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Curie, Marie,

radioactivity physics discovered radium

née Manya Sklodowska (1867–1934) Polish–French physicist: discovered the radio-elements polonium and radium.

Manya Sklodowska grew up in Russian-dominated Poland; her family were intensely patriotic and took part in activities furthering the Polish language and culture. Manya’s father was a teacher of mathematics and physics and her mother the principal of a school for girls. She developed an interest in science, but her parents were poor and there was no provision for higher scientific education for women in Poland. She and her sister Bronya, however, were determined to gain their education. Manya took a post as a governess and helped Bronya go to Paris to study medicine, after which she in turn was to help Manya.

In 1891 Manya went to Paris to study physics. By nature she was a perfectionist, tenacious and independent. She graduated in physics in 1893 from the Sorbonne, coming first in the order of merit. The following year, with a scholarship from Poland, she studied mathematics and graduated in second place. During this year she met , then 35 and working on piezoelectricity at the School of Industrial Physics and Chemistry, and her plans to return to teach in Poland changed; they married in July 1895.

In 1896 had discovered radioactivity in a uranium salt. Marie Curie (as she was now known), looking for a research topic for a doctoral thesis, decided to study the ‘new phenomena’ discovered by Becquerel. Working in her husband’s laboratory, she showed that radioactivity is an atomic property of uranium and discovered that thorium emitted rays similar to uranium. In 1897 she gave birth to their daughter Irène (who also became a Nobel Prize winner in physics). When she examined the natural ores Marie discovered that the radioactivity of pitchblende and chalcolite was more intense than their uranium or thorium content implied, and correctly concluded that they must contain new radioactive elements. To find the new elements she began to separate the components of pitchblende to determine where the radioactivity lay, by a laborious process of fractional crystallization. Pierre Curie left his own research to join his wife in the work. No precautions against radioactivity were taken, as the harmful effects were not then known. Her notebooks were subsequently discovered to be highly radioactive and are still too dangerous to handle.

In July 1898 they announced the discovery of the existence of an element they named polonium, in honour of Marie’s native country, and in December the even more radioactive radium. In order to isolate pure radium they obtained waste ore rich in uranium from mines in Bohemia and, working in an old shed, they purified and repurified the ore, work mostly undertaken by Marie. By 1902 they had obtained one tenth of a gram of radium chloride from several tonnes of ore. It was intensely radioactive, ionizing the surrounding air, decomposing water, evolving heat and glowing in the dark.

In 1903 Marie Curie presented her doctoral thesis (and became the first woman to be awarded such a degree in France). In 1903 she was awarded the Nobel Prize for physics jointly with Pierre Curie and Henri Becquerel for their work on radioactivity. The following year their second daughter Eve was born and the Curies appear to have begun to suffer from radiation sickness. Pierre Curie was named in 1904 as the new professor of physics at the Sorbonne and Marie was appointed ‘chief of work’ in the laboratory that was to be built for him; it was opened in 1915. In 1906 Pierre was killed in a street accident and the professorship was offered to Marie; she became the first woman professor at the Sorbonne. She continued to work on radium and attempted to isolate polonium, but most of her time was spent in supervising the research of others and raising funds, along with caring for her two daughters.

In 1910 Marie was proposed for the decoration of the Légion d’Honneur, but refused it, as her husband had refused a previous offer of the honour. At the same time she was a candidate for election to the Académie des Sciences in Paris (she would have been the first woman member), but was not elected.

In 1911 she was awarded a second Nobel Prize for chemistry for her discovery of polonium and radium. The original unit of measurement of the activity of a radioactive substance was named the curie (Ci); it is now defined as a decay rate of exactly 3.7 × 10 10 disintegrations per second. Characteristically, she insisted on defining the unit herself. In 1914 she organized X-ray services for military hospitals; radiography had hardly begun and there was as yet no provision for it. She died at the age of 67 from leukaemia; her exposure to radioactivity is suggestive in this.

Marie Curie was no theoretician, but she was a remarkably skilful radiochemist and her discoveries did much to focus research on the new and major field of radioactivity; she was the first woman scientist of international distinction.

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