Re-emission of slow positrons from tungsten at elevated temperatures

A series of measurements have been made on the dependence of the intensity and energy spectrum of slow positrons re-emitted from polycrystalline tungsten foil held at temperatures of up to 500 °C. Irrespective of target history, no sharpening of the energy spectrum of re-emitted positrons was observed as the remoderator temperature was increased. Further, a steady decrease in the apparent re-emitted positron intensity was observed, attributed primarily to the increase in positronium formation, as the temperature of the foil was increased from 20 to 500 °C. It is concluded that maintaining a moderator or remoderator at elevated temperatures in standard positron beam systems has no beneficial consequences for the quality or intensity of the beam produced. Reasons for this are discussed.