Scientists discover that heavy element chemistry can change at high pressures

New research shows that one of the heaviest elements known can be manipulated to a greater extent than previously thought, which could pave the way for new strategies for recycling nuclear fuel and better long-term storage of radioactive elements.

An international team of researchers has shown how curium – element 96 on the periodic table and one of the last to be seen with the naked eye – responds to the high pressure application created by squeezing a sample between two diamonds.

Led by Professor Thomas Albrecht-Schmitt from Florida State University and collaborators from the University of Buffalo and Aachen University, the team discovered that the behavior of curium external electrons, influencing its ability to bond with other elements , can be altered by shortening the distance between and the surrounding lighter atoms. The findings are published in the journal. Nature.

“This was not anticipated because curium chemistry makes it resistant to these kinds of changes,” said Albrecht-Schmitt, professor of chemistry Gregory R. Choppin at Florida State University. “In short, it is quite inert.”

Although only certain curium compounds exhibited changes, it was still interesting to scientists because curium is normally completely resistant to alteration of its properties.

In addition to Albrecht-Schmitt, the study was led by the University of Buffalo chemistry professors, Jochen Autschbach and Eva Zurek, as well as by Manfred Speldrich, a researcher at Aachen University in Germany.

Albrecht-Schmitt’s work is part of his laboratory’s overall mission to better understand the heavier elements or actinides at the bottom of the periodic table. In 2016, it received $ 10 million from the Department of Energy to form the Actinide Science and Technology Center to focus on accelerating scientific efforts to clean up nuclear waste.

Despite their presence on the periodic table, the heavier elements remain largely a mystery to scientists, particularly compared to lighter elements such as oxygen or nitrogen. “It is an exciting experiment that showed that we have much more control over the chemistry of these difficult-to-control elements than previously thought,” said Albrecht-Schmitt.

“The curium (3+) ion we studied has a half-filled outer shell of electrons that is very difficult to form chemical bonds,” said Autschbach, a professor of chemistry at Larkin at the University of Buffalo. “An integrated theoretical and experimental approach demonstrated that applying high pressure to a glass containing curium (3+), along with organic sulfur and ammonium ions, causes the outer layer of curium to participate in covalent chemical bonds with sulfur. This The finding may help guide new ways to study the mysterious behavior of chemically resistant actinide deposits. “

Autschbach’s group at the University of Buffalo performed calculations that helped explain what happened during the high-pressure experiments, revealing details about how curium behaves when compounds containing the element are compressed between diamonds. Zurek’s team laid the foundation for these calculations by determining the crystal structures of the compounds at high pressure.

“Compounds and chemical materials under pressure can behave completely differently than atmospheric conditions, which makes the discoveries in high-pressure research so exciting,” said Zurek.

A better understanding of the heavier elements opens the door to additional strategies to control the chemical separation used in nuclear recycling and in the design of resistant materials for the long-term storage of radioactive elements, said Albrecht-Schmitt. The research team believes that the results they obtained in relation to curium will also translate into other heavy elements.

The team plans to continue this work by designing similar experiments for heavier elements such as californium and einsteinium, where the effects of pressure could be even greater than what they have found for curium.