IONIZATION OF ALKALI ATOMS BY ELECTRON BOMBARDMENT

A new experimental method was developed by which relative measurements of ionization cross sections can be normalized to absolute values. The method consists essentially of combining crossed-beam techniques, adsorption of gases on solid surfaces, and radiotracer detection. An atomic beam containing the radioactive tracer is crossed rectilinearly with an electron beam. The reaction products are adsorbed on collector surfaces and detected in a scintillation counter. The atomic beam is also quantitatively sampled by adsorption. Under consideration of experimental parameters, the value of the total ionization cross section is then directly proportional to the ratio of the counting rates R/sub ion//R/sub beam/. The relative ionization cross-section curves of potassium, rubidium, and cesium were normalized and are presented. The values of alpha for the relation Q/sub i/ = alpha E/sup - BETA / expressing the simple ionization cross sections as a function of electron energy are also given. The total scattering cross sections of potassium, rubidium, and cesium were partially resolved into their components. Finally, the autoionization structure of cesium is related to the known energy levels of the atom. (auth)