The Description of the Ejected Electron in K-shell Ionization

Merzbacher and Lewis recently reviewed the treatment of K-shell ionization of atoms on the basis of the Born approximation. They emphasized the importance of the screening effect of the outer electrons which causes the actual K-shell ionization potential to be somewhat less than the approximate value corresponding to the hydrogenic model adopted in theoretieal work. There are two quite different methods of describing the ejected electron. One, due to Beth, has been used in the treatment of nuclear impacts, while the other, due to Stobbe, Massey, and Mohr, has been used in the treatment of photon and electron impacts. The principle aim in both methods is simply to ensure that the threshold of the calculated cross section energy curve coincides with the threshold of the corresponding observed curve. A quantitative comparison of the two methods has not been made. (A.C.)