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Promethium revolution: How a new rare earth element is set to transform technology

Scientists have discovered the elusive properties hidden within promethium, a rare earth element that has remained largely unexplored since its discovery 80 years ago.

This landmark research, published in the journal Nature, marks a significant advance in rare earth studies and has the potential to rewrite chemistry textbooks.

Promethium’s 80-year scientific journey

The story of promethium began in 1945 at the Oak Ridge National Laboratory (ORNL), formerly known as Clinton Laboratories. It was here that the element was first discovered and continues to be produced in minute quantities.

Named after the mythological Titan who delivered fire to humans, promethium symbolizes the human quest for knowledge and understanding.

Alex Ivanov, an ORNL scientist who co-led the research, expressed the team’s sense of obligation to uphold the laboratory’s legacy.

“The whole idea was to explore this very rare element to gain new knowledge. Once we realized it was discovered at this national lab and the place where we work, we felt an obligation to conduct this research to uphold the ORNL legacy,” Ivanov explained.

Unlocking the mysteries of promethium

The research team, led by ORNL scientists, prepared a chemical complex of promethium, enabling its characterization in solution for the first time.

Through a series of meticulous experiments, they exposed the secrets of this extremely rare lanthanide, whose atomic number is 61.

Ilja Popovs, another co-lead of the research from ORNL, highlighted the challenges faced in studying promethium, saying, “Because it has no stable isotopes, promethium was the last lanthanide to be discovered and has been the most difficult to study.”

Rare earth elements, particularly lanthanides (elements 57-71 on the periodic table), are crucial components in many modern technologies, from lasers and permanent magnets to X-ray screens and cancer-fighting medicines.

However, the lack of understanding surrounding promethium has been a significant gap in scientific knowledge.

Santa Jansone-Popova, also a co-lead of the study from ORNL, emphasized the importance of this research.

“There are thousands of publications on lanthanides’ chemistry without promethium. That was a glaring gap for all of science. Scientists have to assume most of its properties. Now we can actually measure some of them,” Jansone-Popova enthused.

Collaborative effort across national labs

The success of this research relied on the unique resources and expertise available at DOE national laboratories.

The team utilized a research reactor, hot cells, and supercomputers, as well as the accumulated knowledge and skills of 18 scientists from various fields.

To study promethium’s properties, the ORNL scientists bound radioactive promethium-147 with special organic molecules called diglycolamide ligands.

Using X-ray spectroscopy, they determined the length of the promethium chemical bond with neighboring atoms, a first for science and a long-missing piece of the periodic table puzzle.

Promethium is incredibly rare; only about a pound occurs naturally in the Earth’s crust at any given time. Unlike other rare earth elements, only minute quantities of synthetic promethium are available due to its lack of stable isotopes. ORNL is the sole producer of promethium-147 in the United States.

Understanding Lanthanide Contraction

One of the most significant findings of this study was the first demonstration of lanthanide contraction in solution for the entire lanthanide series, including promethium.

Lanthanide contraction refers to the phenomenon where elements with atomic numbers between 57 and 71 are smaller than expected, with their ionic radii decreasing as atomic numbers increase.

“It’s really astonishing from a scientific viewpoint. I was struck once we had all the data. The contraction of this chemical bond accelerates along this atomic series, but after promethium, it considerably slows down,” Ivanov noted.

This is an important landmark in understanding the chemical bonding properties of these elements and their structural changes along the periodic table.

Implications for 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, have applications ranging from cancer diagnostics and treatment to renewable energy technologies and long-lived nuclear batteries for deep space exploration.

Jansone-Popova highlighted the importance of this achievement in the separation of these valuable elements.

“You cannot utilize all these lanthanides as a mixture in modern advanced technologies, because first you need to separate them,” Jansone-Popova explained.

“This is where the contraction becomes very important; it basically allows us to separate them, which is still quite a difficult task.”

Promethium ushers in a new rare earth era

The team’s achievement sets the stage for a new era of research in rare earth elements.

“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,” Popovs concluded.

In summary, this important research on promethium opens a new frontier in the exploration of rare earth elements.

By unlocking the secrets of this elusive element, the team has filled a significant gap in scientific knowledge and paved the way for future discoveries.

The implications of this study extend far beyond the realm of basic science, as promethium and other rare earth elements play a crucial role in modern technologies, from medical applications to renewable energy and space exploration.

As scientists continue to build upon this landmark achievement, we can expect to see a new era of innovation and advancement in the fields of chemistry, materials science, and beyond.

The full study was published in the journal Nature.


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