Lise Meitner

Lise Meitner (7 November 1878 – 27 October 1968) was an Austrian-Swedish nuclear physicist. In 1930 she supplied the measurement that made the neutrino necessary in the first place — and in 1939 she was the first to explain what happens in nuclear fission.

The road into physics

Meitner was born in Vienna and was among the first women permitted to study physics there. In 1906 she took her doctorate under Ludwig Boltzmann. In 1907 she went to Berlin, where she attended Max Planck's lectures and began the collaboration with the chemist Otto Hahn that was to last three decades.

The beginnings were arduous. Women were barred from access to the Chemical Institute; Meitner worked at first in a former carpenter's workshop in the basement. In 1926, in Berlin, she became the first female professor of physics in Germany.

The calorimeter experiment of 1930

In beta decay electrons leave the nucleus with quite different energies — a continuous spectrum instead of a sharp value. This had been known since 1914 but was disputed. Many took it for a measurement error: perhaps the electrons only lost energy on their way out.

Meitner and Wilhelm Orthmann settled the question in 1930 with a calorimeter. They measured not individual electrons but the total heat that a sample gave off. If the spectrum were an artefact, the quantity of heat would have had to correspond to the maximum energy. It corresponded to the mean value.

That settled it: in beta decay energy is lost, and really so. In the same year Wolfgang Pauli proposed an invisible particle that carried it away.

Flight and nuclear fission

In 1938 Meitner, as a Jew, had to flee from Germany. By way of the Netherlands she reached Sweden and continued her work in Stockholm.

In December 1938 Hahn wrote to her about an inexplicable finding: bombarding uranium with neutrons produced barium — a far lighter element. Meitner discussed this over Christmas with her nephew Otto Frisch. The two recognised that the uranium nucleus must have divided, and calculated the energy released in the process. Their paper in Nature of February 1939 coined the term nuclear fission.

The Nobel Prize in Chemistry went in 1944 to Otto Hahn alone. Meitner's omission is regarded today as one of the best-known wrong decisions in the history of the prize.

Attitude

Meitner refused to take part in the development of nuclear weapons. She declined an invitation to Los Alamos. After the war she spoke out clearly on the responsibility of scientists.

In 1997 element 109 was named after her: meitnerium. It is one of the few elements that bear the name of a woman.

Significance for neutrino physics

Without the measurement of 1930, Pauli's proposal would have had no firm ground. The question "Is the energy loss real?" had to be answered first, before anyone could invent a new particle for it.

Meitner thus stands at the beginning of a chain that leads by way of Enrico Fermi and Frederick Reines to today's large detectors — and that began with a measurement of heat.

Beta decay — what she measured
Wolfgang Pauli — the answer to her finding
Enrico Fermi — the theory behind it
Neutrino

Sources

L. Meitner, W. Orthmann: Über eine absolute Bestimmung der Energie der primären β-Strahlen von Radium E, Zeitschrift für Physik 60, 143 (1930).
L. Meitner, O. R. Frisch: Disintegration of Uranium by Neutrons: a New Type of Nuclear Reaction, Nature 143, 239 (1939).