Lifetime Measurements with a Scanning Positron Microscope

First lifetime results obtained with a scanning positron microscope will be presented. A pulsed positron beam with a variable energy from 0.5 to 20 keV, with a spot diameter of $2\mu \mathrm{m}$, can be electronically scanned over an area of $0.6\times 0.6{\mathrm{mm}}^2$. This beam is formed after a double-stage stochastic cooling (moderation) of positrons emitted from a radioactive isotope. Included in the system is a conventional scanning electron microprobe for surface analysis. Three-dimensional positron lifetime spectra of a GaAs sample with a small surface scratch reveal the range due to the mechanical damage.