What is the structure of the Nucleus?
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom.
The diameter of the nucleus is in the range of 1.75 fm ($1.75×10^{−15}$ m) for hydrogen (the diameter of a single proton)2 to about 15 fm for the heaviest atoms, such as uranium. These dimensions are much smaller than the diameter of the atom itself (nucleus + electron cloud), by a factor of about 23,000 (uranium) to about 145,000 (hydrogen)



Source:Wikipedia