Oganesson
Oganesson is a synthetic chemical element with the symbol Og and atomic number 118. 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 scient ...
(
118Og) is a
synthetic element
A synthetic element is one of 24 known chemical elements that do not occur naturally on Earth: they have been created by human manipulation of fundamental particles in a nuclear reactor, a particle accelerator, or the explosion of an atomic bomb; ...
created in
particle accelerator
A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.
Large accelerators are used for fundamental research in particle ...
s, and thus a
standard atomic weight cannot be given. Like all synthetic elements, it has no
stable isotope
The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundanc ...
s. The first and only
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
to be synthesized was
294Og in 2002 and 2005; it has a
half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
of 700 microseconds.
List of isotopes
, -
, rowspan=2,
294Og
, rowspan=2 style="text-align:right" , 118
, rowspan=2 style="text-align:right" , 176
, rowspan=2, 294.21392(71)#
, rowspan=2, 700 μs
, α
,
290Lv
, rowspan=2, 0+
, -
, SF
, (various)
Nucleosynthesis
Target-projectile combinations leading to Z=118 compound nuclei
The below table contains various combinations of targets and projectiles that could be used to form compound nuclei with Z=118.
Cold fusion
208Pb(86Kr,''x''n)294-''x''Og
In 1999, a team led by
Victor Ninov
Victor Ninov ( bg, Виктор Нинов, born June 27, 1959) is a Bulgarian physicist and former researcher who worked primarily in creating heavy elements. He is known for the co-discoveries of elements 110, 111, and 112 (darmstadtium, ro ...
at the
Lawrence Berkeley National Laboratory
Lawrence Berkeley National Laboratory (LBNL), commonly referred to as the Berkeley Lab, is a United States Department of Energy National Labs, United States national laboratory that is owned by, and conducts scientific research on behalf of, t ...
performed this experiment, as a 1998 calculation by
Robert Smolańczuk suggested a promising outcome. After eleven days of irradiation, three events of
293Og and its
alpha decay
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atom ...
products were reported in this reaction; this was the first reported discovery of element 118 and then-unknown
element 116.
The following year, they published a retraction after researchers at other laboratories were unable to duplicate the results and the Berkeley lab could not duplicate them either. In June 2002, the director of the lab announced that the original claim of the discovery of these two elements had been based on data fabricated by principal author Victor Ninov. Newer experimental results and theoretical predictions have confirmed the exponential decrease in cross-sections with lead and bismuth targets as the atomic number of the resulting nuclide increases.
Hot fusion
249Cf(48Ca,''x''n)297-''x''Og (''x''=3)
Following successful experiments utilizing
calcium-48
Calcium-48 is a scarce isotope of calcium containing 20 protons and 28 neutrons. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, its beta decay is extremely hindered, and so ...
projectiles and actinide targets to generate elements
114 and 116,
the search for element 118 was first performed at the
Joint Institute for Nuclear Research
The Joint Institute for Nuclear Research (JINR, russian: Объединённый институт ядерных исследований, ОИЯИ), in Dubna, Moscow Oblast (110 km north of Moscow), Russia, is an international research cen ...
(JINR) in 2002. One or two atoms of
294Og were produced in the 2002 experiment, and two more atoms were produced in a 2005 confirmation run. The discovery of element 118 was announced in 2006.
Because of the very small
fusion reaction
Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products is manifeste ...
probability (the fusion
cross section
Cross section may refer to:
* Cross section (geometry)
** Cross-sectional views in architecture & engineering 3D
*Cross section (geology)
* Cross section (electronics)
* Radar cross section, measure of detectability
* Cross section (physics)
**Abs ...
is ), the experiment took four months and involved a beam dose of
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
ions that had to be shot at the
californium
Californium is a radioactive chemical element with the symbol Cf and atomic number 98. The element was first synthesized in 1950 at Lawrence Berkeley National Laboratory (then the University of California Radiation Laboratory), by bombarding ...
target to produce the first recorded event believed to be the synthesis of oganesson.
Nevertheless, researchers were highly confident that the results were not a
false positive
A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test result ...
; the chance that they were random events was estimated to be less than one part in 100,000.
In a 2012 experiment aimed at the confirmation of
tennessine
Tennessine is a synthetic chemical element with the symbol Ts and atomic number 117. It is the second-heaviest known element and the penultimate element of the 7th period of the periodic table.
The discovery of tennessine was officially ann ...
, one alpha decay chain was attributed to
294Og. This synthesis event resulted from the population of
249Cf in the target as the decay product of the
249Bk target (half-life 330 days); the cross section and decays were consistent with previously reported observations of
294Og.
From 1 October 2015 until 6 April 2016, the team at the JINR conducted a search for new isotopes of oganesson using a
48Ca beam and a target comprising a mixture of
249Cf (50.7%),
250Cf (12.9%), and
251Cf (36.4%). The experiment was performed at 252 MeV and 258 MeV beam energies. One event of
294Og was found at the lower beam energy, while no decays of oganesson isotopes were found at the higher beam energy; a cross section of 0.9 pb for the
249Cf(
48Ca,3n) was estimated.
250,251Cf(48Ca,''x''n)298,299-''x''Og
In the 2015–2016 experiment, these reactions were performed in a search for
295Og and
296Og. No events attributable to a reaction with the
250Cf or
251Cf portions of the target were found. A repeat of this experiment was planned for 2017–2018.
248Cm(50Ti,''x''n)298-''x''Og
This reaction was originally planned to be tested at the JINR and
RIKEN in 2017–2018, as it uses the same
50Ti projectile as planned experiments leading to elements
119 and
120.
[
] A search beginning in summer 2016 at RIKEN for
295Og in the 3n channel of this reaction was unsuccessful, though the study is planned to resume; a detailed analysis and cross section limit were not provided.
Theoretical calculations
Theoretical calculations done on the synthetic pathways for, and the half-life of, other isotopes have shown that some could be slightly more
stable
A stable is a building in which livestock, especially horses, are kept. It most commonly means a building that is divided into separate stalls for individual animals and livestock. There are many different types of stables in use today; the ...
than the synthesized isotope
294Og, most likely
293Og,
295Og,
296Og,
297Og,
298Og,
300Og and
302Og.
Of these,
297Og might provide the best chances for obtaining longer-lived nuclei,
and thus might become the focus of future work with this element. Some isotopes with many more neutrons, such as some located around
313Og, could also provide longer-lived nuclei.
Theoretical calculations on evaporation cross sections
The below table contains various targets-projectile combinations for which calculations have provided estimates for cross section yields from various neutron evaporation channels. The channel with the highest expected yield is given.
DNS = Di-nuclear system; 2S = Two-step; σ = cross section
References
* Isotope masses from:
**
**
{{Navbox element isotopes
Oganesson
oganesson
Oganesson is a synthetic chemical element with the symbol Og and atomic number 118. 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 scient ...