Secondary Electron Emission from a Clean Tungsten Surface Bombarded by various Positive Ions

The secondary electron coefficient γ has been measured for singly charged hydrogen, helium, nitrogen, neon, oxygen, argon and krypton ions in the energy range 10-140 keV incident on a tungsten surface. Measurements have been made within the monolayer adsorption time (similar 5 min) after production of an atomically clean surface. In this energy range γ increases with incident ion energy for all ions with the exception of protons for which a maximum is reached at around 110 keV. At constant energy the yield is progressively higher as the ion mass is increased up to that for oxygen. For neon, argon and krypton the yield at a constant energy is, however, less than that for oxygen.