After some years abroad working with William Ramsay — in London and Ernest Rutherford in Canada, Hahn returned to Germany in to join the chemistry department of Berlin University. Although he became professor of chemistry in , Hahn left in for the Kaiser Wilhelm Institute of Chemistry where he spent the rest of his career. Although he had intended to become an industrial chemist, Hahn was so engrossed in radioactivity that he turned instead to academic chemistry.
For some thirty years, in collaboration with the physicist Lise Meitner, he explored the chemistry of the newly discovered radioactive elements. Together they discovered the new element protactinium. Their most important work, in collaboration with Fritz Strassmann —80 , was carried out in the s on uranium.
When uranium was bombarded with slow neutrons they repeatedly found barium in the decay products. It was left to Meitner, and her nephew Otto Frisch, to interpret the reaction as nuclear fission. Hahn himself contributed little to the German war effort and would have nothing to do with nuclear weapons.
In , with seventeen other leading German atomic scientists, he signed a declaration stating that he would never work on the production or testing of atomic weapons. Subjects: Science and technology. View all related items in Oxford Reference ». Search for: 'Otto Hahn' in Oxford Reference ». Their joint work embraced: investigations on beta-rays, their absorbability, magnetic spectra, etc.
Using radioactive methods he investigated the absorption and precipitation of the smallest quantities of substances, normal and abnormal formation of crystals, etc. Hahn used the emanation method to test substances superficially rich or poor, and he elaborated the strontium method to determine the age of geological periods.
Following the discovery of artificial radioactivity by M and Mme. Joliot-Curie and the use of neutrons by Fermi for atomic nuclear processes, Hahn again collaborated with Professor Meitner and afterwards with Dr.
Strassmann on the processes of irradiating uranium and thorium with neutrons. Hahn and Prof. Meitner had also worked together on the discovery of an artificially active uranium isotope, which represents the basic substance of the elements neptunium and plutonium, first revealed later in America.
In he became scientific member of the Kaiser Wilhelm Institute for Chemistry and has been Director of this Institute since His most spectacular discovery came at the end of She became Dozent in and extra-ordinary professor in , the first woman university physics professor in Germany.
After , they were working separately, Hahn the head of the Kaiser Wilhelm Institute for Chemistry and Meitner head of that institute's physics department. But Meitner was well acquainted with Italian physicists and regularly received preprints of their articles, so that she proposed to Hahn that they resume their old collaboration, after a lapse of nearly fifteen years.
In fact, another objection to Fermi's interpretation came from Aristid von Grosse, a former colleague of Hahn's. According to Fermi's assumptions, element 93 should be similar to rhenium, so that von Grosse had argued that some of the active species found by Fermi might be isotopes of the very rare element 91, protactinium, because he had found this element - which he had just isolated - to be carried by rhenium sulphide. In order to work with the very small invisible amounts of radioactive elements produced by irradiation with neutrons - detectable only by their radioactivity - the radiochemical carrier technique was in fact used, according to which a small quantity of a homologous element was added to the solution containing the irradiated sample in the form of a salt, base or acid conveniently chosen.
The solution thus contained large amounts of the original nuclides, plus the products of all nuclear reactions initiated by the incident radiation. Then a characteristic operation for that carrier element, such as a precipitate reaction was performed.
If the radioactivity accompanies the carrier, the radioactive element has similar chemical properties. This was a typical chemical process used to establish the chemical identity of the product of a nuclear reaction.
As discoverers of protactinium, Hahn and Meitner were familiar with its chemical properties and thus especially intrigued by Fermi's experiments on uranium; in particular they hoped to use uranium-Z as tracer for protactinium. Hahn was at the time the world's most experienced radiochemist and, as an authority in the radiochemistry of the heavier metals, he was quite interested in investigating the matter further. Chadwick's discovery of the neutron, the Curie and Joliot's discovery of artificial radioactivity, and Fermi's use of neutron bombardment to produce additional radioactive materials, including some thought to be new elements beyond uranium in the periodic table, were resurrecting radiochemistry, and transforming it into nuclear chemistry, a new research field which Hahn and Meitner were entering with outstanding experience and skill.
As a chemist, Hahn was delighted to have lots of news "transuranium" elements to study, it was like the old days, when "new elements fell like apples when you shook the tree. They concluded, like Fermi, that the elements produced had to be transuranic elements of atomic number 93 or higher, adding to a growing consensus among scientists. Detecting and identifying a few thousand atoms required both standard radiochemical techniques and consummated skill, which Hahn in particular had gained step by step after starting with his work with Rutherford at Montreal.
But with such minuscule amounts, which could only be detected by the ionizing effects of their radiation, it was extremely difficult by the methods of chemical analysis to gain a clear understanding of their chemical properties, even for Hahn and his collaborators, who were masters of such methods. At the same time, the confident expectation that the products would be found among the restricted set of elements whose atomic numbers were within a few units of the atomic number of the bombarded substance represented a main guiding principle for tackling the puzzles of transmutation.
The work of the Berlin team was interdisciplinary, requiring nuclear physics for the reaction processes and chemistry and radiochemistry for analysing the many radioactive products contained in their precipitate, so that in Fritz Strassmann, a young analytical and physical chemist whose scientific talents in separation chemistry complemented those of both Meitner and Hahn, joined the work.
Hahn, Meitner, and Strassmann tried to unravel the multiple series of decays that occurred in the sample of irradiated uranium and in they published a paper showing that three families of transuranic elements were necessary for interpreting the intriguing uranium puzzle.
For some time they were convinced that they had produced a series of transuranic elements with atomic numbers up to 95, with possible extensions even to elements 96 and However, irradiated uranium produced complex products and nobody knew just what the chemistry of transuranium elements should look like. At that time, the actinide series was not yet known in the periodic systems, and thus all elements after actinium were classified incorrectly. The most straightforward guess was that the periodic table could simply be extended downward: if uranium was regarded as lying beneath the similar metallic element tungsten, then the first element beyond uranium, number 93, should lie beneath the element next to tungsten, namely rhenium and so on, with elements homologous to osmium, iridium, etc.
In these attempts to make transuranium elements, two premises were always made which seemed to be firmly established by theory and experiment. First, in nuclear transformations, spontaneous and induced, atomic numbers are changed very little leading only to reaction products in the neighbourhood of the transformed element. Second, it was not yet known whether the periodic system would show another transition group analogous to the rare-earth group that begins with lanthanum, and if so where it would start.
So the exact position of transuranic elements in the periodic system - and hence their exact chemical behaviour - was not yet known. Furthermore, since radioactive alpha decay was understood as a quantum mechanical tunnelling process through a Coulomb barrier, the emission of larger nuclei seemed extremely unlikely.
How could a substantial fragment escape transforming a uranium nucleus into a substantially lighter nucleus? The problem was thus full of pitfalls. However, by the nuclear physics community had little doubt about the existence of the transuranium elements, which were treated as an established fact in textbooks, articles, public lectures.
Between and they stated that they had obtained, by irradiation of uranium with neutrons, a so-called 3. After performing new experiments, they decided, with some hesitation, to include the substance in the transuranium series, with atomic number 93, but the possibilities put forward appeared difficult to understand and unsatisfactory.
In particular, it was not clear how it would fit into Hahn, Meitner and Strassmann's scheme of decay chains. The Curie-Savitch paper was thus a challenge to the Berlin group. However, when the Nazi regime annexed Austria in early , Meitner's situation in Germany had been changed. With the Anschluss of 12 March those laws suddenly applied to her and she could expect to be dismissed from her post and to suffer other penalties.
She was refused an exit visa and a plan was then immediately prepared to get her out of Germany secretly. The last joint paper by Meitner, Hahn and Strassmann had been sent to the editor of Die Naturwissenschaften only a week before she left Germany.
In contrast to earlier papers from Paris, it contained detailed decay curves, which spoke for themselves. They immediately began to test their results. After careful experiments they concluded that, in addition to the transuranic elements they had already found in previous experiments, there were - produced by two successive alpha-emissions - three artificial, beta-active radium isotopes with different half-life times, which in their turn changed into artificial beta-active actinium isotopes.
When identifying these processes, radium had been precipitated using barium as the carrier element, because it is homologue of radium, and hence radium remains closely bound to the carrier in precipitation. It was in any case difficult to explain how could one pass from uranium, number 92 in the periodic table, to radium, number 88, especially as no alpha particles were observed.
On 8 November they reported their preliminary findings and the starting result of the appearance of radium isotopes and their actinium decay elements, and a few days later Hahn secretly met Meitner in Copenhagen. She urged him to double-check his radium data. Thanks to great weight they gave to her opinion and judgment, the two chemists in Berlin immediately undertook the necessary control experiments. Two days later, Meitner replied, "Dear Otto, your radium results are very puzzling […] However, we have experienced many surprises in nuclear physics, so that one cannot say without further consideration that it is impossible.
Frisch, who was visiting her for Christmas coming from Copenhagen, where he worked in Niels Bohr's Institute. Meitner was convinced that Hahn was too good as a chemist and that the result was correct. But how can one get a nucleus of barium from one of uranium?
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