Editing Nuclear technology (section)

=== 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]].