Discovery of radium

While chasing polonium, the Curies saw that another fraction, chemically almost pure barium, was also strongly radioactive. Ordinary barium is not radioactive. If radioactivity belongs to atoms, as Marie had shown, something else had to be inside.

Working with the chemist Gustave Bémont they enriched the barium chloride until it was about 900 times more active than uranium. The spectroscopist Eugène Demarçay then found a spectral line belonging to no known element, and it grew stronger as the samples grew more active.

On 26 December 1898 the three proposed the name radium, from the Latin *radius*, a ray. Their note already marvelled that radium makes a fluorescent screen glow: "a source of light, a very weak one to tell the truth, but one that functions without a source of energy," an apparent challenge to the laws of thermodynamics. The Austrian government had supplied residue from the St. Joachimsthal uranium works, the beginning of years of labour.

Radium would later help Rutherford probe the atom and doctors treat cancer. Marie Curie had first hoped the new substance might make up one per cent of the ore. In fact, she said, there is not even one part of radium in a million parts of good ore.