लोहे के नाभिक का द्रव्यमान $55.85 \,u$ एवं $A =56$ है, इसका नाभिकीय घनत्व ज्ञात कीजिए।

$m_{ Fe }=55.85\,u =9.27 \times 10^{-26} \,kg$

Nuclear density $=\frac{\text { mass }}{\text { volume }}=\frac{9.27 \times 10^{-26}}{(4 \pi / 3)\left(1.2 \times 10^{-15}\right)^{3}} \times \frac{1}{56}$

$=2.29 \times 10^{17} \,kg \,m ^{-3}$

The density of matter in neutron stars (an astrophysical object) is comparable to this density. This shows that matter in these objects has been compressed to such an extent that they resemble a big nucleus.