Editing Radioactive decay (section)

==History of discovery==
[[File:Pierre and Marie Curie.jpg|thumb|upright=0.9|Pierre and Marie Curie in their Paris laboratory, before 1907|left]]

[[Henri Poincaré]] laid the seeds for the discovery of radioactivity through his interest in and studies of [[X-ray]]s, which significantly influenced physicist [[Henri Becquerel]].<ref>{{Cite journal |last1=Radvanyi |first1=Pierre |last2=Villain |first2=Jacques |date=2017-11-01 |title=The discovery of radioactivity |url=https://www.sciencedirect.com/science/article/pii/S1631070517300786 |journal=Comptes Rendus. Physique |language=en |volume=18 |issue=9–10 |pages=544–550 |doi=10.1016/j.crhy.2017.10.008 |bibcode=2017CRPhy..18..544R |issn=1878-1535}}</ref> Radioactivity was discovered in 1896 by Becquerel and independently by [[Marie Curie]], while working with [[Phosphorescence|phosphorescent]] materials.<ref>{{cite book |last=Mould |first=Richard F. |title=A century of X-rays and radioactivity in medicine : with emphasis on photographic records of the early years |date=1995 |publisher=Inst. of Physics Publ. |location=Bristol |isbn=978-0-7503-0224-1 |page=12 |edition=Reprint. with minor corr}}</ref><ref>{{cite journal|author=Henri Becquerel|title=Sur les radiations émises par phosphorescence|journal=Comptes Rendus|volume=122|pages=420–421|year=1896|url=http://gallica.bnf.fr/ark:/12148/bpt6k30780/f422.chemindefer}}</ref><ref>''Comptes Rendus'' '''122''': 420 (1896), [http://web.lemoyne.edu/~giunta/becquerel.html translated by Carmen Giunta]. Retrieved 12 April 2021.</ref><ref>{{cite journal|author=Henri Becquerel|title=Sur les radiations invisibles émises par les corps phosphorescents|journal=Comptes Rendus|volume=122|pages=501–503|year=1896|url=https://gallica.bnf.fr/ark:/12148/bpt6k30780/f503.item}}</ref><ref>''Comptes Rendus'' '''122''': 501–503 (1896), [http://web.lemoyne.edu/~giunta/becquerel.html translated by Carmen Giunta]. Retrieved 12 April 2021.</ref> These materials glow in the dark after exposure to light, and Becquerel suspected that the glow produced in [[cathode-ray tube]]s by X-rays might be associated with phosphorescence. He wrapped a photographic plate in black paper and placed various phosphorescent [[salt (chemistry)|salts]] on it. All results were negative until he used [[uranium]] salts. The uranium salts caused a blackening of the plate in spite of the plate being wrapped in black paper. These radiations were given the name "Becquerel Rays".

It soon became clear that the blackening of the plate had nothing to do with phosphorescence, as the blackening was also produced by non-phosphorescent [[salts]] of uranium and by metallic uranium. It became clear from these experiments that there was a form of invisible radiation that could pass through paper and was causing the plate to react as if exposed to light.

At first, it seemed as though the new radiation was similar to the then recently discovered X-rays. Further research by Becquerel, [[Ernest Rutherford]], [[Paul Villard]], [[Pierre Curie]], [[Marie Curie]], and others showed that this form of radioactivity was significantly more complicated. Rutherford was the first to realize that all such elements decay in accordance with the same mathematical exponential formula. Rutherford and his student [[Frederick Soddy]] were the first to realize that many decay processes resulted in the [[nuclear transmutation|transmutation]] of one element to another. Subsequently, the [[radioactive displacement law of Fajans and Soddy]] was formulated to describe the products of alpha and [[beta decay]].<ref>Kasimir Fajans, "Radioactive transformations and the periodic system of the elements". [[Chemische Berichte|Berichte der Deutschen Chemischen Gesellschaft]], Nr. 46, 1913, pp. 422–439</ref><ref>Frederick Soddy, "The Radio Elements and the Periodic Law", Chem. News, Nr. 107, 1913, pp. 97–99</ref>

The early researchers also discovered that many other [[chemical element]]s, besides uranium, have radioactive isotopes. A systematic search for the total radioactivity in uranium ores also guided Pierre and Marie Curie to isolate two new elements: [[polonium]] and [[radium]]. Except for the radioactivity of radium, the chemical similarity of radium to [[barium]] made these two elements difficult to distinguish.

Marie and Pierre Curie's study of radioactivity is an important factor in science and medicine. After their research on Becquerel's rays led them to the discovery of both radium and polonium, they coined the term "radioactivity"<ref name="L'Annunziata-2007">{{Cite book|title=Radioactivity: Introduction and History|last=L'Annunziata|first=Michael F.|publisher=Elsevier Science|year=2007|isbn=9780080548883|location=Amsterdam, Netherlands|pages=2}}</ref> to define the emission of [[ionizing radiation]] by some heavy elements.<ref>{{cite book |last1=Petrucci |first1=Ralph H. |last2=Harwood |first2=William S. |last3=Herring |first3=F. Geoffrey |title=General chemistry |date=2002 |publisher=Prentice Hall |isbn=0-13-014329-4 |page=1025 |edition=8th}}</ref> (Later the term was generalized to all elements.) Their research on the penetrating rays in uranium and the discovery of radium launched an era of using radium for the treatment of cancer. Their exploration of radium could be seen as the first peaceful use of nuclear energy and the start of modern [[nuclear medicine]].<ref name="L'Annunziata-2007" />