Abstract. Twenty years ago a theoretical analysis showed that electron scattering by high-Z one-electron atoms might lead to interference of exchange and spin-orbit interactions at low electron energies, observable as a crosssection asymmetry if unpolarized electrons are scattered by polarized cesium atoms. By using a highly polarized cesium atomic beam, we studied exchange and spin-orbit effects at different electron energies, 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 ° , it varies between +0.02 and -0.02 and goes through zero near 110 ° being negative at larger angles.

AbStracrWe measured the total ionization asymmetry A in dependence on the incident electron energy E Here 'total' refers to integration over all emission angles and energy partitions of the outgoing electrons. From a threshold value of A=0.125 the A ( € ) curve rises smoothly toward a broad maximum of A,, = 0.31 at E,, = 8.3 eV. The fall-off towards higher energies is quite similar to that of the other one-electron atoms. However, it shows a structure which can be explained by contributions from autoionizing P states.Bartschat has made a theoretical estimate of A ( € ) for various atoms. At low energies the agreement with OUT data is satisfactory, at higher energies the experimental A values are considerably smaller than the thedretical ones. In the threshold region measurements were performed with small electron energy width (0.1 eV). No smctllre in the A ( € ) curve was found. The slope at threshold was determined as dA/dE =(0.136+0.005) eV-'.

Abstract.We have set up an atomic beam of cesium for the study of spin-dependent electron-cesium scattering. The beam is produced by an effusive oven with continuous recirculation of the condensed metal. The beam is optically pumped by circularly polarized light from two laser diodes tuned to the 6 2 S1/2 (F --3) 6 21P3/2 (F' = 4) and 6 2 Sl/2 (F = 4) --, 6 2 P3/2 (F' = 5) transitions, respectively. Nearly all atoms are transferred into the F=4, mF= +4 or m~.=-4 Zeeman level of the ground state, depending on the sense of circular polarization of the pumping light. The population distribution in the optically pumped beam is analyzed in terms of the mj = -1/2 and ms = + 1/2 components with a SternGerlach magnet. We find the atomic polarization to be very close to unity at a density of 8 x 108 atoms/cm 3 in the scattering center. The polarization decreases slightly with increasing density of the cesium beam due to radiation trapping. A spin flipper serves as a means of polarization reversal, introducing no systematic errors in the spin asymmetry measurements. Lock-in technique is used to stabilize the atomic beam polarization by detecting fluorescence light signals.

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