Energy Loss and Range of Fission Fragments in Solid Media

Energy losses and ranges in Mylar have been measured for some representative fission fragments; these data and existing stopping-power measurements for bromine and iodine ions in media from carbon to gold are shown to be consistent with a semiempirical theory which treats electronic stopping processes in terms of an effective charge ${Z_1}^{*}$ which depends on the velocity of the ion. The fractional effective charge $\frac{{Z_1}^{*}}{Z_1}$ is shown to be a universal function of the variable $\frac{v}{v_0{Z_1}^{\frac{2}{3}}}$, where $v_0$ is the Bohr velocity and $Z_1$ is the nuclear charge of the fragment. This semiempirical treatment, when combined with existing theoretical estimates for nuclear stopping powers, correctly predicts ranges of fission-fragment-like ions.