A measurement of the electron-impact ionization cross section of sodium

A novel experimental technique is used to determine accurate relative values of ionization cross sections as a function of electron impact for Na. The ionization efficiency curves are then compared with the recent convergent close-coupling (CCC) calculations of Bray (1994) which have been very successful in predicting ionization cross sections of atomic hydrogen. The present results are also compared with the plane-wave Born approximation calculations of McGuire (1971) which are expected to be accurate at high electron-impact energies (>500 eV). These comparisons show that at electron-impact energies greater than about 60 eV, inner-shell ionization plays an important role in Na.