Editing Otto Hahn (section)

===Discovery of radiothorium and other "new elements"===

[[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}}

Ramsay was enthusiastic when yet another new element was found in his institute, and he intended to announce the discovery in a correspondingly suitable way. In accordance with tradition this was done before the committee of the venerable [[Royal Society]]. At the session of the Royal Society on 16 March 1905 Ramsay communicated Hahn's discovery of radiothorium.{{sfn|Hoffmann|2001|p=35}} The ''[[Daily Telegraph]]'' informed its readers:
{{blockquote|Very soon the scientific papers will be agog with a new discovery which has been added to the many brilliant triumphs of Gower Street. Dr. Otto Hahn, who is working at University College, has discovered a new radioactive element, extracted from a mineral from Ceylon, named Thorianite, and possibly, it is conjectured, the substance which renders thorium radioactive. Its activity is at least 250,000 times as great as that of thorium, weight for weight. It gives off a gas (generally called an emanation), identical with the radioactive emanation from thorium. Another theory of deep interest is that it is the possible source of a radioactive element possibly stronger in radioactivity than radium itself, and capable of producing all the curious effects which are known of radium up to the present. – The discoverer read a paper on the subject to the Royal Society last week, and this should rank, when published, among the most original of recent contributions to scientific literature.<ref>{{cite news |newspaper=[[The Daily Telegraph]] |title=A New Element |location=London |date=18 March 1905}}</ref>}}

[[File:Ernest Rutherford 1905.jpg|thumb|right|[[Ernest Rutherford]] at McGill University, Montreal 1905]]
Hahn published his results in the ''[[Proceedings of the Royal Society]]'' on 24 May 1905.<ref>{{cite journal |title=A New Radio-active Element, Which Evolves Thorium Emanation. Preliminary Communication |first=Otto |last=Hahn |journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character |issn=0080-4630 |volume=76 |issue=508 |date=24 May 1905 |pages=115–117 |doi=10.1098/rspa.1905.0009 |bibcode=1905RSPSA..76..115H |doi-access=free }}</ref> It was the first of more than 250 scientific publications in the field of radiochemistry.<ref>{{harvnb|Spence|1970|pp=303–313}} for a full list</ref> At the end of his time in London, Ramsay asked Hahn about his plans for the future, and Hahn told him about the job offer from Kalle & Co. Ramsay told him radiochemistry had a bright future, and that someone who had discovered a new radioactive element should go to the [[University of Berlin]]. Ramsay wrote to [[Emil Fischer]], the head of the chemistry institute there, who replied that Hahn could work in his laboratory, but could not be a ''[[Privatdozent]]'' because radiochemistry was not taught there. At this point, Hahn decided that he first needed to know more about the subject, so he wrote to the leading expert on the field, [[Ernest Rutherford]]. Rutherford agreed to take Hahn on as an assistant, and Hahn's parents undertook to pay Hahn's expenses.{{sfn|Hahn|1966|pp=15–18}}

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}}