The heaviest known element by the end of the 19th century was uranium with an atomic mass of 238 amu. In the last 20 years, six new elements have been added to the periodic table completing the seventh period. All these elements refer to a unique class known as superheavy elements, or “transactinides,” elements with Z>103. Oganesson (Og), previously known as eka-radon or Uuo (‘ununoctium’), is one of these exotic short-lived superheavy elements, it is placed at the last position in the noble gas group of the periodic table with the highest atomic no. 118. It is the heaviest known element in the periodic table with an atomic mass of 294u. It was first synthesized in 2002 at the Joint Institute for Nuclear Research (JINR) in Dubna, near Moscow, Russia, by a joint team of Russian and American scientists. In December 2015, it was recognized as one of four new elements by the Joint Working Party of the international scientific bodies IUPAC and IUPAP. It was formally named on 28 November 2016. It is named after the nuclear physicist Yuri Oganesson as an honour for its discovery.
Prof. Yuri Oganesson explaining about his research
Scientists have only been able to produce 5 atoms of oganesson in a heavy-ion fusion reaction till now. Existing science to explore these superheavy elements still face many challenges. They can only be created at a production scale of one-atom at a time with the production rate of one-atom per week. The half-Life of the _{ 118}^{ 249 }{ Og } produced in the reaction is 0.69 ms. Although oganesson belongs to the family of noble gases, it is neither entirely noble nor a gas.
Discovery
The possible existence of superheavy elements with an atomic number well beyond that of uranium goes back to 1914 when a German physicist Richard Swinne found a source of radiation belonging to an atom with atomic no. 108 while studying the cosmic rays, but these were not the definitive observation, and therefore, didn’t get much attention from other scientists around the world until an improved version of the nuclear shell model was introduced. Some of the fundamental outcomes of the nuclear shell model are the” island of stability”, and classification of elements as singly magic or doubly magic in reference to the numbers of protons and/or neutrons they possess corresponding to filled shells. The island of stability refers to a region in the periodic table consisting of relatively stable isotopes of superheavy elements. The nuclear shell model is used to predict the location of the “island” based on maximizing the binding energy between protons and neutrons. Isotopes on the island are believed to have magic numbers of neutron and protons that allow them to stabilize.
Oganesson (row 118) is slightly above the “island of stability” (white circle) and thus its nuclei are slightly more stable than otherwise predicted
Based on these predictions, scientists at the Flerov Laboratory of Nuclear Reactions (FLNR) of the JINR at Dubna started bombarding actinide targets, some of which were synthesised and purified at the Radiochemical Engineering Development Center at Oak Ridge National Laboratory, USA, with _{ 20 }^{ 48 }Ca, which is a ‘nearly stable’ (long-lived) ‘doubly magic’ isotope of Ca, which decays via double-beta decay with a half-life of 4.4 × { 10 }^{ 19 } years and forms 0.187% of naturally occurring Ca. This approach led to the discovery of oganesson when scientist bombarded a californium _{ 98 }^{ 249 }Cf target with _{ 20 }^{ 48 }Ca, during a heavy-ion collision reaction.
_{ 20 }^{ 48 }Ca + _{ 98 }^{ 249 }Cf → _{ 118 }^{ 294 }Og + 3n
Cyclotron (particle accelerator) at JINR used to bombard calcium isotopes on californium
The choice of projectile and target nuclides was based on the maximisation of neutron excess in the fusion products.
Isotopes and Stability
Theoretically, eight possible heavy-ion fusion reactions can produce eight different isotopes of oganesson, out of which scientists have only managed to synthesize one _{ 118 }^{ 294 }Og. An unconfirmed isotope _{ }^{ 295 }{ Og } may have been observed in 2011 with the half-life of 181 milliseconds. A lot of research is going on around the world to look for these isotopes.
Theoretical and computational studies suggest that possible isotopes of Oganesson can be _{ }^{ 293 }{ Og }, _{ }^{ 295 }{ Og }, _{ }^{ 296 }{ Og }, _{ }^{ 297 }{ Og }, _{ }^{ 298 }{ Og },_{ }^{ 300 }{ Og }, and _{ }^{ 302 }{ Og } with N =184, in order to achieve shell clouser.
Properties of Oganesson
Oganesson has not been produced in enough quantities to be examined thoroughly. All the predictions of its physical and chemical nature are based on theoretical calculations and computational simulations. In contrast to other noble gases, theories suggest that Oganesson would be liquid at room temperature, and it would have a boiling point of around 320 K – 380 K. Another research indicates that it can be a potential semiconductor.
One thing that scientists are sure about Oganesson is that it has an electronic configuration of [Rn] 5{ f }^{ 14 }6{ d }^{ 10 }7{ s}^{ 2 }7{ p }^{ 6 }, and is a radioactive element which has a half-life of the order of milliseconds that decays further into Livermorium via. alpha decay.
_{ 118 }^{ 294 }{ Og } → _{ 116 }^{ 290 }{ Lv } + _{ 2 }^{ 4 }{ He }
Radioactive decay pathway of the isotope oganesson-294. The decay energy and average half-life are given for the parent isotope and each daughter isotope. The fraction of atoms undergoing spontaneous fission (SF) is given in green
Uses of Oganesson
Till now, there is no known application of Oganesson other than that for research purposes. Similarly, nothing can be postulated about the health effects of oganesson as scientists have only been able to produce a few atoms of oganesson.