Positron Reemission from Thin W(100) Foil in 10-6 Torr Pressure

Abstract
The production of low-energy positron beams for positron-gas scattering experiments has been tested using thin W(100) foils in high-vacuum pressure ( 10-6 Torr). The W foil was baked for cleaning and used as a positron moderator in situ. The efficiency of positrons reemitted from the thin foil was 14±2% for a 1000-Å-thick foil and 10±2% for a 2000-Å-thick one. The positron work function of the W(100) surface in 10-6 Torr was -1.9±0.3 eV. The energy width in situ was 1.5±0.2 eV, narrower than that exposed to air. The feasibility of the brightness-enhancement method in 10-6 Torr for positron-gas scattering experiments was discussed.