An electrostatically-focussed positron beam for surface studies

Construction of an electrostatic positron beam mainly for surface studies is under way. In order to obtain information related to surface states with moderate intensity beams, scanning a target with positron beams is planned. Positron trajectories are calculated for various configurations of lens elements and potentials given to them. Several moderators are evaluated for the slow positron generation. A single crystal tungsten foil gives the best performance among the materials tested. In case of the single crystal tungsten, heat treatment is crucial for obtaining good results. q1999 Published by Elsevier Science B.V. All rights reserved