Deuterium–tritium fusion

Deuterium–tritium fusion (sometimes abbreviated D+T) is a type of nuclear fusion in which one deuterium nucleus fuses with one tritium nucleus, giving one helium nucleus, one free neutron, and 17.6 MeV of total energy coming from both the neutron and helium. It is the best known fusion reaction for fusion devices and in thermonuclear weapons.

Tritium, one of the reactants required for this type of fusion, is radioactive. In fusion reactors, a 'breeding blanket' made of lithium is placed on the walls of the reactor, as lithium, when exposed to energetic neutrons, will produce tritium.

Concept
In deuterium–tritium fusion, one deuterium nucleus fuses with one tritium nucleus, yielding one helium nucleus, a free neutron, and 17.6 MeV, which is derived from approximately 0.02 AMUs. The amount of energy obtained is described by the mass-energy relation: $$E=mc^2$$. 80% of the energy (14.1 MeV) becomes kinetic energy of the neutron traveling at $1/6$ the speed of light.

The mass difference between D+T and neutron+4He is described by the semi-empirical mass formula that describes the relation between mass defects and binding energy in a nucleus.

Discovery
Evidence of the D+T reaction was first detected at the University of Michigan in 1938 by Arthur J. Ruhlig. His experiment detected the signature of neutrons with energy greater than 15 MeV in secondary reactions of tritium created in $$^2$$H$$(d,p)^3$$H reactions of a 0.5 MeV incident deuteron beam on a heavy phosphoric acid target, D$$_3$$PO$$_4$$. This discovery was largely unrecognized until recently.

Reactant sourcing
About 1 in every 5,000 hydrogen atoms in seawater is deuterium, making it easy to acquire.

Tritium, however, is a radioactive isotope, and difficult to source naturally. This can be circumvented by exposing the more readily available lithium to energetic neutrons, which produces tritium nuclei. In addition, the deuterium–tritium reaction itself emits a free neutron, which can be used to bombard lithium. A 'breeding blanket', which consists of lithium, is often placed along the walls of fusion reactors such that free neutrons created during deuterium–tritium fusion react with it to produce more tritium. This process is called tritium breeding.

Use in fusion reactors
Deuterium–tritium fusion is planned to be used in ITER, as well as many other proposed fusion reactors. It provides many advantages over other types of fusion, as it has a relatively low minimum temperature of 100 million degrees C.