Radiation Physics
John H. Hubbell, in Encyclopedia of Physical Science and Technology (Third Edition), 2003
II.C Electrons
Electron beams for research and for irradiation purposes are produced by a variety of orbital and linear accelerators, with output energies from the keV to the GeV regions, and beam currents from microamperes to kiloamperes. Linear accelerators (linacs) consist of an electron gun injector at one end, followed by a series of accelerating cavities containing rf (radio frequency) power. Natural sources of high-energy electrons include β rays from radioisotope decay, and also from electrons in space which have been accelerated in magnetic fields. There is a particularly high concentration of electrons trapped around planets that have high magnetic fields, such as Earth and Jupiter. These trapped-electron concentrations, called Van Allen belts, offer a radiation damage hazard to components in unmanned space vehicles traversing these altitudes, and are avoided as much as possible in the case of manned flights.
https://www.sciencedirect.com/topics/earth-and-planetary-sciences/electron-guns
Resonance assisted hydrogen bond[edit]
The resonance assisted hydrogen bond (commonly abbreviated as RAHB) is a strong type of hydrogen bond. It is characterized by the π-delocalization that involves the hydrogen and cannot be properly described by the electrostatic model alone. This description of the hydrogen bond has been proposed to describe unusually short distances generally observed between O=C-OH∙∙∙ or ∙∙∙O=C-C=C-OH.[citation needed]
Structural details[edit]
The X−H distance is typically ≈110 pm, whereas the H···Y distance is ≈160 to 200 pm. The typical length of a hydrogen bond in water is 197 pm. The ideal bond angle depends on the nature of the hydrogen bond donor. The following hydrogen bond angles between a hydrofluoric acid donor and various acceptors have been determined experimentally:[23]
| Acceptor···donor | VSEPR geometry | Angle (°) |
|---|---|---|
| HCN···HF | linear | 180 |
| H2CO···HF | trigonal planar | 120 |
| H2O···HF | pyramidal | 46 |
| H2S···HF | pyramidal | 89 |
| SO2···HF | trigonal | 142 |
https://en.wikipedia.org/wiki/Bent_bond
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https://www.beamtec.de/en/electron-emitter/
https://ntrs.nasa.gov/citations/20040086006
https://encyclopedia2.thefreedictionary.com/Metal+Propellant
https://www.researchgate.net/publication/269216009_Indium_-_An_alternative_propellant_for_FEEP-thrusters
https://en.wikipedia.org/wiki/Solid-propellant_rocket
https://en.wikipedia.org/wiki/Ion-propelled_aircraft
https://en.wikipedia.org/wiki/Ion_thruster
low barrier resonance hydrogen
photon phonon
History and uses[edit]
The BGT was invented in the 1980s, originally intended to study positron transport in tokamak (fusion) plasmas.[8] Subsequently, the technique was refined and is now used in laboratories worldwide for a variety of applications. They include study of positron interactions with atoms and molecules, materials, and material surfaces;[9][10][11][12] the creation of antihydrogen,[13][14][15][16] the positroniummolecule (i.e., Ps2, e+e−e+e−),[17] and novel positron[18] and positronium beams.[19] BGTs are also expected to play similarly important roles in efforts to create and study positoronium atom Bose–Einstein condensates (BEC)[20] and a classical electron-positron “pair” plasmas.[4][21][22]
https://en.wikipedia.org/wiki/Buffer-gas_trap
https://en.wikipedia.org/wiki/Penning_trap
https://en.wikipedia.org/wiki/Bose–Einstein_condensate
https://en.wikipedia.org/wiki/Antihydrogen
https://en.wikipedia.org/wiki/Cyclotron_radiation
https://en.wikipedia.org/wiki/Ultra-high_vacuum
https://en.wikipedia.org/wiki/Pair_production
https://en.wikipedia.org/wiki/Category:Nucleosynthesis
https://en.wikipedia.org/wiki/Sulfur_hexafluoride
https://en.wikipedia.org/wiki/Carbon_tetrafluoride
n particle physics, annihilation is the process that occurs when a subatomic particle collides with its respective antiparticle to produce other particles, such as an electroncolliding with a positron to produce two photons.[1] The total energy and momentum of the initial pair are conserved in the process and distributed among a set of other particles in the final state. Antiparticles have exactly opposite additive quantum numbers from particles, so the sums of all quantum numbers of such an original pair are zero. Hence, any set of particles may be produced whose total quantum numbers are also zero as long as conservation of energy and conservation of momentum are obeyed.[2]
During a low-energy annihilation, photon production is favored, since these particles have no mass. High-energy particle colliders produce annihilations where a wide variety of exotic heavy particles are created.
The word "annihilation" takes use informally for the interaction of two particles that are not mutual antiparticles – not charge conjugate. Some quantum numbers may then not sum to zero in the initial state, but conserve with the same totals in the final state. An example is the "annihilation" of a high-energy electron antineutrino with an electron to produce a
W−
.
If the annihilating particles are composite, such as mesons or baryons, then several different particles are typically produced in the final state.
https://en.wikipedia.org/wiki/Annihilation
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Charge conjugation[edit]
In the formalism of particle theories, charge-like quantum numbers can sometimes be inverted by means of a charge conjugation operator called C. Charge conjugation simply means that a given symmetry group occurs in two inequivalent (but still isomorphic) group representations. It is usually the case that the two charge-conjugate representations are complex conjugate fundamental representations of the Lie group. Their product then forms the adjoint representation of the group.
Thus, a common example is that the product of two charge-conjugate fundamental representations of SL(2,C) (the spinors) forms the adjoint rep of the Lorentz group SO(3,1); abstractly, one writes
That is, the product of two (Lorentz) spinors is a (Lorentz) vector and a (Lorentz) scalar. Note that the complex Lie algebra sl(2,C) has a compact real form su(2) (in fact, all Lie algebras have a unique compact real form). The same decomposition holds for the compact form as well: the product of two spinors in su(2) being a vector in the rotation group O(3) and a singlet. The decomposition is given by the Clebsch–Gordan coefficients.
A similar phenomenon occurs in the compact group SU(3), where there are two charge-conjugate but inequivalent fundamental representations, dubbed and , the number 3 denoting the dimension of the representation, and with the quarks transforming under and the antiquarks transforming under . The Kronecker product of the two gives
That is, an eight-dimensional representation, the octet of the eight-fold way, and a singlet. The decomposition of such products of representations into direct sums of irreducible representations can in general be written as
for representations . The dimensions of the representations obey the "dimension sum rule":
Here, is the dimension of the representation , and the integers being the Littlewood–Richardson coefficients. The decomposition of the representations is again given by the Clebsch–Gordan coefficients, this time in the general Lie-algebra setting.
See also[edit]
References[edit]
- ^ Fuchs, Jurgen (1992), Affine Lie Algebras and Quantum Groups, Cambridge University Press, ISBN 0-521-48412-X
https://en.wikipedia.org/wiki/Charge_(physics)#Charge_conjugation
https://en.wikipedia.org/wiki/Gauge_boson
