Irene Joliot-Curie

M. P. Shaskolskaya

On March 17 of this year, Irene Joliot-Curie died in Paris—one of the greatest scientists of the twentieth century in the field of radiochemistry and nuclear physics, an outstanding public figure, a member of the World Peace Council, and an honorary laureate of the International Peace Prize (awarded to her posthumously).

Irene Curie was born in Paris on September 12, 1897, a few months before her parents, Pierre and Marie Curie, announced to the French Academy of Sciences their discovery of radium.

The joint work of Pierre and Marie Curie, which led them to the discovery of radium and polonium and to the new science—radioactivity—is widely known. It is impossible to separate the share of Pierre and Marie Curie in their common work. This was a rare case of scientific fellowship, unbroken until the day of Pierre Curie’s tragic death, when he was crushed under the wheels of a dray on April 19, 1906. After her husband’s death, Marie Curie continued her work for another 28 years. Until her death in 1934 she was the unfailing director of the Radium Institute in Paris, whose construction had begun during Pierre Curie’s lifetime. She directed a scientific school that produced a large number of researchers in radioactivity. To this school belonged her daughter Irene Curie and her son-in-law Frédéric Joliot-Curie.

“From childhood I always intended to engage in scientific work with my mother in her laboratory, so it seemed quite natural that I began working in her laboratory,” Irene Curie recalled a year before her death.

Irene was 8 years old when her father died.

Later Marie Curie wrote of this in a brief biography of Pierre Curie: “He was a devoted and tender father to his children, but the daughters were at that time still too young to understand the misfortune that had befallen us. Their grandfather and I, united in our common grief, did everything we could so that their childhood would not be too clouded.”

The mentors of Irène Curie’s childhood and that of her younger sister Ève were her mother and grandfather, Pierre Curie’s father, Dr. Eugène Curie, a physician and participant in the Paris Commune.

The great scientist Marie Curie was also a tender, caring mother. From childhood she developed in Irène an inquisitiveness and a passion for science. Irène’s education began in an unusual way: Marie Curie and her closest friends themselves organized a school for their children, Irène’s peers. Ten children studied physics at the Paris School of Physics with Marie Curie, chemistry in the Sorbonne laboratory under the direction of Jean Perrin, listened to mathematics with Paul Langevin, and also studied literature, history, natural science, modeling, drawing, sewing, and gardening. Naturally, such teachers were able from childhood to develop Irène Curie’s rich abilities. After several years of study in this “school,” Irène Curie entered a college in order to prepare for the examination for the bachelor’s degree.

Marie Curie also took care of her daughters’ athletic upbringing. Irène Curie was throughout her life an excellent swimmer, an indefatigable mountain walker, and a fine skier (skiing—a rare sport for France). Her friends also warmly recall how Irène and Frédéric Joliot-Curie danced together with the fishermen of Brittany or sang folk songs with them. The breadth of Irène Curie’s interests is shown, for example, by the fact that her translations of Kipling’s poems were published in the newspaper Lettre Française.

In the summer of 1914 the new building of Marie Curie’s laboratory, which had been under construction for several years, was completed. But then the First World War broke out, and Marie Curie was left without collaborators, with a single laboratory assistant. To carry out the move, Marie enlisted the help of Irène, who at that time was finishing her preparation for the examination for the bachelor’s degree. The girl carried instruments and reassembled them, helped sort out the library and the specimens of radioactive minerals. Thus began her work at the Radium Institute.

During the years of the First World War Marie Curie devoted all her talent to the cause of aiding the wounded. She constructed the first mobile X-ray unit, herself traveled with it to hospitals and dressing stations at the fronts, and served the wounded with medical aid, being at the same time driver, X-ray technician, and instructor. Having barely reached the age of 17, Irène accompanied her mother on these trips, and then began independently to set up X-ray equipment in field hospitals and to teach doctors how to use it. Later, when Marie Curie organized a school for X-ray technicians in her laboratory, Irène conducted practical classes in it. After the end of the war Irène became an assistant preparator at the Radium Institute in Paris, in Marie Curie’s laboratory. In 1925 she brilliantly defended her doctoral dissertation.

In 1926 Irène Curie married Frédéric Joliot, a laboratory assistant at the Radium Institute. From that time onward, their life together,

scientific and public work of Frédéric and Irène Joliot-Curie (who decided to unite their surnames) is linked just as inseparably and indivisibly as Pierre and Marie Curie were linked with one another. Irène Curie has two already grown children—a daughter, Hélène, and a son, Pierre.

During her lifetime Irène Joliot-Curie published 54 scientific works; most of them were carried out and published by her together with Frédéric Joliot-Curie.

Among Irène Curie’s early works, especially well known is her investigation of the velocities of the α-rays of polonium, carried out by her in 1925 by an elegant method of simultaneous observation of a very large number of paths of α-particles in a Wilson chamber. She also compiled extensive statistics on deviations from the mean range and gave them a theoretical interpretation. This method was later used repeatedly for detecting rays with a long range.

Beginning in 1928, Irène Curie, together with Frédéric Joliot, began a systematic study of the nuclear reactions occurring when the nuclei of light elements are irradiated by the α-rays of polonium. These works led them to remarkable scientific discoveries.

In 1930 Bothe and Becker observed, when some light elements were bombarded with α-rays, the appearance of very hard gamma radiation. The Joliot-Curies carried out an analogous experiment, using a powerful source of polonium α-particles for that time, namely a polonium preparation of 150 millicuries made by them themselves, and employing an ionization chamber to register the radiation. They found that, in addition to gamma rays, there were present here certain special rays combining the ability to penetrate through great thicknesses of matter with the property of knocking out light nuclei. These experiments were the experimental prerequisite for the discovery of new particles—neutrons, whose existence had been predicted by Rutherford as early as 1923. The discovery of neutrons gave science a powerful means for nuclear transformations.

Rutherford’s first works in 1919 showed the possibility of transforming the atomic nucleus of nitrogen into the nucleus of oxygen by bombarding it with α-particles. Subsequently it was shown that bombardment with α-particles makes it possible to bring about nuclear reactions in most light nuclei. At the same time, for heavy nuclei it did not lead to positive results because, as the atomic number increases, the repulsive forces between the nucleus and α-particles grow. It is not surprising that the decade that passed after Rutherford’s work brought no new discoveries in the field of the transformation of elements. This was a period of improving experimental technique and deepening knowledge of the structure of the atom and the atomic nucleus. For the splitting of the atomic nucleus, nuclear physics needed projectiles more powerful than α-particles. These projectiles were precisely the newly discovered particles—neutrons. Only thanks to the discovery of neutrons

and other “projectiles”—neutrons, deuterons, protons—can induce artificial radioactivity. We were surprised that, despite the simplicity of the experiments, no one had obtained these results since the time of the Solvay Congress. There is no doubt that it was precisely the physicists’ distrust of our first results, which we reported, that allowed us to work without competition during the following three months. In fact, it is clear that the cyclotron at Berkeley was already producing many artificial radioelements both in its target and around it. It is possible that the workers themselves were already slightly radioactive.”

For the discovery of artificial radioactivity, Frédéric and Irène Joliot-Curie were awarded the Nobel Prize in Chemistry in 1935. In the speech delivered on receiving the Nobel Prize, Irène Curie said**):

“The discovery of radioactive elements had enormous consequences for the study of the structure of matter. However, radioactivity remained a property that was associated with roughly thirty substances occurring in nature. The artificial preparation of radioactive elements in the science of radioactivity opens a new field and thus represents a continuation of the work of Pierre and Marie Curie.”

The discovery of artificial radioactivity was the pinnacle of the scientific creativity of Irène and Frédéric Joliot-Curie. It is interesting to note that the Joliot-Curies themselves pointed to the possibility of its practical application in 1935, in their speech on the occasion of the award to them of the Nobel Prize for the discovery of artificial radioactivity: “If we turn back to the past and cast a glance at the ever-accelerating advance of continuous scientific progress, we shall be justified in concluding that researchers who have learned to split and create elements at their discretion will subsequently be able to carry out transformations of matter of an explosive type, analogous to chain chemical reactions. If it proves possible to carry out such transformations, one may suppose that an enormous quantity of energy will be released, which can be used.”

Soon after the Joliot-Curies’ discovery it was shown that artificial radioactivity can indeed be induced not only by alpha particles but also by other nuclear “projectiles”—protons, deuterons, neutrons. However, the irradiation of uranium by neutrons confronted investigators with a new riddle. Although uranium irradiated with slow neutrons emitted beta particles, no transuranic heavy elements could be detected by even the most careful radiochemical methods,

* Atomes, 1951, No. 7, p. 11.
* Angew. Chem., 1936, 49, 367; Uspekhi khimii*, 1936, 5, 1366.

which should have arisen according to the schemes of Hahn, Meitner, and Strassmann. The puzzle was solved in 1939 by the work of Irène Joliot-Curie and P. Savitch, who showed that one of the products arising when uranium is irradiated with neutrons is not a transuranium element, as had been expected, but an element from the middle part of the periodic system—lanthanum (No. 57). Thus yet another new phenomenon was discovered—uranium fission. It is common knowledge what role this discovery played in solving the problem of mastering nuclear energy.

Irène Joliot-Curie’s brilliant scientific work was invariably combined with extensive organizational, pedagogical, and public activity. After the death of her mother in 1934, Irène became her successor as director of the Radium Institute, and subsequently also in the chair at the Sorbonne. In 1936, during the Popular Front in France, Irène Joliot-Curie was appointed assistant to the Minister of National Education in France, and she was entrusted with the direction of the country’s scientific-research work. During her work in this post she carried out a number of reforms, in particular with respect to the rights of female students. In those same years Irène Joliot-Curie took an active part in the campaign in defense of the Spanish republicans interned in France and in the organization of aid to anti-fascist refugees.

The war of 1939–1945 interrupted Irène Joliot-Curie’s scientific work. During the years of the Hitlerite occupation she actively participated in the Resistance Movement.

In 1946, after the liberation of France, Irène, together with Frédéric Joliot-Curie, organized the Atomic Energy Committee and for several years was a member of its leadership. Together they tirelessly fought for the use of atomic energy only for peaceful purposes.

It is known that in 1950 Frédéric Joliot-Curie was removed from the post of High Commissioner for Atomic Energy. Less than a year later, on January 11, 1951, Irène Joliot-Curie was likewise removed from work in this committee.

In an article on the occasion of Irène Joliot-Curie’s death, Eugénie Cotton recalls*) that Irène Joliot-Curie’s favorite saying was: “If some cause is just—it must be carried out.” And she carried it out, sparing no strength, overcoming the grave illness caused by the effect of the radioactive radiation to which she had been exposed all her life.

Irène Joliot-Curie was an indefatigable fighter for peace. She was a member of the International Committee for the preparation of the First World Congress of Partisans of Peace and presided at its sessions. She was a member of the World Peace Council, a member

*) L’Humanité, 25.III.1956.

of the presidiums of the First and Second Congresses of the Partisans of Peace, and a member of the French National Council of the Partisans of Peace. “Our people found her in their ranks in all battles for democracy, for progress, for peace,” said the communiqué of the Central Committee of the Communist Party of France on the death of Irène Joliot-Curie*).

Irène Joliot-Curie visited the Soviet Union more than once. The report by Irène and Frédéric Joliot-Curie, “The Structure of Matter and Artificial Radioactivity,” was the subject of the first Mendeleev Reading, held on September 29, 1936. In 1947 Irène Joliot-Curie was elected a corresponding member of the Academy of Sciences of the USSR. She was also a member of the Academies of Sciences of India, Belgium, and Poland, and an honorary doctor of many universities. Only the Academy of Sciences of France did not dare to open its doors to the glorious daughter of the French people, just as it had twice refused to admit Marie Curie.

A professor at the Sorbonne and director of the Radium Institute, an active fighter for peace, Irène Curie did not interrupt her scientific work for a single day. She still made all the measurements herself and prepared the specimens herself.

In the last years of her life, despite a grave illness, Irène Joliot-Curie undertook tremendous work to realize the project of creating a large institute of nuclear physics, to which she hoped to transfer a significant number of projects from the Curie Laboratory. She worked on the creation of this institute until the last days of her life.

The radiant image of Irène Joliot-Curie is dear to the Soviet people as an example of the greatness of scientific creativity and of full awareness of the entire depth of scientists’ responsibility for the fate of science and the future of humanity.

) L’Humanité*, 19.III.1956.