Lise Meitner: The Austrian Marie Curie Who Never Received a Nobel Prize

On November 16, 1945, the Nobel Academy awarded the Chemistry Prize to Otto Hahn, a German chemist, for the “discovery of the fission of heavy nuclei”, a discovery made in December 1938 in Berlin. This discovery was the first step towards creating a chain reaction that could lead to the construction of new weapons.

[Article issu de The Conversation, écrit par Jacques Treiner, Physicien théoricien, Université Paris Cité]

This award was unique in more than one way: 1) the prize was awarded 3 months after the dropping of a bomb on Hiroshima by the Americans; 2) it was awarded for the year 1944, the year in which the Nobel Prize in Chemistry had not been formally awarded, because Hitler had prohibited Germans from receiving the prize since a German journalist, pacifist and declared anti-Nazi, Karl von Ossietzky, received the Nobel Peace Prize in 1936; 3) at the time of the award, the Nobel Academy did not officially know where Otto Hahn was, because he had been arrested by the Allies in July 1945, placed under house arrest and kept incommunicado with the main scientific leaders of the German atomic bomb project, and 4) the Nobel Prize should, as we will see, have been awarded jointly to Lise Meitner, with whom Hahn had worked for more than 30 years in Berlin, and who had been the inspiration for the series of experiments which led to the famous discovery at the end of 1938.

A woman at university? From tolerance to recognition

Lise Meitner was born in 1878 in Vienna into a Jewish family integrated into Viennese society. Attracted by mathematics and physics, she is blocked in her studies by the fact that high school is then forbidden to girls.

But in 1897, the university in Austria became authorized for women, Lise Meitner finished her secondary studies alone and entered the University in 1901, where she benefited from the teaching of Ludwig Boltzmann, one of the greatest physicists of the time. . She defended a thesis in 1906, turned to the study of radioactivity, a nascent branch, and decided to go to Berlin, where Max Planck was. It was there that she met the young chemist Otto Hahn, who had also just turned to radioactivity. They decide to work together… but she must agree to enter the building through the back door, the main entrance being reserved for men! They converted a storage room into an experimental room, and it was not until 1909, the year women's education was legalized in Germany, that she was allowed to enter the chemistry department.

Their close collaboration, particularly concerning the study of beta radiation (radioactivity by electron emission), quickly places them among the best international nuclear physics teams. Lise Meitner, who only received her first salary as a researcher in 1912, gained recognition to the point that in 1917 she was entrusted with setting up a new department of radioactivity at the Kaiser Wilhelm Institute of Physics: a first for a woman!

Induced nuclear reactions

A new era opened for nuclear physics with the discovery of the neutron by James Chadwick in 1932 in England.

With the neutron, physicists have a new probe of the atomic nucleus. Indeed, as it is electrically neutral, it can approach the nucleus without being repelled. It can even be absorbed by the nucleus and induce transformations there by which one element is transformed into another, an old dream of alchemists!

Three groups immediately set to work: Fermi and a group of young physicists in Rome, the Joliot-Curies in Paris, and Lise Meitner and Otto Hahn in Berlin. Over the course of the decade, they bombarded all the nuclei in Mendeleev's table with neutrons and worked to identify the resulting nuclei. But no one imagines, at first, that the absorption of a neutron can break an atomic nucleus into pieces. The atomic nucleus, which remains identical to itself during the most violent chemical transformations, seems unbreakable to them. Think: a material of which 1 cubic meter, if we could put it together, would have a mass of 20,000 billion tons!

Nuclear fission

So what is so extraordinary about fission? Fission is the process by which a large atomic nucleus breaks into two fragments of approximately equal mass. As the two fragments in contact contain electrical charges — protons — they repel each other very violently, then distribute their energy, during collisions, to the surrounding matter, which heats it. Thus, a single fission releases 100 million times more energy than when an equivalent mass participates in chemical combustion.

Apart from nuclear fusion at work in the hearts of stars, fission constitutes the most concentrated source of heat there is. It makes it possible to produce electricity — when the reactions are controlled — or explosions — when an uncontrolled chain reaction develops. As the discovery was made just on the eve of the Second World War, it was the “bomb” application which was the first, which means that the collective imagination associates nuclear and bomb, whereas it does not does not directly associate metallurgy and mass massacres with knives, nor chemistry and the destruction of Dresden by phosphorus bombs.

However, as early as 1934-35, physicists had all the theoretical elements to predict fission. In fact, the core behaves like an electrically charged liquid drop. The charges repel each other, but the nuclear force maintains stability. In the largest nuclei, the electrical charge is sufficient for the slightest flick, such as the absorption of a neutron, to break it. This is also the reason why there is no stable core on Earth beyond uranium.

Lise Meitner and Otto Frisch explain Hahn's observations

This explanation of the limit of stability of heavy nuclei will also be proposed just a few days after the discovery of the fission of the uranium nucleus.

It was Lise Meitner and her nephew Otto Frisch who understood the observations obtained by Hahn in Berlin. Lise Meitner had to flee Germany in July 1938, after the annexation of Austria in March 1938 by the Nazi regime, because her Austrian nationality no longer protected her from anti-Jewish prosecution. She settled in Sweden.

But after her departure from Berlin, she still remained in epistolary contact with Hahn, to the point that they decided to meet discreetly at the Niels Bohr Institute in Copenhagen, on November 13, 1938. They agreed that Otto needed to resume in Berlin a series of experiments with uranium, because the results he had obtained until then remained incomprehensible.

It is this last series of experiments which will lead to the discovery of what Meitner and Frisch will call “nuclear fission”, by analogy with the fission of the nucleus of a living cell – we say in French “cell division”.

As they could no longer publish together, because of Meitner's Jewish origin, Hahn published for his part in January 1939, in the journal Natürwissenschaften (n° 27), the article which would earn him the Nobel Prize in 1945 , while Meitner and Frisch published for their part, in February 1939, in the journal Nature (n° 143), the article explaining fission : there is no doubt that she should have shared the prize.

One prize for another

In 1943, Lise Meitner refused to join the group of physicists who were to work at Los Alamos on the Manhattan Project:

“I will not participate in any activity involving a bomb” (in “Lise Meitner, a life in physics”, by Ruth Levin Sime, published in 1996 by UC Press).

She therefore remained in Stockholm until the end of the war.

Hahn and Meitner would eventually receive together, in 1966, the American Physical Society's highest honor, the Fermi Prize. They are cited for “their pioneering research in the study of natural radioactivity and their intense experimental studies culminating with the discovery of fission.” Neither Meitner's nor Hahn's health would allow them to make the trip to Washington (both were over 80 years old at the time).

The ceremony took place in Vienna, and Glenn Seaborg, then chairman of the United States Atomic Energy Commission, made the trip. But Meitner was unable to go, and it was Frisch who came in his place. Meitner wrote to Hahn that she was happy for him, but that she herself had conflicting feelings, while feeling a “form of pleasure.” “ Why only a form of pleasure ? Hahn asked Frisch. Did she think she left Berlin too soon? Not at all, Frisch replied, she was grateful to everyone who had helped her leave. She had conflicting feelings…because of the bomb.