Marguerite Perey discovered the element Francium.
Born in 1909, Marguerite wanted to become a medical doctor. With the death of her father, the family fell on hard times, and at the age of 19 she was forced to seek employment as a chemist. She approached a local laboratory, the Radium Institute, which was researching cancer treatments. Marie Curie was impressed by the intelligent young woman, and gave her a job as a laboratory assistant.
Marguerite became responsible for preparing and purifying samples of Actinium from Uranium ore. Alerted by some incongruous results, she was able to prove that Actinium (element 89) decayed to give a daughter product, and in 1939 she isolated element 87. She named it Francium, after her country, France.
Francium is an ephemeral element, constantly forming and decaying, the most stable isotope has a half life of only 22 minutes and there are estimated to be no more than a few grams in existence at any time.
It is very rare that a laboratory assistant gets the credit for such a remarkable discovery. Even more remarkable that her two supervisors, Irène Joliot-Curie and André Louis Debierne, supported her.
In 1949, after completing a degree and PhD at the Sorbonne, she became Chair of Nuclear Chemistry at the University of Strasbourg and in 1962, Marguerite was the first woman to be elected to the French Académie des Sciences.
Her exposure to radioactive elements took its toll; after a long and painful illness, Marguerite died of bone cancer in 1975.