Editing Nuclear technology (section)

=== Nuclear fusion ===
{{main|Nuclear fusion}}
{{see also|Timeline of nuclear fusion}}
If nuclei are forced to collide, they can undergo [[nuclear fusion]]. This process may release or absorb energy. When the resulting nucleus is lighter than that of [[iron]], energy is normally released; when the nucleus is heavier than that of iron, energy is generally absorbed. This process of fusion occurs in [[star]]s, which derive their energy from [[hydrogen]] and [[helium]]. They form, through [[stellar nucleosynthesis]], the light elements ([[lithium]] to [[calcium]]) as well as some of the heavy elements (beyond iron and [[nickel]], via the [[S-process]]). The remaining abundance of heavy elements, from nickel to uranium and beyond, is due to [[supernova nucleosynthesis]], the [[R-process]].

Of course, these natural processes of astrophysics are not examples of nuclear "technology". Because of the very strong repulsion of nuclei, fusion is difficult to achieve in a controlled fashion. [[Hydrogen bomb]]s obtain their enormous destructive power from fusion, but their energy cannot be controlled. Controlled fusion is achieved in [[particle accelerator]]s; this is how many [[synthetic element]]s are produced. A [[fusor]] can also produce controlled fusion and is a useful [[neutron source]]. However, both of these devices operate at a net energy loss. Controlled, viable [[fusion power]] has proven elusive, despite the occasional [[cold fusion|hoax]]. Technical and theoretical difficulties have hindered the development of working civilian fusion technology, though research continues to this day around the world.

Nuclear fusion was initially pursued only in theoretical stages during World War II, when scientists on the Manhattan Project (led by [[Edward Teller]]) investigated it as a method to build a bomb. The project abandoned fusion after concluding that it would require a fission reaction to detonate. It took until 1952 for the first full [[hydrogen]] bomb to be detonated, so-called because it used reactions between [[deuterium]] and [[tritium]]. Fusion reactions are much more energetic per unit mass of [[Nuclear fuel|fuel]] than fission reactions, but starting the fusion chain reaction is much more difficult.