The superheavy element 114 (florovium) is a volatile metal
An international research team has succeeded in obtaining new information on the chemical properties of the superheavy element florovium – element 114 – at the accelerator facilities of the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt. Measurements show that flerovium is the most volatile metal in the periodic table. Flerovium is therefore the heaviest element in the periodic table that has been studied chemically. With the results, published in the journal Frontiers in chemistrythe GSI confirms its leading position in the study of the chemistry of superheavy elements and opens new perspectives for the international FAIR (Facility for Antiproton and Ion Research) facility, currently under construction.
Under the direction of groups from Darmstadt and Mainz, the two longest-lived florovium isotopes currently known, flerovium-288 and flerovium-289, were produced using the accelerator facilities of the GSI/FAIR and have been the subject of chemical studies in the experimental device TASCA. In the periodic table, flerovium is placed below lead, a heavy metal. However, early predictions had postulated that the relativistic effects of high charge in the superheavy element’s nucleus on its valence electrons would lead to noble gas-like behavior, while later ones had instead suggested weakly metallic behavior. Two previously conducted chemistry experiments, including one at GSI in Darmstadt in 2009, led to conflicting interpretations. While the three atoms observed in the first experiment were used to infer noble gas-like behavior, the data obtained at GSI indicated a metallic character based on two atoms. Both experiments failed to clearly establish the character. The new results show that, as expected, flerovium is inert but capable of forming stronger chemical bonds than noble gases, if conditions allow. Flerovium is therefore the most volatile metal in the periodic table.
Flerovium is therefore the heaviest chemical element whose character has been studied experimentally. With the determination of chemical properties, GSI/FAIR confirms its leading position in the search for superheavy elements. “Exploring the boundaries of the periodic table has been a mainstay of the research program at GSI from the start and will be at FAIR in the future. The fact that a few atoms can already be used to explore the first fundamental chemical properties, giving a indication of how larger amounts of these substances would behave, is fascinating and possible thanks to the powerful accelerator facility and the expertise of the global collaboration,” explains Professor Paolo Giubellino, Chief Scientific Officer of GSI and FAIR “With FAIR, we bring the universe into the laboratory and explore the limits of matter, but also of chemical elements.”
Six weeks of experimentation
The experiments carried out at GSI/FAIR to clarify the chemical nature of flerovium lasted a total of six weeks. To this end, four trillion calcium-48 ions were accelerated to ten percent of the speed of light every second by the GSI UNILAC linear accelerator and fired at a target containing plutonium-244, resulting in the formation of a few florovium atoms per day.
The formed flerovium atoms recoiled from the target in the TASCA gas-filled separator. In its magnetic field, the isotopes formed, flerovium-288 and flerovium-289, which have lifetimes on the order of a second, were separated from the intense beam of calcium ions and the by-products of the reaction. nuclear. They penetrate a thin film, thus entering the chemistry apparatus, where they are stopped in a helium/argon gas mixture. This gas mixture chased the atoms into the COMPACT gas chromatograph, where they first came into contact with silicon oxide surfaces. If the bond to the silicon oxide was too weak, the atoms were transported further, to gold surfaces – first those kept at room temperature, then to progressively colder surfaces, until about -160°C. The surfaces were deposited as a thin layer on special nuclear radiation detectors, which recorded individual atoms by spatially-resolved detection of radioactive decay. Since decay products undergo further radioactive decay after a short lifetime, each atom leaves a characteristic signature of several events from which the presence of a flerovium atom can be unambiguously inferred.
One atom per week for chemistry
“Thanks to the combination of TASCA separator, chemical separation and detection of radioactive decay, as well as the technical development of the gas chromatography apparatus since the first experiment, we have succeeded in increasing the efficiency and to reduce the time needed for chemical separation to such an extent that we were able to observe one atom of flerovium every week,” explains Dr. Alexander Yakushev of GSI/FAIR, the spokesperson for the international experimental collaboration.
Six such decay chains were found in the data analysis. Since the setup is similar to that of the first GSI experiment, the newly obtained data could be combined with the two atoms observed at that time and analyzed together. None of the decay chains appeared in the range of the silicon oxide coated detector, indicating that flerovium does not form a substantial bond with the silicon oxide. Instead, all were transported with the gas into the gold-covered part of the device in less than a tenth of a second. The eight events formed two zones: a first in the region of the gold surface at room temperature, and a second in the later part of the chromatograph, at temperatures so low that a very thin layer of ice covered the gold, so that adsorption has occurred. on the ice.
From experiments with lead, mercury and radon atoms, which served as representatives of heavy metals, weakly reactive metals as well as noble gases, it was known that lead forms a strong bond with the oxide of silicon, while mercury reaches the gold detector. Radon even flies over the first part of the gold detector at room temperature and is only partially retained at lower temperatures. The results of Flerovium could be compared to this behavior.
Apparently two types of interaction of a species of flerovium with the gold surface have been observed. Deposition on gold at room temperature indicates the formation of a relatively strong chemical bond, which does not occur in noble gases. On the other hand, some of the atoms seem never to have had the opportunity to form such bonds and were transported long distances from the surface of the gold, down to the lowest temperatures. This range of detectors represents a trap for all elementary species. This complicated behavior is explained by the morphology of the auriferous surface: it consists of small clusters of gold, at the limits of which there are highly reactive sites, apparently allowing the binding of flerovium. The fact that some of the flerovium atoms were able to reach the cold region indicates that only the atoms that encountered such sites formed a bond, unlike mercury, which was retained on the gold anyway. Thus, the chemical reactivity of flerovium is lower than that of volatile metallic mercury. Current data cannot completely exclude the possibility that the first deposition zone on gold at room temperature is due to the formation of flerovium molecules. It also follows from this assumption, however, that flerovium is chemically more reactive than a noble gas element.
International and interdisciplinary collaboration as a key to understanding
The exotic plutonium target material for the production of flerovium was provided in part by the Lawrence Livermore National Laboratory (LLNL), USA. At the TRIGA site of the Department of Chemistry at the Johannes Gutenberg University Mainz (JGU), the material was deposited by electrolysis on thin sheets of titanium fabricated at GSI/FAIR. “There isn’t a lot of this material available in the world, and we’re lucky to have been able to use it for these experiments that wouldn’t otherwise be possible,” said Dr. Dawn Shaughnessy, head of the Division of nuclear and chemical sciences at LLNL. “This international collaboration brings together skills and expertise from around the world to solve challenging scientific problems and answer long-standing questions, such as the chemical properties of flerovium.”
“Our accelerator experiment was complemented by a detailed study of the detector surface in collaboration with several departments at GSI as well as the Department of Chemistry and the Institute of Physics at JGU. As a result, the data from the two previous experiments are now understandable and compatible with our new findings,” says Christoph Düllmann, Professor of Nuclear Chemistry at JGU and Head of Research Groups at GSI and the Helmholtz Institute in Mainz (HIM), a collaboration between GSI and JGU.
How relativistic effects affect its neighbors, the elements nihonium (element 113) and moscovium (element 115), which have also only been officially recognized in recent years, is the subject of further experimentation. The first data have already been obtained as part of the FAIR Phase 0 program at GSI. Additionally, researchers expect that there are much more stable isotopes of florovium, but these have yet to be found. However, researchers already know that they can expect to find a metallic element.
In addition to GSI/FAIR and JGU, HIM, University of Liverpool (UK), University of Lund (Sweden), University of Jyväskyla (Finland), University of Oslo (Norway), Institute of Electron Technology (Poland), Lawrence Livermore National Laboratory (USA), Saha Institute of Nuclear Physics and Indian Institute of Technology Roorkee (India), Joint Atomic Energy Agency and RIKEN Research Center (Japan ) as well as the Australian National University (Australia) participated in the experiment.