Electron-radiation interaction

This treatment differs from the usual approach to molecule-radiation interaction through the inclusion of the contribution from the electric field from the beginning and by not treating it as a perturbation to the field free situation. The notation 7/ei(r R, e(f)) makes the parametric dependence of the electronic Hamiltonian on the nuclear coordinates and on the electric field explicit. 

Annihilation (Positron-Electron)—An interaction between a positive and a negative electron in which they both disappear their rest mass, being converted into electromagnetic radiation (called annihilation radiation) with two 0.51 MeV gamma photons emitted at an angle of 180° to each other. 

Radiation, Secondary—A particle or ray that is produced when the primary radiation interacts with a material, and which has sufficient energy to produce its own ionization, such as bremsstrahlung or electrons knocked from atomic orbitals with enough energy to then produce ionization (see Delta Rays). 

From a chemist s viewpoint, the most important act of ionizing radiation (usually X-rays, y-rays or high energy electrons) is electron ejection. Initially the ejected electrons have sufficient energy to eject further electrons on interaction with other molecules, but the electrons ultimately become thermalised and then are able to interact "chemically". We consider first various reaction pathways for these electrons, and then consider the fate of the "hole" centres created by electron ejection. [We refer to electron-gain and electron-loss centres rather than to radical-anions and -cations since, of course, the substrate may comprise ions rather than neutral molecules. 

As radiation interacts in the scintillation crystal, energy is transferred to bound electrons of the crystal s atoms. If the energy that is transferred is greater than the ionization energy, the electron enters the conduction band and is free from the binding forces of the parent atom. 

Radiation interactions with a crystal center cause electrons to be raised to an excited state. 

The low BE region of XPS spectra (<20 — 30 eV) represents delocalized electronic states involved in bonding interactions [7]. Although UV radiation interacts more strongly (greater cross-section because of the similarity of its energy with the ionization threshold) with these states to produce photoelectrons, the valence band spectra measured by ultraviolet photoelectron spectroscopy (UPS) can be complicated to interpret [1], Moreover, there has always been the concern that valence band spectra obtained from UPS are not representative of the bulk solid because it is believed that low KE photoelectrons have a short IMFP compared to high KE photoelectrons and are therefore more surface-sensitive [1], Despite their weaker intensities, valence band spectra are often obtained by XPS instead of UPS because they provide... 

In spectroscopy we study the effect of interaction of electromagnetic radiation on matter. For examples X-rays are produced by bombandment of metal targets with high speed electrons. So the different types of electromagnetic radiation interact with the matter and give different types of spectroscopy. 

The primary event which takes place when high energy radiation, such as gamma radiation, interacts with a polymer molecule involves the ejection of an electron, with formation of the polymer cation radical, as shown in Equation (1) ... 

Emitted y radiation interacts with electrons of the surrounding matter. If the frequency of the emitted radiation exceeds the energy level corresponding to the ionization potential of the element, the electron may be expelled from its localized... 

That the hydrated electron is a separate chemical entity has been demonstrated by the technique of pulse radi l sis This consists of subjecting a sample of pure water to a very short pulse of accelerated electrons. The energetic electrons have the same effect upon water as a beam of y-ray photons. Shortly after the pulse of electrons has interacted with the water, a short flash of radiation (ultraviolet and visible radiation from a discharge tube) is passed through the irradiated water sample at an angle of 90° to the direction of the pulse to detect the absorption spectra... 

There are three reasons why the temperature change can affect the tunnelling luminescence of radiation defects in wide-gap insulators characterized by a strong electron-phonon interaction ... 

When radiation interacts with mailer, a displacement of the outermost electrons in atoms occurs. This displacement can lead to the formation of color centers or to valence slate changes, The most commonly seen gemstones enhanced by irradiation are summarized in Table 4. When properly performed, there is no significant residual radioactivity. 

Ionization in a Solid (Semiconductor Detectors) In a semiconductor radiation detector, incident radiation interacts with the detector material, a semiconductor such as Si or Ge, to create hole-electron pairs. These hole-electron pairs are collected by charged electrodes with the electrons migrating to the positive electrode... 

Owing to the electron-vibrational interaction in molecules, there is one more possible decay channel for SES. This is the nonradiative relaxation (internal conversion), in which the electron energy is transferred into vibrational energy of molecules (in the condensed phase, into thermal energy of the medium). If the molecule fluoresces, there may also occur fluorescence from the lowest excited state. (According to the empirical rule of Kasha,64 the molecular fluorescence occurs from the lowest excitation level irrespective of the wavelength of the exciting radiation.)... 

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