Building on a family legacy that transformed science, Irène Joliot-Curie and her husband Frédéric Joliot discovered how to create radioactivity artificially, a breakthrough that fundamentally altered nuclear physics and unlocked powerful new tools in medicine. For this achievement, the couple was awarded the Nobel Prize in Chemistry in 1935, making the Curies the family with the most Nobel laureates in history. Their work not only established a method for producing radioactive isotopes on demand but also paved the way for countless applications, most notably in the diagnosis and treatment of cancer.
The discovery of artificial, or induced, radioactivity provided a crucial, affordable, and abundant source of radioactive materials that were previously obtainable only through the painstaking and expensive process of extraction from natural ores. By bombarding stable elements with subatomic particles, the Joliot-Curies demonstrated that they could transmute them into new, radioactive versions. This synthesis of “designer” radioactive elements quickly became indispensable in biomedical research and therapy, forming the foundation of the field of nuclear medicine. Their research also contributed to the later discovery of nuclear fission, placing Joliot-Curie at the center of the atomic age’s scientific and ethical crossroads.
A Legacy of Scientific Inheritance
Born in Paris in 1897, Irène Curie was the elder daughter of Marie and Pierre Curie, whose own Nobel Prize-winning work in physics had defined the field of radioactivity. Following the tragic death of her father in 1906, Irène was raised by her mother and paternal grandfather, Eugene, who instilled in her a love of nature and progressive politics. Her education was unconventional; for two years, she attended a special cooperative school organized by her mother and other prominent academics, where she received instruction in science and mathematics directly from leading professors. This intensive, specialized tutoring honed her innate talent for math and science from a young age.
Her formal education continued at the Collège Sévigné and later at the Sorbonne, but her studies were interrupted by the outbreak of World War I. Putting her scientific aptitude to practical use, she joined her mother in the field, serving as a nurse radiographer. Working in mobile X-ray units, known as “petites Curies,” she helped surgeons locate shrapnel in wounded soldiers, gaining firsthand experience of the life-saving applications of radiation. After the war, she returned to Paris and became her mother’s assistant at the Radium Institute. There, she completed her doctoral thesis on the alpha decay of polonium, an element her parents had discovered, earning her Doctor of Science degree in 1925.
The Synthesis of New Elements
It was at the Radium Institute that Irène Curie began her most famous collaboration. Her mother asked her to train a young physicist named Frédéric Joliot, whom she married in 1926. The pair combined their research efforts, focusing on the study of atomic nuclei. In the early 1930s, they came close to several major discoveries, identifying both the neutron and the positron in their experiments but misinterpreting the results. These near-misses, however, set the stage for their ultimate breakthrough.
The 1934 Experiment
In January 1934, the Joliot-Curies conducted a landmark experiment in which they bombarded a thin sheet of aluminum foil with alpha particles—the nuclei of helium atoms—emitted from a polonium source. They observed that the aluminum emitted positrons, as expected. But crucially, they noticed that the positron emission did not stop when they removed the polonium source. The aluminum itself had become radioactive. They correctly deduced that the bombardment had transmuted stable aluminum atoms into an unstable, radioactive isotope of phosphorus, phosphorus-30. This new, man-made isotope decayed by emitting a positron, transforming into a stable isotope of silicon.
They quickly confirmed this phenomenon with other light elements, creating radioactive nitrogen from boron and radioactive silicon from magnesium. For the first time, radioactive elements had been created artificially in the laboratory. The discovery was monumental. It demonstrated that radioactivity was not just a property of a few heavy elements found in nature, but could be induced in ordinary, stable matter. This achievement earned them the 1935 Nobel Prize in Chemistry “in recognition of their synthesis of new radioactive elements.”
Pioneering Nuclear Medicine
The Joliot-Curies’ discovery had an immediate and profound impact, particularly in medicine. Until 1934, the use of radioactive materials was limited by the scarce and costly supply of naturally occurring radioelements like radium. The ability to create artificial radioisotopes cheaply and in large quantities opened up a new frontier. Researchers could now produce a wide variety of radioactive elements with different properties, tailored for specific uses.
This led to the development of radiopharmaceuticals, drugs containing radioactive isotopes that can be used for both diagnosis and therapy. These “radiotracers” could be introduced into the body to monitor biological processes and identify diseases. For example, radioactive iodine was found to be highly effective in diagnosing and treating thyroid cancer, as the thyroid gland naturally absorbs iodine. Phosphorus-32, the isotope the Joliot-Curies first synthesized, found use in treating certain blood disorders. The ability to attach radioactive isotopes to specific molecules allowed doctors to create “magic bullets” that could target and destroy cancer cells with high precision, minimizing damage to surrounding healthy tissue. This principle remains a cornerstone of modern nuclear medicine and has saved countless lives.
Navigating a World of Fission
The discovery of artificial radioactivity came at a time of escalating political tension in Europe and rapid advances in nuclear physics. Joliot-Curie’s work continued to be at the forefront of the field. Her research on the effects of neutrons on heavy elements, particularly uranium, was an important step that contributed to the discovery of nuclear fission by German physicists Otto Hahn and Fritz Strassmann in 1938.
Understanding the immense energy that could be released by splitting the atom, and fearful of its potential military applications in the hands of fascist regimes, Irène and Frédéric Joliot-Curie made a critical decision in 1939. They ceased publishing their work on chain reactions and sealed their research documentation in a vault at the French Academy of Sciences, where it remained throughout World War II. After the war, her expertise was crucial to her nation’s scientific efforts. She was appointed as one of the commissioners of the newly formed French Atomic Energy Commission (CEA) in 1945, helping to guide France into the atomic age and overseeing the construction of the country’s first atomic pile in 1948.
A Voice for Peace and Progress
Beyond the laboratory, Irène Joliot-Curie was a passionate and lifelong advocate for social and political causes. In 1936, years before French women had the right to vote, she was appointed Undersecretary of State for Scientific Research, becoming one of the first women to serve in the French government. She was an outspoken opponent of fascism and Nazism and a member of the World Peace Council.
Her political convictions, however, came at a cost during the Cold War. Her association with leftist movements and her husband’s membership in the Communist Party led to their removal from the CEA in 1950. Joliot-Curie also faced scrutiny abroad; she was once denied a hotel room in Stockholm due to her political views, and her application to the American Chemical Society was initially blocked over suspicions of communism before a public outcry forced the organization to reverse its decision.
Despite these challenges, she remained committed to science and peace until the end of her life. She continued her research and, in 1946, was named director of the Radium Institute she had helped build. Like her mother, her decades of work with radioactive materials took a heavy toll on her health. Irène Joliot-Curie died of leukemia on March 17, 1956, at the age of 58, a consequence of a lifetime of radiation exposure.