Who was Marie Curie? Radioactivity and two Nobel Prizes

Marie Curie was a Polish-born physicist and chemist, born in Warsaw in 1867, who worked in Paris and died in 1934, and who showed that radioactivity is a property of atoms themselves. With her husband Pierre she discovered two new elements, polonium and radium, in 1898. She was the first woman to win a Nobel Prize, the first person to win two, and is still the only person to win in two different sciences.

In short

• Curie found that the strength of uranium's rays depends only on how much uranium is present, which meant the rays came from inside the atom, not from chemistry.
• She and Pierre Curie discovered polonium and radium in 1898, and she spent four years isolating a tenth of a gram of radium compound to prove radium was real.
• She won the 1903 Nobel Prize in Physics and the 1911 prize in Chemistry, and her long exposure to radiation probably caused the illness that killed her.

Who was Marie Curie, in brief?

She was born Maria Skłodowska on 7 November 1867 in Warsaw, then under Russian rule, where universities were closed to women. She studied at an illegal "Flying University," worked as a governess to pay for her sister's medical studies in Paris, and followed her there in 1891 to study at the Sorbonne. She took a degree in physics in 1893, first in her class, and one in mathematics in 1894. In 1895 she married Pierre Curie, a French physicist.

Year	Event
1867	Born Maria Skłodowska in Warsaw, 7 November
1891	Moves to Paris and enrolls at the Sorbonne
1895	Marries Pierre Curie
1897	Begins her doctoral research on Becquerel's uranium rays
1898	Coins the word "radioactivity"; with Pierre, announces polonium (July) and radium (December)
1902	Isolates about 0.1 gram of radium chloride and measures radium's atomic weight
1903	Doctorate; Nobel Prize in Physics with Pierre Curie and Henri Becquerel
1906	Pierre is killed by a horse-drawn wagon; she takes his chair, the Sorbonne's first woman professor
1911	Nobel Prize in Chemistry, alone
1914–18	Runs X-ray services for the French army
1934	Dies of aplastic anemia in Haute-Savoie, France, 4 July

What did "radioactive" mean before anyone knew about the nucleus?

In 1896 the French physicist Henri Becquerel found that uranium salts, kept in the dark, gave off rays that fogged a photographic plate. Nobody knew what atoms were made of. The atom was thought of as the smallest, unchangeable piece of an element, and the nucleus would not be discovered until 1911.

Curie chose these rays for her doctoral thesis in 1897. Instead of photographic plates, she measured how much the rays made the air around them conduct electricity, using a sensitive electrometer Pierre and his brother had invented. She tested uranium in every form she could get: metal, salts, oxides, wet and dry, heated and lit. The strength of the rays depended only on how much uranium was there, not on what it was combined with or what was done to it. Chemistry rearranges how atoms bond; it could not be the cause. The rays had to come from inside the uranium atom itself.

That was the radical step. She named the property "radioactivity," found that thorium has it too, and in effect showed that atoms are not inert, unchanging balls. Later work by Ernest Rutherford and Frederick Soddy showed that a radioactive atom changes into a different element as it gives off its rays, which is the subject of what radioactivity is in modern terms.

How did she discover polonium and radium?

Her measurements turned up a puzzle. Pitchblende, a uranium ore, was several times more active than its uranium content could explain. Curie concluded that it must hold small amounts of an unknown element far more active than uranium. Pierre set aside his own research to join her.

They broke pitchblende down chemically, step by step, and after each separation measured which portion carried the activity. In July 1898 they announced an element they named polonium, after Marie's homeland. In December 1898, with the chemist Gustave Bémont, they announced radium, from the Latin for ray. Both took places on the periodic table.

Chemists wanted to see a new element, not just its rays, and radium was present in pitchblende in traces. Working in a leaky shed at the School of Physics and Chemistry in Paris, Curie processed tonnes of pitchblende residue, by hand, in batches of about 20 kilograms. By 1902 she had about a tenth of a gram of pure radium chloride and had measured radium's atomic weight. The Curies published their methods in full and patented nothing.

Why did she win two Nobel Prizes?

The 1903 Nobel Prize in Physics went a quarter to Marie, a quarter to Pierre and half to Becquerel, "in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel". The first nomination left her out; after Pierre learned of it, he insisted that Marie's part be recognized, and she was added.

The 1911 Nobel Prize in Chemistry was hers alone, "in recognition of her services to the advancement of chemistry by the discovery of the elements radium and polonium, by the isolation of radium and the study of the nature and compounds of this remarkable element". In 1910, with André-Louis Debierne, she had produced radium as a pure metal.

	1903 Physics	1911 Chemistry
Shared with	Pierre Curie, Henri Becquerel	No one
For	Explaining the rays as a property of atoms	Discovering two elements and isolating radium
Field it opened	The physics of radiation	The chemistry of radioactive elements

What did she face as a woman in science?

Curie worked in institutions built for men. In London in 1903 the Royal Institution invited the couple to speak on radium, but by convention Pierre alone gave the lecture on their work while she sat in the audience. In 1911 the French Academy of Sciences narrowly rejected her for membership; parts of the right-wing press attacked her candidacy with what the American Institute of Physics' history of her life calls scurrilous and racist claims about the foreign-born scientist. Later that year newspapers exposed her relationship with the physicist Paul Langevin, who was married, and crowds gathered outside her home. A member of the Nobel committee wrote suggesting she stay away from the 1911 ceremony. She went to Stockholm anyway and gave her lecture.

During World War I she turned to medicine. She built about 20 mobile X-ray units and some 200 fixed X-ray posts for military hospitals, learned to drive so she could take them to the front, and trained other women to run them. After the war she led the Radium Institute in Paris, which became a center of research and cancer treatment. Her daughter Irène Joliot-Curie won the 1935 Nobel Prize in Chemistry there, with her husband Frédéric Joliot.

What did radiation cost her?

Curie handled radium for decades with almost no protection, because no one knew how much harm it did. She carried bottles of radium and polonium in her coat pocket and kept them in her desk drawer. Her fingers were cracked and scarred, and she developed cataracts. She died on 4 July 1934 of aplastic anemia, a failure of the bone marrow that her doctors attributed to long exposure to radiation.

The contamination outlived her. Her papers from the 1890s, now in the Bibliothèque nationale de France, still carry radium, and readers open their lead-lined boxes in protective clothing after signing a waiver, as the Christian Science Monitor reported in 2011. The arithmetic shows why it lasts. Radium-226 has a half-life of about 1,600 years, so after time t the share left is ½ raised to the power t ÷ 1,600:

• From 1898 to 2026 is 128 years, and 128 ÷ 1,600 = 0.08.
• ½ to the power 0.08 is about 0.95.
• So about 95% of the radium on her notebooks is still there, and half will remain in the year 3500.

In 1995 her remains and Pierre's were moved to the Panthéon in Paris; she was the first woman honored there for her own achievements.

What did her work lead to?

Curie's discovery that atoms can change from within opened the way to modern atomic physics, to Rutherford's nucleus and, eventually, to nuclear power. Radium was used to treat cancer for decades before safer sources replaced it. She and Albert Einstein met at the first Solvay physics conference in 1911 and became friends; he wrote to her that autumn urging her to ignore the press. Her method, measuring carefully and following the numbers to a conclusion no one expected, is a model of how science works.

Check yourself

• Without looking back, explain how Curie's measurements showed the rays came from inside atoms rather than from chemistry.
• Why was pitchblende's high activity the clue to new elements?
• What did each of her two Nobel Prizes recognize?

Sources

• Marie Curie, Nobel Prize in Physics 1903, Facts — The Nobel Prize
• Marie Curie, Nobel Prize in Chemistry 1911, Facts — The Nobel Prize
• Marie Curie and the Science of Radioactivity — American Institute of Physics, Center for History of Physics, 2000
• Marie Curie, Research Breakthroughs (1897–1904) — American Institute of Physics, 2000
• Marie Curie: Why her papers are still radioactive — The Christian Science Monitor, 2011
• Marie Curie — Wikipedia