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Although the Periodic Table of the Elements is an impressive feat of human understanding, scientists still discover secrets about certain elements among its carefully arranged rows and columns.
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One such element is promethium, and a new study by scientists at Oak Ridge National Laboratory has successfully analyzed the chemical properties of the rare earth metal some 80 years after its discovery.
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The team used a new technique to create a pure isotope of the element, and the discovery could make protecting this rare element easier, while increasing our understanding of the lanthanide elements in general.
The periodic table of the elements is a testament to the many millennia of human exploration of the chemical world. But no everything is known for the elements that appear in its colorful 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 atomic number 61, and for the next eight decades after its discovery, many of its chemical properties remained a mystery. That hasn’t stopped its use—traces of the element can be found in everything from smartphone screens to nuclear batteries—but studying it has proven difficult. This is because it is an extremely rare element that decays into other elements, meaning you can only really get promethium from fission.
Scientists at Oak Ridge National Laboratory, a descendant of the original laboratory that discovered the element in 1945, implemented a new process last year that allowed 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 binding properties of Promethium using X-ray spectroscopy. The results of the study were published last week in the diary Nature.
“Because it has no stable isotopes, promethium is the last lanthanide discovered and is the most difficult to study,” ORNL’s Ilya Popovs, co-author of the study, said in a press release. “Anything we would call a modern marvel of technology would include in one form or another these rare earth elements…we are adding the missing link.”
To take a closer look at the element Promethium, the researchers first created a compound known as bispyrrolidine diglycolamide (PyDGA). When this is combined with promethium, the resulting electronic structure of Pm-PyDGA creates a pink hue, but more importantly, it allows scientists to shoot X-rays and measure the absorbed frequencies, leading to clues about the chemical bonds of promethium.
Understanding promethium and its bonding properties will help ORNL produce larger quantities of the rare-earth metal while 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 the atomic numbers in the lanthanide series increase, the radii of the ions decrease, according to ORNL. This creates a specific chemical and electronic signature, and the ORNL scientists recorded a clear “promethium signal” that will help understand the trend in other rare earth metals.
“You can’t use all these lanthanides as a mixture in today’s advanced technologies because you have to separate them first,” Santa Jansone-Popova, “This is where shrinkage 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 of humanity’s chemical ingenuity, it is also a science story still unfolding in laboratories around the world.
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