SECONDARY-ELECTRON YIELD INDUCED BY SLOWLY MOVING HEAVY-IONS

The secondary electron yield induced by slowly moving (upsilon = 0.6 u psilon(0), upsilon(0) - Bohr velocity) heavy ions was researched on a thin carbon foil in forward and backward direction in respect to the i on beam. Only for the backwards electron emission an oscillatory behav iour of the yield was observed in dependence of the atomic number Z(1) of the projectiles while in forward direction the electron yield incr eases nearly monotonically with Z(1). For the forward electron emissio n the yield is somewhat higher. The excess of electrons between forwar d and backward electron emission seems to be proportional to the mean charge of the emerging ions which indicates a surface effect for the f orward electron emission. The Z(1)-oscillation in the backwards electr on emission corresponds to oscillations as was found by energy loss me asurements on an argon gas target. These oscillations correlate with t he number of charge exchange events in gases. From the common oscillat ory behaviour it was concluded that charge exchanges during single col lision events are everywhere dominant for the energy loss of slowly mo ving heavy ions in gases as well in solids.