Núkléù ni ibi kiki to ni protoni ati neutroni ni arin atomu. O je wiwari ni 1911, nipase itumo ti Ernest Rutherford fun idanwo Rutherford 1909 ti Hans Geiger ati Ernest Marsden se, labe idari Rutherford. Afiwera protoni–neutroni fun nukleu je aba Dmitry Ivanenko ni 1932. Kìkì gbogbo ìkórajọ atomu lo wa ni inu nukleu ayafi die elektroni ayipo.

A model of the atomic nucleus showing it as a compact bundle of the two types of nucleons: Protons (red) and neutrons (blue). In this picture, the protons and neutrons look like little balls stuck together, but an actual nucleus (as understood by modern nuclear physics) does not look like this. An actual nucleus can only be accurately described using quantum mechanics. For example, in a real nucleus, each nucleon is in multiple locations at once, spread throughout the nucleus.