Ionization Cross Sections of Ca, Sr and Ba by Electron Impact

Abstract

Total ionization cross sections of Ca, Sr and Ba by electron impact have been measured by the crossed beam technique. Intensity of neutral atomic beam is determined by the deposition method. Sample atoms deposited onto a beam collector are quantitatively analyzed by atomic absorption spectrophotometry. The absolute cross sections are determined to be 6.2±0.2 A 2 at 13.6 eV for Ca and 7.2±0.3 A 2 at 12.6 eV for Sr. The absolute cross section of Ba could not be determined because of a poor sensitivity of spectrophotometer for Ba. Possible systematic errors are estimated to be between +8% and -19% for both of Ca and Sr. Relative cross sections of the three elements are obtained for electron energy from 0 eV to 1000 eV. Each curve for the total ionization cross section as a function of electron energy has two maxima in low energy region, one of which is considered to be due to autoionization. The results are compared with some experimental results and theoretical calculations by other workers.