Compton electron

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 ... 

Figure 3-18. Production of Compton electrons. Aj is greater than A, by the amount of energy lost in the collision.

In practice a sample is counted normally as described for the channels ratio method and then counted a second time with a source of y-rays (usually Cs or Ba) positioned in the center of the counting chamber just below the sample vial (see Figure 3-19). Any quenching that occurs has the same effect on the efficiency and spectrum of the Compton electrons as it does on those of the sample j8 particles. Since this technique has incorporated the procedures of both internal standardization and channels ratio correction methods, it is no surprise that the data obtained must be treated as described above for both of these techniques. The first or normal count rate obtained in each channel arises only from the sample and may be represented as follows ... 

The second count rate obtained in the presence of the external standard is a composite of counts arising from the sample and from the external standard (via Compton electrons). It may be represented as follows ... 

Activation energy, also, energy of a neutron or Compton electron... 

Maximum energy of recoil from a Compton electron, or from a neutron... 

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 ... 

Detection of internal conversion electrons. Radioisotopes emitting internal conversion (IC) electrons also emit gammas and X-rays. The use of a single detector to count electrons will record not only IC electrons but also Compton electrons produced in the detector by the gammas. To eliminate the Compton electrons, one can utilize the X-rays that are emitted simultaneously with the IC electrons. Thus, a second detector is added for X-rays and the counting system... 

From the study of the Compton effect (Chap. 4), it is known that Compton electrons have an energy range from zero up to a maximum energy which is... 

The kinetic energy of the pair is deposited in the counter (the arguments are the same as for photoelectrons or Compton electrons). Therefore, pulses proportional to the energy T = E - 1.022 MeV are certainly produced, but what happens to the energy of 1.022 MeV ... 

IC emitters are relatively inexpensive to obtain and very easy to handle. They have the disadvantage that they emit not only IC electrons but also gammas. Thus, when a spectrum is recorded, the result includes both IC electrons and Ckimpton electrons created by gammas that interact in the detector. One may eliminate the Compton electrons by utilizing the X-rays that are also given off by the IC source. The X-rays are emitted in coincidence with the IC electrons, while the gammas, and therefore the Compton electrons too, are not. Thus, if the IC electrons are counted in coincidence with the X-rays, the Compton electrons will not be recorded. 

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. 

An external standard spectrum to determine the QIP is popular with users and instrument vendors. The external gamma-ray source (e.g., Cs, or Eu) that is part of the detector system induces a Compton-electron spectrum in the scintillation cocktail. Each sample is automatically counted with and without the external standard. The Compton-electron spectrum produced in each sample vial is applied with mathematical techniques to derive a QIP for a quench correction curve. 

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. 

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