Lise Meitner
Can the nucleus be split?
That time, that place
An Austrian Jew who worked with Otto Hahn in Berlin for thirty years. In the early days, barred as a woman from the institute's main building, she ran experiments in a basement carpentry room.
In 1938 the Nazi annexation of Austria voided her Austrian passport, and she crossed the border into Sweden. Without a laboratory, without a position, without instruments.
Why this question
That winter Hahn wrote to her: bombarding uranium with neutrons had produced barium.
Barium is about half the size of uranium. Hahn had confirmed it chemically again and again and could not explain it. By the understanding of the day a nucleus might chip, but it could not split in two.
What was found
Over Christmas, walking through snowy woods with her nephew Frisch, Meitner worked it out.
Treat the nucleus as a droplet. A neutron entering sets it wobbling; the droplet elongates and pinches at the middle. As it pinches, the two clusters of positive charge move apart, repulsion overtakes surface tension, and at some point it snaps in two.
Then she calculated. The two fragments together weigh slightly less than the original. That missing mass emerges as energy by Einstein's formula — around two hundred million electron volts per atom. An enormous figure.
She named the phenomenon fission.
A nucleus might chip away, but it does not split in two
Hahn's chemical results, and a calculation converting the missing mass into energy
The 1944 Nobel Prize in Chemistry went to Otto Hahn alone. She refused to join the Manhattan Project, and disliked being called the mother of the atomic bomb for the rest of her life