No abstract

Using beams of polarised electrons and polarised hydrogen atoms we measured the spin antiparallel-parallel ionisation asymmetry from threshold to 500 eV. Our measurements are generally more precise than those of earlier studies and, more significantly, are characterised by an energy spread that is at least an order of magnitude smaller than that of the earlier work. We compare our results with several theoretical models as well as with the results from similar experiments using polarised alkali atoms.

We describe the design and operating characteristics of a simple polarized atomic hydrogen beam particularly suitable for applications to crossed beams experiments. In addition to experimental measurements, we present the results of detailed computer models, using Monte-Carlo ray tracing techniques, optical analogs, and phase-space methods, that not only provide us with a confirmation of our measurement, but also allow us to characterize the density, polarization, and atomic fraction of the beam at all points along its path. As a subsidiary result, we also present measurements of the relative and absolute efficiencies of the VjG Supavac mass analyzer for masses 1 and 2.

We report on several important features of GaAs polarized electron source operation. Specifically we point out the beneficial effect on crystal lifetime produced by the constant low-level application of cesium from a dispenser embedded in an extraction anode. Using our experience in low-energy polarized electron-atom scattering as a reference, we also discuss the importance of frequent energy calibrations of GaAs electron beams for high-resolution investigations.