New insights into the physical and chemical properties of the rare heavy element einsteinium have been gained by researchers working at several labs across the US. The team, led by chemist Rebecca Abergel at Berkeley National Laboratory in California, used cutting-edge approaches in both synthesis and analysis to overcome several significant setbacks in studying the element. Their results shed light on the poorly-understood properties of the heaviest elements and could help scientists synthesize new and even heavier elements.
The periodic table displays the elements in a systematic way that provides great insights into their chemical properties. However, this appears to break down for the heaviest elements, which can behave in unexpected ways given their positions in the table. Understanding the chemistry of these elements is exceedingly difficult because they can only be synthesized in extremely small quantities and have short half-lives.
With an atomic number of 99, einsteinium is in the same actinide row of the periodic table as uranium. A metal, it is currently the heaviest element that can be produced in quantities large enough to carry out classical chemistry experiments.
Tiny sample
In their study, Abergel’s team used a variety of advanced techniques to learn more about the isotope einsteinium-254. This is the most stable form of the element, with a half-life of 276 d. First, they synthesized a 250 ng sample using the High Flux Isotope Reactor at Oak Ridge National Laboratory in Tennessee by bombarding curium targets with neutrons to trigger specific radioactive decay chains.
Unfortunately, the researchers encountered several setbacks in their initial analysis. They discovered californium (element 98) contaminants in their sample, which meant that they could not perform planned X-ray crystallography studies. Furthermore, delays related to the COVID-19 pandemic meant that they were losing their sample due to radioactive decay. To overcome these problems, Abergel and colleagues bonded their einsteinium atoms to groups of organic molecules called ligands, which acted as luminescent antenna. They placed their sample in a specialized holder, which was 3D printed at Los Alamos National Laboratory in New Mexico. With this setup, they could analyse the sample using X-ray absorption spectroscopy, carried out at the Stanford Synchrotron Radiation Lightsource.
By measuring the resulting spectrum of the sample, which was complemented by the luminescence of the ligands, Abergel’s team determined the bond distance of einsteinium, which is crucial in understanding how metallic atoms bind to molecules. In addition, they uncovered aspects of einsteinium’s physical chemistry that deviate from expected trends across the actinide series. This knowledge could open up new avenues of research into how actinides could be used in areas including nuclear power, and novel pharmaceutical drugs.
More broadly, the discoveries improve our understanding of how physics and chemistry is altered towards the edge of the periodic table. This could enable researchers to better predict the processes that occur when einsteinium and its actinide neighbours are bombarded with other atomic nuclei in the hopes of creating even heavier elements that have yet to be discovered.
The research is described in Nature.
