Radium

In 1896 Henri Becquerel found that uranium salts fogged a photographic plate in the dark. Marie Curie took up the phenomenon for her doctoral work and made the crucial measurement: using an electrometer built by her husband Pierre and his brother, she showed that the activity of a uranium compound was proportional to the amount of uranium in it and independent of its chemical form or of the conditions it was kept under. Whatever this was, it was a property of the atom and not of the molecule. She coined the word radioactivity.

She then found that pitchblende, the uranium ore, was substantially more active than its uranium content could account for. The only explanation was an unknown and more active substance present in small quantity. In July 1898 the Curies announced polonium, and on 26 December 1898 radium.

Announcing is not isolating. The Curies obtained tonnes of pitchblende residue from the mines at Jachymov in Bohemia and processed it by hand in an unheated shed, through repeated crystallisations, over four years. By 1902 they had a tenth of a gram of radium chloride and an atomic weight for it. Marie Curie received the Nobel Prize in Physics in 1903 with Pierre and Becquerel, and the Nobel Prize in Chemistry in 1911 for radium and polonium, and remains the only person to have won in two different sciences.

The Curies did not patent the isolation process, taking the view that scientific results should be freely available. Pierre was killed by a horse-drawn wagon in 1906. Marie died in 1934 of aplastic anaemia, consistent with prolonged radiation exposure; her notebooks are still too contaminated to handle without protection and are kept in lead-lined boxes.

Radium glows. A radium salt in the dark emits a faint blue light, because its radiation excites the nitrogen in the surrounding air. It is warm to the touch, generating heat continuously from its own decay. It appeared to produce energy out of nothing.

Nothing in the history of chemistry has been so immediately or so disastrously popular. Between roughly 1900 and 1930 radium was put into toothpaste, face cream, hair tonic, chocolate, suppositories, wool for babies, and water. The Revigator was a radium-lined crock sold so that a household could leave its drinking water in it overnight. Radithor was radium dissolved in water and sold as a tonic; the industrialist Eben Byers drank it by the case and died in 1932 of radiation-induced necrosis of the jaw and skull, and the resulting publicity did more to end the trade than any regulation.

The most serious harm was occupational. Radium mixed into zinc sulfide paint made watch and instrument dials glow, and from 1917 the United States Radium Corporation and others employed young women to paint them. They were instructed to bring the brush to a point with their lips. Radium is chemically similar to calcium and is deposited in bone. The women developed anaemia, bone fractures and necrosis of the jaw, and a number of them died. Five sued in 1927. Their case, and the medical investigation around it, established the principle of employer liability for occupational disease with delayed onset and produced the first serious standards for handling radioactive material. The women who brought it are known as the Radium Girls.

Radium's medical use in cancer treatment, brachytherapy, was genuine and is the one application that survived; it has since been replaced by cheaper and safer artificial isotopes such as cobalt-60 and iridium-192.