Maria Göppert Mayer

Maria Göppert Mayer: The Unpaid Woman Who Cracked the Nucleus

For nearly thirty years she worked for no salary. Universities that were glad to have her husband on the payroll invoked anti-nepotism rules to keep her off it, handing her a desk, a courtesy title, and nothing else. In 1963 the Nobel committee in Stockholm gave her a share of the Physics Prize for discoveries concerning nuclear shell structure — making her only the second woman ever to win it, after Marie Curie in 1903, and the last for more than fifty years afterward.

A Göttingen Childhood

She was the only child of Friedrich Göppert, a pediatrician, and Maria Wolff. Born on 28 June 1906 in Kattowitz — then German, today Katowice in Poland — she was four when the family moved to Göttingen, where her father took the chair of pediatrics.

Her father, by her own account, was the parent who shaped her: "Well, my father was more interesting," she said. "He was after all a scientist." His advice to her has come down in a blunt formulation — don't grow up to be a woman, meaning don't settle for being only a housewife. She attended the Höhere Technische in Göttingen and then a preparatory school run by suffragettes, and she sat the Abitur at seventeen, a year early. Of the small group of girls who took the examination alongside her, all passed. Of the boys, one did.

The Thesis Nobody Could Test

She entered the University of Göttingen in 1924 to read mathematics, spent a year at Cambridge, and returned. Physics won. Her doctorate, completed in 1931, treated two-photon absorption by atoms — a prediction three decades ahead of the technology needed to confirm it, since only the laser made the effect observable. Her examiners were Max Born, James Franck and Adolf Windaus, all three of whom would win Nobel Prizes themselves. Eugene Wigner later called the thesis "a masterpiece of clarity and concreteness." The compliment has outlived the paper's obscurity: the unit physicists now use to measure two-photon absorption cross-sections is called the Goeppert Mayer.

Thirty Years Without a Salary

In January 1930 she married the American chemist Joseph Edward Mayer, and followed him to Johns Hopkins, where he took an associate professorship. They would have two children, Maria Ann and Peter Conrad. Johns Hopkins had strict rules against employing the spouses of faculty; she was given an assistant's post with a nominal salary, a corner of office space, and access to the buildings. She used them. She taught, and in 1935 published a significant paper on double beta decay, one of the rarest and hardest-to-observe processes in nature.

When Joseph was dismissed in 1937 — departmental hostility toward a woman in the building was widely blamed — the couple moved to Columbia, where she again received an office and no pay, and again produced work, this time in the orbit of Harold Urey and Enrico Fermi. The American Physical Society elected her a Fellow in 1941. It was December of that year, at thirty-five, before she held her first paid academic appointment: part-time teaching at Sarah Lawrence College. After Pearl Harbor she also took over Fermi's classes at Columbia — unpaid.

The Bomb Years

In the spring of 1942 she joined the Manhattan Project's Substitute Alloy Materials laboratories at Columbia, working on separating uranium-235 and on the properties of uranium hexafluoride. Edward Teller then drew her into the Opacity Project, an investigation into how matter and radiation behave at the temperatures of a thermonuclear explosion, and in February 1945 she went to Los Alamos to work in Teller's group, returning to New York in July. Her verdict on the opacity work was characteristically dry: "We found nothing, and we were lucky."

Waltzers in a Ballroom

In February 1946 Joseph took a professorship at the University of Chicago's Institute for Nuclear Studies. She was made a voluntary associate professor — unpaid, again — and simultaneously took a part-time senior physicist's job at the newly founded Argonne National Laboratory. Her opening line at Argonne was that she knew nothing about nuclear physics. She then programmed the ENIAC to run Monte Carlo calculations of reactor criticality.

What she noticed in the data was that nuclei containing 2, 8, 20, 28, 50, 82 or 126 protons or neutrons were unusually stable. Wigner called these the magic numbers, and the name stuck. She proposed that nucleons, like electrons in an atom, occupy shells of rising energy, and that a nucleus with completely filled shells is the tightly bound one. The first paper laying out the evidence appeared in *Physical Review* in August 1948.

The mechanism was missing until Fermi, on his way out of her office, asked whether there was any evidence of spin-orbit coupling — of a nucleon's spin interacting with its orbital motion. She saw at once that this was the key that generated exactly that sequence of numbers. "It was like a jigsaw puzzle," she said. "Everything became clear." Fermi, watching her explain it at speed, smiled and left: "Tomorrow, when you are less excited, you can explain it to me."

She liked to describe the result as a ballroom. Think of a room full of waltzers, she said, circle enclosed within circle: you can fit twice as many dancers if one pair spins clockwise and another counterclockwise.

In Germany, Otto Haxel, J. Hans D. Jensen and Hans Suess had reached the same conclusion independently; their announcement came first, in June 1949, though her submission was earlier, in February. Rather than fight over it, she and Jensen became collaborators and friends, co-authoring *Elementary Theory of Nuclear Shell Structure* in 1950. Thirteen years later they shared half of the 1963 Nobel Prize in Physics; Wigner took the other half.

Why Maria Is Called a Genius

The quality on display in her best work is pattern recognition operating on numbers that everyone else could see and nobody else could read. The magic numbers were not hidden; they sat in published tables of nuclear stability. What she supplied was the conviction that an irregular-looking list — 2, 8, 20, 28, 50, 82, 126 — was the signature of a structure, and then the mathematical apparatus to derive that exact list from spin-orbit coupling rather than fudging it. Her doctoral thesis shows the same trait in a different key: a correct prediction of a physical effect thirty years before anyone could measure it, which Wigner judged "a masterpiece of clarity and concreteness."

The honest counter-case has two parts. First, priority: Haxel, Jensen and Suess got there independently and almost simultaneously, which is the classic sign of an idea whose time had arrived rather than a leap only one mind could make. Second, the decisive hint came from Fermi's question about spin-orbit coupling — she did not generate it herself, though she recognised in seconds what it meant, which is its own kind of ability. Set against that: she did this work while holding no paid position, in a field she had entered late, having taught herself nuclear physics after saying plainly that she knew none. Whether or not the word genius fits, that combination of persistence and speed of insight is what the Nobel committee ultimately certified.

Afterward

In 1960, past fifty, she was finally made a full professor, at the University of California, San Diego. A stroke shortly after her arrival did not stop her teaching or her research. She died of a heart attack in San Diego on 20 February 1972, aged 65.

Her name is now attached to the things she was long denied: the Goeppert Mayer unit in optics, the American Physical Society award for early-career women physicists established in 1986, Mayer Hall at UC San Diego, an award at Argonne, a crater on Venus, a 1996 place in the National Women's Hall of Fame, and a US postage stamp issued in 2011.

Achievements

• Nobel Prize in Physics — 1963
• Notable work: nuclear shell model
• Held posts at Argonne National Laboratory, Columbia University and Johns Hopkins University
• Educated at University of Göttingen
• Fields of research: nuclear physics, photochemistry, physical chemistry and physics