BARKAS EFFECT AND EFFECTIVE CHARGE IN THE THEORY OF STOPPING POWER

Experimental and theoretical values of the Barkas function L1 are compared for p, p, ±;, and Li ions. For a gold absorber, existing theories of L1 do not provide a good approximation for the experimental data. Therefore an empirical function is suggested. For Al, Si, Cu, and Ag, parameters b and ; for the Ashley, Ritchie, and Brandt theory [Phys. Rev. B 5, 2393 (1972)] have been determined that give fairly good agreement with experiment for particle energies above 1 MeV/u. The Bloch term L2 is used without any modifications. For Li ions, the charge-state corrections z* used so far appear to be too large. In order to derive reliable experimental values of L1 from p- and ±;-particle data, measurements of stopping power should have an uncertainty of the order of 0.1%. © 1990 The American Physical Society.