The actinides include 14 metallic elements in the periodic system. They include thorium, uranium, neptunium, plutonium and americium. Atoms of these elements have have many electrons, up to more than 100, some of which can be found in their 5f orbitals. The arrangement of these many electrons is much more affected by quantum mechanical phenomena and complex electronic interactions than in almost any other element, leading to special properties and unexpected behaviours that are not fully understood. Although various measurement techniques are available to obtain information about the electronic structure of actinide atoms in chemical bonds, that information is of limited usefulness.
Researchers at KIT’s Institute for Nuclear Waste Disposal (INE) used a special measurement technique called M4 resonant inelastic X-ray scattering for detailed analysis of a relatively high-energy signal that had previously been largely neglected. They found that careful measurement and analysis of this signal enables a better understanding of actinide atoms’ electronic structure and bonding properties. The signal reliably reveals the number of 5f electrons localized in a chemical bond on the actinide atom. Moreover, a slightly different experimental geometry can be used to determine the structure of bonds formed between actinide atoms and other atoms with 5f electrons.
Fundamental Insights into Actinide Compounds
“The information obtained with our method enables the experimental verification of theoretical calculations and computer models,” said Professor Tonya Vitova, who heads the Advanced Spectroscopy in f-element Chemistry department at the INE. Accurate information about the chemical and physical properties of actinide compounds is crucial to predicting their behaviour in the Earth’s crust, in uranium mining, or in nuclear waste storage sites. In addition, actinide compounds include substances that could be used as radiopharmaceuticals to destroy cancer cells.
Research Using the KIT Light Source
Vitova’s working group uses X-rays produced by the KIT Light Source synchrotron. “For our method, we only need very small quantities of a substance, often just thousandths of a gram,” said Dr. Bianca Schacherl, who heads a junior research group for the development of X-ray spectroscopy and radiochemical applications; the group performed most of the experimental measurements. The INE researchers have decades of experience in the safe and rigorously controlled handling of radioactive actinides. “We owe our results to the unique conditions at the KIT Light Source, and also to the opportunity to perform very lengthy measurement processes,” Schacherl said. “But the new measurement technique resulting from our experiments can also be used at other synchrotrons around the world.”
Michelangelo Tagliavini and Professor Maurits W. Haverkort (Institute for Theoretical Physics at the University of Heidelberg) and Dr. Harry Ramanantoanina (INE) carried out extensive calculations to help interpret the signals measured by the Karlsruhe X-ray scattering experiments. Researchers from the United States, France and Switzerland also supported the Karlsruhe scientists, in part by supplying samples containing actinides.
