MULTIPLE IONIZATION OF COPPER BY ELECTRON-IMPACT

A pulsed crossed beam technique previously developed in this laboratory has been used to study the electron impact ionization of copper. Previous measurements have been very limited in scope and exhibit large discrepancies. Relative cross sections sigma(n) for the formation of 1 to 5 times ionized copper have been measured with high accuracy within the range 7.8-2100 eV. Individual cross sections have been obtained by normalization to absolute values of sigma(2) obtained by Freund et al at energies below 200 eV using a fast crossed beam technique. Weak structures in sigma(1) can be attributed to Auger decay processes following the creation of 3s subshell and L shell vacancies but there is a lack of other pronounced structures in sigma(n) for n>1 where many close-lying subshell vacancies are involved. At 2100 eV cross sections as are less than three orders of magnitude smaller than sigma(1).