The corresponding lithium-6 deuteride, 6Li2H, or 6LiD, is the primary fusion fuel in thermonuclear weapons. In hydrogen warheads of the Teller–Ulam design, a nuclear fission trigger explodes to heat and compress the lithium-6 deuteride, and to bombard the 6LiD with neutrons to produce 3H (tritium) in an exothermic reaction: 6Li2H + n → 4He + 3H + H. The deuterium and tritium then fuse to produce helium, one neutron, and 17.59 MeV of free energy in the form of gamma rays, kinetic energy, etc. The helium is an inert byproduct.