Measurement of Large Angle Atomic Scattering Using Axially Symmetric Magnetic Fields

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Abstract
A technique using the focusing properties of a nonuniform axially symmetric magnetic field to study large angle (θ>32°, lab) scattering of ions from atoms and molecules is described. The scattering cell is placed on the magnetic axis at the position of maximum field and ions in the momentum interval |Δp| at |p| scattered into a conical shell Δθ at θ are counted by a detector placed down along the axis in a region of low field. The solid angle is increased by a factor of several hundred over conventional scattering techniques of comparable angular resolution due to the azimuthal symmetry of the apparatus. The magnetic vector potential and the trajectory equation for a charged particle in this type of inhomogeneous, axially symmetric field are derived. As a preliminary test the known differential scattering cross section for He+ on the He was measured from 40 to 52° (lab) at 300 eV. Results of measurements of the absolute differential scattering cross sections for Li+ on He from 36 to 41.7° at 200 and 300 eV, corresponding to CM scattering angles of 90 to 160°, are presented.