Projectiles

McDaniei E W 1989 Atomic Collisions Electron and Photon Projectiles (New York Wiiey)... 

Of course the real projectile-surface interaction potential is not infinitely hard (cf figure A3,9,2. As E increases, the projectile can penetrate deeper into the surface, so that at its turning point (where it momentarily stops before reversing direction to return to the gas phase), an energetic projectile interacts with fewer surface atoms, thus making the effective cube mass smaller. Thus, we expect bE/E to increase with E (and also with W since the well accelerates the projectile towards the surface). 

In this case the projectile has imparted energy D (k a - k )/2m to the target. Assuming the target is initially in... 

In this expression, factors that describe the incident and scattered projectile are separated from the square modulus of an integral that describes the role of the target in detemiining the differential cross section. The temi preceding the... 

Theoretically, the asymptotic fonn of die solution for the electron wave fiinction is the same for low-energy projectiles as it is at high energy however, one must account for the protracted period of interaction between projectile and target at the intennediate stages of the process. The usual procedure is to separate the incident-electron wave fiinction into partial waves... 

The partial wave decomposition of the incident-electron wave provides the basis of an especially appealing picture of strong, low-energy resonant scattering wherein the projectile electron spends a sufficient period of time in the vicinity... 

Figure Bl.7.10. Tliree mass spectra showing the results of reactive collisions between a projectile ion C H. NH, isomeric butenes. (Taken from Usypchiik L L, Harrison A G and Wang J 1992 Reactive...

The dynamics of ion surface scattering at energies exceeding several hundred electronvolts can be described by a series of binary collision approximations (BCAs) in which only the interaction of one energetic particle with a solid atom is considered at a time [25]. This model is reasonable because the interaction time for the collision is short compared witii the period of phonon frequencies in solids, and the interaction distance is shorter tlian the interatomic distances in solids. The BCA simplifies the many-body interactions between a projectile and solid atoms to a series of two-body collisions of the projectile and individual solid atoms. This can be described with results from the well known two-body central force problem [26]. 

Figure Bl.23.1. (a) Two-body collision of a projectile of mass and kinetic energy E approaching a...

Classical ion trajectory computer simulations based on the BCA are a series of evaluations of two-body collisions. The parameters involved in each collision are tire type of atoms of the projectile and the target atom, the kinetic energy of the projectile and the impact parameter. The general procedure for implementation of such computer simulations is as follows. All of the parameters involved in tlie calculation are defined the surface structure in tenns of the types of the constituent atoms, their positions in the surface and their themial vibration amplitude the projectile in tenns of the type of ion to be used, the incident beam direction and the initial kinetic energy the detector in tenns of the position, size and detection efficiency the type of potential fiinctions for possible collision pairs. 

Taking advantage of the synnnetry of the crystal structure, one can list the positions of surface atoms within a certain distance from the projectile. The atoms are sorted in ascending order of the scalar product of the interatomic vector from the atom to the projectile with the unit velocity vector of the projectile. If the collision partner has larger impact parameter than a predefined maximum impact parameter discarded. If a... 

Figure Bl.24.2. A schematic representation of an elastic collision between a particle of massM and energy Eq and a target atom of mass M2. After the collision the projectile and target atoms have energies of and 2 respectively. The angles 0 and ( ) are positive as shown. All quantities refer to tire laboratory frame of reference.

Figure Bl.24.4. Energy loss components for a projectile that scatters from depth t. The particle loses energy A E- via inelastic collisions with electrons along the inward path. There is energy loss A E in the elastic scattering process at depth t. There is energy lost to melastic collisions A along the outward path. For an incident energy Eq the energy of tlie exiting particle is = q - A iv - AE - A E. ...

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