Irene 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 has arrived. In the fall of 1933, Irène Joliot-Curie and her husband Frédéric came to present their innovative study in a conference in front of forty of the brightest minds in nuclear physics. It was a significant moment for them: it was the 36-year-old Irène and 33-year-old Frédéric's opportunity to come out of the dark shadow of Irène’s parents, Nobel Prize laureates, Marie and Pierre Curie.

The couple presented a novel approach to the structure of the atom – a field that had just been emerging at the time. Nowadays, we know that atoms have a nucleus, with positive protons and neutral neutrons, surrounded by negative electrons. But, in the early 1930's, physics only knew about protons and electrons. Irène and Frédéric Joliot-Curie challenged the common notion at the time and claimed there was 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 have performed, not one neutron was identified. The whispers soon turned into shouting and turmoil, forcing the chair to send everyone to take a break in order to calm down.

In hindsight, the criticism was justified, at least partially. Irène and Frédéric Joliot-Curie were, in fact, the first to discover the neutron – and actually, also the positron, and the findings they presented at that conference were true. Nevertheless, their interpretation of the results was wrong, causing them to lose the fame that came along with those discoveries. This led the discoveries of these subatomic particles to become attributed to James Chadwick and Karl David Anderson, respectively.  

Following the conference, they returned to the lab, determined to prove themselves. Three months later, when they were in the lab at the wee hours of the night – Irène at the chemistry lab on the top floor and Frédéric at the physics lab on the bottom floor, they finally found their biggest discovery: induced radioactivity. 

In order to attempt to prove the existence of the neutron the couple bombarded aluminum atoms with alpha particles, which we now know consist of two protons and two neutrons. During this process a proton and a positron were emitted, but they did not realize it since this occurs in two steps. 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 physical aspect of the experiments. He jumped around in happiness and called his wife from upstairs. They began a quick marathon of experiments for proving 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 has won 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 scientist couple, Marie and Pierre on September 12th 1897. Already at a very young age, her parents noticed her mathematical skills and invested time and effort in educating her. Together with a group of parents, who were all world-renowned experts in their field, 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. The two married and decided to change both their names to the joint last name Joliot-Curie, which was quite uncommon at the time.

Towards the end of WWII, science has transformed the world. The nuclear bombs that were dropped on Hiroshima and Nagasaki revealed the great force encapsulated in the atomic nucleus, and the devastating repercussions of abusing it. Nevertheless, this also revealed the promise nuclear fission holds 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, promoting education for women. She perceived science as a tool for advancing society for the better, for the generations to come. Just like her parents, the Joliot-Curie couple published all of their scientific work for the benefit of the scientific community and society. Nevertheless, in fear of exploitation of their research for nuclear weapons, in October 1939 they deposited the documentation of their research in the vaults of the French Academy of Sciences, where it remained until 1949. However, by the time they did this, it was already too late, and the atom bomb was eventually developed.

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

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