Radium (Ra)

Radium was isolated from a waste pile. When Marie and Pierre Curie found that pitchblende from the Joachimsthal mines in Bohemia was more radioactive than its uranium content could account for, the implication was that something far more active was hiding in it in tiny quantities. The Austrian government let them have the residues left after the uranium had been extracted for glassmaking — several tonnes of it, delivered to a leaking shed on the rue Lhomond that Wilhelm Ostwald later described as a cross between a stable and a potato cellar.

The announcement came on 26 December 1898, jointly with Gustave Bémont, and the confirming evidence was spectroscopic: Eugène Demarçay found an unfamiliar line in the concentrate. The data card credits Pierre Curie, as most single-name attributions do. The physical labour of the separation — hundreds of kilograms of residue boiled down, batch after batch, stirred with an iron rod in a courtyard — was Marie's, and by 1902 it had yielded one tenth of a gram of radium chloride and an atomic weight for the element. The metal itself waited until 1910, when she and André-Louis Debierne obtained it by electrolysis.

A unit named for the people who paid for it

Radium is over a million times more radioactive, gram for gram, than uranium. That enormous activity is why it was the reference standard for the first half of the twentieth century: the curie was originally defined as the activity of one gram of radium-226, and though it is now fixed by decree at exactly 3.7 × 10¹⁰ decays per second, the number itself is a fossil of that original definition.

The cost of the work is not metaphorical. Marie Curie died in 1934 of aplastic anaemia. Her laboratory notebooks are held at the Bibliothèque nationale de France in lead-lined boxes, and consulting them requires signing a waiver; with radium-226's half-life of sixteen centuries, they will stay contaminated for around fifteen hundred years.

Undark, and the women who painted it

Radium's faint self-luminescence — the salt excites the air around it, and mixed with zinc sulfide it glows steadily green — made it commercially irresistible. From 1917 the United States Radium Corporation in Orange, New Jersey employed young women to paint watch and instrument dials with a radium compound sold as Undark. To keep a fine point on the brush, the painters were instructed to shape it between their lips. Some painted their nails and teeth with the leftovers for fun.

The chemistry that followed is the whole reason radium is worth understanding. Radium sits directly below barium in group 2 and its ion carries the same 2+ charge as calcium's. The body's calcium-handling machinery cannot tell the difference, so ingested radium is routed into bone and stays there, irradiating the surrounding tissue for the rest of the person's life.

Mollie Maggia died in 1922; her jawbone had disintegrated to the point where her dentist lifted pieces of it out by hand. The condition acquired a name, radium jaw. Grace Fryer and four co-plaintiffs sued in 1927 and settled in 1928; Catherine Donohue, working for the Radium Dial Company in Ottawa, Illinois, won a separate case in 1938 that the Illinois Supreme Court let stand.

Two things came out of it. Employees in the United States gained a workable right to sue an employer over an occupational disease with a long latency, which had previously been all but impossible. And the surviving dial painters were followed medically for decades, producing the human dose-response data on internally deposited alpha emitters that underpins radiation protection limits to this day.

The radium water worked fine

The consumer market was worse than the industrial one, because it was voluntary. Radium was sold in tonics, suppositories, face creams, toothpaste and bath salts, mostly containing far too little radium to do anything at all — which was, in commercial terms, a mercy.

Radithor was not one of those. Manufactured by William Bailey, it was distilled water with a genuine microcurie apiece of radium-226 and radium-228, and the Pittsburgh steel heir and amateur golfer Eben Byers drank something like 1,400 bottles of it on medical advice. He died in 1932 with most of his upper jaw removed and holes through his skull. The Wall Street Journal headlined the story "The Radium Water Worked Fine Until His Jaw Came Off," and the Federal Trade Commission action that followed strengthened the regulatory case that produced the 1938 Food, Drug, and Cosmetic Act.

The same substitution, deliberately

Here is the turn that makes radium more than a cautionary tale. Bone-seeking is a targeting mechanism. If you want to irradiate cancer that has spread to the skeleton, an ion the bone will collect for you is exactly what you want — provided you choose an isotope with a short half-life and a very short range.

Radium-223 dichloride, licensed in 2013, does precisely that for castration-resistant prostate cancer with bone metastases. Radium-223 has a half-life of 11.4 days rather than radium-226's sixteen centuries, and its alpha particles deposit their energy within a few cell diameters, sparing the bone marrow a few tenths of a millimetre away. Radium is being used to treat the organ it destroyed in the dial painters, by the identical chemical route.

That modern use is narrow. Radium's older medical career — needles and tubes implanted for brachytherapy from the 1900s to the 1950s — ended when reactor-produced cobalt-60, cesium-137 and iridium-192 arrived, all cheaper, all easier to shield, and none of them producing a radioactive gas.

Four isotopes, all temporary, one that gets out

No radium isotope is stable, and each of the natural decay chains supplies its own. Radium-226 comes from uranium-238 and dominates by mass because its half-life is the longest. Radium-228, from thorium-232, lasts under six years. Radium-224 and radium-223 are shorter still.

The one that matters for public health is radium-226, and not for its own sake. It decays to radon — a noble gas that does not stay in the rock it was made in. Radium dissolved in groundwater is regulated for the same reason: the United States sets a limit on combined radium-226 and radium-228 in drinking water, and the wells that exceed it are typically drawing from granite or from uranium-bearing sandstone aquifers.

Chemically, radium is the heaviest and most reactive of the alkaline earth metals, and the freshly cut metal blackens in air almost at once. Almost nobody has ever seen it. Total world production across the whole radium era amounted to a few kilograms, and most of what was produced is now regulated legacy waste — old dials, old needles, and the soil around the factories.