AN EMPIRICAL EXPRESSION FOR K-SHELL IONIZATION CROSS-SECTION BY ELECTRON-IMPACT

An empirical expression is proposed to describe the K-shell ionization cross sections by electron impact over a wide range of atomic numbers (i.e. 6 less than or equal to Z less than or equal to 79) and overvol tages U (i.e. 1 less than or equal to U less than or equal to 10(4)) d efined as being the ratio between the incident electron energy and the ionization energy of the electrons in the K shell. The study is based on the analysis of existing experimental: databases for atoms. Agreem ent is obtained with an accuracy of 10% over the entire atomic number and overvoltage ranges including the near-threshold region. Results ar e compared with those obtained with other analytical expressions.