MEASUREMENT OF EXCHANGE AND SPIN-ORBIT EFFECTS AND THEIR INTERFERENCEIN ELASTIC E-CS SCATTERING AT 7-EV

Twenty years ago a theoretical analysis showed that electron scatterin g by high-Z one-electron atoms might lead to interference of exchange and spin-orbit interactions at low electron energies, observable as a cross-section asymmetry if unpolarized electrons are scattered by pola rized cesium atoms. By using a highly polarized cesium atomic beam, we studied exchange and spin-orbit effects at different electron energie s, starting at 20 eV and going down. We observed the first distinctly non-zero interference asymmetry at 7 eV: Over the angular range of 35 to 145 degrees, it varies between +0.02 and -0.02 and goes through zer o near 110 degrees being negative at larger angles.