"Solid" evidence: Oganesson noble, but not a gas
- Feb 8, 2018
- Homepage News, Faculty & Staff, Research, College of Natural Science, Physics & Astronomy
According to the Bohr model of the atom introduced in 1917, electrons orbit only at certain distances from the atomic nucleus, forming "shells" of states of similar energies. The left panel above shows the so-called localization function for elements xenon and oganesson. For the noble gas, xenon, the electron shells can be clearly seen as concentric circles. This well-known pattern is absent for oganesson. This finding is expected to result in significant changes in the chemical and physical properties of this element. Courtesy of MSU.
Scientists at Michigan State University and Massey University have calculated the structure of oganesson, a relatively new element which has proved elusive to study.
First synthesized in 2002 at the Joint Institute for Nuclear Research in Russia, oganesson is the only element of group 18 of the periodic table (noble gases), which doesn't naturally occur and must be synthesized in experiments. It is also one of only two elements to be named after a living scientist, nuclear physicist Yuri Oganessian.
“The superheavy elements represent the limit of nuclear mass and charge; they inhabit the remote corner of the nuclear landscape whose extent is unknown,” said Witek Nazarewicz, Hannah Distinguished Professor of Physics and Facility for Rare Isotope Beams (FRIB) Chief Scientist at MSU. “The questions pertaining to superheavy systems are in the forefront of nuclear and atomic physics, and chemistry research: How can a nucleus with a large atomic number, such as Z=112, survive the huge electrostatic repulsion between its charged proton constituents? What are its physical and chemical properties? Are superheavy elements produced in stellar explosions?”
Studying one of the heaviest elements with the highest atomic number to ever be synthesized, is no easy task. Oganesson is radioactive and extremely unstable with a half-life of less than a millisecond, making it impossible to examine by chemical methods. This means computing its electronic and nuclear structure is the next best thing, which is in itself a formidable task.
Massey's Distinguished Professor Peter Schwerdtfeger of the New Zealand Institute for Advanced Study, together with Nazarewicz and their respective teams, were able to make these calculations.
"Calculations are the only way to get at its behavior with the tools that we currently have, and they have certainly provided some interesting findings," Schwerdtfeger said.
The work suggests that oganesson electrons aren't confined to distinct orbitals and are distributed evenly.
"On paper, we thought that it would have the same rare gas structure as the others in this family,” he continued. “In our calculations however, we predict that oganesson more or less loses its shell structure and becomes a smear of electrons."
Additionally, it was thought to be a gas under normal conditions, but is now predicted to be a solid according to newest research from the Massey group.
"Oganesson is quite different to the other rare gas atoms, as its shells are barely visible in an electron localization function plot and has been smeared to near-invisibility," Schwerdtfeger said. "Oganesson comes quite close to the limiting case of a Fermi gas."
The Michigan State University team complemented atomic calculations by computing the structure of protons and neutrons inside the oganesson nucleus, which indicated a smeared-out structure for the neutrons as well. The protons however retain some shell-like ordering.
In the publication describing the team’s findings, Physical Review Letters, the research was highlighted as the cover story in a recent edition, and was selected for an Editors’ Suggestion and a Viewpoint in Physics. It received media attention, including Nature, Physics Today, Chemistry World and Phys.org.
Banner image courtesy MSU.