Scientists Discovered Promethium in 1945. They Only Just Learned What It Actually Does.

Story by Darren Orf • 3d • POPULAR MECHANICS


Scientists have unveiled the chemical secrets of Promethium, a rare element discovered in 1945© Jose A. Bernat Bacete - Getty Images

Although the Periodic Table of Elements is an impressive achievement of human understanding, scientists are still finding secrets about certain elements among its carefully arranged rows and columns.

One such element is Promethium, and a new study from scientists at Oak Ridge National Laboratory has successfully analyzed chemical properties of the rare earth metal some 80 years after its discovery.

The team used a new technique to create a pure isotope of the element, and the discovery could make protection of this rare element easier, while also increasing our understanding of lanthanide elements in general.

The Periodic Table of Elements is a testament to the many millennia of human exploration of the chemical world. However, not everything is known about the elements that appear in its colored and meticulously arranged rows and columns. One such element is Promethium.

First discovered 80 years ago in 1945, Promethium is a lanthanide (one of a series of 15 metallic chemicals also known as rare earth metals) with the atomic number 61, and in the following eight decades after its discovery, many of its chemical properties remained a mystery. This didn’t stop its use—traces of the element can be found in everything from smartphone screens to nuclear batteries—but studying it has proven difficult. That’s because it’s an extremely rare element that decays into other elements, meaning you can only really get Promethium from fission.

Scientists from the Oak Ridge National Laboratory, a descendant of the original lab that discovered the element back in 1945, implemented a new process last year that allowed for the creation of a pure sample of Promethium-147, an isotope of Promethium. Once this sample was combined with a ligand to form a stable complex in water, the team could finally analyze the bonding properties of Promethium using X-ray spectroscopy. The results of the study were published last week in the journal Nature.

“Because it has no stable isotopes, promethium was the last lanthanide to be discovered and has been the most difficult to study,” ORNL’s Ilja Popovs, a co-author of the study, said in a press statement. “Anything that we would call a modern marvel of technology would include, in one shape or another, these rare earth elements…we are adding the missing link.”

To get a closer look at the Promethium element, researchers first created a compound known as bispyrrolidine diglycolamide (PyDGA). When this was combined with Promethium, the resulting Pm-PyDGA’s electron structure created a pink hue, but more importantly it allowed the scientists to fire x-rays and measure the frequencies absorbed, leading to clues about Promethium’s chemical bonds.

Understanding Promethium and its bonding properties will help ORNL produce greater quantities of the rare earth metal while also improving ways to separate it from other lanthanides. That’s because the team successfully demonstrated a phenomenon known as “lanthanide contraction,” which explains how as atomic numbers increase in the lanthanide series, the radii of ions decrease, according to ORNL. This creates a specific chemical and electronic signature, and ORNL scientists recorded a clear “promethium signal,” which will help understand the trend across other rare earth metals.

“You cannot utilize all these lanthanides as a mixture in modern advanced technologies, because first you need to separate them,” Santa Jansone-Popova, “This is where the contraction becomes very important; it basically allows us to separate them, which is still quite a difficult task.”

So while the Periodic Table of Elements may be a story about humanity’s chemical ingenuity, it’s also a scientific story that’s still unfolding in laboratories across the world.