Projectile charge dependence of electron emission from foils

Abstract

We have precisely measured the secondary-electron-emission yield (\ensuremath{\gamma}) from thin Al, Ag, and Au foils with a thickness of 1 \ensuremath{\mu}m on exposure to fully stripped $6\mathrm{MeV}/n$ heavy ions (H, He, C, N, O, Ne, Si, and Ar). The dependence of the forward and backward yields on the projectile nuclear charge (z) showed a proportionality to the square of the effective charge ${(z}_{\mathrm{eff}}^{2})$ and an oscillatory behavior with atomic number z; the yields were comparatively low for exposures to ${\mathrm{He}}^{2+}$ and ${\mathrm{Ne}}^{10+}$ beams. The forward enhancement was significant for Al foil (light metal), depending on z; in contrast, it was small for Ag and Au foils (heavy metals). The accuracy of the \ensuremath{\gamma} values was evaluated by determination of ${z}_{\mathrm{eff}}$ (\ifmmode\pm\else\textpm\fi{}5%) and the surface reproducibility of the foil (\ifmmode\pm\else\textpm\fi{}2--3 %).