Editing Otto Hahn (section)

==Kaiser Wilhelm Institute for Chemistry==
[[File:Dahlem Thielallee Hahn-Meitner-Bau.JPG|thumb|right|Former Kaiser Wilhelm Institute for Chemistry building in Berlin. Heavily damaged by bombing during the Second World War, it was restored and became part of the [[Free University of Berlin]]. It was renamed the Otto Hahn Building in 1956, and the Hahn-Meitner Building in 2010.{{sfn|Sime|1996|p=368}}<ref>{{cite web |title=Ehrung der Physikerin Lise Meitner Aus dem Otto-Hahn-Bau wird der Hahn-Meitner-Bau |publisher=Free University of Berlin |language=de |trans-title=Honouring physicist Lise Meitner as the Otto Hahn building becomes the Hahn-Meitner building  |url=https://www.fu-berlin.de/campusleben/campus/2010/101028_hahn-meitner/index.html |date=28 October 2010 |access-date=10 June 2020}}</ref> ]]

In 1910, Hahn was appointed professor by the Prussian Minister of Culture and Education, [[August von Trott zu Solz]]. Two years later, Hahn became head of the Radioactivity Department of the newly founded [[Kaiser Wilhelm Institute for Chemistry]] (KWIC) in Berlin-Dahlem (in what is today the Hahn-Meitner-Building of the [[Free University of Berlin]]). This came with an annual salary of 5,000 marks ({{Inflation|DE|5,000|1912|fmt=eq|cursign=€|r=-3}}). In addition, he received 66,000 marks in 1914 ({{Inflation|DE|66,000|1914|fmt=eq|cursign=€|r=-3}}) from Knöfler for the mesothorium process, of which he gave 10 per cent to Meitner. The new institute was inaugurated on 23 October 1912 in a ceremony presided over by [[Kaiser Wilhelm II]].{{sfn|Sime|1996|pp=44–47}} The Kaiser was shown glowing radioactive substances in a dark room.{{sfn|Hahn|1966|pp=70–72}}

The move to new accommodation was fortuitous, as the wood shop had become heavily contaminated by radioactive liquids that had been spilt, and radioactive gases that had vented and then decayed and settled as radioactive dust, making sensitive measurements impossible. To ensure that their clean new laboratories stayed that way, Hahn and Meitner instituted strict procedures. Chemical and physical measurements were conducted in different rooms, people handling radioactive substances had to follow protocols that included not shaking hands, and rolls of toilet paper were hung next to every telephone and door handle. Strongly radioactive substances were stored in the old wood shop, and later in a purpose-built radium house on the institute grounds.{{sfn|Sime|1996|p=48}}
===World War I===
In July 1914—shortly before the outbreak of [[World War I]]—Hahn was recalled to active duty with the army in a ''[[Landwehr]]'' regiment. They marched through Belgium, where the platoon he commanded was armed with captured machine guns. He was awarded the [[Iron Cross]] (2nd Class) for his part in the [[First Battle of Ypres]]. He was a joyful participant in the [[Christmas truce]] of 1914, and was commissioned as a lieutenant.{{sfn|Spence|1970|pp=286–287}} In mid-January 1915, he was summoned to meet chemist [[Fritz Haber]], who explained his plan to break the trench deadlock with [[Chlorine#World War I|chlorine gas]]. Hahn raised the issue that the [[Hague Conventions of 1899 and 1907|Hague Convention]] banned the use of projectiles containing poison gases, but Haber explained that the French had already initiated chemical warfare with tear gas grenades, and he planned to get around the letter of the convention by releasing gas from cylinders instead of shells.<ref name="Van der Kloot-2004">{{cite journal|last1=Van der Kloot|first1=W.|title=April 1918: Five Future Nobel Prize-winners Inaugurate Weapons of Mass Destruction and the Academic-industrial-military Complex |journal=Notes and Records of the Royal Society of London |issn=0035-9149 |date=2004 |volume=58 |issue=2 |pages=149–160 |doi=10.1098/rsnr.2004.0053|s2cid=145243958}}</ref>

[[File:Ottohahn1915.jpg|thumb|left|upright|Hahn in uniform in 1915]]
Haber's new unit was called Pioneer Regiment 35. After brief training in Berlin, Hahn, together with physicists James Franck and Gustav Hertz, was sent to [[Flanders]] again to scout for a site for a [[Second Battle of Ypres|first gas attack]]. He did not witness the attack because he and Franck were off selecting a position for the next attack. Transferred to Poland, at the [[Battle of Bolimów]] on 12 June 1915, they released a mixture of chlorine and [[phosgene]] gas. Some German troops were reluctant to advance when the gas started to blow back, so Hahn led them across [[No Man's land]]. He witnessed the death agonies of Russians they had poisoned, and unsuccessfully attempted to revive some with gas masks. On their next attempt on 7 July, the gas again blew back on German lines, and Hertz was poisoned. This assignment was interrupted by a mission at the front in Flanders and again in 1916 by a mission to [[Battle of Verdun|Verdun]] to introduce shells filled with phosgene to the [[Western Front (World War I)|Western Front]]. Then once again he was hunting along both fronts for sites for gas attacks. In December 1916 he joined the new gas command unit at Imperial Headquarters.<ref name="Van der Kloot-2004" />{{sfn|Sime|1996|pp=57–61}}

Between operations, Hahn returned to Berlin, where he was able to slip back to his old laboratory and work with Meitner, continuing with their research. In September 1917 he was one of three officers, disguised in Austrian uniforms, sent to the [[Battles of the Isonzo|Isonzo front]] in Italy to find a suitable location for an attack, using newly developed rifled ''[[minenwerfer]]s'' that simultaneously hurled hundreds of containers of poison gas onto enemy targets. They selected a site where the Italian trenches were sheltered in a deep valley so that a gas cloud would persist. The following [[Battle of Caporetto]] broke the Italian lines, and the Central Powers overran much of northern Italy. That summer Hahn was accidentally poisoned by phosgene while testing a new model of gas mask. At the end of the war he was in the field in [[mufti (dress)|mufti]] on a secret mission to test a pot that heated and released a cloud of [[arsenical]]s.{{sfn|Spence|1970|pp=287–288}}<ref name="Van der Kloot-2004" />

===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>

===Discovery of nuclear isomerism===
[[File:Decay Chain of Uranium-238corrected.svg|thumb|left|upright|Decay chain of uranium-238]]
With the discovery of protactinium, most of the decay chains of uranium had been mapped. When Hahn returned to his work after the war, he looked back over his 1914 results, and considered some anomalies that had been dismissed or overlooked. He dissolved uranium salts in a [[hydrofluoric acid]] solution with [[tantalum pentoxide|tantalic acid]]. First the tantalum in the ore was precipitated, then the protactinium. In addition to the uranium X1 (thorium-234) and uranium X2 (protactinium-234), Hahn detected traces of a radioactive substance with a half-life of between 6 and 7 hours. There was one isotope known to have a half-life of 6.2 hours, mesothorium II (actinium-228). This was not in any probable decay chain, but it could have been contamination, as the KWICy had experimented with it. Hahn and Meitner demonstrated in 1919 that when actinium is treated with hydrofluoric acid, it remains in the insoluble residue. Since mesothorium II was an isotope of actinium, the substance was not mesothorium II; it was protactinium.{{sfn|Hahn|1966|pp=95–103}}{{sfn|Berninger|1983|pp=213–220}} Hahn was now confident enough he had found something that he named his new isotope "uranium Z". In February 1921, he published the first report on his discovery.<ref>{{cite journal |last1= Hahn |first1= O. |title=Über ein neues radioaktives Zerfallsprodukt im Uran |trans-title=On a New Radioactive Decay Product in Uranium |lang=de |doi=10.1007/BF01491321 |journal= Die Naturwissenschaften |issn=0028-1042 |volume=9 |issue=5 |page=84 |year=1921 |bibcode=1921NW......9...84H |s2cid= 28599831 |url= https://zenodo.org/record/2482506 }}</ref>

Hahn determined that uranium Z had a half-life of around 6.7 hours (with a two per cent margin of error) and that when uranium X1 decayed, it became uranium X2 about 99.75 per cent of the time, and uranium Z around 0.25 per cent of the time. He found that the proportion of uranium X to uranium Z extracted from several kilograms of [[uranyl nitrate]] remained constant over time, strongly indicating that uranium X was the mother of uranium Z. To prove this, Hahn obtained a hundred kilograms of uranyl nitrate; separating the uranium X from it took weeks. He found that the half-life of the parent of uranium Z differed from the known 24-day half-life of uranium X1 by no more than two or three days, but was unable to get a more accurate value. Hahn concluded that uranium Z and uranium X2 were both the same isotope of protactinium ([[protactinium-234]]), and they both decayed into uranium II ([[uranium-234]]), but with different half-lives.{{sfn|Hahn|1966|pp=95–103}}{{sfn|Berninger|1983|pp=213–220}}<ref>{{cite journal |first=Otto |last=Hahn |title=Uber das Uran Z und seine Muttersubstanz |trans-title=About Uranium Z and its Parent Substance |lang=de |journal=Zeitschrift für Physikalische Chemie  |issn=0942-9352  |volume=103 |issue=1 |pages=461–480 |year=1923 |doi=10.1515/zpch-1922-10325  |s2cid=99021215 }}</ref>

Uranium Z was the first example of [[nuclear isomer]]ism. Walther Gerlach later remarked that this was "a discovery that was not understood at the time but later became highly significant for nuclear physics".{{sfn|Gerlach|Hahn|1984|p=39}} Not until 1936 was [[Carl Friedrich von Weizsäcker]] able to provide a theoretical explanation of the phenomenon.{{sfn|Hoffmann|2001|p=93}}{{sfn|Feather|Bretscher|Appleton|1938|pages=530–535}} For this discovery, whose full significance was recognised by very few, Hahn was again proposed for the Nobel Prize in Chemistry by [[Bernhard Naunyn]], Goldschmidt and Planck.<ref name="Nobel Media AB-2020" />

===''Applied Radiochemistry''===
{{quote box|As a young graduate student at the University of California at Berkeley in the mid-1930s and in connection with our work with plutonium a few years later, I used his book ''Applied Radiochemistry'' as my bible. This book was based on a series of lectures which Professor Hahn had given at Cornell in 1933; it set forth the "laws" for the [[co-precipitation]] of minute quantities of radioactive materials when insoluble substances were precipitated from aqueous solutions. I recall reading and rereading every word in these laws of co-precipitation many times, attempting to derive every possible bit of guidance for our work, and perhaps in my zealousness reading into them more than the master himself had intended. I doubt that I have read sections in any other book more carefully or more frequently than those in Hahn's ''Applied Radiochemistry''. In fact, I read the entire volume repeatedly and I recall that my chief disappointment with it was its length. It was too short.|author=Glenn Seaborg |source={{sfn|Hahn|1966|pp=ix–x}} |align=right |width=450px}}

In 1924, Hahn was elected to full membership of the [[Prussian Academy of Sciences]] in Berlin, by a vote of thirty white balls to two black.{{sfn|Hoffmann|2001|p=94}} While still remaining the head of his own department, he became Deputy Director of the KWIC in 1924, and succeeded Alfred Stock as the director in 1928.<ref name="Max-Planck-Gesellschaft">{{cite web |title=Otto Hahn |publisher=Max-Planck-Gesellschaft |url=https://www.mpg.de/8241484/otto-hahn |access-date=24 June 2020}}</ref> Meitner became the director of the Physical Radioactivity Division, while Hahn headed the Chemical Radioactivity Division.{{sfn|Hoffmann|2001|p=95}} 

In the early 1920s, Hahn created a new line of research. Using the "emanation method", which he had recently developed, and the "emanation ability", he founded what became known as "applied radiochemistry" for the researching of general chemical and physical-chemical questions. In 1936 [[Cornell University]] Press published a book in English (and later in Russian) titled ''[[Applied Radiochemistry]]'', which contained the lectures given by Hahn when he was a visiting professor at [[Cornell University]] in [[Ithaca, New York]], in 1933. This publication had a major influence on almost all nuclear chemists and physicists in the United States, the United Kingdom, France, and the Soviet Union during the 1930s and 1940s.{{sfn|Hahn|1966|pp=ix–x}} Hahn is referred to as the father of nuclear chemistry, which emerged from applied radiochemistry.{{sfn|Hahn|1966|p=ix}}<ref>{{cite web |last1=Tietz |first1=Tabea |title=Otto Hahn – the Father of Nuclear Chemistry |url=http://scihi.org/otto-hahn-nuclear-chemistry/ |website=SciHi Blog |date=8 March 2018}}</ref><ref>{{cite web |title=Otto Hahn |url=https://www.atomicheritage.org/profile/otto-hahn |website=Atomic Heritage Foundation |access-date=12 October 2024}}</ref>