Americium , Curium and Californium Oh My ! Crystallizing the Rarest Elements at LLNL

newswise.com · Feb 20, 2026 · Collected from GDELT

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Newswise — Actinides are a group of heavy, radioactive elements that include uranium, plutonium, americium, curium, berkelium and californium. Understanding how these elements bond with other atoms (known as coordination chemistry), how they behave in water and how they can be separated from one another is crucial for safer nuclear waste management, new reactor technologies and advanced materials.However, because heavier elements, like curium and californium, do not occur naturally and must be synthesized in specialized nuclear reactors through long, multistep processes, only tiny amounts are available for research. As a result, they are exceptionally difficult to study. Since californium’s discovery in 1950, only a handful of its coordination compounds have ever been structurally characterized. Californium is the heaviest element on the periodic table for which pure compounds can be synthesized and characterized in laboratories.Despite californium being one of the most elusive elements on Earth, chemists at Lawrence Livermore National Laboratory (LLNL) are putting it on the chemical map by using a novel nanoscale synthesis and crystallization approach to create, isolate and structurally characterize a pure californium-containing compound — the first time this has been achieved at LLNL. The research, conducted by Ian Colliard and Gauthier Deblonde, follows a companion study on americium and curium, making up a set of “twin” papers published in the journal Chemical Communications.To study these elements, the researchers used a class of inorganic molecules called polyoxometalates (POMs) — large, cage-like clusters made primarily of metal and oxygen atoms. They used a specific type of POM, called Wells–Dawson, which provides a carefully shaped “pocket” within a large structure that can sandwich a single metal ion of interest, such as americium, curium or californium, in a very reproducible way.This pocket does two crucial things. First, it stabilizes the radioactive element in a solution. Second, it allows scientists to grow tiny but well-ordered crystals — small enough to be made from nanogram quantities of material, yet detectable enough for single-crystal X-ray diffraction, the gold standard technique for determining atomic structure. With this LLNL-developed approach, the researchers only needed about 300 nanograms of californium to perform the chemical synthesis and subsequent characterization experiments.Colliard and Deblonde first tested this strategy on non-radioactive elements (rare earths) to isolate and crystallize new compounds, eventually extending the same method to americium and curium and then californium. The californium result is particularly noteworthy, as it represents the heaviest element ever crystallized within a POM molecule.The first paper on americium and curium reveals that these elements can form nearly identical molecular structures under carefully controlled conditions. Americium was found to adopt two slightly different crystal arrangements, while curium formed just one. These subtle differences, which can be linked to the way each compound absorbs light, helped the researchers understand how atomic size and electronic structure influence bonding.The second paper builds directly on this foundation by adding californium to the series. Because all three elements were studied using the same techniques, the researchers were able to make clear, side-by-side comparisons, allowing them to observe predictable trends in bond lengths and geometry as the elements get heavier — and smaller — across the series. Based on these experimental trends, the authors were also able to predict how berkelium would likely bond and crystallize, even without directly studying it.Unexpectedly, the work also revealed major differences in solubility, or how readily these compounds dissolve in water. The authors found that when different metals (such as rare earths or actinides) are bound to the POM, they can be separated from each other by adding potassium chloride (a chemical similar to table salt) to the solution.Potassium chloride causes some metal-POM complexes to precipitate (form solids), while others stay dissolved. For example, californium’s compound remained soluble under conditions that caused americium and curium to crystallize. This difference in solubility allows scientists to separate the metals efficiently. These findings open the door to a new, potentially simpler way of separating heavy elements — an important challenge in nuclear science.Beyond the individual discoveries, the real novelty of this work lies in the method itself, demonstrating that meaningful structural chemistry for the rarest elements on the periodic table can be done with quantities of material that are invisible to the human eye. Efforts are currently underway to apply these techniques to other radioactive elements and explore whether the newly observed solubility differences can be developed into practical separation technologies for nuclear energy and critical minerals.- Shelby Conn