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- Charged-Particle Reaction List, 1948-1971
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- Electron - Wikipedia
- Charged–Particle Reaction List 1948–1971 (Atomic and nuclear data reprints)
Because the electron is charged, it produces an orbital magnetic moment that is proportional to the angular momentum. The net magnetic moment of an atom is equal to the vector sum of orbital and spin magnetic moments of all electrons and the nucleus. The magnetic moment of the nucleus is negligible compared with that of the electrons. The magnetic moments of the electrons that occupy the same orbital so called, paired electrons cancel each other out.
William T. Milner
The chemical bond between atoms occurs as a result of electromagnetic interactions, as described by the laws of quantum mechanics. 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 molecular orbitals have different spatial distribution of the electron density. For instance, in bonded pairs i. By contrast, in non-bonded pairs electrons are distributed in a large volume around nuclei.
If a body has more or fewer electrons than are required to balance the positive charge of the nuclei, then that object has a net electric charge. When there is an excess of electrons, the object is said to be negatively charged.
Charged-Particle Reaction List, 1948-1971
When there are fewer electrons than the number of protons in nuclei, the object is said to be positively charged. When the number of electrons and the number of protons are equal, their charges cancel each other and the object is said to be electrically neutral.
A macroscopic body can develop an electric charge through rubbing, by the triboelectric effect. Independent electrons moving in vacuum are termed free electrons. Electrons in metals also behave as if they were free. In reality the particles that are commonly termed electrons in metals and other solids are quasi-electrons— quasiparticles , which have the same electrical charge, spin, and magnetic moment as real electrons but might have a different mass. Likewise a current can be created by a changing magnetic field.
These interactions are described mathematically by Maxwell's equations. At a given temperature, each material has an electrical conductivity that determines the value of electric current when an electric potential is applied. Examples of good conductors include metals such as copper and gold, whereas glass and Teflon are poor conductors. In any dielectric material, the electrons remain bound to their respective atoms and the material behaves as an insulator. Most semiconductors have a variable level of conductivity that lies between the extremes of conduction and insulation.
The presence of such bands allows electrons in metals to behave as if they were free or delocalized electrons. These electrons are not associated with specific atoms, so when an electric field is applied, they are free to move like a gas called Fermi gas  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 millimeters per second.
Metals make relatively good conductors of heat, primarily because the delocalized electrons are free to transport thermal energy between atoms. However, unlike electrical conductivity, the thermal conductivity of a metal is nearly independent of temperature.
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This is expressed mathematically by the Wiedemann—Franz law ,  which states that the ratio of thermal conductivity to the electrical conductivity is proportional to the temperature. The thermal disorder in the metallic lattice increases the electrical resistivity of the material, producing a temperature dependence for electric current.
When cooled below a point called the critical temperature , materials can undergo a phase transition in which they lose all resistivity to electric current, in a process known as superconductivity. In BCS theory , pairs of electrons called Cooper pairs have their motion coupled to nearby matter via lattice vibrations called phonons , thereby avoiding the collisions with atoms that normally create electrical resistance. Electrons inside conducting solids, which are quasi-particles themselves, when tightly confined at temperatures close to absolute zero , behave as though they had split into three other quasiparticles : spinons , orbitons and holons.
According to Einstein's theory of special relativity , 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 accelerate it from within the observer's frame of reference. The speed of an electron can approach, but never reach, the speed of light in a vacuum, c. However, when relativistic electrons—that is, electrons moving at a speed close to c —are injected into a dielectric medium such as water, where the local speed of light is significantly less than c , the electrons temporarily travel faster than light in the medium.ranballpinnci.tk
Electron - Wikipedia
As they interact with the medium, they generate a faint light called Cherenkov radiation. The kinetic energy K e of an electron moving with velocity v is:. The Big Bang theory is the most widely accepted scientific theory to explain the early stages in the evolution of the Universe. These photons were sufficiently energetic that they could react with each other to form pairs of electrons and positrons.
Likewise, positron-electron pairs annihilated each other and emitted energetic photons:. An equilibrium between electrons, positrons and photons was maintained during this phase of the evolution of the Universe.
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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. For reasons that remain uncertain, during the annihilation process there was an excess in the number of particles over antiparticles.
Hence, about one electron for every billion electron-positron pairs survived. This excess matched the excess of protons over antiprotons, in a condition known as baryon asymmetry , resulting in a net charge of zero for the universe.
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This process peaked after about five minutes. Roughly one million years after the big bang, the first generation of stars began to form. These antimatter particles immediately annihilate with electrons, releasing gamma rays. The net result 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.
At the end of its lifetime, a star with more than about 20 solar masses can undergo gravitational collapse to form a black hole. However, quantum mechanical effects are believed to potentially allow the emission of Hawking radiation at this distance.
Charged–Particle Reaction List 1948–1971 (Atomic and nuclear data reprints)
Electrons and positrons are thought to be created at the event horizon of these stellar remnants. When a pair of virtual particles such as an electron and positron is created in the vicinity of the event horizon, random spatial positioning might result in one of them to appear on the exterior; this process is called quantum tunnelling. 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.
The rate of Hawking radiation increases with decreasing mass, eventually causing the black hole to evaporate away until, finally, it explodes. Cosmic rays are particles traveling through space with high energies. Energy events as high as 3.
The particle called a muon is a lepton produced in the upper atmosphere by the decay of a pion. A muon, in turn, can decay to form an electron or positron. Remote observation of electrons requires detection of their radiated energy. For example, in high-energy environments such as the corona of a star, free electrons form a plasma that radiates energy due to Bremsstrahlung radiation.
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 using radio telescopes. The frequency of a photon is proportional to its energy. As a bound electron transitions between different energy levels of an atom, it absorbs or emits photons at characteristic frequencies.
For instance, when atoms are irradiated by a source with a broad spectrum, distinct absorption lines 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. 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.
This enables precise measurements of the particle properties. For example, in one instance a Penning trap was used to contain a single electron for a period of 10 months. The first video images of an electron's energy distribution were captured by a team at Lund University in Sweden, February The scientists used extremely short flashes of light, called attosecond pulses, which allowed an electron's motion to be observed for the first time.
The distribution of the electrons in solid materials can be visualized by angle-resolved photoemission spectroscopy ARPES. This technique employs the photoelectric effect to measure the reciprocal space —a mathematical representation of periodic structures that is used to infer the original structure. ARPES can be used to determine the direction, speed and scattering of electrons within the material.
Electron beams are used in welding. This welding technique must be performed in a vacuum to prevent the electrons from interacting with the gas before reaching their target, and it can be used to join conductive materials that would otherwise be considered unsuitable for welding. Electron-beam lithography EBL is a method of etching semiconductors at resolutions smaller than a micrometer.
For this reason, EBL is primarily used for the production of small numbers of specialized integrated circuits. Electron beam processing is used to irradiate materials in order to change their physical properties or sterilize medical and food products. Linear particle accelerators generate electron beams for treatment of superficial tumors in radiation therapy.
An electron beam can be used to supplement the treatment of areas that have been irradiated by X-rays. Particle accelerators use electric fields to propel electrons and their antiparticles to high energies. These particles emit synchrotron radiation as they pass through magnetic fields. The dependency of the intensity of this radiation upon spin polarizes the electron beam—a process known as the Sokolov—Ternov effect.