A new compact system has been developed to produce monoenergetic positrons of variable energy. The energy range available at present is between 150 eV and 28 keV, so that depth profiles can be measured. This positron beam is being used to investigate defects and defect structures close to the surface in metals and alloys. The technique of Doppler broadening of the annihilation radiation is applied for these measurements. © 1982 The American Physical Society.