Abstract: A high purity, hyperthermal, continuous beam atomic oxygen source capable of retrofitting to existing UHV systems has been developed. The instrument complements a general system capability, while its small size and simplicity of design permits tailoring the instrument for most experimental geometries. The flux level presently available is near 1.times.10.sup.14 cm.sup.-2 s.sup.-1 (.sup.3 P) but may be extended toward the theoretical limit of 3.times.10.sup.15 cm.sup.-2 s.sup.-1. The energy distribution of the emitted neutrals shows that the mean kinetic energy is about the same as observed for the ions or about 5 eV. The energy of the oxygen atoms may be substantially reduced for other applications by collision with a temperature controlled, non-reactive surface (with a concomitant spread in the energy distribution).