Charge state studies of heavy ions passing through gas



The charge state of an ion passing through matter fluctuates as a result of electron capture and loss in the collisions with the target atoms. Despite the existence of a large number of theoretical and experimental studies on this complicated atomic collision system, an accurate prediction of the charge state distribution is still not available. To meet DRAGON’s future experimental needs, the non-equilibrium and equilibrium charge state distributions resulting from the collisions of 16O, 23Na, 24Mg ions passing through a windowless hydrogen and helium gas target with the beam energy in the range of 0.1380.875 MeV/u, 0.2000.478 MeV/u, 0.2000.800 MeV/u, respectively, have been measured using the differentially pumped gas target facility at Naples University, Italy, and DRAGON/ISAC, TRIUMF, Canada. It is determined that the equilibrium distribution is established at low target thickness. The equilibrium distribution depends on the projectile species, its energy and the nature of the target, while independent of the incident charge state. The uncertain- ties of the normalized charge state fractions are estimated to be less than 5% except for very low fractions. The equilibrium distribution is shown to be close to the Gaussian distribution. Semi-empirical formulas have been derived for the average equilibrium charge state and distribution width. Assuming that the probability of multiple electron capture and loss in a single collision are negligible, single electron capture and loss cross sections have been estimated using the least-squares method in cases where sufficient experimental charge state fraction data are available. The dependence of cross sections on projectile energy and charge state has been studied.

Author: Liu, W.