On 10 December 1911, Marie Curie was awarded the Nobel prize in chemistry for ‘services to the advancement of chemistry by the discovery of the elements radium and polonium’. She was the first female recipient of any Nobel prize and the first person ever to be awarded two (she, Pierre Curie and Henri Becquerel had shared the 1903 physics prize for their work on radiation). Such was Marie’s impact on the scientific world – and the role of women within it – that one of the four stated goals of the 2011 international year of chemistry is to celebrate the centenary of her prize.
Early years She was born Maria Salomea Sklodowska on 7 November 1867 in central Warsaw, Poland. Both her parents were teachers (her mother died when Maria was 10) and she was highly motivated and well educated. Poland was then a subject state of Russia and women were excluded from advanced study, so in 1891 she joined her sister Bronia in Paris, enrolling at the Paris Sorbonne University and taking her physics and mathematics degrees with outstanding grades in 1893–4. She met Pierre Curie in the spring of 1894, and they married in 1895 at a civil ceremony in Sceaux in the Parisian suburbs. They were both rather shy and unworldly, caring little for material things; their chief recreation was cycling, but they shared too a deep appreciation of science and an obsessive dedication to it. Their first daughter Irène was born in 1897.
Pierre’s work on piezoelectricity, crystal symmetry and magnetism at the Municipal School of Industrial Physics and Chemistry (EPCI) in Paris is still fundamentally important, especially the concepts of the Curie temperature (above which magnets lose their magnetism) and the Curie law relating magnetism and temperature. Marie published her first paper in 1897 on the magnetisation of steels but looked for a new research topic, which she found in radioactivity. A year after Wilhelm Röntgen’s observation of x-rays in 1895, Henri Becquerel discovered radioactivity of uranium from photographic plates which, when wrapped in black paper close to uranium or its salts, showed images when developed.
Marie was allocated a damp room of the EPCI for her doctoral research, and showed that among a wide variety of inorganic materials, uranium and thorium were the only elements then known to exhibit radioactivity. Her samples were placed on a condenser plate charged to 100 Volts and attached to one of Pierre’s electrometers, and thereby she measured quantitatively their radioactivity. She found the minerals pitchblende (UO2) and chalcolite (Cu(UO2)2(PO4)2.12H2O) to be more radioactive than pure uranium, so reasoned that they must contain other, stronger radioactive constituents. On 12 April 1898 she presented her findings, writing that ‘these minerals may contain an element which is much more active than uranium’.1 She and Pierre decided that she would concentrate on the chemical aspects of element separation, while he would study their radiation properties.
Polonium and radium In April 1898, Marie dissolved pitchblende in HCl and treated the solution with H2S; uranium and thorium remained in solution, but the precipitated sulfides remained highly radioactive. After further manipulation this radioactive material was found to co-precipitate with bismuth. In July she and Pierre published a paper (coining the word ‘radio-active’ in its title), presented by Becquerel to the Academy of Sciences – founded in 1666, this institution was as prestigious in France as the Royal Society in Britain. They suggested, for the first time, that radioactivity was a phenomenon associated with the atom, and proposed that the new element, once its existence was confirmed, should be called polonium.2
They realised that pitchblende must contain yet another highly radioactive material, not precipitated from its solutions by H2S, (NH4)2S
In short It is 100 years since Marie Curie became the first person ever to win two Nobel prizes Marie and her husband Pierre pioneered the study of radiactivity and discovered two new elements, radium and polonium The pair had to process tonnes of minerals under horrific conditions to extract tiny amounts of radium Their daughter, Irène, also won a Nobel prize in chemistry, and Marie is remembered in the names of universities, institutes, charities and the element curium
The Curies isolated traces of radium and polonium from tonnes of pitchblende uranium ore www.chemistryworld.org or ammonia, having a waterinsoluble carbonate akin to BaCO3 and a chloride slightly less soluble than BaCl2 which acted as a carrier for it. This they named radium, publishing their results on Boxing day 1898;2 French spectroscopist Eugène-Anatole Demarçay found a new atomic spectral line from the element, helping to confirm its status. Since it was much more radioactive than polonium the Curies concentrated their efforts on it. It was clear that much more pitchblende was needed to obtain significant quantities of radium, and they eventually obtained some 8000kg of waste ore from Austria. They worked for the next four years under appalling conditions in a leaking unventilated shed, freezing in the winter and dreadfully hot by summer. Marie wrote: ‘I had to spend a whole day mixing a boiling mass with a heavy iron rod nearly as large as myself. I would be broken with fatigue at the day’s end’. Nevertheless she described life in ‘this miserable shed’ as ‘the best and happiest years of our life’, and was much honoured when Lord Kelvin and other famous scientists visited her there.
They worked with 20kg batches of pitchblende: grinding, dissolving and refining them to small quantities of solutions. In 1902 they isolated 0.1g. of anhydrous RaCl2 after thousands of recrystallisations from the moresoluble BaCl2 in HCl, measuring the atomic weight of radium as 225.
In 1901 Pierre and Becquerel published a paper on the physiological effects of radioactivity, and Pierre showed, with medical collaborators, that radiation from radium (and subsequently from radon gas which it and other radioactive elements emit) could destroy cancerous cells.
The physics Nobel prize In June 1903 Pierre came to the UK to give a discourse at London’s Royal Institution. Many eminent scientists were present including Sir William Crookes, Sir Oliver Lodge, Lord Kelvin and the physicist William Ayrton. Ayrton’s wife Hertha, a remarkable scientist in her own right, and Marie became firm friends.
Marie completed her doctoral thesis in June 1903. Later the same day Ernest Rutherford (himself to become a chemistry Nobel laureate in 1908) met the Curies for dinner; Marie trusted him and they formed a lasting friendship. That evening, when Pierre showed him some radium glowing blue in the dark,
THEODORE GRAY
Chemistry World | January 2011 | 43
