A Tenth of a Gram

In 1897 a thirty-year-old physicist in Paris took a routine measurement and got a number that was too big.

The ore in front of her was giving off more radiation than the uranium inside it could possibly produce. There was only one explanation: it contained something else, something nobody had ever seen.

Proving that took four years of shovelling, boiling and crystallising tonnes of ore in a shed with a leaking roof, and produced a tenth of a gram of a new element.

It also killed her, slowly, over the next thirty-six years.

Maria Skłodowska was born in Warsaw in 1867, in a Poland that had been erased from the map and was being run as a Russian province.

Polish was discouraged, Polish history was not taught, and universities did not admit women. She went to an illegal one instead — the Flying University, which met in private apartments and changed address to stay ahead of the police.

She and her sister made a deal: Maria would work as a governess and send money for Bronisława to study medicine in Paris, and then Bronisława would do the same for her.

It took five years. She reached Paris in 1891, aged twenty-three, and enrolled at the Sorbonne as Marie.

She arrived with almost no money and lived in an unheated attic, sometimes fainting from hunger while working.

In 1893 she came first in her class in physics; the next year, second in mathematics.

In 1894 she met Pierre Curie, a quiet physicist who had, with his brother, invented a device that turns tiny electric charges into measurable numbers using a quartz crystal.

They married in 1895. She refused a wedding dress and bought a dark one she could work in. That electrometer is the reason the next four years happened at all.

In 1896 Henri Becquerel noticed that uranium salts fog a photographic plate in the dark. It was a curiosity, and most physicists moved on.

Curie took it up as a thesis topic and did one thing differently. Instead of looking at fogged plates, she measured the rays as electricity: the radiation makes the air conduct, and the tiny current is proportional to the activity.

With Pierre’s quartz electrometer that current became a number she could trust to a few per cent.

Then she measured everything she could get hold of. Press the samples and read the meter.

Her measurements gave a clean rule: the activity of a uranium compound depends only on how much uranium it contains. Not on temperature, not on chemistry, not on light.

Then she measured pitchblende, the ore uranium is mined from. It was four times as active as pure uranium — despite containing less of it.

She checked another ore, chalcolite, and made an artificial version in the laboratory. The artificial one behaved itself; the natural one did not.

There was only one way out. Something else is in there, in traces too small to see, and whatever it is must be enormously more active than uranium.

To prove a new element exists you have to produce some of it, weigh it, and measure its atomic weight. There is no shortcut.

The Austrian government gave them tonnes of pitchblende residue, the waste left after the uranium had been extracted. The new elements were in the waste.

The process is ordinary chemistry done an extraordinary number of times: dissolve, precipitate, filter, crystallise, keep the fraction that is more active, repeat.

She did it in a shed, stirring boiling vats with an iron rod almost as tall as she was, in winter, while raising a child.

Run the separation and watch the mass fall.

By July 1898 the active fraction had been narrowed enough to announce a first new element. She named it polonium, after the country that had been wiped off the map.

It was a political act in a scientific paper, and it was deliberate.

In December they announced a second, far more active element: radium. Four more years of work turned that announcement into a tenth of a gram of pure radium chloride, and an atomic weight of two hundred and twenty-six.

At night the shed glowed. The vials of concentrate gave off a faint blue light, and they would go and look at them in the dark.

What she had found was stranger than a new element. Radioactivity ignores chemistry completely.

Heat a radium sample, freeze it, dissolve it in acid, combine it into different compounds: the rate at which it emits is exactly the same. Nothing we can do to matter touches it.

That is because it comes from the nucleus, and in 1898 nobody knew there was a nucleus. What it meant was that atoms are not eternal and indivisible. They break.

Each atom goes at a random moment, but a large population halves on a fixed schedule. For radium, sixteen hundred years. For polonium, a hundred and thirty-eight days. Set the clock running.

Radium burns living tissue. Pierre proved it by strapping a sample to his own arm and documenting the wound for weeks.

If it destroys tissue, it can destroy a tumour. Within a few years radium was being used against cancer, a treatment the French called curietherapy, and the ancestor of modern radiotherapy.

The same property was also sold as a tonic. Radium water, radium toothpaste, radium face cream. People died of it.

The Curies refused to patent their process. Anyone could use it. They kept almost nothing, and had to beg for the radium they needed to keep working.

In 1903 the Nobel committee prepared to award the physics prize for radioactivity to Henri Becquerel and Pierre Curie.

Pierre was told in advance, and wrote back that the work was hers as much as his and that he would not accept an award that excluded her. Her name was added.

She became the first woman to receive a Nobel Prize. She is still the only person to have won in two different sciences.

Most of the prize money went on equipment and on paying off the loans that had kept the shed running.

On the nineteenth of April 1906 Pierre stepped into a Paris street in the rain and was run over by a heavy wagon. He was forty-six.

She took his chair at the Sorbonne, the first woman to hold one, and kept the laboratory going.

In 1911, days before she was awarded a second Nobel Prize, French newspapers published private letters and ran a campaign against her as a foreigner and a homewrecker. A member of the Swedish Academy wrote suggesting she not come to the ceremony.

She replied that the prize was for radium and polonium, that her private life had nothing to do with her science, and that she would be attending. She went.

When the war started in 1914 she stopped research and did something unglamorous and enormous.

X-rays existed but were in hospitals far behind the lines. Curie raised money, had cars converted into mobile radiography units with their own generators, and got them to the front so surgeons could find shrapnel before operating.

She learned to drive, learned basic vehicle repair, trained women as radiographers, and worked at the front herself with her daughter Irène, who was seventeen.

Twenty vans in the first year, and about two hundred fixed radiological posts. The soldiers called the cars petites Curies.

She died on the fourth of July 1934 of aplastic anaemia: her bone marrow had stopped making blood cells, after nearly forty years of handling radioactive material with no protection at all.

Her laboratory notebooks are still radioactive. They are kept in lead-lined boxes at the Bibliothèque nationale, and anyone who wants to read them signs a waiver.

Radium-226 has a half-life of sixteen hundred years. The notebooks will be dangerous for a very long time, for exactly the reason she worked out.

The year after she died, her daughter Irène won a Nobel Prize of her own.

The whole thing started with a measurement that did not fit, and a refusal to round it away.

Following that discrepancy produced two elements, the word radioactivity, the first evidence that atoms transform, the beginning of nuclear physics, and a cancer treatment still used every day.

The chapter stills in this film are AI-generated. The photographs of Marie and Pierre, their laboratory and the pitchblende are real.

Sources are listed below.