Positron remoderation by gas cooling within an electric drift field

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 novel remoderation unit that is based on inelastic positron scattering and a focusing drift motion of the slowed-down positrons in nitrogen gas. In first measurements at the intense slow positron beam NEPOMUC at the FRM II we succeeded in detecting moderated positrons at the exit of the remoderator stage. The losses were monitored by detection of the annihilation radiation. Possible improvements and applications of the method are discussed.