Scientists have discovered an elusive property hidden within promethium, a rare earth element that has remained largely unstudied since its discovery 80 years ago.
The groundbreaking study was published in the journal NatureThis discovery represents a major advance in rare earth element research and has the potential to rewrite chemistry textbooks.
Promethium's 80-year scientific journey
Promethium's story began in 1945 at Oak Ridge National Laboratory (ORNL) (formerly Clinton Laboratory), where the element was first discovered and where it continues to be produced in minute quantities today.
Named after the mythical giant who brought fire to mankind, Promethium symbolizes humanity's quest for knowledge and understanding.
Alex Ivanov, an ORNL scientist who co-led the study, expressed a sense of obligation to uphold the traditions of his team's institution.
“That was the whole goal of this research, to study this extremely rare element and gain new knowledge. Knowing that this element was discovered here at the national lab and where we work, we felt an obligation to do this research to uphold the ORNL tradition,” Ivanov explained.
Solving the Promethium Mystery
A research team led by ORNL scientists prepared a chemical complex of promethium that allowed them to characterize it in solution for the first time.
Through a series of meticulous experiments, they unraveled the secrets of this extremely rare lanthanide, with atomic number 61.
Ilya Popovs, another co-lead investigator from ORNL, highlighted the challenges facing promethium research, saying, “Promethium was the last lanthanide discovered and has been the most difficult to study because it doesn't have a stable isotope.”
Rare earth elements, particularly the lanthanides (elements 57–71 of the periodic table), are important building blocks in many modern technologies, from lasers and permanent magnets to X-ray screens and anti-cancer drugs.
However, our lack of understanding about promethium creates a major gap in scientific knowledge.
Santa-Jansone-Popova, ORNL's co-leader of the study, emphasized the importance of this research.
“There are thousands of papers on the chemistry of lanthanides without promethium. This was a clear gap for the whole of science: scientists could only guess most of their properties. Now we can actually measure some of them,” enthuses Janssonne Popova.
Collaboration among national laboratories
The success of this research relied on the unique resources and expertise of DOE national laboratories.
The team utilized research reactors, hot cells, and supercomputers, as well as the collective knowledge and skills of 18 scientists from a range of disciplines.
To study promethium's properties, ORNL scientists combined radioactive promethium-147 with an unusual organic molecule called a diglycolamide ligand.
Using X-ray spectroscopy, the researchers were able to determine the length of the chemical bonds between promethium and its neighboring atoms, a scientific first that provides a long-standing piece of the puzzle in the periodic table.
Promethium is extremely rare, with only about one pound occurring naturally in the Earth's crust at any one time. Unlike other rare earth elements, it has no stable isotopes, so synthetic promethium is available in very small quantities. ORNL is the only U.S. producer of promethium-147.
Understanding Lanthanide Contraction
One of the most important findings of this study is the first demonstration of lanthanide contraction in solution across the entire lanthanide series, including promethium.
Lanthanide contraction refers to the phenomenon in which elements with atomic numbers 57 through 71 become smaller than expected and their ionic radius decreases as atomic number increases.
“From a scientific point of view, it's really surprising. When I got all the data, I was shocked. This contraction of chemical bonds accelerates along the atomic series, but from promethium onwards, it slows down significantly,” Ivanov noted.
This is a significant achievement in understanding the chemical bonding properties of these elements and their structural changes along the periodic table.
Influence on modern technology
The discovery of promethium's properties has far-reaching implications for modern technology.
Many rare earth elements, including those in the lanthanide and actinide series, are used in a wide range of applications, from cancer diagnosis and treatment to renewable energy technologies and long-life nuclear batteries for deep space exploration.
Jansone Popova emphasized the importance of this achievement in isolating these valuable elements.
“Today's advanced technologies mean that you can't use all of them as a mixture, because you have to separate the lanthanides first,” Jansone-Popova explained.
“This is where shrinkage becomes really important. It basically allows you to separate them, which is still pretty difficult.”
Promethium heralds a new era of rare earths
The team's achievement marks the beginning of a new era in rare earth element research.
“All of the technological marvels of our time contain these rare earth elements in some form or another. We're filling in the gaps,” Popovs concluded.
In summary, this important study of promethium opens up new territory in the exploration of rare earth elements.
By unlocking the secrets of this elusive element, the research team has filled a major gap in scientific knowledge and paved the way for future discoveries.
The impact of this research goes far beyond the realm of basic science, as promethium and other rare earth elements play a key role in modern technology, from medical applications to renewable energy and space exploration.
As scientists continue to build on this breakthrough, we can expect to see a new era of innovation and advancements in the fields of chemistry, materials science, and more.
The full study was published in the journal Neurology. Nature.
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