Collision knock

Linear Cascade Model Sputtering resulting from elastic collisions knock-on sputtering) is the most well understood of all the other forms of... 

For knock-on collisions, one uses the Rutherford cross section for free electrons, and the number of free electrons is taken equal to the integral of the oscillator strength up to the energy loss e (dispersion approximation). Thus,... 

The contribution of knock-on collisions to the stopping power is now given by... 

To calculate the energy partition between the core and the envelope, Mozumder et al. (1968) considered the equipartition of deposited energy between glancing and knock-on collisions (Sect. 2.3.4). Of the ejected electrons... 

The Moseley equation, v = A(Z -B)2, where v is the frequency of the emitted X-ray radiation, Z is the atomic number and A and B are constants, relates the frequency of emitted X-rays to the nuclear charge for the atoms that make up the target of the cathode ray tube. X-rays are emitted by the element after one of its K-level electrons has been knocked out of the atom by collision with a fast moving electron. In this question, we have been asked to determine the values for the constants A and B. The simplest way to find these values is to plot Vv vs. Z. This plot provides Va as the slope and - Va (B) as the y -intercept. Starting with v = A(Z-B)2, we first take the square root of both sides. This affords Vv = Va (Z - B). Multiplying out this expression gives Vv = Va (Z)... 

For arithmetic convenience, 1010 will be assumed to be the collision frequency in a chemical reacting system such as the knock mixture loosely defined. 

If a surface reaction is to involve more than monolayer-chemisorption, then the species adsorbed on the surface must be able to migrate into the second and deeper layers forming new chemical bonds and often new molecular species. This is step 3, product formation, and it often requires an activation mechanism to proceed, i.e., a monolayer is formed and the reaction stops unless the substrate is held at elevated temperature or there is ion or electron bombardment. Damage-enhanced diffsusion, knock-on collisions, and bond breaking may promote the reaction in the presence of ion bombardment. Although the precise mechanisms are unclear, it is certain that electron and ion bombardment cause step 3 to occur in some instances where the chemical reaction does not proceed in the absence of radiation. 

Let s imagine that we are using one of the early spectrometers. First, we would pump all the air out of the instrument. Then we would let a gaseous element (neon, for instance) or the vapor of a liquid or a solid element (such as mercury or zinc) enter the ionization chamber. In this chamber, the atoms of the gas or vapor are exposed to a beam of rapidly moving electrons. When one of the accelerated electrons collides with an atom, it knocks another electron out of it, thereby leaving the atom with a positive charge. In other words, the collision creates a positive ion, an electrically charged atom. The positive ions are accelerated out of the... 

Radiation Damage. It has been known for many years that bombardment of a crystal with eneigetic (keV to MeV) heavy ions produces regions of lattice disorder. An implanted ion entering a solid with an initial kinetic energy of 100 keV comes to rest in the time scale of about 10 13 due to both electronic and nuclear collisions. As an ion slows down and comes to rest in a crystal, it makes a number of collisions with the lattice atoms. In these collisions, sufficient eneigy may be transferred from the ion to displace an atom from its lattice site. Lattice atoms which are displaced by an incident ion are called primary knock-on atoms (PKA). A PKA can in turn displace other atoms, secondary knock-ons, etc. This process creates a cascade of atomic collisions and is collectively referred to as the collision, or displacement, cascade. The disorder can be directly observed by techniques sensitive to lattice structure, such as electron-transmission microscopy, MeV-partide channeling, and electron diffraction. 

The second subregion corresponds to large to and q and is related to close collisions (the knock-on). At very large transferred momenta (qa0> 1) the inelastic scattering by a molecule (an atom) is actually the elastic scattering by a free electron with the cross section given by Rutherford formula. In this case the function /(to, q) can be presented analytically as a delta function ... 

A heavy charged particle can knock out an electron from a molecule with maximum energy Emax —2/ra>2 (at v>v0), whereas for a fast electron with the same velocity the knocked out electron has max — mu2/2. Consequently, while an electron can knock out electrons with velocity no greater than its own, a heavy particle, in head-on collisions, produces delta electrons with velocities which can be twice as high as that of the ion. As a result, the energy of such delta electrons can be distributed to the regions of the medium far more remote from the point of initial ionization than in the case of electron irradiation. 

Further evidence for the importance of electronic excitation as a primary means of defect creation comes from studies of "sub-threshold" damage in which the energy of the incoming particle is less than that required for a "knock-on" collision. 

Concussion. A sharp or hard knock, blow, or collision. The shock of such a blow or a stunning, damaging, or shattering effect from a blow (Ref... 

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