Editing Otto Hahn (section)

===Discovery of protactinium===
[[File:Decay Chain of Actinium.svg|thumb|right|upright|The decay chain of actinium. [[Alpha decay]] shifts two elements down; [[beta decay]] shifts one element up.]]
In 1913, chemists Frederick Soddy and [[Kasimir Fajans]] independently observed that [[alpha decay]] caused atoms to move down two places on the [[periodic table]], while the loss of two beta particles restored it to its original position. Under the resulting reorganisation of the periodic table, radium was placed in group II, [[actinium]] in group III, thorium in group IV and uranium in group VI. This left a gap between thorium and uranium. Soddy predicted that this unknown element, which he referred to (after [[Dmitri Mendeleev]]) as "ekatantalium", would be an alpha emitter with chemical properties similar to [[tantalum]]. It was not long before Fajans and [[Oswald Helmuth Göhring]] discovered it as a decay product of a beta-emitting product of thorium. Based on the [[radioactive displacement law of Fajans and Soddy]], this was an isotope of the missing element, which they named "brevium" after its short half life. However, it was a beta emitter, and therefore could not be the mother isotope of actinium. This had to be another isotope of the same element.<ref name="Sime-1986">{{cite journal |first=Ruth Lewin |last=Sime |author-link=Ruth Lewin Sime |title=The Discovery of Protactinium |journal=Journal of Chemical Education |issn=0021-9584 |volume=63 |issue=8 |pages=653–657 |date=August 1986 |doi=10.1021/ed063p653 |bibcode=1986JChEd..63..653S }}</ref>

Hahn and Meitner set out to find the missing mother isotope. They developed a new technique for separating the [[refractory metals|tantalum group]] from [[pitchblende]], which they hoped would speed the isolation of the new isotope. The work was interrupted by the [[First World War]]. Meitner became an X-ray nurse, working in Austrian Army hospitals, but she returned to the Kaiser Wilhelm Institute in October 1916. Hahn joined the new gas command unit at Imperial Headquarters in Berlin in December 1916 after travelling between the western and eastern front, Berlin and [[Leverkusen]] between mid-1914 and late 1916.{{sfn|Sime|1996|pp=57–61}}

Most of the students, laboratory assistants and technicians had been called up, so Hahn, who was stationed in Berlin between January and September 1917,{{sfn|Hahn|1988|pp=117–132}} and Meitner had to do everything themselves. By December 1917 she was able to isolate the substance, and after further work were able to prove that it was indeed the missing isotope. Meitner submitted her and Hahn's findings for publication in March 1918 to the scientific paper ''[[Physikalische Zeitschrift|Physikalischen Zeitschrift]]'' under the title {{lang|de|Die Muttersubstanz des Actiniums; Ein Neues Radioaktives Element von Langer Lebensdauer}} ("The Mother Substance of Actinium; A New Radioactive Element with a Long Lifetime").<ref name="Sime-1986" /><ref name=":0">{{cite journal |journal=Zeitschrift für Elektrochemie und Angewandte Physikalische Chemie |issn=0372-8323 |title=Die Muttersubstanz des Actiniums, Ein Neues Radioaktives Element von Langer Lebensdauer |trans-title=The Parent Substance of Actinium; A New Radioactive Element with a Long Lifetime |first=Lise |last=Meitner |author-link=Lise Meitner |date=1 June 1918 |language=de |doi=10.1002/bbpc.19180241107 |volume=24 |issue=11–12 |pages=169–173 |s2cid=94448132}}</ref> Although Fajans and Göhring had been the first to discover the element, custom required that an element was represented by its longest-lived and most abundant isotope, and while brevium had a half life of 1.7 minutes, Hahn and Meitner's isotope had one of 32,500 years. The name brevium no longer seemed appropriate. Fajans agreed to Meitner and Hahn naming the element "[[protactinium|protoactinium]]".<ref>{{cite journal |url=https://www.nature.com/articles/244137a0 |doi=10.1038/244137a0 |title=Discovery and Naming of the Isotopes of Element 91 |year=1973 |last1=Fajans |first1=Kasimir |last2=Morris |first2=Donald F. C. |journal=Nature |issn=0028-0836 |volume=244 |issue=5412 |pages=137–138 |bibcode=1973Natur.244..137F |hdl=2027.42/62921 |s2cid=4224336 |hdl-access=free }}</ref>{{sfn|Scerri|2020|pp=302–306}}

In June 1918, Soddy and [[John Arnold Cranston|John Cranston]] announced that they had extracted a sample of the isotope, but unlike Hahn and Meitner were unable to describe its characteristics. They acknowledged Hahn´s and Meitner's priority, and agreed to the name.{{sfn|Scerri|2020|pp=302–306}} The connection to uranium remained a mystery, as neither of the known [[isotopes of uranium]] decayed into protactinium. It remained unsolved until the mother isotope, [[uranium-235]], was discovered in 1929.<ref name="Sime-1986" /><ref name=":0" /> For their discovery Hahn and Meitner were repeatedly nominated for the [[Nobel Prize in Chemistry]] in the 1920s by several scientists, among them Max Planck, [[Heinrich Jacob Goldschmidt|Heinrich Goldschmidt]], and Fajans himself.<ref name="Nobel Media AB-2020">{{cite web |title=Nomination Archive: Otto Hahn |url=https://www.nobelprize.org/nomination/archive/show_people.php?id=3787 |publisher=Nobel Foundation |access-date=9 June 2020}}</ref><ref>{{cite web |title=Nomination Archive: Lise Meitner |url=https://www.nobelprize.org/nomination/archive/show_people.php?id=6097 |publisher=Nobel Foundation |access-date =9 June 2020}}</ref> In 1949, the International Union of Pure and Applied Chemistry ([[IUPAC]]) named the new element definitively protactinium, and confirmed Hahn and Meitner as discoverers.<ref>{{cite web |title=Protactinium &#124; Pa (Element)  |publisher=National Library of Medicine |website=PubChem |url=https://pubchem.ncbi.nlm.nih.gov/element/Protactinium#section=History |access-date=18 June 2020}}</ref>