In her mother’s shadow: Irène Joliot-Curie

Today, March 8th 2021, is International Women’s day. So I am re-posting a blog I wrote this time last year.

This post is a bit of a departure from previous posts on this blog. It’s the first of a series of posts in which I will be exploring the lives, and contributions to science, of a variety of different people. In particular, I will be writing about scientists who are perhaps not as well recognised as they should be; who are controversial; whose demise occurred before they could realise their potential; or who were just downright quirky. As today is International Women’s Day, I will talk about a woman whose contribution to science was immense, but has been eclipsed by that of her mother.

Think of radioactivity and one name will almost certainly spring to mind: that of Marie Skłodowska Curie. Marie Curie is famous as the discoverer of radium and polonium. She was not only the first woman to win a Nobel Prize, she remains the only person of either gender to have won two for different disciplines: physics and chemistry. This post will explore the life of another female scientist who is less well known, but just as deserving of recognition: Marie’s older daughter, Irène Joliot-Curie. Not only did Irène make some very significant scientific discoveries, she was politically active, being both a pacifist and feminist.

Marie Curie with Irène and Ève in 1905

Irène was born in Paris in 1897 and her earliest years were not always easy. Her parents Marie and Pierre were absorbed in their work, putting in long hours on the research that would win them the 1903 Nobel Prize for Physics alongside Henri Becquerel. In these early years, Irène, and later her sister Ève, were largely raised by their paternal grandfather, retired doctor Eugene Curie. He taught Irène to love nature and the arts, particularly poetry, and also got her interested in radical politics. Marie herself acknowledged the difficulty of balancing work and family, writing that,

“I have frequently been questioned, especially by women, of how I could reconcile family life with a scientific career. Well, it has not been easy.”

By the time Irène was born, the health of her father, Pierre Curie, was declining rapidly, almost certainly due to his exposure to large doses of radiation. He was killed in 1906 when he was hit by a horse-drawn vehicle in a Paris street. This has been attributed to his having been distracted by thinking about his work, but it is highly probable that radiation exposure contributed. Cognitive impairment and fatigue are common in conditions associated with high radiation exposure, such as leukaemia and aplastic anaemia.

Marie was devastated by Pierre’s death, and struggled more than ever to balance her scientific work with the demands of bringing up two young children (Ève was only 16 months old when Pierre died). However, after Pierre’s death, Marie made the decision to spend more time with her children. She withdrew Irène from public school to educate her in a ‘co-operative’ organised by a group of 6 professors, including Marie, who taught each other’s children in their areas of expertise. In this way, Marie was able to nurture Irène’s love of, and obvious talent for, mathematics and science, and the two grew increasingly close. Marie was a demanding teacher though; even on holiday, Irène was expected to study for a certain amount of time each day.

The education that Irène received at the co-operative was not restricted to mathematics and science. On the contrary, it was wide ranging and included arts and languages; there was also considerable emphasis on self-expression and play. It is tempting to believe that Irène was forced into a life of science by her mother, but this was not the case, as is shown by her sister Ève. Ève did not have a scientific bent but preferred the humanities, and Marie supported her wholeheartedly. Ève would go on to have a distinguished career as a journalist and political activist, eventually living to the age of 102. Ève was just as close to her mother as Irène, and both sisters together nursed Marie through her final illness.

For the final two years of high school, Irène returned to a more conventional education, studying at the College Sevigne in Paris. In 1914, she took up a place at the Sorbonne to study mathematics and physics. However, like many young people at the time, her education was to be interrupted by the outbreak of World War 1 in August 1914.

Irène and Marie Curie in an X-ray unit at a hospital in Belgium, 1915

From the very outset of the war, Marie Curie recognised a need for radiography services to be provided as close to the Front as possible, to aid surgeons in operating quickly on wounded soldiers. Her first mobile radiography unit was operational in 1914, and she was appointed director of radiology services for the Red Cross. Irène assisted her mother when she could, taking a nursing course alongside her other studies. In 1916, Irène left the Sorbonne in order to work alongside Marie as a full time nurse-radiographer.

Within a few months, 19-year-old Irène was in sole charge of a battlefield radiography centre in Belgium. She taught herself how to maintain and repair the equipment, and she taught doctors how to locate bullets and shrapnel using X-rays. Irène worked in a number of locations, including Ypres and Amiens. Marie and Irène’s work in developing the use of medical X-rays saved the lives of many soldiers, and also helped to significantly advance the uses of medical radiography.

Irène descending from a mobile X-ray car. These were known to French troops as ‘Petits Curies’

Following the end of the war, Irène returned to the Sorbonne and completed her degree in maths and physics, before moving to the Radium Institute to work once again as her mother’s assistant. In 1925 she completed her doctoral thesis on the radioactive properties of the element polonium.

Irène was an expert in the highly specialised and precise techniques required to study radiation. So much so that in 1924 she was asked by Marie to train a newly appointed researcher at the Institute: chemical engineer Frederic Joliot. Irène and Frederic were married in 1926 and took the surname Joliot-Curie. Irène and Frederic combined their research efforts, just as Marie and Pierre Curie had before them, specialising in the study of atomic structure. Their early work identified the existence of both the neutron and the positron; however, they did not recognise the significance of their results, so the discoveries of both are credited to other scientists.

Irène at the Radium Institute in 1922

Irène and Frederic struggled to get some of their early work accepted by the scientific community. They carried out experiments involving bombarding aluminium with alpha radiation, and their results showed that a proton can change into a neutron by emitting a positron (similar to an electron, but with a positive instead of a negative electrical charge). However, when they tried to present their findings to the wider scientific community, they came in for extensive criticism.

Irène and Frederic at work

It was this early work that led to the discovery that would gain them recognition, and a Nobel Prize. Continuing their experiments with aluminium and alpha particles, they found that if a non-radioactive element is irradiated alpha particles, it is possible to turn it into a different, radioactive one.

How does this work? An alpha particle consists of two protons and two neutrons – it’s basically a helium nucleus without the electrons. If an alpha particle collides with an atomic nucleus with the right amount of energy, it will combine with the nucleus. Aluminium has 13 protons and 14 neutrons. When an alpha particle collides with an aluminium nucleus, two protons and one neutron combine with the nucleus, giving 15 protons and 15 neutrons. If you change the number of protons in a nucleus, you get a different element – in this case, phosphorous. Irène and Frederic had finally achieved what the medieval alchemists never could: changing one element into another.

More importantly, the phosphorous they made by this method was radioactive. The reason for this is that phosphorous normally has 16 neutrons, and the phosphorous made by Irène and Frederic only had 15. Atoms with the same number of protons but different numbers of neutrons are called isotopes, and the only stable isotope of phosphorous has 16 neutrons. The isotope made by Irène and Frederic quickly decayed into a more stable form, changing into the element silicon and emitting radiation in the form of beta particles. Using the same method, Irène and Frederic were able to create several other artificial radioactive isotopes.

The importance of the discovery of artificial radioactivity cannot be over-emphasised. The use of radioactive isotopes in medicine was growing rapidly, and Irène and Frederic’s discovery meant that radioactive materials could be created cheaply and in large quantities. Many of the radioactive isotopes used in modern medicine are manufactured using their method, although usually a beam of neutrons is used rather than alpha particles. For example, cobalt-60, which is used in radiotherapy to treat cancer, is made by bombarding stable cobalt-59 with neutrons.

Irène and Frederic in 1935, shortly before being awarded the Nobel Prize for Chemistry

In 1935, Irène and Frederic were awarded the Nobel Prize for Chemistry, and finally gained the recognition of the scientific community. Irène was also given a professorship in the faculty of science at the Sorbonne. Over the next few years, she and Frederic led research into the element radium which led in 1938 to the discovery of nuclear fission by a group of German scientists.

Throughout the 1930s, Irène and Frederic were aware of, and concerned by, the growth of fascism; during the Spanish Civil War they were strong supporters of the Republican faction. In the late 1930s they stopped publishing their work due to concerns about its possible military uses. In October 1938, they placed all documents relating to their work in a secure vault at the French Academy of Sciences, where it remained until 1948.

In 1941, Irène contracted tuberculosis and was forced to leave France and go to a sanatorium in Switzerland. Her husband and children remained in France, where Frederic became an active member of the resistance. Despite the danger, Irène made several trips back to France to visit her family, and on several occasions was detained by German guards at the Swiss border. In 1943 Irène returned to France, but it was becoming more and more dangerous. In early 1944, Irène returned to Switzerland, this time taking their two children, Helene and Pierre. They remained there for several months, not knowing whether Frederic, who had stayed behind to continue his work with the resistance, was alive or dead. Eventually, the family were reunited in September 1944 when the liberation of Paris made it safe for Irène and the children to return.

After the war, Irène followed in her mother’s footsteps by being appointed director of the Radium Institute. Irène and Frederic both turned their attention to the use of nuclear fission to generate electricity, becoming respectively the commissioner and director of the newly formed French Atomic Agency Commission. Under their direction, the first French nuclear reactor was created in 1948, and was able to generate five kilowatts of power. A long-lasting legacy of the Joliot-Curies is France’s extensive use of nuclear power, which generates approximately 80% of the country’s electricity.

Irène at the controls of the first French nuclear reactor

Irène was a passionate and active member of the feminist movement, who campaigned throughout her life for women in science to get the recognition they deserve. The French Academy of Sciences would not admit women, and she confronted this chauvinism head-on, writing letter after letter of application. She knew that she would be turned down, but felt it her duty to draw attention to their refusal to admit her because she was a woman. Irène used her position and influence to promote education for women, and she served on the National Committee of the Union of French Women. In 1936, she was appointed to a powerful political position as Undersecretary of State for Scientific Research by the French government – ironic, considering that at the time, women could not vote.

Irène with close family friend and fellow pacifist Albert Einstein on the steps of his home in Princeton, NJ, 1948

Irène was also a devoted pacifist. She knew that the discoveries she and Frederic had made could be put to military use, hence their decision to hide their research at the start of WW2. Her bout of TB in 1941 may have been a blessing in disguise; neither side could try to recruit her for their nuclear weapons programs because she was simply too ill. By contrast, her mother’s close friend Albert Einstein was coerced into signing a letter endorsing the Manhattan Project, which he would regret for the rest of his life. In 1948, Irène was an active member of the French delegation to the World Congress of Intellectuals for Peace, and she continued to campaign for peace throughout her life.

Irène would follow in her mother’s footsteps in one last, tragic way. In the early 1950s her health began to decline and she was diagnosed with leukemia. It is highly likely that this was a result of years of exposure to radiation, just as Marie’s death from aplastic anemia had been. Much of Irène’s work had been with one of the most dangerous radioactive isotopes to human health: polonium-210. Polonium-210 is approximately 250,000 times more toxic than hydrogen cyanide, and was famously used in 2006 to kill Russian dissident Alexander Litvinenko. In 1948, Irène was exposed to polonium-210 when a container of it exploded on her laboratory bench; there is speculation that this caused her eventual death.

Irène underwent surgery and treatment with antibiotics to alleviate her condition, and continued to work as much as she could; in 1955, just months before her death, she was working on plans for new physics labs at the University d’Orsay. Her condition continued to deteriorate and on March 17, 1956, she died in hospital in Paris. Frederic did not outlive her by much; he died in 1958 from liver disease, also linked to radiation exposure. After her death, Irène’s family made sure that her principals of atheism and pacifism were upheld. When the French government asked to hold a national funeral in her honour, they insisted that the religious and military portions be omitted. Perhaps a bigger tribute to them both is that they made the use of radioactive isotopes in medical imaging and radiotherapy both practical and affordable. Who knows how many lives their discoveries have saved?

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