Stopping Power of Solids for Fast-Moving Tantalum Ions

The results of measurements of energy losses, $\frac{\mathrm{dE}}{\mathrm{dX}}$, of 10-140-MeV Ta ions in C, Al, Ag, and Au foils are presented. The relative effective charges responsible for the electronic part of the slowing down process are deduced from the data, using the Bethe-Bloch formalism. These agree well with semiempirical extrapolations based on $\frac{\mathrm{dE}}{\mathrm{dX}}$ data, using lighter projectiles. For a given energy the effective mean charges deduced from $\frac{\mathrm{dE}}{\mathrm{dX}}$ measurements in solids are considerably smaller than the mean charges measured directly after passing the ions through such solids, but agree quite well with the mean charges measured after traversing gases.