Promethium

Czech chemist Bohuslav Brauner predicted the existence of element 61 in 1902, speculating that there must be an unknown element between neodymium and samarium. In the ensuing four decades, researchers around the world tried to find this element without success.

But a massive breakthrough happened across the world in 1926! That year, teams in Italy and at the University of Illinois claimed to have found element 61. That same year, British chemist Charles James, who was one of the three researchers to have discovered lutetium, also claimed to have discovered the element.

Today, we know that James couldn’t have found element 61; although the element exists in nature, its short half-life means that it is practically impossible to find. Conclusive evidence of element 61’s discovery came only in 1945, when Jacob A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell at Oak Ridge National Laboratory (then known as Clinton Laboratories) succeeded in separating element 61 from the byproducts of irradiating uranium in a reactor. The researchers named the element promethium, after Prometheus, who in Greek mythology stole fire from the gods!

Promethium is a silvery metal that, true to Bohuslav Brauner’s predictions, has qualities between those of neodymium and samarium. It is a lanthanide, or rare-earth, element. Not all the rare-earth elements are actually rare, but promethium is! All of promethium’s isotopes are radioactive. The longest-lived isotope, promethium-145, has a half-life of only around 18 years.

Promethium-147 is the most widely consumed isotope of the element. It’s often used to make paint glow. Promethium-147 has also been used in atomic batteries, which use the element’s radioactive decay to produce electricity that can be used in aircraft, watches, pacemakers, and more.

Few promethium compounds have been studied, largely because the element is so unstable. However, promethium compounds like promethium(III) chloride have been used in luminous paint, and other compounds are used in atomic batteries.

Researchers have found 41 promethium isotopes, all of which are unstable (radioactive). The longest-lived isotope, promethium-145, has a half-life of around 18 years. Promethium-147, the most used isotope of the element, has a half-life of around 2.6 years. Most other isotopes have half-lives of a few seconds or less!

Although promethium is produced in nature as a byproduct of fissioning uranium, promethium decays too quickly, and occurs in quantities too small, to be gathered from these sources. Some elements just don’t want to be found!

Today, promethium is produced in much the same way that it was at the time of its discovery—as a byproduct of fission in nuclear reactors. Like the saying goes, one person’s trash is another’s promethium! Russia is the only commercial producer of promethium today. Only a few hundred grams of the element are produced each year.