Nuclear radius scaling ($R\simeq r_0{A}^{1/3}$)

The approximate mass-number dependence of a sharp equivalent nuclear radius. Near-constant interior nucleon number density gives $A\simeq (4\pi /3)n_0{R}^3$, hence $R\propto A^{1/3}$. A conventional matter-radius scale is $r_0\simeq 1.2\mathrm{fm}$, with isotope and definition dependence. A charge-weighted root-mean-square radius is a different observable: for a uniform sphere it is $\sqrt{3/5}R$. Diffuse surfaces and neutron skins prevent interpreting the scaling as a universal hard boundary.