Radium

• 1. Introduction

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  Radium glows in the dark, and it can wreck itself while it does. The radiation from radium bromide excites nitrogen molecules in the surrounding air, so the crystals shine faintly. The alpha particles that radium emits quickly gain two electrons and become helium. That gas builds up inside the crystals and weakens them. Sometimes the crystals break, and sometimes they explode. Element 88 is a metal that attacks its own structure. From the 1910s to the 1970s, people still found uses for it in luminous devices and in dubious cures. This documentary asks how two scientists pulled a new element out of rock from Jáchymov. It asks why so little radium exists, and what the human body mistakes it for. And it asks why a substance once treated as a marvel was replaced almost everywhere.

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• 2. Discovery at Jáchymov

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  The 21st of December 1898 is the date given for the discovery of radium, in a sample of pitchblende from Jáchymov. Marie Skłodowska-Curie and her husband Pierre Curie made the find. Earlier, they had removed the uranium from the mineral and found that what remained was still radioactive. In July 1898 they pulled out an element similar to bismuth, which turned out to be polonium. Next they isolated a radioactive mixture with two parts. One part was barium compounds, which gave a brilliant green flame. The other was unknown radioactive compounds that produced carmine spectral lines nobody had documented before. The new compounds behaved much like barium compounds but were less soluble. That small difference let the Curies separate them and recognize a new element. They announced it to the French Academy of Sciences on the 26th of December 1898.

  The name arrived around 1899. It comes from the French radium, which was formed from the Latin radius, meaning ray, because the element sends out energy as rays. In the early 1900s, Friedrich Ernst Dorn studied the gas that radium gives off. At the time it was described as "radium emanations". Today that gas is called radon.

  In September 1910, Marie Curie and André-Louis Debierne announced that they had isolated radium as a pure metal. They ran electrolysis on a solution of pure radium chloride, using a mercury cathode. That produced a radium-mercury amalgam. Heating the amalgam in hydrogen drove off the mercury and left the metal behind. Later that year, E. Ebler isolated the metal by a different route, thermally decomposing its azide. Industrial production was carried out by Biraco, a subsidiary of Union Minière du Haut Katanga, at its plant in Olen, Belgium. From 1922 until World War II, the metal was an important Belgian export.

  The historical unit of radioactivity, the curie, was built on this element. It was first defined as the radioactivity of one gram of radium-226.

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• 3. A Vanishingly Rare Metal

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  One ton of pitchblende typically yields only about one seventh of a gram of radium. The Earth's crust holds roughly one part per trillion, or about 900 picograms in each kilogram. A liter of sea water carries about 89 femtograms. Thorium ores hold even less than uranium ores. Every radium isotope has a half-life far shorter than the age of the Earth, so any radium present at the planet's formation vanished long ago. What remains is continually regenerated, because radium is a daughter product in the slow decay chains of uranium and thorium. Radium-226 dominates, and essentially all natural radium is that isotope.

  In the late 19th century, uranium had no large-scale use, so no large uranium mines existed. The silver mines at Jáchymov, then in Austria-Hungary and now in the Czech Republic, were the only big source of uranium ore. For those mines the ore was merely a byproduct. The Curies worked from the residues left after uranium was dissolved out with sulfuric acid. Those residues contained radium sulfate, which is even less soluble than barium sulfate. Barium sulfate was also present, and it acted as a carrier that dragged the radium along. The Curies then boiled the residue with sodium hydroxide and treated it with hydrochloric acid. They repeated precipitation steps to purify the mixed sulfates, then separated barium from radium by fractional crystallisation. They tracked progress with a spectroscope, since radium shows red lines where barium shows green, and with an electroscope.

  In 1904, the Austrian government nationalised the Jáchymov mines and stopped exporting raw ore. Until 1912, when output rose, radium was hard to obtain. The Austrian monopoly set off a worldwide search for uranium ores. The United States took over as the leading producer in the early 1910s, with 70 grams produced in Pittsburgh alone between 1913 and 1920.

  The Curies' basic process was still used for industrial extraction in 1940, though mixed bromides were then used for the fractionation. In 1954, the entire world supply of purified radium came to about 5 pounds. Zaire and Canada were briefly the largest producers in the late 1970s. By 2018, annual production had fallen below 100 grams, and it came mainly from spent nuclear fuel.

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• 4. Heavy Cousin of Barium

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  Barium is radium's closest chemical relative, and the resemblance explains much of the metal's behavior. Radium is the heaviest known alkaline earth metal and the only radioactive member of its group. Pure radium is a lustrous, volatile, silvery-white metal. Its lighter relatives calcium, strontium and barium carry a slight yellow tint. Exposed to air, radium reacts with nitrogen rather than oxygen and quickly turns black, probably from radium nitride. Its melting point is given as either 700 °C or 960 °C, a range that shows how poorly established the figure is. Its boiling point is 1737 °C, and its density is 5.5 grams per cubic centimeter.

  Solid radium compounds start out white. Over time they turn yellow and then dark, damaged by the element's own alpha decay. Radium chloride is colorless and luminescent, and small amounts of barium impurity can give it a rose color. Radium sulfate is the most insoluble sulfate known, since only 2.1 milligrams will dissolve in a kilogram of water at 20 °C. That stubborn insolubility makes it one of the less biologically dangerous radium compounds.

  Thirty-three isotopes of radium are known, with mass numbers from 202 to 234, and every one is radioactive. Four occur naturally, with half-lives of 11.4 days, 3.64 days, 1,600 years and 5.75 years. A fifth, mostly artificial and with a half-life of 15 days, turns up in nature only through traces of neptunium-237. All other known isotopes last under two hours, and most last under a minute. The longest-lived nuclear isomer, radium-205m, survives only between 130 and 230 milliseconds.

  Radium-226 is the last isotope in the decay chain of uranium-238, and its immediate product is the dense radioactive gas radon. Because its half-life is so much shorter, a given molar amount of it is 2.7 million times more radioactive than natural uranium. A lump of the metal stays warmer than its surroundings from the radiation it emits. Experiments at ISOLDE, using a technique called Coulomb excitation, showed that nuclei of several radium isotopes, including radium-224, are shaped like pears.

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• 5. Paint That Glowed

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  A typical self-luminous watch painted with radium contained around 1 microgram of the element. Radium paint also went onto clocks, aircraft switches, and instrument dials and panels. In the mid-1920s, five dying dial painters, known as the "Radium Girls", sued the United States Radium Corporation. Their job was to paint luminous radium paint onto watch and clock components. They were instructed to lick their brushes to get a fine point, which meant swallowing radium. Their illness included sores, anemia and bone cancer.

  During the litigation, investigators found that the company's scientists and management had taken considerable precautions to protect themselves. The employees received no such protection. For several years the companies also tried to avoid liability by insisting that the women were suffering from syphilis.

  The lawsuit and an extensive study by the U.S. Public Health Service made the harm from radioactivity widely known. Dial painters were given safety instructions and protective gear. Radium dials continued to be made, particularly during World War II, but from 1925 onward there were no further injuries to dial painters.

  From the 1960s, radium paint was dropped. Some dials switched to non-radioactive fluorescent materials that glow after exposure to light, though the glow fades. Where long-lasting glow was needed, makers turned to promethium-147, with a half-life of 2.6 years, or tritium, with a half-life of 12 years. Both were still in use as of 2018. Neither damages the phosphor over time, as radium does. Tritium emits very low-energy beta radiation that cannot penetrate the skin, unlike the gamma radiation from radium.

  Many clocks, watches and instruments from the first half of the 20th century, often military, still carry radium paint. They no longer glow, but the radium has barely decayed. Instead, the radiation wore out the zinc sulfide that made the paint fluoresce. The paint, originally white, has usually tarnished to yellow. An intact device is a hazard mainly when many are grouped together or when one is taken apart.

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• 6. The Cure-All Craze

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  Radithor and the Revigator are two names attached to the "radium water" fashion. Radium was once added to cosmetics, soap, razor blades and even beverages, on the strength of its supposed curative powers. Many products were also falsely advertised as radioactive. Authorities in many countries eventually prohibited such products after serious adverse health effects came to light. The idea has not entirely vanished. Spas with radium-rich water, such as those in Misasa, Tottori, Japan, are still occasionally promoted as beneficial, though their radioactivity may come from radon and other radioisotopes.

  Medicine used radium more seriously and paid for it. In Canada in the 1920s and 1930s, radium chloride or radium bromide served as a source of radon gas for cancer treatment. Many early treatments were abandoned because radium bromide exposure caused anaemia, cancer and genetic mutations. In the United States, from 1940 through the 1960s, nasopharyngeal radium irradiation was given to children to treat hearing loss and chronic otitis. Airmen and submarine crew received it too, for barotrauma.

  Biologists also reached for radium. As early as 1904, Daniel MacDougal used it to test whether it could provoke sudden large mutations and drive major evolutionary shifts. Thomas Hunt Morgan used radium to induce changes that produced white-eyed fruit flies. The Nobel-winning biologist Hermann Muller briefly studied radium's effects on fruit fly mutations. He then moved to x-ray experiments because they were more affordable.

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• 7. The Calcium Impostor

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  Of any radium swallowed, 80 percent leaves the body in feces. The other 20 percent enters the bloodstream and mostly settles in the bones. The body treats radium as if it were calcium, since both sit in group 2 of the periodic table. In bone, the radioactivity degrades marrow and can mutate bone cells. Radium and radon emit alpha and gamma rays as they decay, and these kill and mutate cells. Radium is generally considered the most toxic of the radioactive elements. Radon makes matters worse, because as a gas it enters the body far more readily than radium itself.

  The first case of "radium-dermatitis" was reported in 1900, two years after the discovery. The French physicist Antoine Becquerel carried a small ampoule of radium in his waistcoat pocket for six hours, and his skin became ulcerated. Pierre Curie strapped a tube of radium to his arm for ten hours and developed a skin lesion. He took this as a hint that radium might attack cancerous tissue the way it had attacked healthy tissue.

  Handling radium has been blamed for Marie Curie's death from aplastic anemia. After her death, however, analysis found her radium exposure within accepted safe levels. That analysis pointed instead to her use of radiography.

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• 8. Rules and Remaining Uses

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  In 1928, the first meeting of the International Commission on Radiological Protection adopted the earliest published recommendations for protection against radium and radiation generally. They came from the British X-ray and Radium Protection Committee, following preliminary guidance from the Röntgen Society. The meeting led to radiation protection programs coordinated across all the countries represented. Today the commission and the World Health Organization still regulate exposure internationally. The International Atomic Energy Agency publishes safety standards that members may adopt but that it does not enforce. Since 2022 it has also worked to manage and recycle disused radium sources, to reduce the number of old radiotherapy devices that contain them.

  National rules go further. In the United States, the Environmental Protection Agency sets a maximum contaminant level of 5 pCi/L for radium in drinking water. At the time of the Manhattan Project in the 1940s, the tolerance level for workers was 0.1 micrograms of ingested radium. The Nuclear Regulatory Commission requires a license for anyone holding radium with activity above 0.01 microcuries. In the Republic of Korea, the Korea Radioisotope Institute was established in 1985 and the Korea Institute of Nuclear Safety in 1990.

  As of 2018, radium had no commercial applications outside nuclear medicine. In 2013, the United States Food and Drug Administration approved a solution of radium-223 chloride to treat bone metastases. The main indication is bony metastases from castration-resistant prostate cancer. For other jobs, cobalt-60 and caesium-137 have replaced radium, being safer to handle and available in more concentrated form. As of 2011, linear particle accelerators were also gaining ground over cobalt, because cobalt had grown costly and on-site radioactive sources carry risk. Radium was still used in 2007 in some industrial radiography devices that check metal parts for flaws. Mixed with beryllium, it works as a neutron source, and such sources were still sometimes used up to at least 2004 before polonium and americium became more common. Electron tubes such as the Western Electric 346B contain a small amount of radium bromide. It ionizes the fill gas, typically neon or argon, to keep the tube's current steady. One of the few remaining non-medical uses is making actinium in nuclear reactors.

  Physicists now find new reasons to want radium. As the heaviest alkaline earth element, it is well suited to constraining new physics beyond the standard model. Some of its isotopes, such as radium-225, have pear-like nuclear shapes that raise sensitivity to charge parity violation by two to three orders of magnitude compared with mercury. Radium ions are also promising for trapped-ion optical clocks. One such clock has already been demonstrated, and the hope is a transportable version, because every transition it needs can be driven by direct diode lasers at common wavelengths.

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