Deuteron

The deuteron is the nucleus of the isotope hydrogen-2 (deuterium), consisting of one proton and one neutron bound by the strong nuclear force. It is the simplest stable bound state of two nucleons and the only bound two-nucleon system in nature.

Its ground state has total angular momentum J = 1 with positive parity, arising mainly from an S-wave (L = 0) neutron–proton relative motion, plus a small admixture of D-wave (L = 2) due to the tensor component of the nuclear force. The isospin is I = 0. The deuteron is not an elementary particle but a composite system whose properties reflect the nucleon–nucleon interaction.

Key properties include a binding energy of about 2.2246 MeV. The deuteron carries a net positive electric charge (+1 e). Its mass is approximately 2.013553 atomic mass units, about 2.3 milliamu less than the sum of a free proton and neutron due to binding energy. The root-mean-square radius is around 2.1 fm. Its magnetic moment is μd ≈ 0.857 μN, and its quadrupole moment Q ≈ 0.286 fm^2, evidence of the D-state component in its wavefunction.

Deuterons are stable against decay on cosmological timescales. They form in stellar environments and during Big Bang nucleosynthesis, serving as stepping stones to heavier nuclei. In experiments, deuterons provide a simple system for studying neutron–proton interactions, nuclear forces, and nuclear structure, and deuterated materials have applications in science and medicine. The deuteron remains a cornerstone for testing models of the nuclear force, especially tensor interactions and S–D state mixing.