Computer studies of fast ion trajectories in crystals

Abstract

A computer program has been developed which follows the trajectories of fast ions in crystals, based on the assumption of classical dynamics and binary collisions. Initial work has been directed at various aspects of proton channeling in copper in the energy range 5-509 keV. The critical angle and distance of closest approach in a perfect lattice have been evaluated for both rows and planes and compare well with the predictions of the continuum mods1 as developed by Lindhard (1965). We also discuss the overlap of close-packed rows and planes, and the modifications necessary to the basic theory when thermal vibrations are introduced. Experiments have been simulated directly by obtaining a statistical analysis of the velocity distribution of protons reflected from a (1W) face of copper and transmitted through a thin (-1800 A) crystal. In reflection, distinct miniina were obtained along directions corresponding to close-packed rows and planes, in good agreement with experimental "blocking patterns" (Nelson 1967~). Transmission patterns also revealed 2 !ack of large-angle scattering parallel to close-packed planes, analogous to the white arms observed experimentally with thinner crystals.

Epitaxial growth and properties of YBaCuO thin films

“…Therefore the experimental results were analyzed with Monte Carlo computer simulations [ 42,48]. In these calculations the trajectories of a fixed number of charged particles on their way through the YBa2Cu3Ü7 lattice are calculated applying a binary-collision model.…”

Channeling in solid Xe, Ar and Ne direct dark matter detectors

“…In reality, in a dark matter direct detection experiment, the distribution of recoil directions is expected to be peaked in the direction of the average WIMP flow. At room temperature and pressure Our calculation is based on the classical analytic models developed in the 1960's and 70's, in particular by Lindhard and collaborators [6,[14][15][16][17][18][19][20][21]. In these models the discrete series of binary collisions of the propagating ion with atoms is replaced by interactions between the ion and uniformly charged strings or planes.…”

“…Morgan and Van Vliet [16,17]. In Molière's approximation [22] the axial continuum potential, as a function of the transverse distance r to the string, is…”

“…Thus the moving ion does not encounter atoms at a fixed separation or at fixed impact parameter as is the case for a row. To find the static critical distance x c of a planar channel we follow the procedure of defining a "fictitious string", introduced by Morgan and Van Vliet [16,21]. They reduced the problem of scattering from a plane of atoms to the scattering from an equivalent fictitious row contained in a strip of width 2R centered on the projection of the ion path onto the plane of atoms.…”

Methods of channeling simulation

“…Thereby, theirs became the first channeling simulation program; since that time, many others have been written [2][3][4][5][6][7][8][9]. This paper will offer a brief review and explanation of the methodology involved in the simulation of channeling of H and heavier ions having energies of 50 keV/amu or above; no attempt will be made to cover the related fields of channeling calculations using semianalytic methods or continuum potentials or of the simulation of lower energy ion scattering phenomena or collision cascades.…”