Marguerite Perey

Marguerite Catherine Perey (19 October 1909 – 13 May 1975) was a French physicist who studied under Marie Curie. In 1939, she identified the element francium by refining lanthanum samples that contained actinium. She earned her Doctorate of Physics from the Sorbonne in 1946, writing her thesis on element 87, which she had recently discovered. In 1962, she became the first woman elected to the French Académie des Sciences, a distinction that had been withheld from her mentor, Curie.

Born in Villemomble, just outside Paris, Perey initially hoped to study medicine, but her father’s death left her family struggling financially. In 1929, she earned a chemistry diploma from the Technical School of Women’s Education in Paris, which qualified her as a chemistry technician. That same year, at age 19, she applied for and got a job as a personal assistant to Marie Curie at the Radium Institute. Curie took Perey under her wing as a mentor.

Under Curie’s guidance, Perey learned to isolate and purify radioactive elements, concentrating on actinium, which had been discovered in Curie’s lab in 1899 by André-Louis Debierne. For a decade, she separated actinium from other components of uranium ore, which Curie used to study the element’s decay. Curie died of aplastic anemia five years after Perey began working with her, but Perey and Debierne continued their actinium research, and Perey was promoted to radiochemist.

In 1935, Perey read a paper by American scientists claiming that actinium emitted beta particles. Skeptical because the reported energy didn’t match actinium, she investigated on her own, theorizing that actinium was decaying into another element and that the beta particles came from that daughter atom. By isolating very pure actinium and quickly studying its radiation, she detected a small amount of alpha radiation, which involves losing protons and changes an atom’s identity. Losing an alpha particle (2 protons, 2 neutrons) would turn actinium (element 89) into the predicted but undiscovered element 87.

Perey announced the discovery of element 87 in a note presented to the Académie des Sciences by Jean Baptiste Perrin on 9 January 1939, titled “On an element 87, derived from actinium.” Perrin presented it because Perey was only a lab assistant without a university degree. She named the element francium after France, placing it among the alkali metals in Group 1 of the periodic table. Francium is the second rarest element (after astatine)—only about 550 grams exists in Earth’s crust at any time—and was the last element discovered in nature. (Five synthetically discovered elements were later found in nature: technetium, promethium, astatine, neptunium, and plutonium.)

Perey received a grant to study at the Sorbonne, but lacking a bachelor’s degree, she had to take courses and earn the equivalent of a B.S. before pursuing a PhD. She graduated in 1946 with a Doctorate of Physics, her thesis on element 87. Her jury included Debierne, Irène Joliot-Curie, and biologist Pierre-Paul Grassé. During her defense, Joliot-Curie remarked that her “mother [Marie Curie] would have been happy.”

After earning her PhD, Perey returned to the Radium Institute as a senior scientist, staying until 1949. In 1949, she became head of nuclear chemistry at the University of Strasbourg, where she built the radiochemistry and nuclear chemistry program and continued studying francium. She founded a lab that became the Laboratory of Nuclear Chemistry in the Center for Nuclear Research in 1958, serving as its director. From 1950 to 1963, she also served on the Atomic Weights Commission.

Perey was nominated five times for a Nobel Prize but never won. She hoped francium could help diagnose cancer, but it turned out to be carcinogenic, and she developed bone cancer that eventually killed her. She died on 13 May 1975 at age 65. She is credited with advocating for better safety measures for scientists working with radiation.

Perey was elected to the French Academy of Sciences in 1962 as a “corresponding member” rather than a full member, which came with limited privileges. She was the first woman elected to the Académie since its founding in 1666. Her other honors include the Wilde Prize (1950), Le Conte Prize (1960), the City of Paris Science Grand Prize (1960), Officier of the Légion d’Honneur (1960), Grand Prix de la Ville de Paris (1960), Lavoisier Prize (1964), Silver Medal of the Société Chimique de France (1964), and Commandeur of the Ordre National du Mérite (1974). In 2026, she was announced as one of 72 historical women in STEM proposed to be added to the 72 men already celebrated on the Eiffel Tower, a plan announced by the Mayor of Paris.