Marie Curie and her husband Pierre spent nearly four years boiling and processing tonnes of uraninite in a leaky Paris shed without proper ventilation to isolate a tiny amount of radium, and more than a century later, her notebooks from those experiments remain radioactive and are kept in lead-lined boxes

More than a century after Marie and Pierre Curie conducted their pioneering experiments on radioactivity, some of Marie Curie’s personal belongings remain radioactive enough to require special handling. Her laboratory notebooks, furniture and other possessions are kept under protective conditions because of contamination left behind by radium.

Between 1899 and 1902, the Curies spent years processing tonnes of pitchblende, a uranium-rich ore, in a poorly equipped Paris laboratory. Their work eventually led to the isolation of radium chloride, with the couple producing only a tiny quantity after years of grinding, boiling, dissolving and recrystallising the material.

Today, some of Curie’s notebooks are stored in lead-lined boxes at the Bibliothèque nationale de France. Researchers seeking access must sign a waiver and follow safety procedures. Other objects associated with Curie, including furniture, cookbooks and personal belongings, are also preserved with precautions because of radioactive contamination.

The Curies’ makeshift laboratory

The Curies did not conduct their early radioactivity experiments in a modern research facility. Their workspace was an abandoned dissecting room behind the Municipal School of Industrial Physics and Chemistry in Paris.

The building had a leaking glass roof and lacked proper ventilation and fume hoods. It became extremely hot during summer and cold during winter.

The Curies focused on pitchblende after Pierre’s measurements showed that the ore was more radioactive than its uranium content could explain. They concluded that another, more radioactive substance had to be present.

Austria’s government supplied them with uranium-processing waste from Bohemia. Several tonnes of the material were delivered to Paris, and Marie processed it in batches, separating increasingly concentrated radioactive material.

The work was physically demanding. It involved repeatedly heating, mixing and processing large quantities of ore, often with heavy equipment.

Years of chemical processing

The extraction process required repeated chemical separation. The Curies dissolved the ore, precipitated different compounds and separated the radioactive portions before processing them again.

Radium presented a particular challenge because its chemical properties are similar to those of barium. Marie therefore relied on repeated fractional crystallisation to gradually separate radium chloride from barium chloride.

The process took years and produced only a very small amount of radium chloride.

By 1902, Marie had determined radium’s atomic weight at about 225, close to the modern value of 226. The material emitted a faint glow and generated heat without an obvious external energy source.

At the time, the dangers of prolonged exposure to ionising radiation were not fully understood.

The health risks of radium

The Curies recognised that radium could damage living tissue. Pierre even exposed his arm to a radium sample to study the resulting injury. Radium was later used in early cancer treatments because of its ability to destroy cells.

However, the long-term effects of repeated radiation exposure were not yet understood.

The Curies regularly handled radioactive materials and kept samples close to them. Marie also stored radium in her home and laboratory.

Marie Curie died in 1934 at the age of 66 from aplastic anaemia. Her daughter Irène Joliot-Curie, who also worked with radioactive materials, died of leukaemia in 1956. Prolonged radiation exposure has been associated with both conditions, although the precise causes of individual illnesses cannot always be established.

Why Curie’s belongings remain radioactive

Radium-226 has a half-life of about 1,600 years. A radioactive substance's half-life is the time required for half of its radioactive nuclei to decay.

Because of that long half-life, radioactive material that contaminated Curie’s notebooks and belongings more than a century ago remains present today.

Her papers at the Bibliothèque nationale de France are therefore stored in protective conditions, while researchers may need special precautions to examine them. Objects preserved at the Musée Curie in Paris are similarly handled with care.

Curie’s remains were transferred to the Panthéon in Paris in 1995. Her coffin was lined with lead as a precaution because her remains were still measurably radioactive.

A legacy that transformed science

The Curies’ work earned them the 1903 Nobel Prize in Physics, which they shared with Henri Becquerel for their research into radioactivity. Marie became the first woman to receive a Nobel Prize.

After Pierre Curie died in a road accident in 1906, Marie took over his teaching position at the Sorbonne, becoming the university’s first female professor.

She went on to win a second Nobel Prize in Chemistry in 1911 for her work on radium and polonium. She remains the only person to have received Nobel Prizes in two different scientific fields.

The original laboratory where the Curies carried out their early experiments no longer exists, but their scientific legacy continues through the Institut Curie, a major cancer research and treatment centre in Paris.

The radium they worked with may have faded from practical use, but traces of their experiments remain in the notebooks and objects they left behind. Because radium-226 decays so slowly, those traces could remain measurable for centuries to come.