High-velocity limit for the ratio of helium double-to-single ionization for highly charged, bare-ion impact

Abstract

The ratio R of helium double-to-single ionization cross sections was measured for ${\mathrm{Ne}}^{10+}$ and ${\mathrm{Ni}}^{28+}$ projectiles at velocities of 0.39\ensuremath{\le}${\mathit{v}}_{\mathit{P}}$/c\ensuremath{\le}0.93 intending to explore the high-velocity limit of R for highly charged ion impact. For ${\mathrm{Ne}}^{10+}$ projectiles R was observed to become independent of ${\mathit{v}}_{\mathit{P}}$ for ${\mathit{v}}_{\mathit{P}}$/c\ensuremath{\gtrsim}0.73 and an asymptotic experimental value R=(2.57\ifmmode\pm\else\textpm\fi{}0.10)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ has been established. This is in good agreement with experimental results for proton, antiproton, electron, and positron impact and in excellent accordance with the theoretical prediction of (2.59\ifmmode\pm\else\textpm\fi{}0.03)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$.