Ion implantation is now finding applications in many diverse fields1, 2, 3in addition to its established use for the fabrication of electronic devices. For such purposes it is essential that fundamental data on the spatial distribution of implanted ions be available. The Lindhard, Scharff and Schiøtt (LSS) theory4for the slowing down of energetic ions in solids enables range distributions in amorphous solids to be predicted. Measurements of ion ranges at low doses using a variety of techniques have proved the general validity of this theory.5In some circumstances, however, the conditions employed in an implantation experiment may produce a range profile different to that predicted theoretically, and hence direct experimental measurement becomes essential.