ANGULAR-DISTRIBUTION OF IONS AXIALLY CHANNELED IN AVERY THIN CRYSTAL - EXPERIMENTAL AND THEORETICAL RESULTS

We have studied the angular distributions for 6-30-MeV C-q+ (q = 4-6) and 2-9-MeV H+ ions axially channeled in the [001] direction of a thin silicon crystal (1792 and 1906 Angstrom). We:report highly structured two-dimensional angular distributions that depend sensitively on the projectile's velocity and incident charge state and the target's thick ness and azimuthal orientation. Some structure in the angular contour maps is the result of a rainbow effect in axial channeling (i.e., extr ema in the classical deflection function). State-to-state charge-state distributions, which are required to interpret the data accurately, h ave also been measured. All measured angular distributions have been e xplained via Monte Carlo trajectory calculations using Moliere's appro ximation to the Thomas-Fermi screening function and. a screening lengt h given by target electrons alone. The calculations indicate that all projectile velocity and charge-state effects and the target-thickness effects observed are the result of the projectile's transverse oscilla tory motion in the channel. Using this information, we show that swift heavy-ion and proton angular distributions are simply related using a scaling law that depends only on the projectile's velocity-and charge -to-mass ratio and on the crystal thickness.