A several tens-keV monoenergetic positron surface analyzer with 22Na and electrostatic fields

A positron beam surface analyzer equipped with a 10 mCi 22NaCl positron source and three five-element Einzel-lens systems, without guiding magnetic fields, has been constructed. The equipotential surfaces of the electrostatic fields and profiles of the beam trajectories were calculated and tested using an electron gun and the positron source. Meanwhile, a vacuum vessel for UHV was fabricated using large casting blocks of aluminium alloy (#2000) cut by forging and boring without welding. The results ascertained that positrons, moderated with a 10 μm tungsten foil, were accelerated and transported by the electrostatic lens system. Also, the positron beams were extremely sensitive to terrestrial magnetism and to the residual magnetization of materials in and around the electrode system. Concerning the vacuum vessel, the degassing rate of the aluminium chamber, worked on with forging and boring, was ∼ 8.6 × 10−13 Torr ℓ/s·cm2, as low as aluminium from the EX process.