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In 1898, working in a leaky shed in Paris, Marie and Pierre Curie discovered two new elements using a completely new method: they followed an invisible property, radioactivity, through a mountain of ore until it led them to substances no one had seen before. The elements were polonium and radium, and the work changed chemistry, physics and medicine.
The starting point: Becquerel’s rays
In 1896 Henri Becquerel discovered that uranium salts gave off rays that could fog a photographic plate wrapped in black paper, without any exposure to light. Marie Skłodowska Curie, a Polish-born physicist working in Paris, chose these mysterious rays as the subject of her doctoral research.
Using a sensitive electrometer that Pierre and his brother Jacques had developed, she measured how strongly different substances made air conduct electricity. She found that:
- the intensity of the rays depended only on the amount of uranium, not on its chemical form — so the rays came from the atoms themselves, not from any chemical reaction;
- thorium gave off similar rays.
She coined the word radioactivity for this property.
The clue: pitchblende was too active
Pitchblende, a uranium ore, was more radioactive than its uranium content could explain — about four times more. Marie Curie concluded that it must contain small amounts of one or more unknown elements that were far more radioactive than uranium.
Pierre set aside his own research to join her. Together they started chemically separating pitchblende into fractions and measuring the radioactivity of each one, following the activity wherever it went.
Polonium (July 1898)
One fraction, which behaved chemically like bismuth, was hundreds of times more active than uranium. The Curies announced a new element and named it polonium, after Marie’s homeland, Poland — then divided between Russia, Prussia and Austria and absent from the map. The name was a deliberate political statement.
Radium (December 1898)
Another fraction, behaving like barium, was even more active. It contained a second new element, which they named radium, from the Latin radius, “ray”. Its spectrum showed new lines, confirming it was a genuine new element.
Proving it: tonnes of ore
Other chemists wanted to see the element itself and measure its atomic weight. The problem was that radium made up only a tiny fraction of the ore. Over nearly four years, largely by hand, in a poorly ventilated shed with a leaking roof, Marie Curie processed several tonnes of pitchblende residues, stirring vats of boiling material with an iron rod almost as tall as herself.
By 1902 she had isolated about 0.1 gram of pure radium chloride and measured radium’s atomic weight. In 1910 she and André-Louis Debierne isolated radium metal itself. Pure radium glows faintly blue in the dark and is constantly warmer than its surroundings, powered by its own radioactive decay.
Two Nobel Prizes
- 1903, Physics — shared by Henri Becquerel and Pierre and Marie Curie, for their research on radioactivity. Marie was the first woman to win a Nobel Prize.
- 1911, Chemistry — Marie Curie alone, for the discovery of polonium and radium and the isolation of radium.
She remains the only person to win Nobel Prizes in two different sciences. Pierre had died in a street accident in 1906; Marie took over his professorship, becoming the first woman to teach at the Sorbonne.
The legacy
- Medicine: radium was used in early cancer treatment (brachytherapy). During the First World War, Marie Curie developed mobile X-ray units — “petites Curies” — and trained women to operate them, helping treat around a million soldiers.
- Science: radioactivity revealed that atoms were not unchanging, and led directly to the discovery of the atomic nucleus. See atomic models.
- Family: their daughter Irène Joliot-Curie and her husband Frédéric won the 1935 Nobel Prize in Chemistry for discovering artificial radioactivity.
- Element 96, curium, is named in the Curies’ honour. See elements named after scientists.
The danger nobody understood
The Curies had no idea how harmful radiation was. They carried samples in their pockets, and Marie kept radium by her bedside because of its glow. Her hands were scarred by radiation burns. She died in 1934 of aplastic anaemia, almost certainly caused by radiation exposure. Her laboratory notebooks from the 1890s are still radioactive and are stored in lead-lined boxes; people who consult them sign a waiver and wear protective clothing.
In the 1910s and 1920s, radium became a craze in consumer products, and factory workers who painted watch dials with radium paint — licking their brushes to a fine point — suffered terrible illnesses. Their case, the “Radium Girls”, helped establish workplace safety laws.
Quick answers
What elements did Marie Curie discover? Polonium and radium, with Pierre Curie, in 1898.
Why is polonium named after Poland? To draw attention to Poland, Marie Curie’s homeland, which at the time wasn’t an independent country.
Is radium still used? Rarely. Safer isotopes have replaced it in medicine, although radium-223 is used to treat some bone cancers.
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