Gas moderation of positrons

A variety of low-energy positron experiments need an improved brilliance of the beam by means of a remoderator. Conventionally, a tungsten foil or single crystal is used as a remoderator in transmission or reflection geometry. We have developed a new remoderation unit which is based on inelastic positron scattering and the drift of positrons in nitrogen gas. In first measurements we succeeded in detecting fully thermalized positrons. High positron losses occurred at the entrance of the gas cell, and therefore the injection of positrons will be improved for next measurements. (C) 2008 Elsevier B.V. All rights reserved.