Cross Sections for Electron Loss and Capture for Ions Passing through a Helium Gas Jet Target

The St. George recoil mass separator at the University of Notre Dame uses inverse kinematics to study alpha capture reactions induced by ions passing through a helium gas jet target. It uses a series of dipole and quadrupole magnets and a Wien filter to allow ions with a selected charge state and a specific momentum to pass through to the detector. The charge state of the ion changes as it passes through the target because of electron exchanges with the target gas, and it is important to know what fraction of the ions emerging from the target are in the selected charge state. The distribution of charge states can be calculated if the cross sections for electron loss and electron capture from and by the ion are known. A number of methods for calculating these cross sections, as well as some measured electron-loss and electron-capture cross sections, are available in the literature, and we are evaluating the ability of these calculational methods to accurately predict the measured charge state distributions.