Otto Hahn: Difference between revisions

{{Short description|German chemist (1879–1968)}}

{{For-multi|the petrologist|Otto Hahn (petrologist)|the nuclear-powered merchant vessel|Otto Hahn (ship){{!}}''Otto Hahn'' (ship)}}

{{Use dmy dates|date=September 2023}}

{{Use British English|date=September 2024}}

{{Infobox scientist

| image = Otto Hahn 1970.jpg

| birth_date = {{birth date|1879|03|08|df=yes}}

| known_for = {{plainlist|

* Discovery of radioactive elements (1905–1921)

* [[Radioactinium]] (²²⁷Th, 1906)

* [[Mesothorium]] (²²⁸Ra, 1907)

* [[Nuclear isomerism]] (1921)

* {{nowrap|''[[Applied Radiochemistry]]'' (1936)}}

* [[Rubidium-strontium dating]] (1938)

* [[Discovery of nuclear fission]] (1938)

}}

| spouse = {{marriage|Edith Junghans|1913}}

| children = {{ill|v=ib|Hanno Hahn|de}} <!-- (1922–1960) -->

| signature = Otto Hahn signature.svg

}}

 

A graduate of the [[University of Marburg]], which awarded him a doctorate in 1901, Hahn studied under Sir [[William Ramsay]] at [[University College London]] and at [[McGill University]] in Montreal under [[Ernest Rutherford]], where he discovered several new radioactive isotopes. He returned to Germany in 1906; [[Emil Fischer]] let him use a former woodworking shop in the basement of the Chemical Institute at the [[University of Berlin]] as a laboratory. Hahn completed his [[habilitation]] in early 1907 and became a ''[[Privatdozent]]''. In 1912, he became head of the Radioactivity Department of the newly founded [[Kaiser Wilhelm Institute for Chemistry]] (KWIC). Working with the Austrian physicist Lise Meitner in the building that now bears their names, they made a series of groundbreaking discoveries, culminating with her isolation of the longest-lived isotope of protactinium in 1918.

 

 

Hahn served as the last president of the [[Kaiser Wilhelm Society|Kaiser Wilhelm Society for the Advancement of Science]] in 1946 and as the founding president of its successor, the [[Max Planck Society]] from 1948 to 1960. In 1959 in Berlin he co-founded the [[Federation of German Scientists]], a non-governmental organisation committed to the ideal of responsible science. As he worked to rebuild German science, he became one of the most influential and respected citizens of post-war [[West Germany]].

 

Otto Hahn was born in [[Frankfurt am Main]] on 8 March 1879, the youngest son of Heinrich Hahn (1845–1922), a prosperous [[glazier]] (and founder of the Glasbau Hahn company), and Charlotte Hahn née Giese (1845–1905). He had an older half-brother Karl, his mother's son from her previous marriage, and two older brothers, Heiner and Julius. The family lived above his father's workshop. The younger three boys were educated at the ''Klinger Oberrealschule'' in Frankfurt. At the age of 15, he began to take a special interest in chemistry, and carried out simple experiments in the laundry room of the family home. His father wanted Otto to study architecture, as he had built or acquired several residential and business properties, but Otto persuaded him that his ambition was to become an [[industrial chemist]].{{sfn|Hahn|1966|pp=2–6}}

 

In 1897, after passing his ''[[Abitur]]'', Hahn began to study [[chemistry]] at the [[University of Marburg]]. His subsidiary subjects were mathematics, [[physics]], [[mineralogy]] and philosophy. Hahn joined the Students' Association of Natural Sciences and Medicine, a student fraternity and a forerunner of today's ''Landsmannschaft Nibelungi'' ([[Coburger Convent der akademischen Landsmannschaften und Turnerschaften]]). He spent his third and fourth semesters at the [[University of Munich]], studying organic chemistry under [[Adolf von Baeyer]], physical chemistry under {{ill|Wilhelm Muthmann|de|Wilhelm Muthmann (Chemiker)}}, and inorganic chemistry under [[Karl Andreas Hofmann]]. In 1901, Hahn received his doctorate in Marburg for a dissertation entitled "On Bromine Derivates of Isoeugenol", a topic in classical [[organic chemistry]]. He completed his one-year military service (instead of the usual two because he had a doctorate) in the 81st Infantry Regiment, but unlike his brothers, did not apply for a commission. He then returned to the University of Marburg, where he worked for two years as assistant to his doctoral supervisor, ''[[Geheimrat]]'' professor [[Theodor Zincke]].{{sfn|Hahn|1966|pp=7–11}}{{sfn|Spence|1970|pp=281–282}}

 

[[File:William Ramsay.jpg|thumb|left|upright|[[William Ramsay]], London 1905]]

Hahn's intention was still to work in industry. He received an offer of employment from Eugen Fischer, the director of {{ill|Kalle & Co.|de|Chemische Fabrik Kalle}} (and the father of organic chemist [[Hans Fischer]]), but a condition of employment was that Hahn had to have lived in another country and have a reasonable command of another language. With this in mind, and to improve his knowledge of English, Hahn took up a post at [[University College London]] in 1904, working under Sir [[William Ramsay]], who was known for having discovered the [[noble gas]]es. Here Hahn worked on [[radiochemistry]], at that time a very new field. In early 1905, in the course of his work with salts of [[radium]], Hahn discovered a new substance he called [[radiothorium]] (thorium-228), which at that time was believed to be a new [[radioactive]] element.{{sfn|Hahn|1966|pp=7–11}} In fact, it was an [[isotope]] of the known element [[thorium]]; the concept of an isotope, along with the term, was coined in 1913 by the British chemist [[Frederick Soddy]].{{sfn|Hughes|2009|p=135}}

 

From September 1905 until mid-1906, Hahn worked with Rutherford's group in the basement of the Macdonald Physics Building at [[McGill University]] in Montreal. There was some scepticism about the existence of radiothorium, which [[Bertram Boltwood]] memorably described as a compound of thorium X and stupidity. Boltwood was soon convinced that it did exist, although he and Hahn differed on what its [[half-life]] was. [[William Henry Bragg]] and [[Richard Kleeman]] had noted that the [[alpha particles]] emitted from radioactive substances always had the same energy, providing a second way of identifying them, so Hahn set about measuring the alpha particle emissions of radiothorium. In the process, he found that a precipitation of thorium A ([[polonium]]-216) and thorium B (lead-212) also contained a short-lived "element", which he named thorium C (which was later identified as polonium-212). Hahn was unable to separate it, and concluded that it had a very short half-life (it is about 300 ns). He also identified radioactinium (thorium-227) and radium D (later identified as lead-210).{{sfn|Spence|1970|pp=282–283}}{{sfn|Hahn|1966|pp=24–25}} Rutherford remarked that: "Hahn has a special nose for discovering new elements."{{sfn|Hahn|1988|p=59}}

[[File:Otto Hahn und Lise Meitner.jpg|thumb|left|upright|Hahn and Meitner, 1913, in the chemical laboratory of the [[Kaiser Wilhelm Institute for Chemistry]]. When a colleague she did not recognise said that they had met before, Meitner replied: "You probably mistake me for Professor Hahn."{{sfn|Hahn|1966|p=66}}]]

In 1906, Hahn returned to Germany, where Fischer placed at his disposal a former woodworking shop (''Holzwerkstatt'') in the basement of the Chemical Institute to use as a laboratory. Hahn equipped it with [[electroscope]]s to measure alpha and [[beta particle]]s and [[gamma rays]]. In Montreal these had been made from discarded coffee tins; Hahn made the ones in Berlin from brass, with aluminium strips insulated with amber. These were charged with hard rubber sticks that he rubbed against the sleeves of his suit.{{sfn|Hahn|1966|pp=37–38}} It was not possible to conduct research in the wood shop, but [[Alfred Stock]], the head of the inorganic chemistry department, let Hahn use a space in one of his two private laboratories.{{sfn|Hahn|1966|p=52}} Hahn purchased two milligrams of radium from [[Friedrich Oskar Giesel]], the discoverer of [[emanium]] (radon), for 100 marks a milligram ({{Inflation|DE|100|1906|fmt=eq|cursign=€|r=-2}}),{{sfn|Hahn|1966|pp=37–38}} and obtained thorium for free from Otto Knöfler, whose Berlin firm was a major producer of thorium products.{{sfn|Hahn|1966|pp=39–40}}

In Montreal, Hahn had worked with physicists including at least one woman, [[Harriet Brooks]], but it was difficult for Meitner at first. Women were not yet admitted to universities in [[Prussia]]. Meitner was allowed to work in the wood shop, which had its own external entrance, but could not enter the rest of the institute, including Hahn's laboratory space upstairs. If she wanted to go to the toilet, she had to use one at the restaurant down the street. The following year, women were admitted to universities, and Fischer lifted the restrictions and had women's toilets installed in the building.{{sfn|Sime|1996|pp=28–29}}

 

 

 

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}}

 

[[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. He was transferred to Berlin as a human guinea pig testing poisonous gases and 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" />

 

[[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 [[tantalium]]. 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>

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}}

 

 

[[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>

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" />

 

{{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}}

 

 

 

 

 

The April 1933 [[Law for the Restoration of the Professional Civil Service]] banned Jews and communists from academia. Meitner was exempt from its impact because she was an Austrian rather than a German citizen.{{sfn|Sime|1996|pp=138–139}} Haber was likewise exempt as a veteran of World War I, but chose to resign his directorship of the Kaiser Wilhelm Institute of Physical Chemistry and Electrochemistry in protest on 30 April 1933. The directors of the other Kaiser Wilhelm Institutes, even the Jewish ones, complied with the new law,{{sfn|Sime|1996|pp=8–9}} which applied to the KWS as a whole and those Kaiser Wilhelm institutes with more than 50% state support, which exempted the KWI for Chemistry.{{sfn|Sime|2006|p=7}} Hahn therefore did not have to fire any of his own full-time staff, but as the interim director of Haber's institute, he dismissed a quarter of its staff, including three department heads. [[Gerhart Jander]] was appointed the new director of Haber's old institute, and reoriented it towards chemical warfare research.{{sfn|Sime|2006|p=10}}

[[File:München-2025-Deutsches_Museum-Hahn.jpg|thumb|left|upright|Otto Hahn's marble bust at the [[Deutsches Museum]] in Munich]]

 

 

While Hahn was in North America in 1905–1906, his attention had been drawn to a mica-like mineral from [[Manitoba]] that contained [[rubidium]]. He had studied the radioactive decay of [[rubidium-87]], and had estimated its half-life at 2 x 10¹¹ years. It occurred to him that by comparing the quantity of strontium in the mineral (which had once been rubidium) with that of the remaining rubidium, he could measure the age of the mineral, assuming that his original calculation of the half-life was reasonably accurate. This would be a superior dating method to studying the decay of uranium, because some of the uranium turns into helium, which then escapes, resulting in rocks appearing to be younger than they really were. [[Jacob Papish]] helped Hahn obtain several kilograms of the mineral.{{sfn|Hahn|1966|pp=85–88}}

 

In 1937, Strassmann and Ernst Walling extracted 253.4 milligrams of strontium carbonate from 1,012 grams of the mineral, all of which was the [[strontium-87]] isotope, indicating that it had all been produced from radioactive decay of rubidium-87. The age of the mineral had been estimated at 1,975 million years from uranium minerals in the same deposit, which implied that the half-life of rubidium-87 was 2.3 x 10¹¹ years: quite close to Hahn's original calculation.<ref>{{cite journal |last1=Hahn |first1=O. |last2=Strassman |first2=F. |last3=Walling |first3=E. |title=Herstellung wägbaren Mengen des Strontiumisotops 87 als Umwandlungsprodukt des Rubidiums aus einem kanadischen Glimmer |trans-title=Production of Weighable Amounts of the Strontium Isotope 87 as a Conversion Product of Rubidium from Canadian Mica |language=de |journal=Naturwissenschaften |issn=0028-1042 |volume=25 |issue=12 |date=19 March 1937 |page=189 |doi=10.1007/BF01492269 |bibcode=1937NW.....25..189H |doi-access=free }}</ref><ref>{{cite journal |last1=Hahn |first1=O. |last2=Walling |first2=E. |title=Über die Möglichkeit geologischer Alterbestimmung rubidiumhaltiger Mineralen und Gesteine |trans-title=On the Possibility of Geological Age Determination of Minerals and Rocks Containing Rubidium |language=de |journal=Zeitschrift für anorganische und allgemeine Chemie |issn=0044-2313 |volume=236 |issue=1 |date=12 March 1938 |pages=78–82 |doi=10.1002/zaac.19382360109 }}</ref> [[Rubidium–strontium dating]] became a widely used technique for dating rocks in the 1950s, when [[mass spectrometry]] became common.{{sfn|Bowen|1994|pp=162–163}}

 

{{main|Discovery of nuclear fission}}

[[File:Nuclear Fission Experimental Apparatus 1938 - Deutsches Museum - Munich.jpg|thumb|right| This set up is on display in the [[Deutsches Museum]] in [[Munich]]. The table and instruments are original, but the instruments would not have been together on the one table in the same room.<ref>{{cite web |url=https://digital.deutsches-museum.de/de/digital-catalogue/collection-object/71930/ |title=Originalgeräte zur Entdeckung der Kernspaltung, 'Hahn-Meitner-Straßmann-Tisch' |trans-title=Original equipment for the discovery of nuclear fission, 'Hahn-Meitner-Straßmann table' |lang=de |publisher=Deutsches Museum |access-date=8 October 2024 }}</ref> Pressure from historians, scientists and feminists caused the museum to alter the display in 1988 to acknowledge [[Lise Meitner]], [[Otto Frisch]] and [[Fritz Strassmann]].{{sfn|Sime|2010|pages=206–210}} ]]

 

The radioactive displacement law of Fajans and Soddy said that beta decay causes isotopes to move one element up on the periodic table, and alpha decay causes them to move two down. When Fermi's group bombarded uranium atoms with neutrons, they found a complex mix of half-lives. Fermi therefore concluded that the new elements with atomic numbers greater than 92 (known as [[transuranium elements]]) had been created.<ref name="Segrè-1989">{{cite journal |title=Discovery of Nuclear Fission |first=Emilio G. |last=Segrè |author-link=Emilio Segrè |journal=Physics Today |issn=0031-9228 |volume=42 |issue=7 |date=July 1989 |pages=38–43 |doi=10.1063/1.881174 |bibcode=1989PhT....42g..38S }}</ref> Meitner and Hahn had not collaborated for many years, but Meitner was eager to investigate Fermi's results. Hahn, initially, was not, but he changed his mind when [[Aristid von Grosse]] suggested that what Fermi had found was an isotope of protactinium.{{sfn|Sime|1996|pp=164–165}} They set out to determine whether or not the 13-minute isotope was indeed an isotope of protactinium.{{sfn|Hahn|1966|pp=140–141}}

Between 1934 and 1938, Hahn, Meitner and Strassmann found a great number of radioactive transmutation products, all of which they regarded as transuranic.<ref>{{cite magazine|last1=Hahn |first1=O. |title=The Discovery of Fission |doi= 10.1038/scientificamerican0258-76 |magazine=Scientific American |volume=198 |issue=2 |pages=76–84 |year=1958 |bibcode=1958SciAm.198b..76H}}</ref> At that time, the existence of [[actinide]]s was not yet established, and uranium was wrongly believed to be a [[group 6 element]] similar to [[tungsten]]. It followed that the first transuranic elements would be similar to group 7 to 10 elements, i.e. [[rhenium]] and [[platinoid]]s. They established the presence of multiple isotopes of at least four such elements, and (mistakenly) identified them as elements with atomic numbers 93 through 96. They were the first scientists to measure the 23-minute half-life of uranium-239 and to establish chemically that it was an isotope of uranium, but were unable to continue this work to its logical conclusion and identify the real element 93.{{sfn|Sime|1996|pp=170–172}} They identified ten different half-lives, with varying degrees of certainty. To account for them, Meitner had to hypothesise a new class of reaction and the alpha decay of uranium, neither of which had ever been reported before, and for which physical evidence was lacking. Hahn and Strassmann refined their chemical procedures, while Meitner devised new experiments to shine more light on the reaction processes.{{sfn|Sime|1996|pp=170–172}}

[[File:Otto Hahn's notebook 1938 - Deutsches Museum - Munich.jpg|thumb|left|Otto Hahn's notebook]]

In May 1937, they issued parallel reports, one in the ''[[Zeitschrift für Physik]]'' with Meitner as the principal author, and one in the ''[[Chemische Berichte]]'' with Hahn as the principal author.{{sfn|Sime|1996|pp=170–172}}<ref name="L.-1937">{{cite journal |first1=Meitner |last1=L. |author-link1=Lise Meitner |first2=Hahn |last2=O. |first3=F. |last3=Strassmann |author-link3=Fritz Strassmann |title=Über die Umwandlungsreihen des Urans, die durch Neutronenbestrahlung erzeugt werden |trans-title=On the series of transformations of uranium that are generated by neutron radiation |language=de |journal=Zeitschrift für Physik |issn=0939-7922 |volume=106 |issue=3–4 |pages=249–270 |date=May 1937 |doi=10.1007/BF01340321 |bibcode=1937ZPhy..106..249M |s2cid=122830315 }}</ref><ref name="O.-1937">{{cite journal |first1=Hahn |last1=O. |first2=Meitner |last2=L. |author-link2=Lise Meitner |first3=F. |last3=Strassmann |author-link3=Fritz Strassmann |title=Über die Trans-Urane und ihr chemisches Verhalten |trans-title=On the transuranes and their chemical behaviour |lang=de |journal=Berichte der Deutschen Chemischen Gesellschaft |issn=0365-9496 |date=9 June 1937 |volume=70 |issue=6 |pages=1374–1392 |doi=10.1002/cber.19370700634 }}</ref> Hahn concluded his by stating emphatically: {{lang|de|Vor allem steht ihre chemische Verschiedenheit von allen bisher bekannten Elementen außerhalb jeder Diskussion}} ("Above all, their chemical distinction from all previously known elements needs no further discussion").<ref name="O.-1937"/> Meitner, however, was increasingly uncertain. She considered the possibility that the reactions were from different isotopes of uranium; three were known: uranium-238, uranium-235 and uranium-234. However, when she calculated the [[neutron cross section]], it was too large to be anything other than the most abundant isotope, uranium-238. She concluded that it must be another case of the nuclear isomerism that Hahn had discovered in protactinium. She therefore ended her report on a very different note to Hahn,{{sfn|Sime|1996|p=177}} reporting that: {{lang|de|Also miissen die ProzesSe Einfangprozesse des Uran 238 sein, was zu drei isomeren Kernen Uran 239 fiihrt. Dieses Ergebnis ist mit den bisherigen Kernvorstellungen sehr schwer in Ubereinstimmung zu bringen}} ("The process must be neutron capture by uranium-238, which leads to three isomeric nuclei of uranium-239. This result is very difficult to reconcile with current concepts of the nucleus.")<ref name="L.-1937" />

At the KWIC, [[Kurt Starke]] independently produced element 93, using only the weak neutron sources available there. Hahn and Strassmann then began researching its chemical properties.{{sfn|Hahn|1966|pp=175–177}} They knew that it should decay into the [[plutonium|real element 94]], which according to the latest version of the [[liquid drop model]] of the nucleus propounded by Bohr and [[John Archibald Wheeler]], would be even more [[fissile]] than uranium-235, but were unable to detect its radioactive decay. They concluded that it must have an extremely long half-life, perhaps millions of years.{{sfn|Walker|1993|pp=22–23}} Part of the problem was that they still believed that element 94 was a platinoid, which confounded their attempts at chemical separation.{{sfn|Hahn|1966|pp=175–177}}

 

{{main|German nuclear weapons program}}

On 24 April 1939, [[Paul Harteck]] and his assistant, [[Wilhelm Groth]], had written to the [[Oberkommando der Wehrmacht|Armed Forces High Command]] (OKW), alerting it to the possibility of the development of an [[atomic bomb]]. In response, the Army Weapons Branch (HWA) had established a physics section under the nuclear physicist [[Kurt Diebner]]. After [[World War II]] broke out on 1 September 1939, the HWA moved to control the [[German nuclear weapons program]]. From then on, Hahn participated in a ceaseless series of meetings related to the project. After the Director of the Kaiser Wilhelm Institute for Physics, [[Peter Debye]], left for the United States in 1940 and never returned, Diebner was installed as its director.{{sfn|Hoffmann|2001|pp=156–161}} Hahn reported to the HWA on the progress of his research. Together with his assistants, [[Hans-Joachim Born]], [[Siegfried Flügge]], Hans Götte, [[Walter Seelmann-Eggebert]] and Strassmann, he catalogued about one hundred [[fission product]] isotopes. They also investigated means of isotope separation; the chemistry of element 93; and methods for purifying uranium oxides and salts.{{sfn|Walker|2006|p=132}}

Life became precarious for those married to Jewish women. One was Philipp Hoernes, a chemist working for [[Auergesellschaft]], the firm that mined the uranium ore used by the project. After the firm let him go in 1944, Hoernes faced being [[Forced labour under German rule during World War II|conscripted for forced labour]]. At the age of 60, it was doubtful that he would survive. Hahn and [[Nikolaus Riehl]] arranged for Hoernes to work at the KWIC, claiming that his work was essential to the uranium project and that uranium was highly toxic, making it hard to find people to work with it. Hahn was aware that uranium ore was fairly safe in the laboratory, although not so much for the 2,000 female slave labourers from the [[Sachsenhausen concentration camp]] who mined it in [[Oranienburg]]. Another physicist with a Jewish wife was {{ill|Heinrich Rausch von Traubenberg|de|Heinrich Rausch von Traubenberg}}. Hahn certified that his work was important to the war effort, and that his wife Maria, who had a doctorate in physics, was required as his assistant. After he died on 19 September 1944, Maria faced being sent to a concentration camp. Hahn mounted a lobbying campaign to get her released, but to no avail, and she was sent to the [[Theresienstadt Ghetto]] in January 1945. She survived the war, and was reunited with her daughters in England after the war.{{sfn|Walker|1993|pp=132–133}}{{sfn|Sime|2006|pp=19–21}}

 

{{main|Operation Epsilon}}

On 25 April 1945, an armoured task force from the British/American [[Alsos Mission]] arrived in Tailfingen, and surrounded the KWIC. Hahn was informed that he was under arrest. When asked about reports related to his secret work on uranium, Hahn replied: "I have them all here", and handed over 150 reports. He was taken to [[Hechingen]], where he joined [[Erich Bagge]], [[Horst Korsching]], [[Max von Laue]], Carl Friedrich von Weizsäcker and [[Karl Wirtz]]. They were then taken to a dilapidated château in [[Versailles]], where they heard about the signing of the [[German Instrument of Surrender]] at [[Reims]] on 7 May. Over the following days they were joined by Kurt Diebner, Walther Gerlach, Paul Harteck and [[Werner Heisenberg]].{{sfn|Hahn|1966|p=179}}{{sfn|Walker|1993|pp=158–159}}{{sfn|Hoffmann|2001|p=195}} All were physicists except Hahn and Harteck, who were chemists, and all had worked on the German nuclear weapons program except von Laue, although he was well aware of it.{{sfn|Sime|2006|pp=24–25}}

As they recovered from the shock of the announcement, they began to rationalise what had happened. Hahn noted that he was glad that they had not succeeded, and von Weizsäcker suggested that they should claim that they had not wanted to. They drafted a memorandum on the project, noting that fission was discovered by Hahn and Strassmann. The revelation that Nagasaki had been destroyed by a plutonium bomb came as another shock, as it meant that the Allies had not only been able to successfully conduct [[uranium enrichment]], but had mastered [[nuclear reactor]] technology as well. The memorandum became the first draft of a postwar apologia. The idea that Germany had lost the war because its scientists were morally superior was as outrageous as it was unbelievable, but struck a chord in postwar German academia.{{sfn|Sime|2006|pp=26–28}} It infuriated Goudsmit, whose parents had been murdered in [[Auschwitz]].{{sfn|Sime|1996|p=319}} On 3 January 1946, exactly six months after they had arrived at Farm Hall, the group was allowed to return to Germany.{{sfn|Hoffmann|2001|p=201}} Hahn, Heisenberg, von Laue and von Weizsäcker were brought to [[Göttingen]], which was controlled by the British occupation authorities.{{sfn|Hoffmann|2001|pp=205–206}}

 

 

Hahn had been nominated for the chemistry and the physics Nobel prizes many times even before the discovery of nuclear fission. Several more followed for the discovery of fission.<ref name="Nobel Media AB-2020"/> The Nobel prize nominations were vetted by committees of five, one for each award. Although Hahn and Meitner received nominations for physics, radioactivity and radioactive elements had traditionally been seen as the domain of chemistry, and so the [[Nobel Committee for Chemistry]] evaluated the nominations. The committee received reports from [[Theodor Svedberg]] and {{ill|Arne Westgren|de||sv}}. These chemists were impressed by Hahn's work, but felt that of Meitner and Frisch was not extraordinary, and did not understand why the physics community regarded their work as seminal. As for Strassmann, although his name was on the papers, there was a long-standing policy of conferring awards on the most senior scientist in a collaboration. The committee therefore recommended that Hahn alone be given the chemistry prize.{{sfn|Crawford|Sime|Walker|1997|pp=27–32}}

Hahn was repatriated from Farm Hall on 3 January 1946, but it soon became apparent that difficulties obtaining permission to travel from the British government meant that he would be unable to travel to Sweden before December 1946. Accordingly, the Academy of Sciences and the Nobel Foundation obtained an extension from the Swedish government.{{sfn|Crawford|2000|pp=49–50}} Hahn attended the year after he was awarded the prize. On 10 December 1946, the anniversary of the death of [[Alfred Nobel]], King [[Gustav V of Sweden]] presented him with his Nobel Prize medal and diploma.<ref name="Nobel Foundation"/>{{sfn|Crawford|2000|pp=49–50}}{{sfn|Hoffmann|2001|p=209}} Hahn gave 10,000 krona of his prize to Strassmann, who refused to use it.{{sfn|Hoffmann|2001|p=209}}{{sfn|Sime|1996|p=343}}

 

[[File:Gedenktafel Otto Hahn.jpg|thumb|upright|Monument in Berlin-Dahlem, in front of the Otto-Hahn-Platz]]

The suicide of [[Albert Vögler]] on 14 April 1945 left the KWS without a president.<ref name="Max-Planck-Gesellschaft" /> The British chemist Bertie Blount was placed in charge of its affairs while the Allies decided what to do with it, and he decided to install Max Planck as an interim president. Now aged 87, Planck was in the small town of [[Rogätz]], in an area that the Americans were preparing to hand over to the [[Soviet Union]]. The Dutch astronomer [[Gerard Kuiper]] from the Alsos Mission fetched Planck in a jeep and brought him to Göttingen on 16 May.<ref>{{cite web |title=Gerard Kuiper's Daring Rescue of Max Planck at the End of World War II |first=Brandon R. |last=Brown |date=16 May 2015 |publisher=Scientific American Blog Network |url=https://blogs.scientificamerican.com/guest-blog/gerard-kuiper-s-daring-rescue-of-max-planck-at-the-end-of-world-war-ii/ |access-date=27 June 2020}}</ref><ref>{{cite web |title=The End of the War and Transition. Max Planck is Interim President of the KWS |publisher=Max-Planck-Gesellschaft |url=https://www.mpg.de/955542/3_event1-1945 |access-date=27 June 2020}}</ref> Planck wrote to Hahn, who was still in captivity in England, on 25 July, and informed Hahn that the directors of the KWS had voted to make him the next president, and asked if he would accept the position.<ref name="Max-Planck-Gesellschaft" /> Hahn did not receive the letter until September, and did not think he was a good choice, as he regarded himself as a poor negotiator, but his colleagues persuaded him to accept. After his return to Germany, he assumed the office on 1 April 1946.{{sfn|Hoffmann|2001|p=199}}{{sfn|Macrakis|1993|pp=189–190}}

In September 1946, a new Max Planck Society was established at [[Bad Driburg]] in the British Zone.<ref name="Max-Planck-Gesellschaft-2"/> On 26 February 1948, after the US and British zones were fused into [[Bizonia]], it was dissolved to make way for the [[Max Planck Society]], with Hahn as the founding president. It took over the 29 institutes of the former Kaiser Wilhelm Society that were located in the British and American zones. When the [[Federal Republic of Germany]] (or West-Germany) was formed in 1949, the five institutes located in the French zone joined them.<ref>{{cite web |title=The Founding of Today's Max Planck Society |publisher=Max-Planck-Gesellschaft |url=https://www.mpg.de/955620/7_event3-1948 |access-date=27 June 2020}}</ref> The KWIC, now under Strassmann, built and renovated new accommodation in [[Mainz]], but work proceeded slowly, and it did not relocate from Tailfingen until 1949.<ref>{{cite web |title=Overview |publisher= Max Planck Institute for Chemistry |url=https://www.mpic.de/3537786/Overview |access-date=27 June 2020}}</ref> Hahn's insistence on retaining Telschow as the general secretary nearly caused a rebellion against his presidency.{{sfn|Sime|2006|p=12}} In his efforts to rebuild German science, Hahn was generous in issuing ''[[persilschein]]'' (whitewash certificates), writing one for [[Gottfried von Droste]], who had joined the ''[[Sturmabteilung]]'' (SA) in 1933 and the NSDAP in 1937, and wore his SA uniform at the KWIC,{{sfn|Walker|2006|p=124}} and for [[Heinrich Hörlein]] and [[Fritz ter Meer]] from IG Farben.{{sfn|Sime|2004|p=48}} Hahn served as president of the Max Planck Society until 1960, and succeeded in regaining the renown that had once been enjoyed by the Kaiser Wilhelm Society. New institutes were founded and old ones expanded, the budget rose from 12 million [[Deutsche Mark]]s in 1949 (equivalent to €{{Inflation|DE|12|1949}} million in {{Inflation/year|DE}}) to 47 million in 1960 (equivalent to €{{Inflation|DE|47|1960}} million in {{Inflation/year|DE}}), and the workforce grew from 1,400 to nearly 3,000.<ref name="Max-Planck-Gesellschaft" />

 

After the Second World War, Hahn came out strongly against the use of nuclear energy for military purposes. He saw the application of his scientific discoveries to such ends as a misuse, or even a crime. The historian [[Lawrence Badash]] wrote: "His wartime recognition of the perversion of science for the construction of weapons, and his postwar activity in planning the direction of his country's scientific endeavours now inclined him increasingly toward being a spokesman for social responsibility."{{sfn|Badash|1983|p=176}}

 

In early 1954, he wrote the article "Cobalt 60 – Danger or Blessing for Mankind?", about the misuse of atomic energy, which was widely reprinted and transmitted in the radio in Germany, Norway, Austria, and Denmark, and in an English version worldwide via the BBC. The international reaction was encouraging.{{sfn|Hoffmann|2001|pp=218–221}} The following year he initiated and organized the [[Mainau Declaration]] of 1955, in which he and other international Nobel Prize-winners called attention to the dangers of atomic weapons and urgently warned the nations of the world against the use of "force as a final resort", and which was issued a week after the similar [[Russell-Einstein Manifesto]]. In 1956, Hahn repeated his appeal with the signature of 52 of his Nobel colleagues from all parts of the world.{{sfn|Hoffmann|2001|pp=221–222}}

 

Hahn was also instrumental in and one of the authors of the [[Göttinger Manifest|Göttingen Manifesto]] of 13 April 1957, in which, together with 17 leading German atomic scientists, he protested against a proposed nuclear arming of the West German armed forces (''[[Bundeswehr]]'').{{sfn|Hoffmann|2001|pp=231–232}} This resulted in Hahn receiving an invitation to meet the [[Chancellor of Germany]], [[Konrad Adenauer]] and other senior officials, including the Defense Minister, [[Franz Josef Strauss]], and Generals [[Hans Speidel]] and [[Adolf Heusinger]] (who had both been generals in the Nazi era). The two generals argued that the ''Bundeswehr'' needed nuclear weapons, and Adenauer accepted their advice. A communiqué was drafted that said that the Federal Republic did not manufacture nuclear weapons, and would not ask its scientists to do so.{{sfn|Hoffmann|2001|pp=235–238}} Instead, the German forces were equipped with US nuclear weapons.<ref>{{cite magazine |title=NATO Chief Backs Germany's Vow to Keep War-Ready US Nukes |magazine=Defence News |first=Sebastian |last=Sprenger |date=11 May 2020 |url=https://www.defensenews.com/global/europe/2020/05/11/nato-chief-backs-german-vow-to-keep-war-ready-us-nukes/ |access-date=28 June 2020}}</ref>

 

On 13 November 1957, in the ''Konzerthaus'' (Concert Hall) in [[Vienna]], Hahn warned of the "dangers of A- and H-bomb-experiments", and declared that "today war is no means of politics anymore – it will only destroy all countries in the world". His highly acclaimed speech was transmitted internationally by the Austrian radio, [[Österreichischer Rundfunk]] (ÖR). On 28 December 1957, Hahn repeated his appeal in an English translation for the Bulgarian Radio in [[Sofia]], which was broadcast in all [[Warsaw pact]] states.{{sfn|Hahn|1988|p=288}}{{sfn|Hoffmann|2001|p=242}}

In 1959 Hahn co-founded in Berlin the [[Federation of German Scientists]] (VDW), a non-governmental organisation, which has been committed to the ideal of responsible science. The members of the Federation feel committed to taking into consideration the possible military, political, and economic implications and possibilities of atomic misuse when carrying out their scientific research and teaching. With the results of its interdisciplinary work the VDW not only addresses the general public, but also the decision-makers at all levels of politics and society.<ref>{{cite web|title=FGS Brochure|url=https://www.cbd.int/doc/external/mop-04/fgs-1-en.pdf |archive-url=https://web.archive.org/web/20080511012724/http://www.cbd.int/doc/external/mop-04/fgs-1-en.pdf |archive-date=11 May 2008 |url-status=live|website=Convention on Biological Diversity|publisher=Federation of German Scientists|access-date=28 June 2020}}</ref> Right up to his death, Otto Hahn never tired of warning of the dangers of the [[nuclear arms race]] between the great powers and of the [[radioactive contamination]] of the planet.{{sfn|Hoffmann|2001|p=248}}

Lawrence Badash wrote:

{{blockquote|The important thing is not that scientists may disagree on where their responsibility to society lies, but that they are conscious that a responsibility exists, are vocal about it, and when they speak out they expect to affect policy. Otto Hahn, it would seem, was even more than just an example of this twentieth-century conceptual evolution; he was a leader in the process.{{sfn|Badash|1983|p=178}} }}

He was one of the signatories of the agreement to convene a convention for drafting a [[world constitution]].<ref>{{Cite web |title=Letters from Thane Read asking Helen Keller to sign the World Constitution for world peace. 1961 |url=https://www.afb.org/HelenKellerArchive?a=d&d=A-HK01-07-B149-F04-022.1.8 |access-date=1 July 2023 |department=Helen Keller Archive |publisher=American Foundation for the Blind}}</ref><ref>{{Cite web |title=Letter from World Constitution Coordinating Committee to Helen, enclosing current materials |url=https://www.afb.org/HelenKellerArchive?a=d&d=A-HK01-07-B154-F05-028.1.6 |access-date=3 July 2023 |department=Helen Keller Archive |publisher=American Foundation for the Blind}}</ref> As a result, for the first time in human history, a [[World Constituent Assembly]] convened to draft and adopt a [[Constitution for the Federation of Earth]].<ref>{{Cite encyclopedia |title=Preparing Earth Constitution |url=http://encyclopedia.uia.org/en/strategy/193465 |access-date=15 July 2023 |encyclopedia=The Encyclopedia of World Problems |publisher=Union of International Associations }}</ref>

 

 

 

Hahn was shot in the back in October 1951 by a disgruntled inventor who wished to highlight the neglect of his ideas by mainstream scientists. Hahn was injured in a motor vehicle accident in 1952, and had a minor heart attack the following year. In 1962, he published a book, ''Vom Radiothor zur Uranspaltung'' (''From the radiothor to Uranium fission''). It was released in English in 1966 with the title ''Otto Hahn: A Scientific Autobiography'', with an introduction by Glenn Seaborg. The success of this book may have prompted him to write another, fuller autobiography, ''Otto Hahn. Mein Leben'', but before it could be published, he fractured one of the vertebrae in his neck while getting out of a car. He gradually became weaker and died in Göttingen on 28 July 1968. His wife Edith survived him by only a fortnight.{{sfn|Spence|1970|pp=300–301}} He was buried in the [[Stadtfriedhof (Göttingen)|Stadtfriedhof]] in Göttingen.<ref>{{cite web |title=Grab von Otto Hahn aus Göttingen |website=www.friedhofguide.de |url=https://www.friedhofguide.de/grab/deutschland/G%C3%B6ttingen/Stadtfriedhof+G%C3%B6ttingen/Otto+Hahn+08.03.1879_28.07.1968 |access-date=28 June 2020 |archive-url=https://web.archive.org/web/20200629233454/https://www.friedhofguide.de/grab/deutschland/G%C3%B6ttingen/Stadtfriedhof+G%C3%B6ttingen/Otto+Hahn+08.03.1879_28.07.1968 |archive-date=29 June 2020}}</ref><ref>{{cite web |title=Nobelpreisträger auf dem Stadtfriedhof |trans-title=Nobel Prize winners at the City Cemetery |publisher=City of Göttingen |lang=de |url=http://www.goettingen.de/pics/medien/1_1229606299/Nobel-Rondell.pdf |archive-url=https://web.archive.org/web/20150924022846/http://www.goettingen.de/pics/medien/1_1229606299/Nobel-Rondell.pdf |archive-date=24 September 2015 |url-status=dead |df=mdy-all}}</ref>

The day after his death, the Max Planck Society published the following obituary notice:

Fritz Strassmann wrote:

{{blockquote|The number of those who had been able to be near Otto Hahn is small. His behaviour was completely natural for him, but for the next generations he will serve as a model, regardless of whether one admires in the attitude of Otto Hahn his humane and scientific sense of responsibility or his personal courage.<ref>{{cite news |last=Strassmann |first=Fritz |date=29 July 1968 |title=Zum Tode von Otto Hahn |trans-title=On the Death of Otto Hahn |lang=de |newspaper=Die Welt |location=Hamburg}}</ref>}}

Otto Robert Frisch recalled:

{{blockquote|Hahn remained modest and informal all his life. His disarming frankness, unfailing kindness, good common sense, and impish humour will be remembered by his many friends all over the world.<ref>{{cite journal |last=Frisch |first=Otto R. |author-link=Otto Robert Frisch |title=Otto Hahn |journal=Physics Bulletin |issn=0031-9112 |volume=19 |issue=10 |year=1968 |page=354 |doi=10.1088/0031-9112/19/10/010}}</ref>}}

{{blockquote|It was remarkable, how, after the war, this rather unassuming scientist who had spent a lifetime in the laboratory, became an effective administrator and an important public figure in Germany. Hahn, famous as the discoverer of nuclear fission, was respected and trusted for his human qualities, simplicity of manner, transparent honesty, common sense and loyalty.{{sfn|Spence|1970|pp=301–302}} }}

 

 

During his lifetime Hahn was awarded orders, medals, scientific prizes, and fellowships of Academies, Societies, and Institutions from all over the world. At the end of 1999, the German news magazine ''[[Focus (German magazine)|Focus]]'' published an inquiry of 500 leading natural scientists, engineers, and physicians about the most important scientists of the 20th century. In this poll Hahn was elected third (with 81 points), after the theoretical physicists [[Albert Einstein]] and Max Planck, and thus the most significant chemist of his time.<ref>{{cite magazine |magazine=Focus |title=Die Allmacht Der Unschärfe |trans-title=The Omnipotence of Blurring |language=de |first=Ernst Peter |last=Fischer |author-link=Ernst Peter Fischer |issue=52 |date=27 December 1999 |pages=103–108 |url=https://www.focus.de/wissen/mensch/focus-liste-die-50-top-forscher-die-allmacht-der-unschaerfe_aid_179705.html |access-date=28 June 2020 }}</ref>

 

* the [[Emil Fischer Medal]] of the Society of German Chemists (1922),{{sfn|Spence|1970|p=302}}

* the Cannizaro Prize of the Royal Academy of Science in Rome (1938),{{sfn|Spence|1970|p=302}}

 

Objects named after Hahn include:

* and the asteroid ''[[19126 Ottohahn]]'';<ref>{{cite web |title=IAU Minor Planet Center |website=minorplanetcenter.net |url=https://minorplanetcenter.net/db_search/show_object?object_id=19126 |access-date=28 June 2020}}</ref>

* the [[Otto Hahn Prize]] of both the German Chemical and Physical Societies and the city of Frankfurt/Main;<ref>{{cite web |title=GDCh-Preise |publisher= Gesellschaft Deutscher Chemiker |url=https://www.gdch.de/gdch/preise-und-auszeichnungen/gdch-preise.html |access-date=28 June 2020}}</ref>

* and the [[Otto Hahn Peace Medal]] in Gold of the United Nations Association of Germany (DGVN) in Berlin (1988).<ref>{{cite web |title=Verleihung der Otto-Hahn-Friedensmedaille |trans-title=Award of the Otto Hahn Peace Medal |lang=de |publisher=Deutsche Gesellschaft für die Vereinten Nationen e.V. |url=https://dgvn.de/aktivitaeten/einzelansicht/verleihung-der-otto-hahn-friedensmedaille/ |access-date=28 June 2020 |archive-date=2 July 2020 |archive-url=https://web.archive.org/web/20200702000534/https://dgvn.de/aktivitaeten/einzelansicht/verleihung-der-otto-hahn-friedensmedaille/ |url-status=dead }}</ref>

 

* {{cite journal |last=Sime |first=Ruth Lewin |author-link=Ruth Lewin Sime |journal=Physics in Perspective |issn=1422-6944 |date=15 June 2010 |title=An Inconvenient History: The Nuclear-Fission Display in the Deutsches Museum |volume=12 |issue=2 |pages=190–218 |doi=10.1007/s00016-009-0013-x |bibcode=2010PhP....12..190S |s2cid=120584702 }}

* {{cite journal |last=Spence |first=Robert |year=1970 |title=Otto Hahn 1879–1968 |journal=Biographical Memoirs of Fellows of the Royal Society |volume=16 |pages=279–313 |doi=10.1098/rsbm.1970.0010 |doi-access=free}}

* {{cite journal |last=Walker |first=Mark |title=Otto Hahn: Responsibility and Repression |date=May 2006 |journal=Physics in Perspective |volume=8 |issue=2 |pages=116–163 |issn=1422-6944 |doi=10.1007/s00016-006-0277-3 |bibcode=2006PhP.....8..116W |s2cid=120992662}}

* {{cite book |last=Walker |first=Mark |title=German National Socialism and the Quest for Nuclear Power |year=1993 |location=Cambridge |publisher=Cambridge University Press |isbn=0-521-36413-2 |oclc=722061969}}