The radius R of a nucleus of mass number A can be estimated by the formula  $R = (1.3 \times {10}^{–15})A^{1/3} m$. It follows that the mass density of a nucleus is of the order of : $\left({\mathrm{M}}_{\text{prot }}\cong {\mathrm{M}}_{\text{neut }}=1.67\times {10}^{-27} \mathrm{kg}\right)$