Fusion and Thermonuclear Fuel
Thermonuclear weapons are frequently named hydrogen bombs or H-bombs. This is
because the thermonuclear reactions relevant for nuclear weapons involve isotopes of
- D + T → He-4 + n (14.1 MeV) + 17.6 MeV
- D + D → He-3 + n (2.45 MeV) + 3.3 MeV
- D + D → T + p + 4.03 MeV
- He-3 + D → He-4 + p + 18.35 MeV
There are other thermonuclear reactions which can occur. However the reaction rates are
too low in order to be significant.
The first thermonuclear fuel which was considered for a weapon was deuterium. This is:
- (Relatively) easy to ignite and burn
- Abundant in nature (in comparison with tritium)
- (Relatively) inexpensive to produce
One other thermonuclear fuel is easier to ignite- this is a mixture of deuterium and tritium.
At thermonuclear temperatures, the D+T reaction rate (reaction 1) is two magnitude orders
faster than D+D (reaction 2 or 3). However, tritium does not occur in nature and is very
expensive to manufacture.
The cheapest and most usual manufacturing on an industrial scale is to breed it in reactors.
Generally it is produced in the same reactors which produce plutonium - thus the
production of plutonium and tritium are usually in competition. Tritium has a half-life of
approximately 12 years, thus it is expensive simply to maintain an inventory of tritium.
The other method is to produce tritium in situ from other reactions in a functioning weapon.
There are two main reactions which produce tritium; reaction 3 (D+D) produces a triton and
lithium-6 and lithium-7 (7% and 93% of natural lithium respectively) can undergo reactions
which produce tritium:
- Li-6 + n → T + He-4 + 4.8 MeV
- Li-7 + n → T + He-4 + n - 2.5 MeV