Work on radioactivity
The Curies became research workers at the School of Chemistry and Physics in Paris and there they began their pioneering work into invisible rays given off by uranium – a new phenomenon which had recently been discovered by Professor Henri Becquerel.
He had shown that the rays were able to pass through solid matter, fog and photographic film and caused air to conduct electricity.
Marie also noticed that samples of a mineral called pitchblende, which contains uranium ore, were a great deal more radioactive than the pure element uranium. Further work convinced her the very large readings she was getting could not be caused by uranium alone – there was something else in the pitchblende. Since nobody had ever found it before, it could only be present in tiny quantities, and it seemed to be very radioactive. Marie was convinced she had found a new chemical element – other scientists doubted her results.
Pierre and Marie Curie set about working to search for the unknown element. They ground up samples of pitchblende, dissolved them in acid, and began to separate the different elements present, using the standard analytical chemistry techniques of the time. Eventually, they extracted a black powder 330 times more radioactive than uranium, which they called polonium . Polonium was a new chemical element, atomic number 84.
When the Curies investigated further, they found that the liquid left behind after they had extracted polonium was still extremely radioactive. They realised that pitchblende contained another new element, far more radioactive than polonium, but present in even smaller quantities.
In 1898, the Curies published strong evidence supporting the existence of the new element – which they called radium – but they still had no sample of it. Pitchblende is an expensive mineral, because it contains valuable uranium, and Marie needed a lot of it.
She got in touch with a factory in Austria that removed the uranium from pitchblende for industrial use and bought several tonnes of the worthless waste product, which was even more radioactive than the original pitchblende, and was much cheaper. Marie set about processing the pitchblende to extract the tiny quantities of radium. This involved working on a much larger scale than before, with 20 kg batches of the mineral – grinding, dissolving, filtering, precipitating, collecting, redissolving, crystallising and recrystallising.
The work was heavy and physically demanding – and involved dangers the Curies did not appreciate. During this time they began to feel sick and physically exhausted; today we can attribute their ill-health to the early symptoms of radiation sickness. At the time they persevered in ignorance of the risks, often with raw and inflamed hands because they were continually handling highly radioactive material.
In 1902 Marie eventually isolated radium (as radium chloride), determining its atomic weight as 225.93. The journey to the discovery had been long and arduous.
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Marie Curie ©Marie Curie was a Polish-born physicist and chemist and one of the most famous scientists of her time. Together with her husband Pierre, she was awarded the Nobel Prize in 1903, and she went on to win another in 1911.
Marie Sklodowska was born in Warsaw on 7 November 1867, the daughter of a teacher. In 1891, she went to Paris to study physics and mathematics at the Sorbonne where she met Pierre Curie, professor of the School of Physics. They were married in 1895.
The Curies worked together investigating radioactivity, building on the work of the German physicist Roentgen and the French physicist Becquerel. In July 1898, the Curies announced the discovery of a new chemical element, polonium. At the end of the year, they announced the discovery of another, radium. The Curies, along with Becquerel, were awarded the Nobel Prize for Physics in 1903.
Pierre's life was cut short in 1906 when he was knocked down and killed by a carriage. Marie took over his teaching post, becoming the first woman to teach at the Sorbonne, and devoted herself to continuing the work that they had begun together. She received a second Nobel Prize, for Chemistry, in 1911.
The Curie's research was crucial in the development of x-rays in surgery. During World War One Curie helped to equip ambulances with x-ray equipment, which she herself drove to the front lines. The International Red Cross made her head of its radiological service and she held training courses for medical orderlies and doctors in the new techniques.
Despite her success, Marie continued to face great opposition from male scientists in France, and she never received significant financial benefits from her work. By the late 1920s her health was beginning to deteriorate. She died on 4 July 1934 from leukaemia, caused by exposure to high-energy radiation from her research. The Curies' eldest daughter Irene was herself a scientist and winner of the Nobel Prize for Chemistry.