Higher-order Z1 effects in stopping powers

The history of experimental and theoretical evidence for Z13 ('Barkas') and Z14 ('Bloch') corrections to the Bethe stopping formula is outlined. It is found that Lindhard's theory of the Barkas effect and Bloch's original theory for the Z14 term describe experimental evidence from hydrogen, helium, and lithium stopping in a satisfactory manner. It is not clear to how high Z1 values the theoretical corrections may be extended as experiments with heavier ions involve the use of partially stripped ions. Although effective charges may be deduced in a consistent manner from stopping data for such ions by means of the theory of higher-order corrections, interpretation of the results obtained is not straightforward. (Auth.)