A compact mono-energetic positron beam system has been constructed at The University of Hong Kong in order to perform positron re-emission measurements, after fast positrons from a radioactive Na-22 source moderated by a variety of samples. The positron re-emission measurements are performed at a vacuum of 10(-8) Torr. Re-emitted slow positrons are guided by longitudinal magnetic fields provided by three field coils located outside the vacuum tank and are detected by a gamma photon insensitive channel electron multiplier (CEM). The radioactive source, the sample, the focusing and, the retarding-field energy analyzer (REA) and the CEM detector were put into a compact assembly having a length of 33 cm and a diameter of 6 cm. Positron re-emission from W(1 1 1), GaN/SiC, Ga/GaN/SiC, 4H and 6H-SiC surfaces have been studied. The moderator conversion efficiencies of these samples are reported. (C) 2002 Elsevier Science B.V. All rights reserved.