Differential Cross-Section Measurements for Large-Angle Collisions of Helium, Neon, and Argon Ions with Argon Atoms at Energies to 100 kev

The differential cross section for the scattering of positive charge from collisions of noble gas ions with the target gas argon has been measured. The ion beam is passed through a chamber containing the target gas at a pressure of a few microns of mercury, which is low enough to insure that single collisions will predominate. The particles scattered out of the beam are collected and the total positive charge is measured. The collector incorporates collimating holes to select only those particles at a chosen scattering angle with a resolution of about two degrees. The apparatus allows the angle to be varied continuously up to thirty-eight degrees. Data are presented for collisions of singly ionized helium, neon, and argon ions with argon atoms at 25, 50, and 100 kev. The cross sections observed differ from those expected from the Rutherford scattering law and these differences are interpreted in terms of electron screening, ionization, and charge exchange.