Editing Henri Becquerel (section)

==Biography==

===Family and education===
Becquerel was born in Paris, France, into a wealthy family which produced four generations of notable physicists, including Becquerel's grandfather ([[Antoine César Becquerel]]), father ([[Edmond Becquerel]]), and son ([[Jean Becquerel]]).<ref name=":2">{{Cite book|title=Henri Becquerel|date=2006|publisher=Great Neck Publishing|isbn=9781429816434|location=[S.l.]|oclc=1002022209}}</ref> Henri started off his education by attending the [[Lycée Louis-le-Grand]] school, a prep school in Paris.<ref name=":2" /> He studied engineering at the [[École polytechnique]] and the [[École Nationale des Ponts et Chaussées|École des ponts et chaussées]].<ref name=":0">{{Cite web|url=https://www.nobelprize.org/prizes/physics/1903/becquerel/biographical/|title=Henri Becquerel|date=1903|publisher=Nobel Prize|access-date=15 July 2019}}</ref>
[[File:Portrait d'Antoine-César Becquerel.jpg|thumb|190px|Portrait of Henri's grandfather, Antoine César Becquerel, by [[Antoine-Jean Gros]]]]

===Career===
Becquerel's earliest works centered on the subject of his [[doctoral]] [[thesis]] supervised by [[Charles Friedel]]<ref>{{Cite web|title=Becquerel, Henri, 1852–1908 |url=https://history.aip.org/phn/11706009.html |access-date=17 April 2022 |publisher=history.aip.org}}</ref> at the Faculty of Sciences of the [[University of Paris|Sorbonne]]: the [[plane polarization]] of light, with the phenomenon of [[phosphorescence]] and [[absorption (electromagnetic radiation)|absorption]] of light by crystals.<ref>{{Cite web|author=Henri Becquerel|year=1888|title=Recherches sur l’absorption de la lumière dans les cristaux|url=https://sciences.gloubik.info/spip.php?article1868}}</ref> He was awarded a [[Doctor of Science]] in 1888.<ref name=":4">[https://www.nobelprize.org/prizes/physics/1903/becquerel/biographical/ Henri Becquerel – Biographical]. Nobelprize.org.</ref> 

Early in his career, Becquerel also studied the [[Earth's magnetic field]]s.<ref name=":4" /> Becquerel became the third in his family to occupy the Chair of [[Applied Physics]] at the [[Muséum national d'histoire naturelle]] in 1892. Later on in 1894, Becquerel became chief engineer in the Department of Bridges and Highways before he started with his early experiments. In 1895, he was appointed as a professor at the École polytechnique.<ref>{{Cite web |title=Henri Becquerel – Nuclear Museum |author=Atomic Heritage Foundation |work=Nuclear Museum |date= |access-date=10 July 2023 |url= https://ahf.nuclearmuseum.org/ahf/profile/henri-becquerel/}}</ref>

Becquerel's discovery of [[Radioactive decay|spontaneous radioactivity]] is a famous example of [[serendipity]], of how chance favors the prepared mind. Becquerel had long been interested in [[phosphorescence]], the emission of light of one color following the object's exposure to light of another color. In early 1896, there was a wave of excitement following [[Wilhelm Conrad Röntgen]]'s discovery of [[X-rays]] on 5 January. During the experiment, Röntgen "found that the [[Crookes tube]]s he had been using to study cathode rays emitted a new kind of invisible ray that was capable of penetrating through black paper".<ref name=":6">{{Cite web|url=https://www.aps.org/publications/apsnews/200803/physicshistory.cfm|title=American Physical Society|last=Tretkoff|first=Ernie|date=March 2008}}</ref> Becquerel learned of Röntgen's discovery during a meeting of the [[French Academy of Sciences]] on 20 January where his colleague [[Henri Poincaré]] read out Röntgen's preprint paper.<ref name=PaisInward>{{Cite book |last=Pais |first=Abraham |title=Inward bound: of matter and forces in the physical world |date=2002 |publisher=Clarendon Press [u.a.] |isbn=978-0-19-851997-3 |edition=Reprint |location=Oxford}}</ref> {{rp|43}}  Becquerel "began looking for a connection between the [[phosphorescence]] he had already been investigating and the newly discovered x-rays"<ref name=":6" /> of Röntgen, and thought that phosphorescent materials might emit penetrating X-ray-like radiation when illuminated by bright sunlight; he had various phosphorescent materials including some [[uranium]] salts for his experiments.<ref name=PaisInward/>

Throughout the first weeks of February, Becquerel layered photographic plates with coins or other objects then wrapped this in thick black paper, placed phosphorescent materials on top, placed these in bright sun light for several hours. The developed plate showed shadows of the objects. Already on 24 February he reported his first results. However, the 26 and 27 February were dark and overcast during the day, so Becquerel left his layered plates in a dark cabinet for these days. He nevertheless proceeded to develop the plates on 1 March and then made his astonishing discovery: the object shadows were just as distinct when left in the dark as when exposed to sunlight. Both [[William Crookes]] and Becquerel's 18 year old son [[Jean Becquerel|Jean]] witnessed the discovery.<ref name=PaisInward/>{{rp|46}}

By May 1896, after other experiments involving non-phosphorescent uranium salts, he arrived at the correct explanation, namely that the penetrating radiation came from the uranium itself, without any need for excitation by an external energy source.<ref name=":5">{{cite journal|date=March 2008|title=This month in physics history March 1, 1896 Henri Becquerel discovers radioactivity|url=http://www.aps.org/publications/apsnews/200803/physicshistory.cfm|journal=APS News|volume=17|issue=3 }}</ref> There followed a period of intense research into radioactivity, including the determination that the element [[thorium]] is also radioactive and the discovery of additional radioactive elements [[polonium]] and [[radium]] by [[Marie Skłodowska-Curie]] and her husband [[Pierre Curie]]. The intensive research of [[Radioactive decay|radioactivity]] led to Becquerel publishing seven papers on the subject in 1896.<ref name=":0" /> Becquerel's other experiments allowed him to research more into radioactivity and figure out different aspects of the [[magnetic field]] when radiation is introduced into the magnetic field. "When different radioactive substances were put in the magnetic field, they deflected in different directions or not at all, showing that there were three classes of radioactivity: negative, positive, and electrically neutral."<ref>{{Cite web|url=http://www2.lbl.gov/abc/wallchart/chapters/03/4.html|title=The Discovery of Radioactivity|date=9 August 2000|website=Guide to the Nuclear Wallchart}}</ref>

As simultaneity often happens in science, radioactivity came close to being discovered nearly four decades earlier in 1857, when [[Abel Niépce de Saint-Victor]], who was investigating photography under [[Michel Eugène Chevreul]], observed that uranium salts emitted radiation that could darken photographic emulsions.<ref>Niepce de Saint-Victor (1857) [https://books.google.com/books?id=wplDAQAAIAAJ&pg=PA811 "Mémoire sur une nouvelle action de la lumière"] (On a new action of light), ''Comptes rendus'' ... , vol. 45, pages 811–815.</ref><ref>Niepce de Saint-Victor (1858) [http://visualiseur.bnf.fr/CadresFenetre?O=NUMM-3003&I=448&M=tdm "Deuxième mémoire sur une nouvelle action de la lumière"] {{Webarchive|url=https://web.archive.org/web/20170717094559/http://visualiseur.bnf.fr/CadresFenetre?O=NUMM-3003&I=448&M=tdm |date=17 July 2017 }} (Second memoir on a new action of light), ''Comptes rendus'' ... , vol. 46, pages 448–452.</ref> By 1861, Niepce de Saint-Victor realized that uranium salts produce "a radiation that is invisible to our eyes".<ref>{{Cite web|url=http://famousinfomation.blogspot.com/|title=The man who Discover the world|last=Frog|first=Max|language=en|access-date=13 April 2018}}</ref> Niepce de Saint-Victor knew Edmond Becquerel, Henri Becquerel's father.  In 1868, Edmond Becquerel published a book, ''La lumière: ses causes et ses effets'' (Light:  Its causes and its effects).  On page 50 of volume 2, Edmond noted that Niepce de Saint-Victor had observed that some objects that had been exposed to sunlight could expose photographic plates even in the dark.<ref name=":7" /> Niepce further noted that on the one hand, the effect was diminished if an obstruction were placed between a photographic plate and the object that had been exposed to the sun, but " … ''d'un autre côté, l'augmentation d'effet quand la surface insolée est couverte de substances facilement altérables à la lumière, comme le nitrate d'urane'' … " ( ... on the other hand, the increase in the effect when the surface exposed to the sun is covered with substances that are easily altered by light, such as uranium nitrate ... ).<ref name=":7">Edmond Becquerel, ''La lumière:  ses causes et ses effets'', vol. 2 (Paris, France:  F. Didot, 1868), [https://books.google.com/books?id=LoA5AAAAcAAJ&pg=PA50 page 50].</ref>

==== Experiments ====
[[File:Becquerel in the lab.jpg|thumb|upright|Becquerel in the lab]]

Describing them to the [[French Academy of Sciences]] on 27 February 1896, he said:

<blockquote>One wraps a [[Auguste and Louis Lumière|Lumière]] photographic plate with a bromide emulsion in two sheets of very thick black paper, such that the plate does not become clouded upon being exposed to the sun for a day. One places on the sheet of paper, on the outside, a slab of the phosphorescent substance, and one exposes the whole to the sun for several hours. When one then develops the photographic plate, one recognizes that the silhouette of the phosphorescent substance appears in black on the negative. If one places between the phosphorescent substance and the paper a piece of money or a metal screen pierced with a cut-out design, one sees the image of these objects appear on the negative&nbsp;... One must conclude from these experiments that the phosphorescent substance in question emits rays which pass through the opaque paper and reduce silver salts.<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]. Accessed 02 March 2019.</ref></blockquote>

But further experiments led him to doubt and then abandon this hypothesis. On 2 March 1896 he reported:

<blockquote>I will insist particularly upon the following fact, which seems to me quite important and beyond the phenomena which one could expect to observe: The same crystalline crusts [of potassium uranyl sulfate], arranged the same way with respect to the photographic plates, in the same conditions and through the same screens, but sheltered from the excitation of incident rays and kept in darkness, still produce the same photographic images. Here is how I was led to make this observation: among the preceding experiments, some had been prepared on Wednesday the 26th and Thursday the 27th of February, and since the sun was out only intermittently on these days, I kept the apparatuses prepared and returned the cases to the darkness of a bureau drawer, leaving in place the crusts of the uranium salt. Since the sun did not come out in the following days, I developed the photographic plates on the 1st of March, expecting to find the images very weak. Instead the silhouettes appeared with great intensity ... One hypothesis which presents itself to the mind naturally enough would be to suppose that these rays, whose effects have a great similarity to the effects produced by the rays studied by M. Lenard and M. Röntgen, are invisible rays emitted by phosphorescence and persisting infinitely longer than the duration of the luminous rays emitted by these bodies. However, the present experiments, without being contrary to this hypothesis, do not warrant this conclusion. I hope that the experiments which I am pursuing at the moment will be able to bring some clarification to this new class of phenomena.<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]. Accessed 02 March 2019.</ref></blockquote>

===Late career===
Later in his life in 1900, Becquerel measured the properties of [[beta particle]]s, and he realized that they had the same measurements as high speed electrons leaving the nucleus.<ref name=":0" /><ref name=":3">{{Cite web|url=https://www.famousscientists.org/henri-becquerel/|title=Henri Becquerel – Biography, Facts and Pictures|publisher=www.famousscientists.org|language=en-US|access-date=6 March 2018}}</ref>  In 1901 Becquerel made the discovery that radioactivity could be used for medicine. Henri made this discovery when he left a piece of radium in his vest pocket and noticed that he had been burnt by it. This discovery led to the development of [[radiotherapy]], which is now used to treat cancer.<ref name=":0" /> In 1908 Becquerel was elected president of [[Académie des Sciences]], but he died on 25 August 1908, at the age of 55, in [[Le Croisic]], France.<ref name=":4" /> He died of a heart attack,<ref name=PaisInward/>{{rp|49}} but it was reported that "he had developed serious burns on his skin, likely from the handling of radioactive materials."<ref>{{Cite news|url=https://www.earthmagazine.org/article/benchmarks-henri-becquerel-discovers-radioactivity-february-26-1896|title=Benchmarks: Henri Becquerel discovers radioactivity on February 26, 1896|date=5 January 2012|work=EARTH Magazine|access-date=13 April 2018|language=en}}</ref>