Maria Geppert-Mayer

Maria Geppert-Mayer

Physicist
Date of Birth: 28.06.1906
Country: Poland

Biography of Maria Goeppert-Mayer

Maria Goeppert-Mayer, a German-American physicist, was born Maria Goeppert in Kattowitz (now Katowice, Poland). She was the only child of Friedrich Goeppert, a professor of medicine, and Maria Wolf, a school teacher. After moving to the United States, Goeppert anglicized the spelling of her maiden name.

Goeppert-Mayer's family relocated to Gottingen, where her father became a professor at the local university. The family had close friends such as Max Born and James Franck, both prominent physicists. Gottingen University was a leading center for research in quantum mechanics, a new field of physics. Goeppert-Mayer developed an early love for science, as her father encouraged her interest in nature and collected fossils with her.

When Max Born invited Goeppert-Mayer to participate in his physics seminar, her interests shifted from mathematics to physics, focusing on quantum mechanics, which studies the behavior of atoms, nuclei, and subatomic particles. She spent a semester at the University of Cambridge, where she met the renowned English physicist Ernest Rutherford. Goeppert-Mayer obtained her doctorate in 1930 from Gottingen, defending her dissertation on "Elementary Processes with Two Quantum Jumps." Despite facing the loss of her father in 1927, she continued her studies and received her doctorate while being examined by Max Born, James Franck, and Adolf Windaus.

In January 1930, Goeppert-Mayer married Joseph E. Mayer, an American chemist from the California Institute of Technology. They had a son and a daughter together. After their wedding, they moved to the United States, where Joseph was offered a position as an assistant professor of chemistry at Johns Hopkins University in Baltimore, Maryland. Despite her doctoral degree and excellent recommendations, Goeppert-Mayer was not able to secure a paid teaching position at Johns Hopkins due to the prevailing attitude towards faculty wives. However, she managed to work as an assistant to a member of the physics faculty, handling German correspondence. This modest position provided her with a small stipend, a tiny office, and some involvement in university life.

Goeppert-Mayer chose to specialize in chemical physics, which studies molecules and their interactions, but she also took advantage of opportunities in the physics and mathematics departments. She collaborated with physicist Carl F. Herzfeld, with whom she maintained a lifelong friendship, on research regarding energy distribution along the surfaces of solid bodies and the behavior of hydrogen dissolved in metallic palladium. After Herzfeld left Johns Hopkins University, Goeppert-Mayer worked with one of his former students, Alfred Sklar, on the study of quantum-mechanical electronic levels of benzene and the structure of several organic dyes. In this work, she demonstrated her excellent mathematical skills and applied methods from group theory and matrix theory.

Throughout the summers of 1931, 1932, and 1933, Goeppert-Mayer, feeling homesick, spent time in Gottingen working with Born. In 1933, the same year the Nazis came to power in Germany, Goeppert-Mayer became a naturalized American citizen. The rise of anti-Semitism and racist laws had a devastating impact on German science, leading many prominent Jewish scientists, including Born and Franck, to leave Germany. The Mayers' house in Baltimore became a refuge for German refugees, many of whom were Jewish.

When Joseph Mayer became a professor of chemistry at the University of Chicago after the war, Goeppert-Mayer was appointed as an assistant professor of physics at the same university in 1946. However, due to university rules aimed at combating nepotism, she did not receive a salary. In 1946, she also became a senior physicist at the Argonne National Laboratory near Chicago, where a nuclear reactor was being constructed. At Argonne, Goeppert-Mayer collaborated with Fermi, Yuri, Frank, and Teller and worked on calculations related to the criticality of a breeder liquid-metal reactor. These calculations were performed using the first electronic computer, the Electronic Numerical Integrator and Computer (ENIAC), which had recently been completed at the Aberdeen Proving Ground in Maryland. It was during this time, while working with Teller on the theory of element formation, that Goeppert-Mayer encountered the concept of "magic numbers" mentioned by German physicist Walter Elsasser in 1933. Atomic nuclei are made up of protons and neutrons, and Goeppert-Mayer discovered that certain nuclei are significantly more abundant than others, indicating exceptionally high stability. These stable nuclei accumulate due to the tendency of unstable nuclei to undergo radioactive decay. Stable nuclei have a specific number of protons or neutrons that correspond to one of the magic numbers: 2, 8, 20, 28, 50, 82, 126, and occasionally others.

Goeppert-Mayer knew that a similar situation existed for atomic electrons orbiting the nucleus. The stability of atoms is of a chemical nature, as chemical reactions involve the loss, gain, or sharing of electrons (the atomic nuclei remain unchanged). The periodic table of elements shows that as the atomic number increases, the chemical properties of elements repeat in cycles or periods. The atomic number is the number of protons in the nucleus, which is equal to the number of electrons in the unexcited atom, making the atom overall electrically neutral. Periodic stability, occurring at specific atomic numbers, was explained based on atomic energy levels associated with the angular momentum of the electrons orbiting the nucleus. According to quantum theory, energy levels are discrete values. Angular momenta arise from the motion of electrons around the nucleus (orbital angular momentum) and the rotation of the electron around its own axis, similar to a spinning top (spin). Since moving electrons constitute an electric current, they create a magnetic field. Just as two magnets repel or attract each other, the orbital angular momenta and spins of electrons interact with each other (spin-orbit coupling). According to quantum theory, each allowed angular momentum level corresponds to a set of discrete energy states. When these states are coupled with the electron spin, an energy level system is formed, each of which is defined by a set of four quantum numbers. Additionally, there is a restriction imposed by the Pauli exclusion principle. According to this principle, each quantum state, defined by a set of four quantum numbers, can only accommodate one electron. As the atomic number increases and each electron occupies the next available, unoccupied level, the energy of the system increases step by step.

The steps by which the energy increases are not uniform: clusters of small steps are separated by incredibly large steps. Based on early notions of electrons orbiting the nucleus at various distances, these clusters of levels were called shells. An element whose atom has its farthest electron on the last level before a large gap is said to have a closed shell. The next element with a higher atomic number, which has one more electron than the previous element, starts the next shell. Closed shells correspond to stable elements. Since removing or adding an electron to a closed shell requires more energy than usual, elements with closed shells are less reactive in chemical reactions.

The shell scheme was applied to the nucleus, assuming that protons and neutrons orbit each other. However, the nucleus differs significantly from the atom. In the atom, the central force of attraction between the protons in the nucleus and the electrons is well-known as the force of interaction between electric charges. Electrons are relatively far apart, and their mutual repulsion is weak, so the energy of one electron is not significantly influenced by the positions of the others. On the other hand, nuclear forces between protons and between protons and neutrons act at short distances, so the energy of one particle depends heavily on the positions of others inside the nucleus. There is no single attractive center in the nucleus. These differences led theoretical physicists in the early stages of research to conclude that spin-orbit coupling for protons and neutrons in the nucleus must be almost negligible.

Goeppert-Mayer worked persistently to solve the problem of nuclear structure. In the early stages of her work, she identified two magic numbers: 50 and 82. Then, analyzing experimental data, she discovered five additional magic numbers but could not explain them. The breakthrough came in 1948 when Fermi asked her, "Are there any signs of spin-orbit coupling?" Realizing that spin-orbit coupling held the key to the problem, she was able to explain nuclear magic numbers the same evening. Goeppert-Mayer showed that the nucleus also consists of shells. According to her, the atomic nucleus resembles an onion in its structure: it consists of layers containing protons and neutrons that orbit each other and circulate through the orbit, like couples waltzing at a ball. Nuclei are stable when the shells of protons or neutrons are filled. Nuclear magic numbers differ from magic numbers for atomic electrons, but there is an analogy between them with the appropriate corrections.

Goeppert-Mayer published her work on nuclear shell theory in two articles in Physical Review in 1948 and 1949. These publications coincided with the publication of a similar theory by J. Hans D. Jensen from Heidelberg University, who worked with Otto Haxel and Hans E. Suess. Goeppert-Mayer and Jensen met in 1950 in Germany, became friends, and collaborated on the book "Elementary Theory of Nuclear Shell Structure," published in 1955.

Goeppert-Mayer and Jensen were awarded the Nobel Prize in Physics in 1963 "for their discoveries concerning nuclear shell structure." The other half of the prize that year was awarded to Eugene P. Wigner. In presenting the new laureates, Ivar Waller of the Royal Swedish Academy of Sciences reminded the audience that before Goeppert-Mayer's discoveries, "no more than three magic numbers could be explained... She and Jensen convincingly demonstrated the importance of the shell model for systematizing the accumulated material and predicting new phenomena associated with the ground state and low-lying excited states of nuclei."

In 1960, the University of California, San Diego invited the Mayers to join their faculty. Goeppert-Mayer was offered a full professorship in physics, while Joseph was offered a professorship in chemistry. Shortly after their move to California, Goeppert-Mayer suffered a stroke, possibly due to a viral infection. She was partially paralyzed and experienced speech difficulties. Despite her health setback, she continued her teaching and research on nuclear physics. Goeppert-Mayer continued to collaborate with Jensen, and their final joint work was published in 1966, six years before she passed away in San Diego from a heart attack.

Goeppert-Mayer was elected to the National Academy of Sciences in the United States, the American Academy of Arts and Sciences, and was a corresponding member of the Heidelberg Academy of Sciences. She received honorary doctorates from Smith College, Russell Sage College, and Mount Holyoke College.

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