This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (January 2011)

francium ← radium → actinium Ba ↑ Ra ↓ Ubn 88Ra Periodic table
Appearance
silvery white metallic
General properties
Name, symbol, number	radium, Ra, 88
Pronunciation	/ˈreɪdiəm/ RAY-dee-əm
Element category	alkaline earth metal
Group, period, block	2, 7, s
Standard atomic weight	(226.03)
Electron configuration	[Rn] 7s2
Electrons per shell	2, 8, 18, 32, 18, 8, 2 (Image)
Physical properties
Phase	solid
Density (near r.t.)	5.5 g·cm−3
Melting point	973 K, 700 °C, 1292 °F
Boiling point	2010 K, 1737 °C, 3158.6 °F
Heat of fusion	8.5 kJ·mol−1
Heat of vaporization	113 kJ·mol−1
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 819 906 1037 1209 1446 1799
Atomic properties
Oxidation states	2 (strongly basic oxide)
Electronegativity	0.9 (Pauling scale)
Ionization energies	1st: 509.3 kJ·mol−1
	2nd: 979.0 kJ·mol−1
Covalent radius	221±2 pm
Van der Waals radius	283 pm
Miscellanea
Crystal structure	body-centered cubic
Magnetic ordering	nonmagnetic
Electrical resistivity	(20 °C) 1 µΩ·m
Thermal conductivity	18.6 W·m−1·K−1
CAS registry number	7440-14-4
Most stable isotopes
Main article: Isotopes of radium
iso NA half-life DM DE (MeV) DP 223Ra trace 11.43 d α 5.99 219Rn 224Ra trace 3.6319 d α 5.789 220Rn 226Ra ~100% 1601 y α 4.871 222Rn 228Ra trace 5.75 y β− 0.046 228Ac
v t e · r

Radium ( /ˈreɪdiəm/ RAY-dee-əm) is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226, which has a half-life of 1601 years and decays into radon gas. Because of such instability, radium is luminescent, glowing a faint blue.

Radium, in the form of radium chloride, was discovered by Marie Skłodowska-Curie and Pierre Curie in 1898. They extracted the radium compound from uraninite and published the discovery at the French Academy of Sciences five days later. Radium was isolated in its metallic state by Marie Curie and André-Louis Debierne through the electrolysis of radium chloride in 1910. Since its discovery, it has given names like radium A and radium C₂ to several isotopes of other elements that are decay products of radium-226.

In nature, radium is found in uranium ores in trace amounts as small as a seventh of a gram per ton of uraninite. Radium is not necessary for living organisms, and adverse health effects are likely when it is incorporated into biochemical processes because of its radioactivity and chemical reactivity.

Characteristics[link]

Physical characteristics[link]

Although radium is not as well studied as its stable lighter homologue barium, the two elements have very similar properties. Their first two ionization energies are very similar: 509.3 and 979.0 kJ·mol⁻¹ for radium and 502.9 and 965.2 kJ·mol⁻¹ for barium. Such low figures yield both elements' high reactivity and the formation of the very stable Ra²⁺ ion and similar Ba²⁺.

Pure radium is a white, silvery, solid metal, melting at 700 °C (1292 °F) and boiling at 1737 °C (3159 °F), similar to barium. Radium has density of 5.5 g•cm³; the radium-barium density ratio is comparable to the radium-barium atomic mass ratio, as these elements have very similar body-centered cubic structures.

Chemical characteristics and compounds[link]

Radium is the heaviest known alkaline earth metal; its chemical properties mostly resemble those of barium. When exposed to air, radium reacts violently with it, forming radium nitride,^[1] which causes blackening of this white metal. It exhibits only the +2 oxidation state in solution. Radium ions do not form complexes easily, due to highly basic character of the ions. Most radium compounds coprecipitate with all barium, most strontium, and most lead compounds, and are ionic salts. The radium ion is colorless, making radium salts white when freshly prepared, turning yellow and ultimately dark with age owing to self-decomposition from the alpha radiation. Compounds of radium flame red-purple and give a characteristic spectrum. Like other alkaline earth metals, radium reacts violently with water and oil to form radium hydroxide and is slightly more volatile than barium, which leads to lesser solubility of radium compounds compared to those of corresponding barium ones. Because of its geologically short half-life and intense radioactivity, radium compounds are quite rare, occurring almost exclusively in uranium ores.

Radium chloride, radium bromide, radium hydroxide and radium nitrate are soluble in water, with solubilities slightly lower than those of barium analogs for bromide and chloride, and higher for nitrate. Radium hydroxide is more soluble than hydroxides of other alkaline earth metals, actinium, and thorium, and more basic than barium hydroxide. It can be separated from these elements by their precipitation with ammonia.^[1] Out of insoluble radium compounds, radium sulfate, radium chromate, radium iodate, radium carbonate, and radium tetrafluoroberyllate are characterized.^[1] Radium oxide, however, remains uncharacterized, despite the fact that other alkaline-earth metals' oxides are common compounds for the corresponding metals.

Isotopes[link]

Radium has 25 different known isotopes, four of which are found in nature, with ²²⁶Ra being the most common. ²²³Ra, ²²⁴Ra, ²²⁶Ra and ²²⁸Ra are all generated naturally in the decay of either uranium (U) or thorium (Th). ²²⁶Ra is a product of ²³⁸U decay, and is the longest-lived isotope of radium with a half-life of 1601 years; next longest is ²²⁸Ra, a product of ²³²Th breakdown, with a half-life of 5.75 years.^[2]

Radium has no stable isotopes; however, four isotopes of radium are present in decay chains, having atomic masses of 223, 224, 226 and 228, all of which are present in trace amounts. The most abundant and the longest-living one is radium-226, with a half-life of 1601 years. To date, 33 isotopes of radium have been synthesized, ranging in mass number from 202 to 234.

To date, at least 12 nuclear isomers have been reported; the most stable of them is radium-205m, with a half-life of between 130 and 230 milliseconds. All ground states of isotopes from radium-205 to radium-214, and from radium-221 to radium-234, have longer ones.

Three other natural radioisotopes had received historical names in the early twentieth century: radium-223 was known as actinium X, radium-224 as thorium X and radium-228 as mesothorium I. Radium-226 has given historical names to its decay products after the whole element, such as radium A for polonium-218.

Radioactivity[link]

Radium is over one million times as radioactive as the same mass of uranium. Its decay occurs in at least seven stages; the successive main products have been studied and were called radium emanation or exradio (now identified as radon), radium A (polonium), radium B (lead), radium C (bismuth), etc. Radon is a heavy gas, and the later products are solids. These products are themselves radioactive elements, each with an atomic weight a little lower than its predecessor.^[3][4]

Radium loses about 1% of its activity in 25 years, being transformed into elements of lower atomic weight, with lead being the final product of disintegration.^[5]

The SI unit of radioactivity is the becquerel (Bq), equal to one disintegration per second. The curie is a non-SI unit defined as that amount of radioactive material that has the same disintegration rate as 1 gram of radium-226 (3.7×10¹⁰ disintegrations per second, or 37 GBq).^[6]

Radium metal maintains itself at a higher temperature than its surroundings because of the radiation it emits – alpha particles, beta particles, and gamma rays. More specifically, the alpha particles are produced by the radium decay, whereas the beta particles and gamma rays are produced by relatively short-half-life elements further down the decay chain.^[7]

Occurrence[link]

Radium-226 is a decay product of uranium and is therefore found in all uranium-bearing ores. (One ton of pitchblende typically yields about one seventh of a gram of radium).^[8] Radium was originally acquired from pitchblende ore from Joachimsthal, Bohemia, now located in the Czech Republic. Carnotite sands in Colorado provide some of the element, but richer ores are found in the Congo and the area of the Great Bear Lake and the Great Slave Lake of northwestern Canada.^[9] Radium can also be extracted from the waste from nuclear reactors. Large radium-containing uranium deposits are located in Russia, Canada (the Northwest Territories), the United States (New Mexico, Utah and Colorado, for example) and Australia.

Production[link]

All radium occurring today is produced by the decay of heavier elements, being present in decay chains. Owing to such short half-lives of its isotopes, radium is not primordial but trace. It cannot occur in large quantities due both to the fact that isotopes of radium have short half-lives and that parent nuclides have very long ones. Radium is found in tiny quantities in the uranium ore uraninite and various other uranium minerals, and in even tinier quantities in thorium minerals.

The amounts produced were aways relatively small; for example, in 1918 13.6 g of radium were produced in the United states.^[10] As of 1954, the total worldwide supply of purified radium amounted to about 5 pounds (2.3 kg).^[11]

History[link]

Marie and Pierre Curie experimenting with radium, a drawing by André Castaigne

Radium (Latin radius, ray) was discovered by Marie Skłodowska-Curie and her husband Pierre on December 21, 1898 in a uraninite sample. While studying the mineral, the Curies removed uranium from it and found that the remaining material was still radioactive. They then separated out a radioactive mixture consisting mostly of compounds of barium which gave a brilliant green flame color and crimson carmine spectral lines that had never been documented before. The Curies announced their discovery to the French Academy of Sciences on 26 December 1898.^[12] The naming of radium dates to circa 1899, from French radium, formed in Modern Latin from radius (ray), called for its power of emitting energy in the form of rays.^[13] In 1910, radium was isolated as a pure metal by Curie and André-Louis Debierne through the electrolysis of a pure radium chloride solution by using a mercury cathode and distilling in an atmosphere of hydrogen gas.^[14] The Curies' new element was first industrially produced in the beginning of the 20th century by Biraco, a subsidiary company of Union Minière du Haut Katanga (UMHK) in its Olen plant in Belgium. UMHK offered to Marie Curie her first gram of radium. It gave historical names to the decay products of radium, such as radium A, B, C, etc., now known to be isotopes of other elements.

On 4 February 1936, radium E (bismuth-210) became the first radioactive element to be made synthetically in the United States. Dr. John Jacob Livingood, at the radiation lab at University of California, Berkeley, was bombarding several elements with 5-MeV deuterons. He noted that irradiated bismuth emits fast electrons with a 5-day half-life, which matched the behavior of radium E.^{[15][16][17][18]}

The common historical unit for radioactivity, the curie, is based on the radioactivity of ²²⁶Ra.^[19]

Applications[link]

Some of the few practical uses of radium are derived from its radioactive properties. More recently discovered radioisotopes, such as 60
Co and 137
Cs, are replacing radium in even these limited uses because several of these isotopes are more powerful emitters, safer to handle, and available in more concentrated form.^[20][21]

When mixed with beryllium, it is a neutron source for physics experiments.^[22]

Historical uses[link]

Self-luminous white paint which contains radium on the face and hand of an old clock.

Radium hands in darkness

Radium was formerly used in self-luminous paints for watches, nuclear panels, aircraft switches, clocks, and instrument dials. A typical self-luminous watch that uses radium paint contains around 1 microgram of radium.^[11] In the mid-1920s, a lawsuit was filed by five dying "Radium Girl" dial painters who had painted radium-based luminous paint on the dials of watches and clocks. The dial painters' exposure to radium caused serious health effects which included sores, anemia, and bone cancer. This is because radium is treated as calcium by the body, and deposited in the bones, where radioactivity degrades marrow and can mutate bone cells.

During the litigation, it was determined that company scientists and management had taken considerable precautions to protect themselves from the effects of radiation, yet had not seen fit to protect their employees. Worse, for several years the companies had attempted to cover up the effects and avoid liability by insisting that the Radium Girls were instead suffering from syphilis. This complete disregard for employee welfare had a significant impact on the formulation of occupational disease labor law.^[23]

As a result of the lawsuit, the adverse effects of radioactivity became widely known, and radium-dial painters were instructed in proper safety precautions and provided with protective gear. In particular, dial painters no longer shaped paint brushes by lip (which led to accidental ingestion of the radium salts). Radium was still used in dials as late as the 1960s, but there were no further injuries to dial painters. This further highlighted that the plight of the Radium Girls was completely preventable.

After the 1960s, radium paint was first replaced with promethium paint, and later by tritium bottles which continue to be used today. Although the beta radiation from tritium is potentially dangerous if tritium is ingested, tritium has replaced radium in these applications.

Radium was once an additive in products such as toothpaste, hair creams, and even food items due to its supposed curative powers.^[24] Such products soon fell out of vogue and were prohibited by authorities in many countries after it was discovered they could have serious adverse health effects. (See, for instance, Radithor or Revigator types of "Radium water" or "Standard Radium Solution for Drinking".) Spas featuring radium-rich water are still occasionally touted as beneficial, such as those in Misasa, Tottori, Japan. In the U.S., nasal radium irradiation was also administered to children to prevent middle-ear problems or enlarged tonsils from the late 1940s through the early 1970s.^[25]

In 1909, the famous Rutherford experiment used radium as an alpha source to probe the atomic structure of gold. This experiment led to the Rutherford model of the atom and revolutionized the field of nuclear physics.

Radium (usually in the form of radium chloride) was used in medicine to produce radon gas which in turn was used as a cancer treatment; for example, several of these radon sources were used in Canada in the 1920s and 1930s.^[26] The isotope 223
Ra is currently under investigation for use in medicine as a cancer treatment of bone metastasis.

Precautions[link]

Radium is highly radioactive and its decay product, radon gas, is also radioactive. Since radium is chemically similar to calcium, it has the potential to cause great harm by replacing calcium in bones. Exposure to radium can cause cancer and other disorders, because radium and its decay product radon emit alpha particles upon their decay, which kill and mutate cells. The dangers of radium were apparent from the start. The first case of so-called "radium-dermatitis" was reported in 1900, only 2 years after the element's discovery. The French physicist Antoine Becquerel carried a small ampoule of radium around in his waistcoat pocket for 6 hours and reported that his skin became ulcerated. Marie Curie also had a similar incident in which she experimented with a tiny sample that she kept in contact with her skin for 10 hours and noted how an ulcer appeared, although not for several days.^[27] Handling of radium has also been blamed for Curie's death due to aplastic anemia. Stored radium should be ventilated to prevent accumulation of radon. Emitted energy from the decay of radium also ionizes gases, affects photographic plates, and produces many other detrimental effects – to the extent that at the time of the Manhattan Project in 1944, the "tolerance dose" for workers was set at 0.1 microgram of ingested radium.^[28][29]

See also[link]

• Decay chains
• Radium Girls

Books View or order collections of articles	Radium Period 7 elements Alkaline earth metals Chemical elements (sorted alphabetically) Chemical elements (sorted by number)
Portals Access related topics	Chemistry portal Medicine portal
Find out more on Wikipedia's Sister projects	Images and media from Commons Definitions from Wiktionary Learning resources from Wikiversity

References[link]

Further reading[link]

• Albert Stwertka (1998). Guide to the Elements – Revised Edition. Oxford University Press. ISBN 0-19-508083-1. 
• Denise Grady (October 6, 1998). "A Glow in the Dark, and a Lesson in Scientific Peril". The New York Times. http://www.nytimes.com/library/national/science/100698sci-radium.html. Retrieved 2007-12-25. 
• Nanny Fröman (1 December 1996). "Marie and Pierre Curie and the Discovery of Polonium and Radium". Nobel Foundation. http://nobelprize.org/nobel_prizes/physics/articles/curie/index.html. Retrieved 2007-12-25. 
• Macklis, R. M. (1993). "The great radium scandal". Scientific American 269 (2): 94–99. DOI:10.1038/scientificamerican0893-94. PMID 8351514. 
• Clark, Claudia (1987). Radium Girls: Women and Industrial Health Reform, 1910–1935. University of North Carolina Press. ISBN 0-8078-4640-6. 

External links[link]

• WebElements.com – Radium (also used as a reference)
• Lateral Science – Radium Discovery
• Photos of Radium Water Bath in Oklahoma
• NLM Hazardous Substances Databank – Radium, Radioactive
• Reproduction of a 1942 comic book ad selling a "Radiumscope" to children
• Annotated bibliography for radium from the Alsos Digital Library for Nuclear Issues
• The Poisoner Next Door – Japan Today, 10/20/2001

vep:Radii

Marie Skłodowska-Curie
Marie Curie, ca. 1920
Born	(1867-11-07)7 November 1867 Warsaw, Kingdom of Poland, then part of Russian Empire[1]
Died	4 July 1934(1934-07-04) (aged 66) Passy, Haute-Savoie, France
Citizenship	Russian, later French
Nationality	Polish
Fields	Physics, chemistry
Institutions	University of Paris
Alma mater	University of Paris ESPCI
Doctoral advisor	Henri Becquerel
Doctoral students	André-Louis Debierne Óscar Moreno Marguerite Catherine Perey
Known for	Radioactivity, polonium, radium
Notable awards	Nobel Prize in Physics (1903) Davy Medal (1903) Matteucci Medal (1904) Nobel Prize in Chemistry (1911)
Spouse	Pierre Curie (1859–1906)
Signature
Notes She is the only person to win a Nobel Prize in two different sciences. She was the wife of Pierre Curie, and the mother of Irène Joliot-Curie and Ève Curie.

Marie Skłodowska-Curie (7 November 1867 – 4 July 1934) was a French-Polish physicist and chemist famous for her pioneering research on radioactivity. She was the first person honored with two Nobel Prizes^[2]—in physics and chemistry. She was the first female professor at the University of Paris, and in 1995 became the first woman to be entombed on her own merits in the Panthéon in Paris.^[3]

She was born Maria Salomea Skłodowska ([ˈmarja salɔˈmɛa skwɔˈdɔfska]) in Warsaw, in what was then the Kingdom of Poland. She studied at Warsaw's clandestine Floating University and began her practical scientific training in Warsaw. In 1891, aged 24, she followed her older sister Bronisława to study in Paris, where she earned her higher degrees and conducted her subsequent scientific work. She shared her 1903 Nobel Prize in Physics with her husband Pierre Curie and with the physicist Henri Becquerel. Her daughter Irène Joliot-Curie and son-in-law, Frédéric Joliot-Curie, would similarly share a Nobel Prize. She was the sole winner of the 1911 Nobel Prize in Chemistry. Skłodowska-Curie was the first woman to win a Nobel Prize, the only woman to date to win in two fields, and the only person to win in multiple sciences.

Her achievements included a theory of radioactivity (a term that she coined^[4]), techniques for isolating radioactive isotopes, and the discovery of two elements, polonium and radium. ^[5] Under her direction, the world's first studies were conducted into the treatment of neoplasms, using radioactive isotopes. She founded the Curie Institutes in Paris and Warsaw, which remain major centres of medical research today.

While an actively loyal French citizen, Skłodowska-Curie (she used both surnames) never lost her sense of Polish identity. She taught her daughters the Polish language and took them on visits to Poland. She named the first chemical element that she discovered – polonium, which she first isolated in 1898 – after her native country.^[6] During World War I she became a member of the Committee for a Free Poland (Komitet Wolnej Polski).^[7] In 1932, she founded a Radium Institute (now the Maria Skłodowska–Curie Institute of Oncology) in her home town, Warsaw, headed by her physician-sister Bronisława. Curie died in 1934 of aplastic anemia brought on by her years of exposure to radiation.^[8]

Biography[link]

Early life[link]

Władysław Skłodowski with daughters (from left) Maria, Bronisława, Helena, 1890

Birthplace on ulica Freta in Warsaw's "New Town" – now home to the Maria Skłodowska-Curie Museum

Maria Skłodowska was born in Warsaw, in the Russian partition of Poland, on 7 November 1867, the fifth and youngest child of well-known teachers Bronisława and Władysław Skłodowski. Maria's older siblings were Zofia (born 1862), Józef (1863), Bronisława (1865) and Helena (1866).

Maria's paternal grandfather Józef Skłodowski had been a respected teacher in Lublin, where he taught the young Bolesław Prus.^[9] Her father Władysław Skłodowski taught mathematics and physics, subjects that Maria was to pursue, and was also director of two Warsaw gymnasia for boys, in addition to lodging boys in the family home. Maria's mother Bronisława operated a prestigious Warsaw boarding school for girls; she suffered from tuberculosis and died when Maria was twelve.

Maria's father was an atheist; her mother—a devout Catholic.^[10] Two years earlier Maria's oldest sibling, Zofia, had died of typhus. The deaths of her mother and sister, according to Robert William Reid, caused Maria to give up Catholicism and become agnostic.^[11]

When she was ten years old, Maria began attending the boarding school that her mother had operated while she was well; next Maria attended a gymnasium for girls, from which she graduated on 12 June 1883. She spent the following year in the countryside with relatives of her father's, and the next with her father in Warsaw, where she did some tutoring.

On both the paternal and maternal sides, the family had lost their property and fortunes through patriotic involvements in Polish national uprisings aiming at the restoration of Poland's independence (most recent of which was the January Uprising). This condemned each subsequent generation, including that of Maria, her elder sisters and her brother, to a difficult struggle to get ahead in life.^[12]

At a Warsaw lab here, in 1890–91, Skłodowska did her first scientific work.

Maria made an agreement with her sister, Bronisława, that she would give her financial assistance during Bronisława's medical studies in Paris, in exchange for similar assistance two years later.^[13] In connection with this, Maria took a position as governess: first with a lawyer's family in Kraków; then for two years in Ciechanów with a landed family, the Żorawskis, who were relatives of her father. While working for the latter family, she fell in love with their son, Kazimierz Żorawski, which was reciprocated by this future eminent mathematician. His parents, however, rejected the idea of his marrying the penniless relative, and Kazimierz was unable to oppose them. Maria lost her position as governess.^[14] She found another with the Fuchs family in Sopot, on the Baltic Sea coast, where she spent the next year, all the while financially assisting her sister.

At the beginning of 1890, Bronisława, a few months after she married Kazimierz Dłuski, invited Maria to join them in Paris. Maria declined because she could not afford the university tuition and was still counting on marrying Kazimierz Żorawski. She returned home to her father in Warsaw, where she remained till the fall of 1891. She tutored, studied at the clandestine Floating University,^[15] and began her practical scientific training (1890–91) in a laboratory at the Museum of Industry and Agriculture at Krakowskie Przedmieście 66, near Warsaw's Old Town.^[16] The laboratory was run by her cousin Józef Boguski, who had been assistant in Saint Petersburg to the great Russian chemist Dmitri Mendeleev.^[17]

In October 1891, at her sister's insistence and after receiving a letter from Żorawski, in which he definitively broke his relationship with her, she decided to go to France after all.^[10]

Maria's loss of the relationship with Żorawski was tragic for both. He soon earned a doctorate and pursued an academic career as a mathematician, becoming a professor and rector of Kraków University and president of the Warsaw Society of Learning. Still, as an old man and a mathematics professor at the Warsaw Polytechnic, he would sit contemplatively before the statue of Maria Skłodowska which had been erected in 1935 before the Radium Institute that she had founded in 1932.^[18]

In Paris, Maria briefly found shelter with her sister and brother-in-law before renting a primitive garret^[19] and proceeding with her studies of physics, chemistry, and mathematics at the Sorbonne (the University of Paris).

Pierre Curie[link]

Pierre Curie

Skłodowska studied during the day and tutored evenings, barely earning her keep. In 1893, she was awarded a degree in physics and began work in an industrial laboratory at Lippman's. Meanwhile she continued studying at the Sorbonne, and in 1894, earned a degree in mathematics.

That same year, Pierre Curie entered her life. He was an instructor at the School of Physics and Chemistry, the École supérieure de physique et de chimie industrielles de la ville de Paris (ESPCI). Skłodowska had begun her scientific career in Paris with an investigation of the magnetic properties of various steels; it was their mutual interest in magnetism that drew Skłodowska and Curie together.^[20]

Her departure for the summer to Warsaw only enhanced their mutual feelings for each other. She still was laboring under the illusion that she would be able to return to Poland and work in her chosen field of study. When she was denied a place at Kraków University merely because she was a woman, she returned to Paris.^[21] Almost a year later, in July 1895, she and Pierre Curie married, and thereafter the two physicists hardly ever left their laboratory. They shared two hobbies, long bicycle trips and journeys abroad, which brought them even closer. Maria had found a new love, a partner, and a scientific collaborator upon whom she could depend.^[21]

New elements[link]

In 1896 Henri Becquerel discovered that uranium salts emitted rays that resembled X-rays in their penetrating power. He demonstrated that this radiation, unlike phosphorescence, did not depend on an external source of energy, but seemed to arise spontaneously from uranium itself. Becquerel had, in fact, discovered radioactivity.

Curie decided to look into uranium rays as a possible field of research for a thesis. She used a clever technique to investigate samples. Fifteen years earlier, her husband and his brother had invented the electrometer, a sensitive device for measuring electrical charge. Using the Curie electrometer, she discovered that uranium rays caused the air around a sample to conduct electricity.^[22] Using this technique, her first result was the finding that the activity of the uranium compounds depended only on the quantity of uranium present. She had shown that the radiation was not the outcome of some interaction of molecules, but must come from the atom itself. In scientific terms, this was the most important single piece of work that she conducted.^[23]

Curie's systematic studies had included two uranium minerals, pitchblende and torbernite (also known as chalcolite). Her electrometer showed that pitchblende was four times as active as uranium itself, and chalcolite twice as active. She concluded that, if her earlier results relating the quantity of uranium to its activity were correct, then these two minerals must contain small quantities of some other substance that was far more active than uranium itself.^[24]

The idea [writes Reid] was her own; no one helped her formulate it, and although she took it to her husband for his opinion she clearly established her ownership of it. She later recorded the fact twice in her biography of her husband to ensure there was no chance whatever of any ambiguity. It [is] likely that already at this early stage of her career [she] realized that... many scientists would find it difficult to believe that a woman could be capable of the original work in which she was involved.^[25]

In her systematic search for other substances beside uranium salts that emitted radiation, Curie had found that the element thorium likewise, was radioactive.

Pierre and Marie Curie in the laboratory

Pierre and Marie Curie in the laboratory

She was acutely aware of the importance of promptly publishing her discoveries and thus establishing her priority. Had not Becquerel, two years earlier, presented his discovery to the Académie des Sciences the day after he made it, credit for the discovery of radioactivity, and even a Nobel Prize, would have gone to Silvanus Thompson instead. Curie chose the same rapid means of publication. Her paper, giving a brief and simple account of her work, was presented for her to the Académie on 12 April 1898 by her former professor, Gabriel Lippmann.^[26]

Even so, just as Thompson had been beaten by Becquerel, so Curie was beaten in the race to tell of her discovery that thorium gives off rays in the same way as uranium. Two months earlier, Gerhard Schmidt had published his own finding in Berlin.^[27]

At that time, however, no one else in the world of physics had noticed what Curie recorded in a sentence of her paper, describing how much greater were the activities of pitchblende and chalcolite than uranium itself: "The fact is very remarkable, and leads to the belief that these minerals may contain an element which is much more active than uranium." She later would recall how she felt "a passionate desire to verify this hypothesis as rapidly as possible."^[28]

Pierre Curie was sure that what she had discovered was not a spurious effect. He was so intrigued that he decided to drop his work on crystals temporarily and to join her. On 14 April 1898, they optimistically weighed out a 100-gram sample of pitchblende and ground it with a pestle and mortar. They did not realize at the time that what they were searching for was present in such minute quantities that they eventually would have to process tons of the ore.^[28]

As they were unaware of the deleterious effects of radiation exposure attendant on their chronic unprotected work with radioactive substances, Curie and her husband had no idea what price they would pay for the effect of their research upon their health.^[21]

Pierre, Irène, Marie Curie

In July 1898, Curie and her husband published a paper together, announcing the existence of an element which they named "polonium", in honor of her native Poland, which would for another twenty years remain partitioned among three empires. On 26 December 1898, the Curies announced the existence of a second element, which they named "radium" for its intense radioactivity — a word that they coined.

Pitchblende is a complex mineral. The chemical separation of its constituents was an arduous task. The discovery of polonium had been relatively easy; chemically it resembles the element bismuth, and polonium was the only bismuth-like substance in the ore. Radium, however, was more elusive. It is closely related, chemically, to barium, and pitchblende contains both elements. By 1898, the Curies had obtained traces of radium, but appreciable quantities, uncontaminated with barium, still were beyond reach.^[29]

The Curies undertook the arduous task of separating out radium salt by differential crystallization. From a ton of pitchblende, one-tenth of a gram of radium chloride was separated in 1902. By 1910, Curie, working on without her husband, who had been killed accidentally by a horse drawn vehicle^[30] in 1906, had isolated the pure radium metal.^[31]

In an unusual decision, Marie Curie intentionally refrained from patenting the radium-isolation process, so that the scientific community could do research unhindered.^[32]

In 1903, under the supervision of Henri Becquerel,^[33] Marie was awarded her DSc from the University of Paris.

Nobel Prizes[link]

1903

1911, awarded second Nobel Prize

In 1903 the Royal Swedish Academy of Sciences awarded Pierre Curie, Marie Curie and Henri Becquerel the Nobel Prize in Physics, "in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel."

Curie and her husband were unable to go to Stockholm to receive the prize in person, but they shared its financial proceeds with needy acquaintances, including students.^[21]

On receiving the Nobel Prize, Marie and Pierre Curie suddenly became very famous. The Sorbonne gave Pierre a professorship and permitted him to establish his own laboratory, in which Curie became the director of research.

In 1897 and 1904, respectively, Curie gave birth to their daughters, Irène and Ève Curie. She later hired Polish governesses to teach her daughters her native language, and sent or took them on visits to Poland.^[34]

Curie was the first woman to be awarded a Nobel Prize. Eight years later, in 1911, she received the Nobel Prize in Chemistry, "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."

1911 Nobel Prize

A month after accepting her 1911 Nobel Prize, she was hospitalized with depression and a kidney ailment.

Curie was the first person to win or share two Nobel Prizes. She is one of only two people who have been awarded a Nobel Prize in two different fields, the other person being Linus Pauling (for chemistry and for peace). Nevertheless, in 1911 the French Academy of Sciences did not elect her to be a member by two votes. Elected instead was Édouard Branly, an inventor who had helped Guglielmo Marconi develop the wireless telegraph.^[35] It would be a doctoral student of Curie, Marguerite Perey, who would become the first woman elected to membership in the Academy – over half a century later, in 1962.

Pierre's death[link]

On 19 April 1906 Pierre was killed in a street accident. Walking across the Rue Dauphine in heavy rain, he was struck by a horse-drawn vehicle and fell under its wheels; his skull was fractured.^[30] While it has been speculated that previously he may have been weakened by prolonged radiation exposure, there are no indications that this contributed to the accident.

Curie was devastated by the death of her husband. She noted that, as of that moment she suddenly had become "an incurably and wretchedly lonely person". On 13 May 1906, the Sorbonne physics department decided to retain the chair that had been created for Pierre Curie and they entrusted it to Marie Curie together with full authority over the laboratory. This allowed her to emerge from Pierre's shadow. She became the first woman to become a professor at the Sorbonne, and in her exhausting work regime she sought a meaning for her life.

At First Solvay Conference (1911), Curie (seated, 2nd from right) confers with Henri Poincaré. Standing, 4th from right, is Rutherford; 2nd from right, Einstein; far right, Paul Langevin

Recognition for her work grew to new heights, and in 1911 the Royal Swedish Academy of Sciences awarded her a second Nobel Prize, this time for Chemistry. A delegation of celebrated Polish men of learning, headed by world-famous novelist Henryk Sienkiewicz, encouraged her to return to Poland and continue her research in her native country.^[21]

In 1911 it was revealed that in 1910–11 Curie had conducted an affair of about a year's duration with physicist Paul Langevin, a former student of Pierre Curie's.^[36] He was a married man who was estranged from his wife. This resulted in a press scandal that was exploited by her academic opponents. Despite her fame as a scientist working for France, the public's attitude tended toward xenophobia—the same that had led to the Dreyfus affair–which also fueled false speculation that Curie was Jewish. She was five years older than Langevin and was portrayed in the tabloids as a home-wrecker.^[37] Later, Curie's granddaughter, Hélène Joliot, married Langevin's grandson, Michel Langevin.

Curie's second Nobel Prize, in 1911, enabled her to talk the French government into funding the building of a private Radium Institute (Institut du radium, now the Institut Curie), which was built in 1914 and at which research was conducted in chemistry, physics, and medicine. The Institute became a crucible of Nobel Prize winners, producing four more, including her daughter Irène Joliot-Curie and her son-in-law, Frédéric Joliot-Curie.

World War I[link]

Curie in a World War I mobile x-ray vehicle

During World War I, Marie saw a need for field radiological centers near the front lines to assist battlefield surgeons. After a quick study of radiology, anatomy and automotive mechanics she procured x-ray equipment, vehicles, auxiliary generators and developed mobile radiography units, which came to be popularly known as petites Curies ("Little Curies"). She directed the installation of twenty mobile radiological vehicles and another 200 radiological units at field hospitals in the first year of the war. It is estimated that over one million wounded soldiers were treated with her x-ray units.^[11]

Afterwards, Marie produced hollow needles containing 'radium emanation', a colorless, radioactive gas given off by radium, later identified as radon to be used for sterilizing infected tissue. Curie provided the radium, from her own personal one gram supply.

Also, promptly after the war started, she attempted to donate her gold Nobel Prize medals to the war effort but the official refused to accept them. She was also active member in committees of Polish Polonia in France dedicated to Polish cause.^[38]

Post-war years[link]

In 1921 Curie was welcomed triumphantly when she toured the United States to raise funds for research on radium. Mrs. William Brown Meloney, after interviewing Curie, raised money to buy 1 gram of radium and publicized the trip.^[39] President Warren Harding received her at the White House.^[40]

Her second American tour, in 1929, succeeded in equipping the Warsaw Radium Institute, founded in 1925 with her sister Bronisława as director.^[41]

These distractions from her scientific labors and the attendant publicity caused her much discomfort but provided resources needed for her work.

In her later years Curie headed the Curie Pavilion, a radioactivity laboratory created for her by the Pasteur Institute and the University of Paris. It was one of four major radioactivity-research laboratories, the others being the Cavendish Laboratory, with Ernest Rutherford; the Institute for Radium Research, Vienna, with Stefan Meyer; and the Kaiser Wilhelm Institute for Chemistry, with Otto Hahn and Lise Meitner. ^[42]

In 1933, when Russian physicists George Gamow and his wife — who had together been trying for two years to defect from the Soviet Union — attended the 7th Solvay Conference on physics, in Brussels, Marie Curie and other physicists helped them extend their stay, and Gamow obtained temporary work at the Curie Institute.

Death[link]

1935 statue, facing the Radium Institute, Warsaw

Curie visited Poland for the last time in the spring of 1934.^[21] Only a few months later, on 4 July 1934, Curie died at the Sancellemoz Sanatorium in Passy, in Haute-Savoie, eastern France, from aplastic anemia contracted from her long-term exposure to radiation.^[8] The damaging effects of ionizing radiation were not then known, and much of her work had been carried out in a shed, without the safety measures that would later be developed. She had carried test tubes containing radioactive isotopes in her pocket^{[citation needed]} and stored them in her desk drawer, remarking on the faint light that the substances gave off in the dark.^[43] Marie was also exposed to x-rays from unshielded equipment while serving as a radiologist in field hospitals during the war.

She was interred at the cemetery in Sceaux, alongside her husband Pierre. Sixty years later, in 1995, in honor of their achievements, the remains of both were transferred to the Panthéon, Paris. She became the first – and so far the only – woman to be honored with interment in the Panthéon on her own merits.

Her laboratory is preserved at the Musée Curie.

Because of their levels of radioactivity, her papers from the 1890s are considered too dangerous to handle. Even her cookbook is highly radioactive. They are kept in lead-lined boxes, and those who wish to consult them must wear protective clothing.^[44]

Legacy[link]

Statue, Maria Curie-Skłodowska University, Lublin, Poland

The physical and societal aspects of the work of the Curies contributed substantially to shaping the world of the twentieth and twenty-first centuries. Cornell University professor L. Pearce Williams observes:

The result of the Curies' work was epoch-making. Radium's radioactivity was so great that it could not be ignored. It seemed to contradict the principle of the conservation of energy and therefore forced a reconsideration of the foundations of physics. On the experimental level the discovery of radium provided men like Ernest Rutherford with sources of radioactivity with which they could probe the structure of the atom. As a result of Rutherford's experiments with alpha radiation, the nuclear atom was first postulated. In medicine, the radioactivity of radium appeared to offer a means by which cancer could be successfully attacked.^[31]