MULTIPLE IONIZATION OF COPPER BY ELECTRON-IMPACT

A pulsed crossed beam technique previously developed in this laborator y has been used to study the electron impact ionization of copper. Pre vious measurements have been very limited in scope and exhibit large d iscrepancies. 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 b y normalization to absolute values of sigma(2) obtained by Freund et a l at energies below 200 eV using a fast crossed beam technique. Weak s tructures in sigma(1) can be attributed to Auger decay processes follo wing 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 clo se-lying subshell vacancies are involved. At 2100 eV cross sections as are less than three orders of magnitude smaller than sigma(1).