Marguerite Perey discovered the chemical element francium in 1939. Francium was the last element ever discovered in a natural source. All elements discovered after Perey’s discovery have been produced by artificial methods in the laboratory.
Education and Marie Curie
Marguerite Catherine Perey was born in Paris, France on October 19, 1909.
In 1929 she qualified with a chemistry diploma from Paris’s Technical School of Women’s Education. This qualification enabled her to apply for chemistry technician positions. She hoped to get a good job, because her family was badly off financially.
She applied for work in Marie Curie’s laboratory in Paris – The Radium Institute – and was amazed to be interviewed by the great Marie Curie herself. Marie Curie was one of the most famous people in the world at that time. In terms of scientists, only Albert Einstein was better known to the world’s public, and in France itself Marie Curie, with two Nobel Prizes, was the greatest of all scientists.
This could have been an intimidating experience for the 19 year-old girl, and indeed the interview seemed to go badly. However, Perey was surprised to learn she had been hired. She was going to work alongside Marie Curie.
Becoming a Radiochemist
After starting work at the Radium Institute, Perey was trained in the isolation and purification of radioactive elements. In time, she became responsible for preparing and purifying samples of the chemical element actinium.
Actinium is radioactive. It was discovered in Curie’s laboratory in 1899 by the chemist André-Louis Debierne. 30 years later, Marie Curie was still studying the element, cataloging its radioactive properties in exacting detail.
Five years after Perey started work, Marie Curie died of aplastic anemia; she was 66 years old. The disease was probably caused by the radiation she exposed herself to during her scientific career.
Nevertheless, the show must go on, and André-Louis Debierne pushed on with actinium related work. Marguerite Perey continued preparing the samples.
She had good ideas, and her work was high quality; this was recognized with a promotion to radiochemist. Her work was dangerous. Marie Curie was not the first person at the Radium Institute whose death was probably caused by radiation and, tragically, would not be the last.
The Discovery of Francium
Surely the Americans are wrong
In 1935, age 26, Perey read a research paper from the USA. The American researchers had found beta particles being emitted by actinium.
Perey knew as much about actinium as anyone else in the world – she had been working with it for seven years. She decided the American researchers were probably wrong about actinium being the source of beta particles. While actinium did emit beta particles, Perey thought the energy of the beta particles seen in America was wrong for actinium.
She suspected actinium was decaying into a different atom – this is called a daughter atom or daughter product – and the daughter atom was emitting the beta particles reported in America.
Seeking the Daughter Atom
Perey decided to produce an ultra-pure sample of actinium and study its radiation before it had the chance to form daughter products. This was exceptionally difficult: the ultra-pure actinium sample would have to be prepared and its radiation studied in a very short time-frame.
The nucleus of a radioactive atom emits an alpha particle. As a result, it loses two protons and two neutrons. The loss of protons means it becomes a different chemical element.
An alpha particle consists of 2 protons and 2 neutrons. Actinium is element 89 in the periodic table, meaning it has 89 protons. If it emits an alpha particle it loses 2 protons and becomes an atom with 87 protons: so the daughter atom was element 87.
The Daughter Atom – A New Element
In 1939 there was no element 87 in the periodic table. Although people had suspected it existed, nobody had been able to find it. Perey had discovered a new element! The new element was made when actinium emitted alpha particles.
And she had been right about the American research work. The beta particles with unexpected energy were not from actinium, but from the new element.
With 87 protons the new element belonged in Group 1 of the periodic table, joining the other alkali metals: lithium, sodium, potassium, rubidium, and cesium.
Actinium Produces Francium and an Alpha Particle
Perey discovered that actinium could decay by emitting a helium nucleus from its own nucleus. Such a helium nucleus is called an alpha particle. The daughter nucleus formed was a previously undiscovered element which she chose to call francium.
Marie Curie had named the first element she discovered polonium in honor of her home country – Poland.
After some discussion, Perey decided to name the new element to honor her home country – France. And so a new element was added to the periodic table – francium.
Less than 30 grams of natural francium is present on Earth at any time, because although it is constantly made by the radioactive decay of actinium, it is constantly undergoing radioactive decay into its own daughter products. Its half-life is only about 22 minutes, so it doesn’t hang around for long.
Perey hoped the new element would be of use in cancer treatments, but this did not prove to be the case.
Recognition, Future Career and Awards
After joining the elite group of scientists who have discovered a chemical element, Marguerite Perey was given leave to study for a Ph.D. at Paris’s prestigious Sorbonne. The award of a Ph.D. was not in doubt, because her thesis would describe her discovery of a new element.
The trouble was she didn’t have good enough high school qualifications to be admitted to the Sorbonne, and she did not have a bachelor’s degree. The Sorbonne refused to award Ph.D. degrees to people who had not achieved their entry requirements – even if they had discovered a new element!
So, during the years of World War 2, Perey spent time taking courses at the Sorbonne to eventually get the equivalent of a B.S. degree. After she had done this, she was awarded her Ph.D. degree in 1946. She became Doctor Marguerite Perey.
(Maybe it’s just me, but the Sorbonne comes over as a pretty stuffy sort of place!)
With her Ph.D. Perey immediately became a senior scientist at the Radium Institute. She continued working there until, in 1949, at age 40, she took the Chair of Nuclear Chemistry at the University of Strasbourg.
Perey also served as a member of the Atomic Weights Commission between 1950 and 1963.
In 1962 she became the first woman to be elected to the French Academy of Sciences. In addition to this, she was awarded:
1950: The French Academy of Science Wilde Prize
1960: The French Academy of Science Le Conte Prize
1960: The City of Paris Science Grand Prize
1960: Officer of the Legion of Honor
1964: Lavoisier Prize of the French Chemical Society
1964: Silver Medal of the City of Paris
1973: Commander of the National Order of Merit
The End
Marguerite Perey died at age 65 on May 13, 1975. Like Marie Curie and a number of other scientists who had worked at the Radium Institute, she died of a radiation-linked illness. In fact, her body was found to be unusually radioactive. She had been instrumental in the introduction of better safety measures in the laboratories under her control. Sadly, this was too late to save her own life, but it was a lifesaver for future generations of nuclear scientists.
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