Thermonuclear weapons, lithium

Lithium metal had few uses until after World War II, when thermonuclear weapons were developed (see Section 17.11). This application has had an effect on the molar mass of lithium. Because only lithium-6 could be used in these weapons, the proportion of lithium-7 and, as a result, the molar mass of commercially available lithium has increased. A growing application of lithium is in the rechargeable lithium-ion battery. Because lithium has the most negative standard potential of all the elements, it can produce a high potential when used in a galvanic cell. Furthermore, because lithium has such a low density, lithium-ion batteries are light. 

A particular benefit of lithium in thermonuclear weapons comes as a result of its stable nature. Pure deuterium is difficult to store, as it must be kept at very low temperatures. When combined with lithium, however, into lithium deuteride (LiD)—a solid with low reactivity—deuterium can be easily transported at ambient temperatures. The lithium itself is usually enriched with the lithium 6 isotope when used for this purpose. 

A nuclear application of lithium is in thermonuclear weapons and fusion research. In a weapon or fusion reactor, nuclear fusion occurs between two isotopes of hydrogen—deuterium and tritium. Deuterium occurs naturally and has an abundant supply in the worlds oceans (it is present in about 0.015 percent of water molecules). Tritium, on the other hand, is radioactive, has a relatively short half-life, and does not occur naturally. Tritium can be manufactured, however, by bombarding lithium 6 with neutrons. 

Aldermaston was already investigating lithimn 6 as early as 1953. Plans were put into place to produce up to 10 kg per year, to be increased up to 100 kg per year. There were some problems with this plan, one being that if the British government started purchasing large quantities of lithium, it would reveal that the UK was intending to produce thermonuclear weapons. 

---