On Irène Joliot-Curie’s 119th birthday, a second generation to the dynasty of great scientists, who won the Nobel Prize with her husband for discovering induced radioactivity
Finally, the big moment had arrived. In the fall of 1933, Irène Joliot-Curie and her husband Frédéric were invited to present their innovative study in a conference with forty of the brightest minds in nuclear physics. This was an important moment for the 36-year-old Irène and 33-year-old Frédéric: the opportunity to step out of the shadow of Irène’s parents, Nobel Prize laureates, Marie and Pierre Curie.
The couple presented a novel approach to the structure of the atom – an emerging field at the time. Nowadays, we know that atoms have a nucleus, with positively charged protons and electrically neutral neutrons, surrounded by negatively charged electrons. But in the early 1930s, physicists knew only about protons and electrons. Challenging the generally accepted notion of the time, Irène and Frédéric Joliot-Curie claimed there is another significant particle in the atom: the neutron.
The two were not prepared for the harsh criticism they had to face. The audience began whispering and the well-known German scientist Lise Meitner raised her hand and told the audience that in the experiments that she and other scientists had performed, not a single neutron was identified. The murmurs soon turned into shouts and turmoil ensued, forcing the chair to send everyone to take a break in order to calm down.
In hindsight, the criticism was justified, at least partially. The couple were, in fact, the first to discover the neutron – and actually, also the positron, and the findings they presented at that conference were correct. Nevertheless, their interpretation of the results was wrong, costing them the fame that came along with those discoveries, and leading the discoveries of these subatomic particles to be attributed to James Chadwick and Karl David Anderson, respectively.
Following the conference, the couple returned to the lab, determined to prove themselves. Three months later, working in the wee hours of the night – Irène in the chemistry lab on the top floor and Frédéric in the physics lab on the bottom floor, they made their biggest discovery: induced radioactivity.
In an attempt to prove the existence of the neutron, the couple bombarded aluminum atoms with alpha particles, now known to consist of two protons and two neutrons. During this process, a proton and a positron were emitted, but, since this occurs in two steps, they did not realize it. The end result is that the aluminum atom becomes a silicon atom, which has a slightly larger mass, but during the intermediate stage, lasting a number of minutes, the aluminum itself briefly turns into radioactive phosphorus.
This stage was identified by Frédéric, who was in charge of the physics aspect of the experiments. He jumped around in happiness and called his wife from upstairs. They began a quick marathon of experiments to prove the phenomenon, and within three days, they sent a paper out to the French Academy, which explains how an induced radioactive atom was created for the first time. This publication paved the way for producing radioactive materials for a variety of purposes, without the need to search for natural ones. This discovery earned the couple the 1935 Nobel Prize in Chemistry. In that same year, the Nobel Prize in Physics was awarded to James Chadwick, for discovering the neutron.
Promising future from a young age
Irène Curie was born to scientists Marie and Pierre Curie on September 12th 1897. From a very young age, her parents noticed her mathematical skills and invested time and effort in educating her. Together with a group of parents, all world-renowned experts in their fields, they established a cooperative for teaching their children subjects like physics, chemistry, mathematics, music and art. When she grew up, she continued her studies in the research institute founded by her parents. During her PhD studies, in which she also taught younger students, she fell in love with one of them – a young engineer named Frédéric Joliot. When the two married, they decided to change both their names to the compound last name Joliot-Curie, which was quite uncommon at the time.
Towards the end of WWII, science had transformed the world. The nuclear bombs that were dropped on Hiroshima and Nagasaki revealed the immense force encapsulated in the atomic nucleus, and the devastating repercussions of abusing it. Nevertheless, this also showed the promise of nuclear fission as a peaceful, nearly endless energy source. Nuclear fission would not be possible if it were not for the discovery of induced radioactivity, and the breakthroughs that followed.
Along with her scientific work, Irène Joliot-Curie was a socialist activist and worked to advance education for women. She perceived science as a tool for bettering society for the generations to come. Just like the elder Curies, Irène and Frédéric published all of their scientific work for the benefit of the scientific community and society. Nevertheless, fearing their research would be exploited for nuclear weapon development, in October 1939 they deposited the documentation of their research in the vaults of the French Academy of Sciences, where it remained until 1949. But by the time the vaults were locked, the ball of the atom bomb was already rolling, and their move did not prevent its eventual development.
Joliot-Curie was proud of her accomplishment of creating the first induced radioactive element. Later on, she said she was grateful for being able to share this exciting experience with her mother, who was already in her last days. At that moment, the work and scientific achievements of both generations merged. Like her mother, Irène Joliot-Curie’s health was affected by her work with radioactive materials, and she died from leukemia on March 17th 1956, at the age of 59.
The two children of Irène and Frédéric Joliot-Curie also carried on the glorious scientific family tradition. Pierre Joliot-Curie is a world-renowned professor of biophysics, and his older sister, Hélène Langevin-Joliot is a physics professor. She also closed another family circle – her husband, Michel, was the grandson of Paul Langevin, Marie Curie’s partner after she became widowed at a young age.
Translated by Elee Shimshoni