Gross ionization cross sections for rare-gas atoms and simple molecules in 6-MeV/amu fully stripped–ion impact

Abstract

Using the parallel-plate-condenser method, we have measured gross ionization cross sections in fully stripped--ion (charge state $q=2--18)$ impact on rare gases and simple molecules $({\mathrm{H}}_{2},{\mathrm{N}}_{2},{\mathrm{O}}_{2},$ and ${\mathrm{CO}}_{2})$ at a fixed collision energy E of 6 MeV/amu. The observed cross sections have been found to depend weakly on the charge state q compared with the ${q}^{2}$ dependence, especially for highly charged projectiles and/or heavy target elements. Therefore, the Bethe-Born calculations tend to overestimate the gross ionization cross sections in multiply charged ion impact at the present collision energy. For a particular target, the gross ionization cross sections have been found to gather on a common curve irrespective of the projectile energy and charge state when the cross section divided by the charge state is plotted against the projectile energy per nucleon divided by the charge state, giving some credence to a scaling law based upon the classical trajectory Monte Carlo (CTMC) method. However, CTMC calculations tend to underestimate the ionization cross sections especially at the high-energy region of $E/q>0.3(\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{a}\mathrm{m}\mathrm{u}).$ A scaling for the gross ionization cross sections of rare gases in fully stripped--ion impact is proposed.