Marguerite Perey: When The Lab Assistant Gets The Credit

Most people obtain a bachelor’s degree before getting their masters, and even that is a prerequisite for a doctorate. Most people, however, don’t discover a new chemical element.

Marguerite Perey graduated with a chemistry diploma from Paris’ Technical School of Women’s Education in 1929, and applied for work at the Curie Institute, at the time one of the leading chemistry and physics labs in the world. She was hired, and put to work cataloging and preparing samples of the element actinium. This element had been discovered thirty years before by a chemist who had also been working in the Curie laboratory, but this was the height of the chemical revolution and the studies and research must continue.

When Marie Curie died in 1934, the discoverer of actinium, André-Louis Debierne, continued his research and Perey kept providing samples. Marguerite’s work was recognized, and in time she was promoted from a simple lab assistant to a  radiochemist. It would not be an exaggeration to say that Marguerite was, at the time, the world’s leading expert in the preparation of actinium. This expertise would lead her to the discovery of the bottom left corner of the periodic table: francium, element 87, the least electronegative element, and arguably the most difficult naturally occurring element to isolate.

The First Few Times Element 87 Was Discovered

Francium is a rare element, and the most stable isotope has a half-life of only twenty-two minutes. It has been estimated that only a few dozen grams of Francium can ever be found in Earth’s crust at any one time. Due to this incredible rarity, there was a hole in the periodic table below Cesium and to the left of Radium and Actinium. Thanks to Mendeleev, chemists of the late 1800s knew element 87 existed, and fame would be bestowed to the first scientist to find it.

With the development of x-ray emission spectroscopy in the first years of the twentieth century, scientists were on the hunt for element 87. In 1925, Gerald J.F. Druce and Frederick H. Loring announced their discovery of ‘alkalinium’ in samples of cesium. Their research could not be reproduced. That same year, D. K. Doboroserdov wrote about the presence of element 87 in samples of potassium, naming this new element ‘russium’ after his homeland. In 1930, Fred Allison discovered element 87 yet again using a, ‘magneto-optic method of chemical analysis’ in a sample of the minerals lepidolite and pollucite, naming their discovery ‘virginum’. Nine years later, Horia Hulubel and Yvette Cauchois discovered element 87 in samples of pollucite using their high-resolution x-ray spectrometer, naming it ‘moldavium’. None of these “discoveries” actually got element 87 right.

Perey’s Discovery of Catium

Marguerite Perey after being inducted to the Academy of Sciences

In her position as a lab assistant at the Curie Institute, Perey was tasked with analyzing samples of actinium. As a worker in one of the greatest labs on the planet, she was expected to keep abreast of the latest developments in her field, and in 1935, she read a paper reporting an alpha particle emission from actinium-227. All of Perey’s analyses of this isotope told her there would be one decay product, a beta particle, with a decay energy of 220 keV. Nevertheless, she prepared an ultra-pure sample of actinium-227 and found what the paper reported: a decay particle with an energy below 80 keV. The test was repeated, and tests eliminated the possibility of the decay product being thorium, radium, lead, bismuth, or thallium. Chemical tests revealed this decay product of actinium had the properties of an alkali metal, and with that element 87 was discovered.

In 1946, in preparing her submission to the International Union of Pure and Applied Chemistry, Perey proposed the name ‘catium’ for her element, as the most electronegative cation out of all the elements. One of her supervisors at the Curie Institute, Irène Joliot-Cure, daughter of Marie and Pierre Curie, thankfully spoke English. Perey then suggested ‘francium’, with the symbol ‘Fa’, but this was quickly changed to ‘Fr’.


Although peeling away two protons from actinium via alpha decay obviously results in element 87, there were issues with her discovery. Hulubei’s earlier work with his high-resolution x-ray spectroscopy was convincing and his mentor was Nobel Prize winner Jean Baptiste Perrin. Perrin wrote to the Académie des Sciences de Paris endorsing Hulubei’s discovery, and downplayed Perey’s work. Perey had no such mentor of equal scientific standing, and for a time it seemed the credit for the discovery of element 87 would go to Hulubei, and the last alkali metal would be named moldavium.

However, Perey kept meticulous notes, had the data, and fortunately had the support of Irène Joliot-Cure and André Debierne, her two supervisors at the Curie Institute. In a devastating and detailed criticism of Hulubei’s work, Perey was finally credited as the sole discoverer of element 87, and all previous discoveries were ruled out due to the element’s exceptionally short half-life.


After her discovery of francium, Perey was accepted to study for a Ph.D. at the Sorbonne with a thesis that would obviously be accepted. There was a problem with this plan; Perey did not hold a bachelor’s degree, and the Sorbonne refused anyone who did not achieve their entry requirements. Perey studied for her bachelors during World War II and in 1946 was awarded a doctorate.

In her later years, Perey became a senior scientist at the Curie Institute, the Chair of Nuclear Chemistry at the University of Strasbourg, a member of the Atomic Weights Commission, and in 1962 received the honor of being the first woman elected to the French Academy of Sciences. Perey died in 1975 at the age of 65 of bone cancer, most certainly caused by her work with nuclear chemistry.

Perey’s work is an astonishing story. Francium was the last naturally occurring element to be discovered, and the least stable of all the naturally occurring elements. This something that could only be done with exacting technique and years of experience. The fact that a lab assistant could prepare the samples and make a discovery shouldn’t be surprising, but the fact that she would get the credit is.

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