If you want to see Marie Curie’s lab notebooks today, you have to sign a form first. It says you understand the risk. Then you put on protective clothing and a librarian brings out a lead-lined box.

Inside are ordinary-looking hardback notebooks filled with neat handwriting, columns of figures and small sketches. They are more than 120 years old and they are still giving off radiation. They will keep doing so for roughly 1,500 more years.

A shed on the rue Lhomond

The story of how they got that way starts in 1898. Marie Curie was 30, a Polish immigrant in Paris who had just finished a physics degree and was looking for a topic for her doctorate. She chose a strange new phenomenon that Henri Becquerel had noticed the year before: uranium salts gave off invisible rays that could fog a photographic plate.

Marie began measuring the rays with an instrument her husband Pierre had built. She soon found that pitchblende, a heavy black uranium ore mined in what is now the Czech Republic, was far more active than the uranium in it could explain. Something else in the rock was giving off rays. Something new.

She and Pierre needed a place to find out what it was. The school where Pierre taught, on the rue Lhomond, gave them an abandoned shed across the courtyard. It had once been a dissecting room for medical students. The glass roof leaked when it rained. In winter it was close to freezing, and in summer the heat was brutal. There was no proper ventilation, so a lot of the work had to be done outside in the yard, and when the weather forced them in, the fumes stayed in with them.

Tonnes in, a pinch out

Pitchblende was expensive. The Curies could not afford much, so they arranged to get the leftover waste from a uranium mine in Bohemia, the crushed rock left after the uranium had been taken out. It arrived by the cartload, mixed with pine needles from the forest floor where it had been dumped.

Marie did most of the heavy work. She later wrote that she sometimes spent a whole day stirring a boiling mass in a cast-iron basin with an iron rod nearly as tall as she was. The ore was dissolved in acid, filtered, precipitated, redissolved and crystallized again and again. Each round threw away the ordinary elements and kept a slightly purer, slightly more radioactive residue.

The numbers were staggering. To get anything they could hold up and call radium, they eventually worked through several tonnes of ore, commonly put at around seven, over close to four years. In 1902 Marie finally had one-tenth of a gram of pure radium chloride, roughly the weight of a few grains of rice, enough to measure the new element’s atomic weight and give it a place on the periodic table.

Working in the dark

The shed had one feature the Curies loved. At night the shelves glowed. Rows of little glass dishes and tubes of concentrated radium salts gave off a faint blue-green light. Marie wrote that she and Pierre would sometimes go back after dinner just to look at them.

Nobody yet understood what those glowing tubes were doing to the people around them. Pierre carried a sample of radium in his waistcoat pocket to show colleagues and got a burn on his skin that took months to heal. Marie handled the material with bare hands, kept samples in her desk drawer and breathed the shed’s air for years. Radioactive dust settled on everything: benches, papers, clothing, the pages she was writing on.

Radium-226, the isotope they had isolated, has a half-life of about 1,600 years. That is why the contamination has not gone anywhere. Their notebooks, letters, furniture, even a cookbook from the Curie household, all still register on a Geiger counter.

What the notebooks say

The books themselves are mostly the daily grind of the work: weights, readings, temperatures, dates. In one you can see the entry from the days when Marie recorded the atomic weight of radium. In others there are notes in Pierre’s hand alongside hers, before his death in a street accident in 1906.

The Bibliothèque nationale de France in Paris holds them now, along with a great deal of the Curies’ other papers. Because they are contaminated, they are kept in lead-lined containers and handled under conditions closer to a radiation lab than a reading room. Scholars can still consult them, which is how the details of the waiver and the protective clothing became widely known.

Marie Curie herself was reburied in the Panthéon in 1995, the first woman honored there on her own merits. Her coffin was lined with an inch of lead. When it was opened before the transfer, her remains were found to be far less radioactive than expected, which led researchers to suspect that the radiation that eventually killed her came less from radium than from the X-ray work she did during the First World War, driving mobile radiography units to the front.

The cost of the shed

The Curies shared the 1903 Nobel Prize in Physics with Becquerel for the discovery of radioactivity. Marie won a second Nobel, in Chemistry, in 1911 for isolating radium and polonium, and remains the only person to have won in two different sciences. She died in 1934 of aplastic anemia, almost certainly caused by decades of radiation exposure.

The shed on the rue Lhomond was demolished long ago. What survives of it are the notebooks, still warm in the way that only radium can make a piece of paper warm, waiting in their lead boxes for the next reader willing to sign the form.