Otto Hahn

Otto Hahn: The Chemist Who Split the Atom and Regretted It

"We are more and more coming to the awful conclusion that our Ra isotopes behave not like Ra, but like Ba," Otto Hahn wrote to his exiled former partner Lise Meitner on December 19, 1938, unable to believe his own careful chemistry. "Perhaps you can come up with some fantastic explanation." She could. Uranium was splitting in two. Hahn would spend the rest of his life as the discoverer of nuclear fission, the sole Nobel laureate for it, and — increasingly, publicly — one of its loudest opponents.

The Nose for New Elements

Born in Frankfurt in 1879 to a prosperous glazier, Hahn defied his father's wish that he study architecture and pursued chemistry instead, running early experiments in the family laundry room. After a doctorate at Marburg in 1901, a postdoctoral stint under William Ramsay at University College London in 1904 produced his first real discovery: radiothorium, made by chance while handling radium salts. Ramsay sent him on to Ernest Rutherford's lab at McGill, where Rutherford remarked that "Hahn has a special nose for discovering new elements" — a compliment Hahn would justify repeatedly, isolating radioactinium, mesothorium, and ionium over the following years, working at one point out of a converted woodworking shop in Berlin equipped with electroscopes he built from coffee tins.

Thirty Years With Lise Meitner

In 1907 Hahn began a scientific partnership with the Austrian physicist Lise Meitner that would last three decades and reshape radiochemistry. Meitner, barred as a woman from the main university building, worked for a time through a separate entrance and in a converted carpentry shop. Together the two discovered radioactive recoil and, in 1918, isolated protactinium, the long-sought missing link between thorium and uranium in the periodic table — work for which Max Planck nominated them for the Nobel Prize repeatedly through the 1920s without success. Hahn also identified nuclear isomerism in 1921, describing an unexplained puzzle that Carl Friedrich von Weizsäcker would not theoretically resolve until 1936. Through the 1920s and 1930s he became, by near-universal consensus, the father of the discipline of radiochemistry, publishing the standard textbook *Applied Radiochemistry* and training a generation of nuclear chemists.

Fission

After James Chadwick's discovery of the neutron in 1932 and Enrico Fermi's experiments bombarding uranium with neutrons, Hahn, Meitner, and the chemist Fritz Strassmann spent years chasing what they believed were new transuranic elements produced by the bombardment — heavier-than-uranium atoms with baffling, inconsistent half-lives. In March 1938 the Anschluss stripped Meitner of her Austrian citizenship and forced her to flee to Sweden with almost nothing; Hahn pressed a diamond ring inherited from his mother into her hand as she left. The two kept corresponding. In December 1938, Hahn and Strassmann found that their supposedly heavy new products behaved chemically exactly like barium — a much lighter element roughly half uranium's mass. Hahn, a careful chemist uneasy about drawing revolutionary physical conclusions, sent Meitner the data rather than the theory. Walking in the snow near Kungälv with her nephew Otto Frisch over the Christmas holiday, Meitner worked out the physics: the uranium nucleus was not shedding small fragments but splitting roughly in half, releasing enormous energy predicted by Einstein's mass-energy equivalence. Frisch borrowed the word "fission" from biology to describe it. Hahn and Strassmann's January 1939 paper reporting "Uranspaltung" — uranium fission — and predicting the extra neutrons that could sustain a chain reaction, opened the nuclear age within months, as Frédéric Joliot's Paris laboratory confirmed the chain-reaction possibility that March.

War, Farm Hall, and a Prize Delayed

Conscripted into chemical-warfare units in the First World War under Fritz Haber, Hahn survived poison-gas testing and later, in the Second World War, worked on Germany's stalled nuclear program while quietly intervening to protect Jewish and part-Jewish colleagues from persecution. Captured by an Allied Alsos Mission team in April 1945, he was interned with nine other German physicists at Farm Hall in England, their conversations secretly recorded. It was there, listening to the BBC report the bombing of Hiroshima in August 1945, that Hahn — by his own colleagues' account devastated — learned what his discovery had made possible; he later said he was glad the German program had failed to build a bomb first. Three months later he learned, again from a British newspaper rather than any official notice, that he had won the 1944 Nobel Prize in Chemistry, awarded for a year the Swedish Academy had withheld while Germans were barred from accepting Nobel honors under Nazi law. He could not travel to Stockholm to collect it until December 1946, and he gave a share of the prize money to Strassmann, who had done essential chemical work but received no formal credit — a decision widely read since as an attempt to correct, in a small way, an award that many historians and scientists believe should have gone to Meitner as well.

Rebuilding German Science, Then Renouncing the Bomb

From 1946 Hahn led the postwar reconstruction of German science, first as the last president of the tainted Kaiser Wilhelm Society and then as founding president of its successor, the Max Planck Society, a role he held until 1960 and used to rebuild German research funding roughly fourfold. At the same time he became an outspoken campaigner against nuclear weapons, calling their use "a misuse, or even a crime" of the physics he had helped discover. He organized the 1955 Mainau Declaration, in which dozens of Nobel laureates warned against nuclear war, and in 1957 co-authored the Göttingen Manifesto, in which eighteen leading German scientists publicly refused to help arm West Germany's military with nuclear weapons — a stand that put him face to face with Chancellor Konrad Adenauer's defense ministry.

Why Otto Is Called a Genius

Hahn's claim rests on an unusual kind of genius: not theoretical brilliance but an almost unmatched instinct for hands-on discovery, sustained across six decades and dozens of new isotopes. Rutherford's remark that he had "a special nose" for finding new elements was not flattery so much as an accurate professional assessment — Hahn kept finding what others missed, from radiothorium in 1905 to fission itself in 1938, using painstaking chemical separation rather than mathematical prediction.

The honest counter-case is central to his story, not incidental to it. The physics that explained what Hahn had found — why uranium split, and what made it possible — came from Lise Meitner and Otto Frisch, working in exile, days after Hahn sent them his puzzling results. Hahn himself, by his own admission, could not draw that conclusion; he needed her. That the Nobel Prize for fission went to Hahn alone, while Meitner and Strassmann went unrecognized, is now widely regarded by historians of science as one of the twentieth century's clearer Nobel injustices — a case where institutional convention, not a fair accounting of who did the essential thinking, decided who was called a genius.

Legacy

Hahn died in 1968, having spent his final decades trying to ensure his discovery served medicine and energy rather than weapons — an ambition only partly realized. Element 105, hahnium, briefly bore his name in American nomenclature disputes before being settled as dubnium; the Otto Hahn Peace Medal and the German research vessel and institutes that carry his name still mark a life spent, as he put it himself, trying to answer for what nuclear fission had unleashed.

Achievements

• Pour le Mérite
• Officer of the Legion of Honour — 1959
• Max Planck Medal — 1949
• Grand Cross 1st class of the Order of Merit of the Federal Republic of Germany — 1959
• Great Cross with Star and Sash of the Order of Merit of the Federal Republic of Germany — 1954
• Foreign Member of the Royal Society — 1957
• Held posts at Cornell University, Frederick William University Berlin and Freie Universität Berlin
• Educated at Humboldt-Universität zu Berlin, Ludwig-Maximilians-Universität München and University of Marburg
• Fields of research: nuclear chemistry and radiochemistry