Marie and Pierre Curie discovered two chemical elements: polonium and radium. Both were identified in 1898, extracted painstakingly from tons of a uranium-bearing mineral called pitchblende at a modest laboratory in Paris. The discoveries transformed the young field of radioactivity and eventually earned Marie Curie two Nobel Prizes, but the story of how the Curies found these elements involves far more sweat and ingenuity than the brief textbook version suggests.
Polonium Came First
The starting point was a puzzle. In 1896, the French physicist Henri Becquerel had noticed that uranium salts emitted rays capable of fogging a photographic plate, even in the dark. Marie Curie, then searching for a doctoral research topic, decided to investigate whether other substances produced similar rays. Using a sensitive instrument called a piezoelectric electrometer, originally designed by Pierre Curie and his brother Jacques, she measured the electrical conductivity of air around various substances to detect radioactive emissions.1Research Starter. Pierre Curie She tested every element and mineral she could get her hands on, and quickly found that thorium was also radioactive. But the real breakthrough came when she noticed something strange: pitchblende, the ore from which uranium was extracted, was significantly more radioactive than pure uranium itself. That meant something else inside the ore had to be producing the extra radiation.
Marie and Pierre worked together to isolate whatever was generating those excess rays. Through a series of chemical separations, they progressively concentrated the radioactive component. In July 1898, they announced the discovery of a new element that behaved chemically like bismuth but was intensely radioactive. Marie named it polonium, after her native Poland, which at the time was partitioned among three empires and did not exist as an independent country on any map. The naming was a deliberate political statement embedded in a scientific paper.
Radium Followed Months Later
Even after polonium was separated out, the remaining pitchblende residues still showed powerful radioactivity. The Curies, now joined by chemist Gustave Bémont, continued their fractional crystallization work and in December 1898 announced a second new element. This one behaved chemically like barium but emitted radiation far stronger than anything previously measured. They called it radium, from the Latin word for “ray.”2PubMed. Marie Curie: recipient of the 1911 Nobel Prize in Chemistry and discoverer of the chemical elements polonium and radium
Announcing a new element was one thing; proving it was quite another. The scientific community of the late 1890s required a measured atomic weight and a distinct spectral signature before a new element would be accepted into the periodic table. The Curies had identified radium by its extraordinary radioactivity, but they had not yet isolated it in pure form. That task would take Marie another four years of brutal physical labor.
The Scale of the Extraction Work
Polonium and radium exist in pitchblende in almost inconceivably small quantities. To isolate enough radium to determine its atomic weight, Marie Curie processed roughly eight tons of pitchblende residue, much of it donated by the Austrian government from mines in Bohemia. The Curies worked in a converted shed at the School of Physics and Chemistry in Paris, a space that had no proper ventilation and leaked when it rained. Pierre focused on studying the physical properties of the radiation, while Marie handled most of the chemical processing, stirring boiling mixite in iron cauldrons, pouring off liquids, and repeating the crystallization steps hundreds of times.
By 1902, Marie had isolated about one-tenth of a gram of radium chloride from all that ore. She measured its atomic weight at roughly 225 (later refined to 226), confirming it as a genuinely new element. Polonium proved even harder to isolate in visible quantities because of its much shorter half-life. A sample of polonium decays rapidly, losing half its mass in about 138 days, which meant that by the time enough was concentrated, much of it had already transformed into lead.
Why Radioactivity Was So Revolutionary
To appreciate what the Curies accomplished, it helps to understand how disruptive radioactivity was to the physics of their era. The prevailing view was that atoms were stable, indivisible units. When the Curies showed that certain atoms spontaneously emitted energetic particles and rays, they were effectively demonstrating that atoms could change from one form to another. Marie Curie coined the term “radioactivity” itself, and her systematic survey of minerals proved that this was not a quirk of uranium alone but a property shared by several elements.
Radium was the showpiece. It glowed faintly in the dark, it was warm to the touch because of the energy its decay released, and it was roughly a million times more radioactive per gram than uranium. Scientists and the public alike were fascinated. Within a few years, radium became one of the most famous substances on Earth, and small quantities commanded prices higher than gold.
Pierre’s Contributions and the Question of Credit
Popular accounts sometimes treat the discoveries as Marie’s alone, or conversely, as primarily Pierre’s with Marie as an assistant. The historical record supports neither version. The initial insight that pitchblende contained unknown radioactive elements was Marie’s, arising from her doctoral research. But Pierre abandoned his own research on crystal symmetry to join her, and his expertise in precision measurement and instrumentation was essential to the project. The piezoelectric electrometer he had co-invented was the key tool that allowed them to detect and quantify radioactivity with enough accuracy to track it through successive chemical separations.1Research Starter. Pierre Curie
The papers announcing polonium and radium listed both Marie and Pierre as authors (along with Bémont for the radium paper). Pierre contributed more to the physics side, studying the nature of the radiation itself and its effects on matter. Marie contributed more to the chemistry, performing the separations and ultimately producing the pure samples. It was genuinely a partnership, and one of the most productive in the history of science. Pierre’s death in a traffic accident in 1906 left Marie to carry the work forward alone, which she did for nearly three more decades.
Two Nobel Prizes, Two Different Fields
In 1903, Marie and Pierre Curie shared the Nobel Prize in Physics with Henri Becquerel. The prize recognized their collective work on radioactivity. There is a well-documented backstory: the original nomination included only Pierre and Becquerel. Pierre insisted that Marie be added, and the committee relented. Marie Curie became the first woman to win a Nobel Prize.
In 1911, Marie received a second Nobel Prize, this time in Chemistry, specifically for her discovery of polonium and radium and her work isolating radium and studying its chemical properties.3PubMed Central. Marie Curie (1867-1934): Twice Nobel Laureate and Her Enduring Legacy in Radiation Medicine She remains the only person ever to have won Nobel Prizes in two different scientific disciplines.2PubMed. Marie Curie: recipient of the 1911 Nobel Prize in Chemistry and discoverer of the chemical elements polonium and radium A handful of people have won two Nobels, but the others won in the same field or in the Peace category. Marie’s two prizes bridged physics and chemistry, reflecting the genuinely interdisciplinary nature of her work.
What Happened to Polonium and Radium After Discovery
The two elements the Curies found went on to have very different histories. Radium became a cultural sensation in the early twentieth century. Doctors began using it almost immediately to treat cancer, placing small radium sources near tumors to destroy malignant cells. This practice, which evolved into what we now call brachytherapy, was one of the earliest forms of radiation therapy and remains in use today in modified form.4International Journal of Radiation Oncology, Biology, Physics. A Story of Hypofractionation and the Table on the Wall Beyond medicine, radium found its way into consumer products: luminous watch dials, quack health tonics, even toothpaste. The dangers of chronic radium exposure only became widely understood after factory workers painting radium dials began developing bone cancer and jaw necrosis in the 1920s.
Polonium, by contrast, remained obscure for most of the twentieth century. Its rapid decay and extreme scarcity made it impractical for most applications. It found niche industrial uses as a static eliminator in manufacturing and as a lightweight heat source in certain space missions. Polonium re-entered public consciousness in 2006 when the former Russian intelligence officer Alexander Litvinenko was assassinated in London with polonium-210 slipped into his tea. The case highlighted just how toxic the element is: a speck invisible to the naked eye can deliver a lethal dose of radiation internally.
Where Polonium and Radium Sit in the Periodic Table
Polonium (element 84) sits in the chalcogen group, the same column as oxygen, sulfur, and selenium, though it has almost nothing in common with those lighter elements in practical terms. It is a metal, silvery in appearance, and so radioactive that it self-heats to the point of glowing. Every isotope of polonium is radioactive, and the most stable one has a half-life of only about 103 years, which is why almost none exists naturally on Earth except in trace amounts from the decay of uranium.
Radium (element 88) belongs to the alkaline earth metals, in the same column as calcium and barium. Chemically, it behaves a lot like barium, which is precisely why separating the two was such an ordeal for Marie Curie. Radium’s most stable isotope, radium-226, has a half-life of about 1,600 years. That is long enough for small quantities to accumulate in uranium ore but short enough on geological timescales that radium is always in the process of being both created and destroyed. Neither element has any stable isotope, meaning both are inherently radioactive regardless of conditions.
Common Misconceptions About the Curies’ Discoveries
One persistent myth is that the Curies “discovered radioactivity.” They did not. Becquerel discovered the phenomenon in 1896. What the Curies did was far more systematic: Marie coined the term, proved the phenomenon was an atomic property rather than a chemical reaction, showed it was not limited to uranium, and then used it as a detection tool to find entirely new elements. The Curies advanced and exploited radioactivity, but Becquerel gets credit for noticing it first.
Another misconception is that Marie Curie worked in heroic isolation. In reality, the Paris research community provided essential support. Eugène Demarçay, a spectroscopist, confirmed the spectral lines of radium. Bémont assisted with the chemical separations. The Austrian government supplied the pitchblende residues. And Pierre’s contributions were indispensable. Marie’s tenacity and brilliance are not diminished by acknowledging that science, even groundbreaking science, is collaborative.
A third misconception concerns Marie’s death. People often say she “died of radiation exposure.” She did die of aplastic anemia in 1934, and decades of handling radioactive materials almost certainly contributed. But the exact causal chain is impossible to confirm retrospectively. What is well-documented is that the Curies worked without any radiation shielding. Pierre frequently carried vials of radium in his pocket; Marie kept samples on her desk. Her personal notebooks from the 1890s remain so radioactive that researchers at the Bibliothèque nationale de France must sign a liability waiver and wear protective clothing to handle them. They are stored in lead-lined boxes.
Elements Named by the Curie Family
The Curie legacy extends beyond polonium and radium. In 1944, Glenn Seaborg and his team at the University of California, Berkeley, synthesized element 96 and named it curium in honor of both Marie and Pierre. Curium is a synthetic, highly radioactive actinide that does not occur in nature. It has been used as a power source in space probes and as an alpha particle source in scientific instruments. The naming was a deliberate tribute: Seaborg chose to honor the Curies in the same way that gadolinium had been named after Johan Gadolin, recognizing pioneers whose work opened entire fields.
Curium sits two rows below radium on the periodic table, in the actinide series. Its most common isotope, curium-244, has a half-life of about 18 years and generates enough heat from its own radioactive decay to be useful in thermoelectric generators. The element is produced in nuclear reactors in tiny amounts and is one of the materials that contributes to the long-term radioactivity of spent nuclear fuel. Marie Curie never knew about it, of course, but the fact that an element forged in reactors bears her name underscores how thoroughly her work reshaped our understanding of the atom.