Double ionization of ﹩{\mathrm{He}}^{0+}﹩ forming ﹩{\mathrm{He}}^{2+}﹩. The data points show the experimental results of Shah et al. (1988; filled circles) and Rejoub et al. (2002; filled squares). The dashed line illustrates the semiempirical formula following Shevelko et al. (2005), and the solid line uses the cross-section scaling found here for He-like systems.