Secondary electron yield induced by slowly moving heavy ions

Abstract

The secondary electron yield induced by slowly moving ( v = 0.6 v 0, v 0 - Bohr velocity) heavy ions was researched on a thin carbon foil in forward and backward direction in respect to the ion beam. Only for the backwards electron emission an oscillatory behaviour of the yield was observed in dependence of the atomic number Z 1 of the projectiles while in forward direction the electron yield increases nearly monotonically with Z 1. For the forward electron emission the yield is somewhat higher. The excess of electrons between forward and backward electron emission seems to be proportional to the mean charge of the emerging ions which indicates a surface effect for the forward electron emission. The Z 1-oscillation in the backwards electron emission corresponds to oscillations as was found by energy loss measurements on an argon gas target. These oscillations correlate with the number of charge exchange events in gases. From the common oscillatory behaviour it was concluded that charge exchanges during single collision events are everywhere dominant for the energy loss of slowly moving heavy ions in gases as well in solids.