Magnetic Moment Using a One-Electron Quantum Cyclotron". Physical Review Letters 97: 030801(1–4). doi:10.1103/ PhysRevLett.97.030801. [80]Huang, Kerson (2007). Fundamental Forces of Nature: The Story of Gauge Fields. World Scientific. pp. 123–125. ISBN 9812706453. [81]^ Staff (2008). "The Nobel Prize in Physics 1989". The Nobel Foundation. http://nobelprize.org/nobel_prizes/ physics/laureates/1989/illpres/. Retrieved on 2008-09-24. From Wikipedia, the free encyclopedia Electron 19 [82]Foldy, Leslie L.; Wouthuysen, Siegfried A. (1950). "On the Dirac Theory of Spin 1/2 Particles and Its Non-Relativistic Limit". Physical Review 78: 29–36. doi:10.1103/PhysRev.78.29. [83]Sidharth, Burra G. (August 2008). "Revisiting Zitterbewegung". International Journal of Theoretical Physics 48: 497. doi:10.1007/ s10773-008-9825-8. http://arxiv.org/abs/ 0806.0985. Retrieved on 2008-11-10. [84]Elliott, R. S. (1978). "The history of electromagnetics as Hertz would have known it". IEEE Transactions on Microwave Theory and Techniques 36 (5): 806–823. doi:10.1109/22.3600. http://ieeexplore.ieee.org/xpls/ abs_all.jsp?arnumber=3600. Retrieved on 2008-09-22. A subscription required for access. [85]Munowitz (2005:140). [86]Crowell, Benjamin (2000). Electricity and Magnetism. Light and Matter. pp. 129–152. ISBN 0970467044. [87]Munowitz (2005:160). [88]Mahadevan, Rohan; Narayan, Ramesh; Yi, Insu (1996). "Harmony in Electrons: Cyclotron and Synchrotron Emission by Thermal Electrons in a Magnetic Field". Astrophysical Journal 465: 327–. doi:10.1086/177422. http://arxiv.org/abs/ astro-ph/9601073v1. Retrieved on 2008-09-28. [89]Rohrlich, F. (December 1999). "The self- force and radiation reaction". American Journal of Physics 68 (12): 1109–1112. doi:10.1119/1.1286430. [90]Georgi, Howard (1989). Davies, Paul. ed. The New Physics. Cambridge University Press. p. 427. ISBN 0521438314. [91]Blumenthal, George J.; Gould, Robert J. (1970). "Bremsstrahlung, Synchrotron Radiation, and Compton Scattering of High-Energy Electrons Traversing Dilute Gases". Reviews of Modern Physics 42: 237–270. doi:10.1103/ RevModPhys.42.237. [92]Staff (2008). "The Nobel Prize in Physics 1927". The Nobel Foundation. http://nobelprize.org/nobel_prizes/ physics/laureates/1927/. Retrieved on 2008-09-28. [93]Beringer, Robert; Montgomery, C. G. (1942). "The Angular Distribution of Positron Annihilation Radiation". Physical Review 61 (5–6): 222–224. doi:10.1103/PhysRev.61.222. [94]Wilson, Jerry; Buffa, Anthony (2000). College Physics (4th. ed.). Prentice Hall. pp. 888. ISBN 0130824445. [95]Eichler, Jörg (2005-11-14). "Electron–positron pair production in relativistic ion–atom collisions". Physics Letters A 347 (1–3): 67–72. doi:10.1016/ j.physleta.2005.06.105. [96]Hubbell, J. H. (June 2006). "Electron positron pair production by photons: A historical overview". Radiation Physics and Chemistry 75 (6): 614–623. doi:10.1016/j.radphyschem.2005.10.008. Bibcode: 2006RaPC...75..614H. [97]Mulliken, Robert S. (1967). "Spectroscopy, Molecular Orbitals, and Chemical Bonding". Science 157 (3784): 13–24. doi:10.1126/science.157.3784.13. PMID 5338306. [98]Burhop, Eric H. S. (1952). The Auger Effect and Other Radiationless Transitions. New York: Cambridge University Press. pp. 2–3. [99]^ Grupen, C. (June 28-July 10 1999). "Physics of Particle Detection". AIP Conference Proceedings, Instrumentation in Elementary Particle Physics, VIII 536: 3–34, Istanbul: Dordrecht, D. Reidel Publishing Company. doi:10.1063/1.1361756. [100]Jiles, David (1998). Introduction to Magnetism and Magnetic Materials. CRC Press. pp. 280–287. ISBN 0412798603. [101]Löwdin, Per Olov; Erkki Brändas, Erkki; Kryachko, Eugene S. (2003). Fundamental World of Quantum Chemistry: A Tribute to the Memory of Per- Olov Löwdin. Springer. pp. 393–394. ISBN 140201290X. [102]Pauling, Linus (1960). The Nature of the Chemical Bond and the Structure of Molecules and Crystals: An Introduction to Modern Structural Chemistry. Cornell University Press. pp. 5–10. ISBN 0801403332. [103]McQuarrie, Donald Allan; Simon, John Douglas (1997). Physical Chemistry: A Molecular Approach. University Science Books. pp. 325–361. ISBN 0935702997. [104]Daudel, R.; Bader, R. F. W.; Stephens, M. E.; Borrett, D. S. (1973-10-11). "The Electron Pair in Chemistry". Canadian Journal of Chemistry 52: 1310–1320. doi:10.1139/v74-201. From Wikipedia, the free encyclopedia Electron 20 http://article.pubs.nrc-cnrc.gc.ca/ppv/ RPViewDoc?issn=1480-3291&volume=52&issue=8&startPage=1310. Retrieved on 2008-10-12. [105]Freeman, G. R.; March, N. H. (1999). "Triboelectricity and some associated phenomena". Materials science and technology 15 (12): 1454–1458. [106]Weinberg, Steven (2003). The Discovery of Subatomic Particles. Cambridge University Press. pp. 15–16. ISBN 052182351X. [107]Guru, Bhag S.; Hızıroğlu, Hüseyin R. (2004). Electromagnetic Field Theory. Cambridge University Press. pp. 138, 276. ISBN 0521830168. [108]Achuthan, M. K.; Bhat, K. N. (2007). Fundamentals of Semiconductor Devices. Tata McGraw-Hill. pp. 49–67. ISBN 007061220X. [109]̂ Ziman, J. M. (2001). Electrons and Phonons: The Theory of Transport Phenomena in Solids. Oxford University Press. p. 260. ISBN 0198507798. [110]Main, Peter (1993-06-12). "When electrons go with the flow: Remove the obstacles that create electrical resistance, and you get ballistic electrons and a quantum surprise". New Scientist 1887: 30. http://www.newscientist.com/ article/mg13818774.500-when-electrons- go-with-the-flow-remove-the-obstacles- thatcreate-electrical-resistance-and-you- get-ballistic-electrons-and-a- quantumsurprise.html. Retrieved on 2008-10-09. [111]Blackwell, Glenn R. (2000). The Electronic Packaging Handbook. CRC Press. pp. 6.39–6.40. ISBN 0849385911. [112]Durrant, Alan (2000). Quantum Physics of Matter: The Physical World. CRC Press. pp. 43, 71–78. ISBN 0750307218. [113]Staff (2008). "The Nobel Prize in Physics 1972". The Nobel Foundation. http://nobelprize.org/nobel_prizes/ physics/laureates/1972/. Retrieved on 2008-10-13. [114]Kadin, Alan M. (2007). "Spatial Structure of the Cooper Pair". Journal of Superconductivity and Novel Magnetism 20 (4): 285–292. doi:10.1007/ s10948-006-0198-z. http://arxiv.org/abs/ cond-mat/0510279. Retrieved on 2008-10-13. [115]Staff (2008). "The Nobel Prize in Physics 1958, for the discovery and the interpretation of the Cherenkov effect". The Nobel Foundation. http://nobelprize.org/nobel_prizes/ physics/laureates/1958/. Retrieved on 2008-09-25. [116]Staff (2008-08-26). "Special Relativity". Stanford Linear Accelerator Center. http://www2.slac.stanford.edu/vvc/ theory/relativity.html. Retrieved on 2008-09-25. [117]Adams, Steve (2000). Frontiers: Twentieth Century Physics. CRC Press. p. 215. ISBN 0748408401. [118]Lurquin, Paul F. (2003). The Origins of Life and the Universe. Columbia University Press. p. 2. ISBN 0231126557. [119]Silk, Joseph (2000). The Big Bang: The Creation and Evolution of the Universe (3rd ed.). Macmillan. pp. 110–112, 134–137. ISBN 080507256X. [120]Christianto, Vic; Smarandache, Florentin (October 2007). "Thirty Unsolved Problems in the Physics of Elementary Particles" (PDF). Progress in Physics 4: 112–114. http://www.ptep-online.com/ index_files/2007/PP-11-16.PDF. Retrieved on 2008-09-04. [121]Kolb, Edward W.; Wolfram, Stephen (1980-04-07). "The Development of Baryon Asymmetry in the Early Universe". Physics Letters B 91 (2): 217–221. doi:10.1016/ 0370-2693(80)90435-9. [122]Sather, Eric (Spring/Summer 1996). "The Mystery of Matter Asymmetry" (PDF). Beam Line. University of Stanford. http://www.slac.stanford.edu/pubs/ beamline/26/1/26-1-sather.pdf. Retrieved on 2008-11-01. [123]Burles, Scott; Nollett, Kenneth M.; Turner, Michael S. (1999-03-19). "Big- Bang Nucleosynthesis: Linking Inner Space and Outer Space". arXiv, University of Chicago. http://arxiv.org/ abs/astro-ph/9903300. Retrieved on 2008-10-15. [124]Boesgaard, A. M.; Steigman, G. (1985). "Big bang nucleosynthesis - Theories and observations". Annual review of astronomy and astrophysics 23 (2): 319–378. doi:10.1146/ annurev.aa.23.090185.001535. http://adsabs.harvard.edu/cgi-bin/ bib_query?1985ARA%26A..23..319B. Retrieved on 2008-08-28. From Wikipedia, the free encyclopedia Electron 21 [125]̂ Barkana, Rennan (2006-08-18). "The First Stars in the Universe and Cosmic Reionization". Science 313 (5789): 931–934. doi:10.1126/science.1125644. PMID 16917052. http://www.sciencemag.org/cgi/content/ full/313/5789/931. Retrieved on 2008-11-01. [126]Burbidge, E. Margaret; Burbidge, G. R.; Fowler, William A.; Hoyle, F. (1957). "Synthesis of Elements in Stars". Reviews of Modern Physics 29 (4): 548–647. doi:10.1103/ RevModPhys.29.547. [127]Rodberg, L. S.; Weisskopf, V. F. (1957). "Fall of Parity: Recent Discoveries Related to Symmetry of Laws of Nature". Science 125 (3249): 627–633. doi:10.1126/science.125.3249.627. PMID 17810563. [128]Fryer, Chris L. (September 1999). "Mass Limits For Black Hole Formation". The Astrophysical Journal 522 (1): 413–418. doi:10.1086/307647. Bibcode: 1999ApJ...522..413F. [129]Parikh, Maulik K.; Wilczek, Frank (2000). "Hawking Radiation As Tunneling". Physical Review Letters 85 (24): 5042–5045. doi:10.1103/ PhysRevLett.85.5042. [130]Hawking, S. W. (1974-03-01). "Black hole explosions?". Nature 248: 30–31. doi:10.1038/248030a0. [131]Halzen, F.; Hooper, D. (2002). "High- energy neutrino astronomy: the cosmic ray connection". Reports on Progress in Physics 66: 1025–1078. doi:10.1088/ 0034-4885/65/7/201. http://adsabs.harvard.edu/abs/ 2002astro.ph..4527H. Retrieved on 2008-08-28. [132]Ziegler, J. F.. "Terrestrial cosmic ray intensities". IBM Journal of Research and Development 42 (1): 117–139. doi:10.1147/rd.421.0117. [133]Sutton, Christine (1990-08-04). "Muons, pions and other strange particles". New Scientist. http://www.newscientist.com/ article/mg12717284.700-muons-pions- and-other-strange-particles-.html. Retrieved on 2008-08-28. [134]Wolpert, Stuart (2008-07-24). "Scientists solve 30-year-old aurora borealis mystery". University of California. http://www.universityofcalifornia.edu/ news/article/18277. Retrieved on 2008-10-11. [135]Gurnett, Donald A.; Anderson, Roger R. (1976-12-10). "Electron Plasma Oscillations Associated with Type III Radio Bursts". Science 194 (4270): 1159–1162. doi:10.1126/ science.194.4270.1159. PMID 17790910. [136]Martin, W. C.; Wiese, W. L. (May 2007). "Atomic Spectroscopy: A Compendium of Basic Ideas, Notation, Data, and Formulas". National Institute of Standards and Technology. http://physics.nist.gov/Pubs/AtSpec/. Retrieved on 2007-01-08. [137]Fowles, Grant R. (1989). Introduction to Modern Optics. Courier Dover Publications. pp. 227–233. ISBN 0486659577. [138]Ekstrom, Philip; Wineland, David (1980). "The isolated Electron" (PDF). Scientific American 243 (2): 91–101. http://tf.nist.gov/general/pdf/166.pdf. Retrieved on 2008-09-24. [139]Mauritsson, Johan. "Electron filmed for the first time ever" (PDF). Lunds Universitet. http://www.atto.fysik.lth.se/ video/pressrelen.pdf. Retrieved on 2008-09-17. [140]Mauritsson, J.; Johnsson, P.; Mansten, E. et al (2008). "Coherent Electron Scattering Captured by an Attosecond Quantum Stroboscope" (pdf). Physical Review Letters 100: 073003. doi:10.1103/PhysRevLett.100.073003. http://www.atto.fysik.lth.se/publications/ papers/MauritssonPRL2008.pdf. [141]Damascelli, Andrea (2004). "Probing the Electronic Structure of Complex Systems by ARPES". Physica Scripta T109: 61–74. doi:10.1238/ Physica.Topical.109a00061. [142]Staff (1975-04-14). "Image # L-1975-02972". Langley Research Center, NASA. http://grin.hq.nasa.gov/ ABSTRACTS/GPN-2000-003012.html. Retrieved on 2008-09-20. [143]Elmer, John (2008-03-03). "Standardizing the Art of Electron-Beam Welding". Lawrence Livermore National Laboratory. https://www.llnl.gov/str/ MarApr08/elmer.html. Retrieved on 2008-10-16. [144]Ozdemir, Faik S. (June 25–27, 1979). "Electron beam lithography". From Wikipedia, the free encyclopedia Electron 22 Proceedings of the 16th Conference on Design automation: 383–391, San Diego, CA, USA: IEEE Press. Retrieved on 2008-10-16. [145]Jongen, Yves; Herer, Arnold (May 2-5, 1996). "Electron Beam Scanning in Industrial Applications". APS/AAPT Joint Meeting, American Physical Society. Retrieved on 2008-10-16. [146]Beddar, A. S.; Domanovic, M. A.; Kubu, M. L.; Ellis, R. J.; Sibata, C. H.; Kinsella, T. J. (November 2001). "Mobile linear accelerators for intraoperative radiation therapy". AORN Journal 74: 700. doi:10.1016/S0001-2092(06)61769-9. http://findarticles.com/p/articles/ mi_m0FSL/is_/ai_81161386. Retrieved on 2008-10-26. [147]Gazda, Michael J.; Coia, Lawrence R. (2007-06-01). "Principles of Radiation Therapy". Cancer Network. http://www.cancernetwork.com/cancer- management/chapter02/article/10165/ 1165822. Retrieved on 2008-10-26. [148]Chao, Alexander W.; Tigner, Maury (1999). Handbook of Accelerator Physics and Engineering. World Scientific Publishing Company. pp. 155, 188. ISBN 9810235003. [149]Oura, K.; Lifshifts, V. G.; Saranin, A. A.; Zotov, A. V.; Katayama, M. (2003). Surface Science: An Introduction. Springer-Verlag. pp. 1–45. ISBN 3540005455. [150]Ichimiya, Ayahiko; Cohen, Philip I. (2004). Reflection High-energy Electron Diffraction. Cambridge University Press. p. 1. ISBN 0521453739. [151]Heppell, T. A. (1967). "A combined low energy and reflection high energy electron diffraction apparatus". Journal of Scientific Instruments 44: 686–688. doi:10.1088/0950-7671/44/9/311. [152]McMullan, D. (August 1993). "Scanning Electron Microscopy: 1928–1965". University of Cambridge. http://www- g.eng.cam.ac.uk/125/achievements/ mcmullan/mcm.htm. Retrieved on 2009-03-23. [153]Cember, Herman (1996). Introduction to Health Physics. McGraw-Hill Professional. pp. 42–43. ISBN 0071054618. [154]Staff (2008-01-22). "Debut of TEAM 0.5, the World’s Best Microscope". PhysOrg. http://www.physorg.com/ news120231316.html. Retrieved on 2008-10-21. [155]̂ Bozzola, John J.; Russell, Lonnie D. (1999). Electron Microscopy: Principles and Techniques for Biologists. Jones & Bartlett Publishers. pp. 12, 197–199. ISBN 0763701920. [156]Flegler, Stanley L.; Heckman Jr., John W.; Klomparens, Karen L. (1995-10-01). Scanning and Transmission Electron Microscopy: An Introduction (Reprint ed.). Oxford University Press. pp. 43–45. ISBN 0195107519. [157]Freund, Henry P.; Antonsen, Thomas (1996). Principles of Free-Electron Lasers. Springer. pp. 1–30. ISBN 0412725401. [158]Kitzmiller, John W. (1995). Television Picture Tubes and Other Cathode-Ray Tubes: Industry and Trade Summary. DIANE Publishing. pp. 3–5. ISBN 0788121006. [159]Sclater, Neil (1999). Electronic Technology Handbook. McGraw-Hill Professional. pp. 227–228. ISBN 0070580480. [160]Staff (2008). "The History of the Integrated Circuit". The Nobel Foundation. http://nobelprize.org/ educational_games/physics/ integrated_circuit/history/. Retrieved on 2008-10-18. External links • "The Discovery of the Electron". American Institute of Physics, Center for History of Physics. http://www.aip.org/history/ electron/. Retrieved on 2006-08-10. • "Particle Data Group". University of California. http://pdg.lbl.gov/. Retrieved on 2008-11-17. • Bock, Rudolf K.; Vasilescu, Angela (1998). The Particle Detector BriefBook (14th ed.). Springer. ISBN 3540641203. http://physics.web.cern.ch/Physics/ ParticleDetector/BriefBook/. Retrieved on 2008-10-02. • Brown University. Single Electron on Video [Shockwave/Flash]. Educated Earth. Retrieved on 2009-01-23. Retrieved from "http://en.wikipedia.org/wiki/Electron" From Wikipedia, the free encyclopedia Electron 23 Categories: Electron, Leptons, Fundamental physics concepts, Quantum electrodynamics, Spintronics, Greek loanwords This page was last modified on 18 May 2009, at 19:30 (UTC). All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.) Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a U.S. registered 501(c)(3) tax- deductible nonprofit charity. Privacy policy About Wikipedia Disclaimers From Wikipedia, the free encyclopedia Electron 24