Atomic nucleus

The nucleus (atomic nucleus) is the center of an atom. Nuclei are composed of protons and neutrons. The number of protons in an atomic nucleus is called the atomic number, and determines which element the atom is. For example, a nucleus with one proton (which is the only nucleus that may have no neutrons) constitutes an atom of hydrogen, with six protons, carbon, or with eight, oxygen. The number of neutrons determines the isotope of the element. The numbers of protons and neutrons in a nucleus are correlated; in light nuclei they are approximately equal, while heavier nuclei have a larger number of neutrons. The two numbers together determine the nuclide (type of nucleus). Protons and neutrons have nearly equal masses, and their combined number, the mass number, is approximately equal to the atomic mass of an atom. The mass of the electrons is small in comparison to the mass of the nucleus.

External links

• SCK.CEN Belgian Nuclear Research Centre Mol, Belgium