Marguerite Perey: Biography, Discovery & Contribution

Instructor: Betsy Chesnutt

Betsy has a Ph.D. in biomedical engineering from the University of Memphis, M.S. from the University of Virginia, and B.S. from Mississippi State University. She has over 10 years of experience developing STEM curriculum and teaching physics, engineering, and biology.

Marguerite Perey was a French scientist who worked with Marie Curie and discovered a new element that no one had ever found before! In this lesson, learn more about her discovery and her unexpected life story.

Who was Marguerite Perey?

One day in 1929, a young French woman nervously walked into a laboratory in the Radium Institute in Paris. Her name was Marguerite Perey, and she was there to interview for a job working with one of the greatest scientists in the world, Marie Curie. Every year, Marie Curie would select one student graduating from a lab technician training course to work at the Radium Institute, and today, Perey really hoped it would be her.

Once, she had dreamed of going to college to become a doctor, but now, her family couldn't afford it. Working for Marie Curie would allow her to still be part of the scientific world while helping to support her family. A few days later, Perey found out she got the job! The partnership between Curie and Perey would turn out to be an important one in the history of science. Eventually, Marguerite Perey would go from being a laboratory assistant to a respected scientist who discovered a new element no one had ever found before!

Early Life

In 1909, Marguerite Perey was born just outside Paris, France in the village of Villemomble. Her father owned a flour mill when she was young, but when he died, the family was left in a pretty bad financial situation. Her mother tried to support the family by herself by giving piano lessons, but it was hard. Perey was forced to give up her dream of going to college, and instead signed up for a short training course at a local vocational school. It was near the end of this course that she was hired to work at the Radium Institute by Marie Curie.

Discovery of Francium

At the Radium Institute, Perey learned how to carefully isolate and purify radioactive elements. Her specialty was preparing samples of a highly radioactive element, known as actinium, that Marie Curie had been studying for many years. Just five years after Perey came to the Radium Institute, Marie Curie died of anemia, likely caused by all the radiation she was exposed to during her lifetime.

Perey's work with actinium continued even after Curie's death, and she was soon promoted from laboratory technician to radiochemist. In 1935, a group of American scientists published a paper in which they reported they had found samples of actinium that released beta particles with an unusual amount of energy. When Perey read the article, she was immediately skeptical. She knew a lot about actinium, maybe more than anyone else in the world at that time, and she didn't think that those beta particles were coming from actinium at all! What was really going on? She didn't know, but she was determined to find out.

Perey suspected that the actinium samples were decaying to produce another element, and that it was this new daughter element that was really releasing the beta particles reported by the American scientists. To see whether she was right or not, Perey decided to prepare an extremely pure sample of actinium and measure its radioactivity immediately, before any daughter elements would have time to form. This was very technically challenging, but Perey was very skilled at this kind of work, so she was able to successfully perform the experiment.

What she found was quite surprising. Her experiment showed that actinium was actually giving off alpha particles. An alpha particle is a radioactive particle that contains exactly two protons and two neutrons. When an atom emits alpha particles, it loses some protons, and therefore, turns into a different element. Actinium always has exactly 89 protons, so if atoms of actinium were emitting alpha particles, that must mean that they would now have only 87 protons.

When actinium decays, it gives off an alpha particle and turns into the element francium.
Actinium decays to give an alpha particle and the element francium

At the time of Perey's discovery, there was no known element that had an atomic number of 87, but she had just found that one must exist! She named this new element francium in honor of her country, France.

She had not only discovered a new element, but also proved the American scientists wrong. The mysterious beta particles were NOT coming from actinium at all, but instead from this new element, francium.

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