Retarding field and timing measurements of positrons from a W[100] foil

Measurements with the new prebuncher for the existing pulsed positron beam (presented at ICPA‐9) show the possibility of bunching a dc‐beam with a time structure of 2.1ns (FWHM). The pulse width is very sensitive to the longitudinal energy distribution of the moderated positrons. A pulse width of 2.1ns corresponds to a longitudinal energy distribution of 0.35(5) eV. With a retarding grid configuration we measured the positron yield. Measurements with inhomogenic magnetic guiding fields clearly show the influence of elastically scattered events. Their fraction is very sensitive to the surface condition of the moderator. The nonscattered positrons are very well represented by a Gaussian distribution function. Its FWHM is in good overall agreement with the timing measurements.