Compton electron scattering

R. A. Bonham and H. F. Wellenstein, Electron scattering, in Compton Scattering The Investigation of Electron Momentum Distributions, B. G. Williams, ed. (McGraw-Hill, New York, 1977), pp. 234-272. 

The interpretation given above is simplified, since fluorescence is not the only process that allows the atom to lose its excess energy. Other phenomena such as Rayleigh scattering (elastic scattering) and the Compton effect (inelastic scattering with release of Compton electrons) can complicate the X-ray emission spectrum. 

The acronym kerma for kinetic energy released in absorbing material has been used to conceptually connect the energy deposited by ionizing radiation with the radiation field. It is defined to include the kinetic energy, which is locally absorbed from products of interaction with the particular medium such as Compton electrons, photoelectrons, and pah production while excluding the energy, which is not locally absorbed, from Compton-scattered photons, characteristic fluorescence radiation, and annihilation photons. The kerma is defined as ... 

PROBLEM 2.11.2. Evaluate the speed of the orbital motion of an electron that has orbital angular momentum m,vr0 = h, if the mass is concentrated at the electron radius r0 estimated above either from electron-electron scattering (1(P16 m) or from its "classical radius" (2.892 x 10-15 m) or from the Compton wav elength Ac (2.426 x 10 12m). 

The scattering just discussed, whose amplitude is expressed in terms of the atomic scattering factor, is coherent, or unmodified, scattering, which is the only kind capable of being diffracted. On the other hand, incoherent, or Compton modified, scattering is occurring at the same time. Since the latter is due to collisions of quanta with loosely bound electrons, its intensity relative to that of the... 

The scattering of x-rays discussed above is elastic, in the sense that there is no transfer of energy from the photon to the electron, and therefore the scattered x-ray retains the same wavelength. The scattering is also coherent, because the phase relationships between the incident and scattered rays are maintained so that interference phenomena can occur among the scattered rays. There is, however, another mechanism by which the electrons scatter x-rays, and this is called the Compton-modified scattering. This is best explained in terms of the particle nature of the x-rays. 

Figure 1.8 Geometry of the Compton-modified scattering. The electron, initially at rest, moves away at velocity v after having been struck by an x-ray photon of energy hv and momentum h/a.

A 1.5-MeV gamma undergoes Compton scattering. What is the maximum energy the Compton electron can have What is the minimum energy of the scattered photon ... 

In the Compton effect, the photon interacts with an election of an ion in the solid and transfers part of its eneigy to this electron. The result is a Compton scattered photon with energy hr> (v < v) and a so-called Compton electron with energy Ej. The scattered photon may leave the scintillator or may interact with the scintillator (but at a site different from the first interaction). In the latter case the incident photon gives two light centers at different sites which makes the Compton effect undesirable for po.sition-sensitive detection. If the scattered photon leaves the scintillator crystal, less luminescent radiation is produced than in the case of the photoelectric effect. 

The initial result of the interaction of a gamma photon or an electron with a material is the formation of ionized and excited species via Compton scattering and the photo-electron effect.For each initial 1 MeV electron or photon entering a material there may be around lO particles formed, distributed in the main track of the particle, branch tracks formed by the passage of Compton electrons, and blobs of particles formed as the electron energy drops towards thermal levels. It is the reaction of these particles which leads to dramatic changes in the material properties of polymers. 

Compton scatter telescopes utilize two detector planes designed to scatter the incident radiation in the top plane and capture the scattered photon in the lower plane. Measurements of the energy losses and positions of the interactions in the two detector planes permits the reconstruction of the incident photon direction, hi telescopes such as this and COMPTEL on GRO [4], it is not possible to measure the direction of the Compton electron in the top detector and the possible directions, when projected onto the sky, produce a small circle of the half-angle specified by the scatter angle and centered on the direction of the scattered photon. A point source of gamma... 

Compton (incoherent) scattering is the interaction of a photon with a free electron that is considered to be at rest. The process is the most important interaction mechanism in tissue-like materials. From conservation of momentum and energy, the following equations are derived ... 

There is a sharp drop at the end of the continuous energy spectrum of the Compton electrons, the Compton edge, distinctly below the full energy of the original photon. The electron energy reaches its maximum when the photon is totally back scattered 9 - 180°). The energy of such backscattered photons - Ey — is therefore at minimum, but for... 

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