Nuclear density is the density of the nucleons (neutrons and protons) in the nucleus. For heavy nuclei, it is close to the nuclear saturation density <math>n_0=0.15\pm0.01</math> nucleons/fm<sup>3</sup>, which minimizes the energy density of an infinite nuclear matter. The nuclear saturation mass density is thus <math>\rho_0=n_0 m_{\rm u} \approx 2.5\times10^{17}</math> kg/m<sup>3</sup>, where m<sub>u</sub> is the atomic mass constant. The descriptive term nuclear density is also applied to situations where similarly high densities occur, such as within neutron stars.
Evaluation
The nuclear density of a typical nucleus can be approximately calculated from the size of the nucleus, which itself can be approximated based on the number of protons and neutrons in it. The radius of a typical nucleus, in terms of number of nucleons, is
<math>R=A^{1/3}R_0</math>
where <math>A</math> is the mass number and <math>R_0</math> is 1.25 fm, with typical deviations of up to 0.2 fm from this value. The number density of the nucleus is thus:
:<math>n = \frac{A}