(thermonuclear reaction). An endothermic nuclear reaction yielding large amounts of energy in which the nuclei of light atoms (chiefly the hydrogen isotopes D [deuterium] and T [tritium]) unite or fuse to form helium. Uncontrolled fusion was achieved some years ago in the hydrogen bomb, in which the initiating temperature was supplied by a fission reaction. Research efforts are now being devoted to developing a controlled and sustained fusion reaction that would utilize the deuterium and tritium in water. Several reactions are possible, but the most efficient is, for each fusion event, D + T + e → 4He + n + 17.5 MeV. An energy input (e) equivalent to at least 44 million degrees C is necessary. One approach utilizes powerful laser beams impinging on a mixture of deuterium and tritium in glass microspheres coated with “Teflon” and beryllium, which have an ablative effect. Fusion reactions have been successfully attained by this method at the Lawrence Livermore Laboratory. The other approach is a magnetic fusion device called a tokamak, located in Princeton, N.J. The Joint European Torus (JET) is located in Cambridge, England. Fusion has two great advantages over fission as an energy source: (1) it utilizes water and readily available lithium as its raw materials instead of scarce and costly uranium; (2) it produces only tritium as a radioactive by-product. As indicated, the D + T reaction yields 4He nuclei, as well as 24 MeV neutrons, which carry off 80% of the energy.See JET; Tokamak.
