Resolution of the frozen-charge paradox in stopping of channeled heavy ions

The long-standing problem of the lacking signature of a Barkas effect in th e stopping of swift heavy ions under channeling conditions has been analyze d theoretically. The stopping model provides explicit dependences on impact parameter and allows for projectile screening and higher-order ZI correcti ons. The analysis differentiates between principal target shells. A distinc t Barkas correction is found in accordance with standard theory. It is less pronounced fur channeled than fur random stopping because of the dominance of outer target shells. Varying contributions from different target shells to the stopping force may give rise to an inversion of the commonly observ ed variation with ion energy and charge state of the Barkas correction.