An atomic nucleus is short for "nucleus". Located at the core of an atom, it is made up of two kinds of particles, protons and neutrons. The proton, in turn, consists of two up quarks and one down quark, and the neutron, in turn, consists of two down quarks and one up quark.The nucleus is very small, with a diameter of 10 meters to 10 meters. The volume only accounts for one hundred billion of the volume of the atom. In this very small nucleus, more than 99.96% of the mass of the atom is concentrated. The nucleus is extremely dense, the density of the nucleus is about 10^17kg/m, that is, if the volume of 1 meter is full of nucleus, its mass will reach 10^14t, that is, 1 trillion tons. Nuclei are extremely energetic.