Charge distribution of 8 MeV/u Xe ions emerging from carbon foils

Charge distributions were measured as a function of target thickness using an analyzing magnet and a one-dimensional position-sensitive microchannel plate detector. The equilibrium charge distribution (obtained with 400 μg/cm2 carbon target) was compared with the predictions of several semiempirical formulations. All of them were found to give good representation of the experimental data. It was noticed that the charge distribution obtained with a combination of two carbon foils sandwiched together differed from the one obtained with a single carbon foil of the same total thickness. Moreover, it was found that the resulting charge distribution depended on the relative ordering of two foils. A simple model was developed in an effort to understand this effect. The model was based upon the integrated rate equation expressing the thickness dependence of the ionic charge in terms of average, ionization, and capture cross sections with an additional term to represent the thickness dependence of charge multiplication by Auger decay after the ion exited the foil. The predictions of this model agree quite well with the measured values and also account for the fact that the average charge is higher when the thinner foil is first in line