Cross Section Measurements for Electron-Impact Ionization of Atoms.

Absolute electron impact cross sections have been measured from 0 to 200 eV for single ionization of 16 atoms (Mg, Fe, Cu, Ag, Al, Si, Ge, Sn, Pb, P, As, Sb, Bi, S, Se, and Te) with an estimated accuracy of +- 10%. Combined with our recent measurements of He, Ne, Ar, Kr, Xe, F, Cl, Br, I, Ga, and In, [Phys. Rev. 35, 559 (1987); 35, 578 (1987); 39, 5588 (1989)] a set of 27 atomic single ionization cross sections has now been measured with the same apparatus. In addition, cross sections are reported for double ionization of 10 atoms, and triple ionization of 8 atoms. The measurements are made on a 3 keV beam of neutral atoms, prepared by charge transfer neutralization of a mass selected ion beam, by crossing it with an electron beam. The critical measurement of absolute neutral beam flux is made with a calibrated pyroelectric crystal. The magnitudes of the single ionization peak cross sections decrease monotonically across rows of the periodic table from group IIIA (Al, Ga, In) to group VIIIA (Ar, Kr, Xe), varying much more than predicted by various empirical formulas and classical and quantum mechanical theories.