We have precisely measured the secondary-electron-emission yield (gamma) fr
om thin Al, Ag, and Au foils with a thickness of 1 mu m on exposure to full
y stripped 6 MeV/n heavy ions (H, He, C, N, O, Ne, Si, and Ar). The depende
nce of the forward and backward yields on the projectile nuclear charge (z)
showed a proportionality to the square of the effective charge (z(eff)(2))
and an oscillatory behavior with atomic number z; the yields were comparat
ively low for exposures to He2+ and Ne10+ beams. The forward enhancement wa
s significant for Al foil (light metal), depending on z; in contrast, it wa
s small for Ag and Au foils (heavy metals). The accuracy of the gamma value
s was evaluated by determination of z(eff) (+/-5%) and the surface reproduc
ibility of the foil (+/-2-3%).