An electrostatic positron beam for atomic and molecular collision experiments

A new electrostatic positron beam at UCL is described. The beam incorporates a re-moderator to achieve brightness enhancement, time of flight facility for beam energy determination and improved signal to background ratio and a position sensitive detector for 2-D imaging of the beam spot. The apparatus is being employed for measuring the total cross section of positron scattering from krypton and helium in the energy range of (10 — 200) eV. Results will be presented at the conference.