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Oganesson: a most unusual ‘inert gas’

Posted on 19. July, 2018.

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Oganesson, with the symbol Og, is the artificially prepared (i.e. ‘man-made’) elementwith atomic number 118, previously known as eka-radon or Uuo (‘ununoctium’), and recently ‘blessed’ with an official name by IUPAC3. Atoms of the element were first produced using the U400 cyclotron at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, via a heavy-ion fusion reaction utilising collision of a 4820Ca beam with a 24998Cf target. 

The choice of projectile and target nuclides was made on the basis of maximisation of neutron excess in the fusion products. Initial identification of the new element was via its characteristic decay pattern, successive alpha decays into the even–even nuclides 290116Lv , 286114Fl, and 282112Cn, the last of which decays 100% through spontaneous fission. 

Within the nuclear shell model, nuclei are sometimes referred to as ‘singly magic’ or ‘doubly magic’ because they possess numbers of protons and/or neutrons corresponding to filled shells. Doubly magic nuclei are spherical, and correspond to ‘islands of stability’ on the table of all possible isotopes (created by plotting number of protons on one axis and number of neutrons on the other). One productive approach to the synthesis of long-lived superheavy nuclei is the bombardment of a singly or doubly magic nucleus such as 208Pb or 209Bi with stable neutron-rich projectiles such as 70Zn; however, this method leads to ‘diminishing returns’ beyond around Z = 113. A new approach began to be pursued around the turn of the 21st century at the Flerov Laboratory of Nuclear Reactions (FLNR) of the JINR at Dubna, involving the bombardment of actinide targets, some of which were synthesised and purified at the Radiochemical Engineering Development Center at Oak Ridge National Laboratory, USA, with 4820Ca. 4820Ca is a ‘nearly stable’ (i.e. long-lived) ‘doubly magic’ isotope of Ca, which decays via double-beta decay with a half-life of 4.4 × 1019 years and forms 0.187% of naturallyoccurring Ca. This is the approach that led to the discovery of oganesson, as well as multiple new isotopes of elements 112–117. Previous reports of the production of 293118 in the Berkeley separator failed to be confirmed by experiments at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt at the same energies.
 
Read the full article in Science Progress.

DOI:  https://doi.org/10.3184/003685018X15173976099750

Authors: Roderick M. Macraea and Terence J. Kempb 
aLechleiter Endowed Professor of Chemistry, Marian University, Indianapolis, Indiana, USA 
bEmeritus Professor of Chemistry, University of Warwick, UK 
E-mail: rmacrae@marian.edu and t.j.kemp@sciencereviews.co.uk

Image: Professor Yuri Oganessian after whom oganesson was named. Credit: VPRO, https://commons.wikimedia.org/wiki/File:Yuri_Oganessian.jpg