New method produces curium crystals for research in a radiochemistry first

September 21, 2022, 7:00AMNuclear News
A new compound of curium photographed at LLNL during crystallography experiments. Crystals of this curium compound are uncolored under ambient light but glow an intense pink-red when exposed to ultraviolet light. (Image: LLNL/Deblonde)

Scientists at Lawrence Livermore National Laboratory and Oregon State University (OSU) have developed a promising new method to isolate and study some of the rarest elements on Earth. Focused first on curium, they have identified three new complexes containing curium ions and revealed the molecules’ 3D structures, as well as previously unknown features.

The work was described in a news release from LLNL. “In a nutshell, we found a new way to study radioactive elements that drastically cuts costs, reduces the radiation exposure to workers, and preserves the nation’s stockpile of research isotopes,” Gauthier Deblonde told Nuclear News. Deblonde is a staff scientist in the Nuclear and Chemical Sciences Division at LLNL and the project lead for the work, which was published in the journal Nature Chemistry and featured in a research highlight in Nature.

A new method: Until now, rare radioisotopes have typically been synthesized into small inorganic or organic chemical complexes for study. The process requires several milligrams of the radioisotope being studied, but for some isotopes that equates to one year’s global supply, according to LLNL.

“Most people do not realize that studying radioactive materials is not just challenging because of radiation and toxicity constraints. In most cases, laboratories are primarily limited by the amount of research isotopes that is available and by their considerable cost,” Deblonde explained. “Our new approach solves all these problems by requiring about 1,000 times less material than state-of-the-art methods and without compromising the data quality. This a new tool in the radiochemists’ arsenal that preserves the nation’s stockpile of research isotopes. We will also be able to harvest chemical information on elements or isotopes that have remained out of reach.”

In the new research, the team demonstrated that by leveraging fundamental chemical properties, such as molecular weight and solubility, they could synthesize coordination compounds of certain elements while using as little as 1–10 micrograms of the isotope. Radiation-resistant heavy polyoxometalate ligands (POMs) were enlisted to form and crystalize complexes that the researchers then used to perform detailed spectroscopic and structural characterization.

Discovery: The researchers identified several new single crystal X-ray diffraction structures, including three new compounds of curium. According to LLNL, until the new research was completed just 10 curium complexes had been isolated and characterized by single crystal X-ray diffraction since the discovery of the element in 1944. The new approach also yielded the very first experimental measurement of the 8-coordinated ionic radius of the Cm3+ ion.

“The very nature of the materials involved in this research has its many limitations, but the new method overcomes them. Enough so that we can start to understand their chemistry and appreciate their beauty," said Ian Colliard, first author of the publication, who was an OSU Ph.D. candidate at the time of the study and is now a postdoctoral researcher at LLNL.

The team found that the curium crystals within most POMs are highly luminescent, which aids in their detection even at very low concentrations. The POMs also form highly luminescent complexes with many other elements such as europium, terbium, dysprosium, and samarium, according to LLNL.

Applications: The newly proposed approach could be used to discover and study many new compounds containing rare isotopes, such as actinides and radiolanthanides.

“It opens the door to the discovery of many new compounds of heavy elements at the edge of the periodic table—actinium, plutonium, californium, etc.—with ramifications into nuclear reactions, medicine, waste management, and more,” said Deblonde.

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