Editing Lise Meitner (section)

==Transmutation==
After Chadwick discovered the [[neutron]] in 1932,{{sfn|Rhodes|1986|pp=39, 160–167, 793}} [[Irène Curie]] and [[Frédéric Joliot]] irradiated aluminium foil with alpha particles, and found that this results in a short-lived radioactive [[isotopes of phosphorus|isotope of phosphorus]]. They noted that [[positron emission]] continued after the irradiation ceased. Not only had they discovered a new form of radioactive decay, they had transmuted an element into a hitherto unknown radioactive isotope of another, thereby inducing radioactivity where there had been none before. Radiochemistry was now no longer confined to certain heavy elements, but extended to the entire periodic table.{{sfn|Rhodes|1986|pp=200–201}}{{sfn|Sime|1996|pp=161–162}} Chadwick noted that being electrically neutral, neutrons could penetrate the nucleus more easily than protons or alpha particles.{{sfn|Fergusson|2011|p=1151}} Enrico Fermi and his colleagues in Rome picked up on this idea,{{sfn|Rhodes|1986|pp=210–211}} and began irradiating elements with neutrons.{{sfn|Segrè|1989|pp=39–40}}

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 new elements with atomic numbers greater than 92 (known as [[transuranium elements]]) had been created.{{sfn|Segrè|1989|pp=39–40}} 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&nbsp;Grosse]] suggested that what Fermi had found was an isotope of protactinium.{{sfn|Sime|1996|pp=164–165}} "The only question", Hahn later wrote, "seemed to be whether Fermi had found isotopes of transuranium elements, or isotopes of the next-lower element, protactinium. At that time Lise Meitner and I decided to repeat Fermi's experiments in order to find out whether the 13-minute isotope was a protactinium isotope or not. It was a logical decision, having been the discoverers 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.{{sfn|Hahn|1958|p=78}} 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, [[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 to 96. They were the first scientists to measure the 23-minute half life of the [[synthetic radioisotope]] uranium-239 and to establish chemically that it was an isotope of uranium, but with their weak neutron sources they were unable to continue this work to its logical conclusion and identify the real element 93. 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 examine the reaction processes.{{sfn|Sime|1996|pp=170–172}}

In May 1937, Hahn and Meitner issued parallel reports, one in {{lang|de|Zeitschrift für Physik}} with Meitner as the first author, and one in {{lang|de|Chemische Berichte}} with Hahn as the first author.{{sfn|Sime|1996|pp=170–172}}<ref name="Meitner 1937">{{cite journal |first1=L. |last1=Meitner |author-link1=Lise Meitner |first2=O. |last2=Hahn |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="Hahn 1937">{{cite journal |first1=O. |last1=Hahn |first2=L. |last2=Meitner |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 |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}} ({{gloss|Above all, their chemical distinction from all previously known elements needs no further discussion}}).<ref name="Hahn 1937"/> Meitner 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, and concluded that it must be another case of [[nuclear isomerism]], a phenomenon Hahn had discovered in protactinium years before. She therefore ended her report on a very different note to Hahn, reporting that: "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="Meitner 1937" />{{sfn|Sime|1996|p=177}}