As she neared the end of her doctorate in 1924, Irène Curie was asked to teach the precision laboratory techniques required for radiochemical research to the young chemical engineer Frédéric Joliot, whom she would later wed. From 1928 Joliot-Curie and her husband Frédéric combined their research efforts on the study of atomic nuclei. In 1932, Joliot-Curie and her husband Frédéric had full access to Maries polonium. Experiments were done using gamma rays to identify the positron. Though their experiments identified both the positron and the neutron, they failed to interpret the significance of the results and the discoveries were later claimed by Carl David Anderson and James Chadwick respectively. These discoveries would have secured greatness indeed, as together with J. J. Thomsons discovery of the electron in 1897, they finally replaced John Dalton's model of atoms as solid spherical particles.
However, in 1933, Joliot-Curie and her husband were the first to calculate the accurate mass of the neutron. The Joliot-Curies continued trying to get their name into the scientific community; in doing so they developed a new theory from an interesting experiment they conducted. During an experiment bombarding aluminium with alpha rays, they discovered that only protons were detected. Based on the undetectable electron and positron pair, they proposed that the protons changed into neutrons and positrons. Later in October 1933, this new theory was presented to the Seventh Solvay Conference. The Solvay Conferences consisted of prominent scientists in the physics and chemistry community. Irene and her husband presented their theory and results to their fellow scientists, but they received criticism of their finding from most of the 46 scientists attending. However they were able to build on the controversial theory later on.
In 1934, the Joliot-Curies finally made the discovery that sealed their place in scientific history. Building on the work of Marie and Pierre Curie, who had isolated naturally occurring radioactive elements, the Joliot-Curies realised the alchemist's dream of turning one element into another: creating radioactive nitrogen from boron, radioactive isotopes of phosphorus from aluminium, and silicon from magnesium. Irradiating the natural stable isotope of aluminium with alpha particles (i.e. helium nuclei) resulted in an unstable isotope of phosphorus: Al + He → P + n. This phosporus isotope is not found in nature and dacays emiting a positron. This discovery is formally known as positron emission or beta decay, where a proton in the radioactive nucleus changes to a neutron and releases a positron and an electron neutrino. By then, the application of radioactive materials for use in medicine was growing and this discovery allowed radioactive materials to be created quickly, cheaply, and plentifully. The Nobel Prize for chemistry in 1935 brought with it fame and recognition from the scientific community and Joliot-Curie was awarded a professorship at the Faculty of Science.
The work that Irènes laboratory pioneered in research into radium nuclei that led a separate group of German physicists, led by Otto Hahn, Lise Meitner, and Fritz Strassman, to discover nuclear fission: the splitting of the nucleus itself, emitting vast amounts of energy. Lise Meitners now-famous calculations actually disproved Irène's results to show that nuclear fission was possible.
In 1948, using work on nuclear fission, the Joliot-Curies along with other scientists created the first French nuclear reactor. The Joliot-Curies were a part of the organization in charge of the project, the Atomic Energy Commission, Commissariat à lénergie atomique (CEA). Irène was the commissioner of the CEA and Irènes husband, Frédéric, was the director of the CEA. The reactor, Zoé (Zéro énergie Oxyde et Eau lourde) used nuclear fission to generate five kilowatts of power. This was the beginning of nuclear energy as a source of power for France.
Years of working so closely with radioactive materials finally caught up with Joliot-Curie and she was diagnosed with leukemia. She had been accidentally exposed to polonium when a sealed capsule of the element exploded on her laboratory bench in 1946. Treatment with antibiotics and a series of operations relieved her suffering temporarily but her condition continued to deteriorate. Despite this, Joliot-Curie continued to work and in 1955 drew up plans for new physics laboratories at the Orsay Faculty of Sciences, which is now a part of the Paris-Saclay University, south of Paris.