Irene Joliot-Curie's artificial radioactivity discovery revolutionized modern cancer treatment

In 1935, a husband-and-wife team of physicists stood at the threshold of a discovery that would reshape medicine for the next century. Irene Joliot-Curie and her husband Frederic had just created something that nature had never made available to science before: a radioactive element born not from the earth's ancient ores, but from their own hands in the laboratory. For this work, they shared the Nobel Prize in Chemistry. The irony was not lost on anyone who knew her story—Irene's parents, Marie and Pierre Curie, had won their own Nobel for discovering natural radioactivity decades earlier. The daughter had taken her inheritance and transformed it into something entirely new.

Irene was born in Paris in 1897 into a household where physics was not a subject to be studied but a way of life. Her mother, already famous, taught her alongside other children in an unconventional schooling arrangement. When World War I erupted in 1914, the seventeen-year-old abandoned her formal studies to work alongside Marie, learning to operate portable X-ray machines to locate bomb fragments in wounded soldiers. She became so skilled that she began training nurses in the technique. After the war ended, she returned to the Radium Institute, where she met Frederic Joliot. They married and began working together on experiments that would eventually lead them to their breakthrough.

The physics behind their discovery was elegant in its simplicity. Atoms of different elements contain the same number of protons but can vary in their number of neutrons—these variations are called isotopes. Most isotopes are unstable; they spontaneously decay, transforming into other elements and releasing radiation in the process. Before 1934, the only radioactive isotopes known to science came from natural sources, extracted through painstaking work from tons of ore. Marie and Pierre had spent years on this labor. But Irene and Frederic asked a different question: could they create radioactivity artificially?

In their experiment, they bombarded aluminum with alpha particles—the nuclei of helium atoms, consisting of two protons and two neutrons bound together. They had done similar experiments before and noticed that radiation would stop as soon as they removed the alpha particle source. This time, something unexpected happened. The radiation continued even after they turned off the source. It decreased by half every three minutes, and when they analyzed what was happening, they realized they had created phosphorus-30, an element with two more protons than aluminum. The alpha particles had fused with the aluminum nuclei, and the resulting isotope was radioactive. They had induced radioactivity where none had existed before.

The implications rippled outward immediately. Irene did not simply retreat into pure research. In 1936, nearly a decade before French women could vote, she was appointed undersecretary of state for scientific research. She helped establish what would become France's National Centre for Scientific Research. After World War II, she co-created the French Atomic Energy Commission and oversaw the development of France's first nuclear reactor. She held professorships and directorships. She was, in every sense, a public scientist.

But the true revolution was medical. Radioactive iodine became a standard treatment for thyroid disease. Radioisotopes that emit positrons—the antimatter twin of electrons—could be injected into a patient's body, where they would accumulate in specific organs. A PET scanner could then detect the radiation from outside the body, allowing doctors to see how organs were functioning without surgery. For cancer, larger doses of radiation could be targeted directly at tumors to kill the cells. The key was choosing the right isotope for the right job. Iodine alone has more than forty known radioactive forms, each with different properties. Iodine-131, which decays over a few days, proved ideal for thyroid treatment—long enough to do its work, short enough not to harm the patient or their family.

Ninety years after the Joliot-Curies' first artificial radioisotope, science has identified roughly three thousand of them. Theory suggests as many as seven thousand may be possible. At Michigan State University, a new facility called the Facility for Rare Isotope Beams can accelerate stable isotopes to half the speed of light and smash them into targets, creating radioisotopes that would take nature millions of years to produce. Since it opened in 2022, it has already discovered five new ones. Each isotope has its own half-life, its own decay pattern, its own energy signature. This variability is what makes them useful—the right isotope for cancer imaging, another for thyroid treatment, another for studying how stars burn in their cores. The doors that Irene and Frederic opened have not stopped swinging.