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 qϭ2 -18) impact on rare gases and simple molecules (H 2 , N 2 , O 2 , and 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 ͑CTMC͒ method. However, CTMC calculations tend to underestimate the ionization cross sections especially at the high-energy region of E/qϾ0.3 ͑MeV/amu͒. A scaling for the gross ionization cross sections of rare gases in fully stripped-ion impact is proposed.

Scaling and formulary of cross-sections for ion–atom impact ionization

“…( 11) was studied experimentally in Refs. [32,55,57,59]. It was confirmed that the necessary condition for the validity of the Bethe formula is given by the condition in Eq.…”

“…The ion velocity corresponds to v = 12v 0 or v = 8.9v nl , whereas Z p = 24, 43, 54, and does not satisfy the condition in Eq. (32). As a result, the cross sections are much smaller than given by the Bethe formula, as evident from Fig.…”

“…It was confirmed that the necessary condition for the validity of the Bethe formula is given by the condition in Eq. (32). The failure of the Bethe formula for large Z p is apparent from the experimental data for gold ions shown in Fig.…”

“…Whereas in the opposite limit, when an ionizing collision is predominantly a consequence of the electron scattering at large impact parameters far from the nucleus, the quantum mechanical uncertainty in the scattering angle is large compared with the angle itself, and the classical calculation can remarkably fail in computing the ionization cross section [31,32].…”

Gross and partial ionization cross sections in 6-MeV/amu bare-ion collisions with methane

“…Secondary ions produced in collisions were extracted with an electrostatic lens, mass/charge analyzed by a double focusing sector magnet and finally detected by a Channeltron detector. Detailed description of the experimental setup and procedure have been reported in previous papers [7,8].…”