By Harriet Teare
Irene Joliot-Curie’s success as a scientist, principally involved in continuing the investigation into artificial radiation, rivalled even that of her mother, Marie. This article intends to briefly explore some of the outstanding science that led this woman, as part of a collaboration of husband and wife, to some of the extraordinary findings that ultimately resulted in her being the second female in history to receive a Nobel Prize in Chemistry.
As the first child of Pierre and Marie Curie, born in 1897, just months before their publication of the papers announcing the discovery of polonium and radium, Irene grew up with radioactivity, and her working life was devoted to its study. Her training in the physical and chemical aspects of radiochemistry really began during the First World War, when she served first as a radiographer, and later as ‘preparateur’ to her mother at the Laboratoire Curie of the Institut du Radium in Paris. It was in this lab that she met her husband, Frederic Joliot, and there began a collaboration of outstanding productive genius.
Their research was principally involved in the investigation of radioactive elements; elements which undergo the spontaneous emission of particles and/or energy from the atomic nucleus. Each emission is accompanied by a change in the structure of the parent atom with the energy associated with this transmutation coming from within the atom itself. The atom which results from this transmutation will similarly undergo spontaneous emission leading to a ‘decay series’. Each atom generated in this series of radio-elements has well-defined chemical properties, much like their stable counterparts.
The discovery of radio-elements called into question a number of previous assumptions about the structure of the atom. It was Democritus (460 BC – ca. 370 BC) who first suggested that all matter is made up of various imperishable, indivisible elements which he called atoma; a notion supported some two millennia later by the eminent scientist John Dalton. J. J. Thompson further expanded this theory following his discovery of the electron by suggesting that rather than thinking of the atom as being solid and indestructible, it is more accurate to imagine that it is composed of electrons, like negatively-charged ‘plums’ surrounded by positively-charged ‘pudding’ (‘plum pudding theory’).
This hypothesis sparked a great deal of experimental interest, capturing the imagination of scientists at numerous great research institutes across the globe. It was not long before more light was shed upon the composition of the atom, firstly with the discovery of the dense, positive core or ‘nucleus” by Ernst Rutherford, Hans Geiger and Earnest Marsden, and secondly by the detection of isotopes (atoms of an element with the same number of protons but a different number of neutrons) by Frederick Soddy. The birth of quantum mechanics courtesy of great scientists such as Max Planck, Albert Einstein and Neils Bohr fuelled a race to understand atomic behaviour.
One of the most illuminating pieces in this nuclear puzzle was the discovery of the neutron, an achievement which relied heavily on experiments carried out by Irene and Frederic. Their investigation into the radiation emitted when beryllium was bombarded with two protons and two neutrons bound together in a particle identical to a helium nucleus led James Chadwick to his recognition of a ‘neutral component with a mass approximately equal to that of a proton’, a discovery which in turn led Chadwick to a Nobel Prize in 1932.
The Joliot-Curies followed Chadwick’s discovery with a series of studies into the behaviour of different elements under the impact of these particles. They showed that it was in fact possible to ‘create’ radioactivity by bombardment of atoms with rays. This was first shown by experiments on boron and magnesium atoms where the bombardment process was found to produce isotopes of the atom which are not naturally occurring and which undergo spontaneous decay pathways by emission of positive electrons or ‘positrons’. These artificial radio-elements behave in all respects like the natural radio-elements. With the discovery of artificial radioactivity, Irene and Frederic Joliot-Curie had realised every alchemists’ dream – they’d found a method to turn one element into another. It was for this synthesis of artificial radio-elements that Irene and her husband won the Nobel Prize in 1935, aptly following the Prize awarded to Pierre and Marie Curie in 1903, and to Marie alone in 1911, for the discovery of radio-elements.
It was not only in the laboratory that Irene Juliot-Curie made her contribution to science. In 1936 she was appointed Undersecretary of State for Scientific Research, despite the fact that women did not have the right to vote in France; she was one of the first three women to participate in government. It was within this role that she helped to lay the foundations, with Jean Perrin, for what would later become the Centre National de la Recherche Scientifique (National Centre for Scientific Research).
Despite this office and her numerous other duties, Irene Juliot-Curie’s scientific work continued without abatement. She carried out a great deal of research on the artificial radio-elements produced by the irradiation of uranium by slow neutrons, work that provided an invaluable contribution to the eventual discovery of uranium fission by Lise Meitner and Otto Hahn.
The years of exposure to radiation while working with strongly radioactive materials eventually caught up with Irene and she was diagnosed with leukaemia, however neither failing health, nor administrative duties could keep her from her laboratory, with numerous publications on various aspects of radioactivity and the planning of new physics laboratories at the Universitie D’Orsay, South of Paris, continuing until her death on 17th March 1956.
Irene Joliot-Curie’s contribution to physics is unquestionable; her success has been recognised by a number of distinguished awards and also by the prominent positions, both academic and administrative, that she held at a time when women were still fighting for a vote. Indeed she is still contributing to modern science through an eponymous prize, with three of the four prize categories being aimed specifically at female scientists.
Farber. E, Prize Winners in Chemistry (London, 1953)
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Chadwick. J. ‘Mme Irene Joliot-Curie’. Nature 177, 964 – 965 (1956)