Editing Nuclear technology (section)

==History and scientific background==

=== Discovery ===
{{main|Nuclear physics}}
The vast majority of common, natural phenomena on Earth only involve [[gravity]] and [[electromagnetism]], and not nuclear reactions. This is because atomic nuclei are generally kept apart because they contain positive electrical charges and therefore repel each other.

In 1896, [[Henri Becquerel]] was investigating [[phosphorescence]] in [[uranium]] salts when he discovered a new phenomenon which came to be called [[radioactivity]].<ref>{{cite web|url=http://nobelprize.org/nobel_prizes/physics/laureates/1903/becquerel-bio.html|title=Henri Becquerel - Biographical|website=nobelprize.org|access-date=9 May 2018|url-status=live|archive-url=https://web.archive.org/web/20170904065620/https://www.nobelprize.org/nobel_prizes/physics/laureates/1903/becquerel-bio.html|archive-date=4 September 2017}}</ref> He, [[Pierre Curie]] and [[Marie Curie]] began investigating the phenomenon. In the process, they isolated the element [[radium]], which is highly radioactive. They discovered that radioactive materials produce intense, penetrating rays of three distinct sorts, which they labeled alpha, beta, and gamma after the first three [[Greek alphabet|Greek letters]]. Some of these kinds of radiation could pass through ordinary matter, and all of them could be harmful in large amounts. All of the early researchers received various [[radiation burn]]s, much like [[sunburn]], and thought little of it.

The new phenomenon of radioactivity was seized upon by the manufacturers of [[quack medicine]] (as had the discoveries of [[electricity]] and [[magnetism]], earlier), and a number of [[patent medicine]]s and treatments involving radioactivity were put forward.

Gradually it was realized that the radiation produced by radioactive decay was [[ionizing radiation]], and that even quantities too small to burn could pose a [[nuclear safety|severe long-term hazard]]. Many of the scientists working on radioactivity died of [[cancer]] as a result of their exposure. Radioactive patent medicines mostly disappeared, but other applications of radioactive materials persisted, such as the use of radium salts to produce [[Radium Girls|glowing dials on meters]].

As the atom came to be better understood, the nature of radioactivity became clearer. Some larger atomic nuclei are unstable, and so [[radioactive decay|decay]] (release matter or energy) after a random interval. The three forms of [[Ionizing radiation|radiation]] that Becquerel and the Curies discovered are also more fully understood. [[Alpha decay]] is when a nucleus releases an [[alpha particle]], which is two [[proton]]s and two [[neutron]]s, equivalent to a [[helium]] nucleus. [[Beta decay]] is the release of a [[beta particle]], a high-energy [[electron]]. [[Gamma decay]] releases [[gamma rays]], which unlike alpha and beta radiation are not matter but [[electromagnetic radiation]] of very high [[frequency]], and therefore [[energy]]. This type of radiation is the most dangerous and most difficult to block. All three types of radiation occur naturally in [[List of elements by stability of isotopes|certain elements]].

It has also become clear that the ultimate source of most terrestrial energy is nuclear, either through radiation from the [[Sun]] caused by [[Stellar surface fusion|stellar thermonuclear reactions]] or by radioactive decay of uranium within the Earth, the principal source of [[geothermal energy]].

=== Nuclear fission ===
{{main|Nuclear fission}}
In natural nuclear radiation, the byproducts are very small compared to the nuclei from which they originate. Nuclear fission is the process of splitting a nucleus into roughly equal parts, and releasing energy and neutrons in the process. If these neutrons are captured by another unstable nucleus, they can fission as well, leading to a [[chain reaction]]. The average number of neutrons released per nucleus that go on to fission another nucleus is referred to as ''k''. Values of ''k'' larger than 1 mean that the fission reaction is releasing more neutrons than it absorbs, and therefore is referred to as a self-sustaining chain reaction. A mass of fissile material large enough (and in a suitable configuration) to induce a self-sustaining chain reaction is called a [[Critical mass (nuclear)|critical mass]].

When a neutron is captured by a suitable nucleus, fission may occur immediately, or the nucleus may persist in an unstable state for a short time. If there are enough immediate decays to carry on the chain reaction, the mass is said to be [[Prompt criticality|prompt critical]], and the energy release will grow rapidly and uncontrollably, usually leading to an explosion.

When discovered on the eve of [[World War II]], this insight led multiple countries to begin programs investigating the possibility of constructing an [[atomic bomb]] — a weapon which utilized fission reactions to generate far more energy than could be created with chemical explosives. The [[Manhattan Project]], run by the [[United States]] with the help of the [[United Kingdom]] and [[Canada]], developed multiple fission weapons which were used against [[Japan]] in 1945 at [[Hiroshima]] and [[Nagasaki]]. During the project, the first [[nuclear reactor|fission reactors]] were developed as well, though they were primarily for weapons manufacture and did not generate electricity.

In 1951, the first nuclear fission power plant was the first to produce electricity at the Experimental Breeder Reactor No. 1 (EBR-1), in Arco, Idaho, ushering in the "Atomic Age" of more intensive human energy use.<ref>{{cite web|url=https://futurism.com/images/a-brief-history-of-technology/|title=A Brief History of Technology|website=futurism.com|access-date=9 May 2018|url-status=live|archive-url=https://web.archive.org/web/20180423093858/https://futurism.com/images/a-brief-history-of-technology/|archive-date=23 April 2018}}</ref>

However, if the mass is critical only when the delayed neutrons are included, then the reaction can be controlled, for example by the introduction or removal of [[neutron absorber]]s. This is what allows [[nuclear reactor]]s to be built. Fast neutrons are not easily captured by nuclei; they must be slowed (slow neutrons), generally by collision with the nuclei of a [[neutron moderator]], before they can be easily captured. Today, this type of fission is commonly used to generate electricity.

=== 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, formally known as thermonuclear weapons, 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.