EXTENDED PERIODIC TABLE

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There are currently seven periods in the periodic table of chemical elements, culminating with atomic number 118. If further elements with higher atomic numbers than this are discovered, they will be placed in additional periods, laid out (as with the existing periods) to illustrate periodically recurring trends in the properties of the elements concerned. Any additional periods are expected to contain a larger number of elements than the seventh period, as they are calculated to have an additional so-called g-block, containing 18 elements with partially filled g-orbitals in each period. An eight-period table containing this block was suggested by Glenn T. Seaborg in 1969.

No elements in this region have been synthesized or discovered in nature. (Element 122 was claimed to exist naturally in April 2008, but this claim was widely believed to be erroneous.) The first element of the g-block may have atomic number 121, and thus would have the systematic name Unbiunium. Elements in this region are likely to be highly unstable with respect to radioactive decay, and have extremely short half lives, although element 126 is hypothesized to be within an island of stability that is resistant to fission but not to alpha decay. It is not clear how many elements beyond the expected island of stability are physically possible, if period 8 is complete, or if there is a period 9. If period 9 does exist, it is likely to be the last.

According to the orbital approximation in quantum mechanical descriptions of atomic structure, the g-block would correspond to elements with partially-filled g-orbitals. However, spin-orbit coupling effects reduce the validity of the orbital approximation substantially for elements of high atomic number.

EXTENDED PERIODIC TABLE, INCLUDING THE G-BLOCK

It is unknown how far the periodic table extends beyond the known 118 elements. Some suggest that the highest possible element may be under Z=130. However, if higher elements do exist, it is unlikely that they can be meaningfully assigned to the periodic table above Z=173, as discussed in the next section. This chart therefore ends at that number, without meaning to imply that all of those 173 elements are actually possible, nor to imply that heavier elements are not possible.

END OF THE PERIODIC TABLE

The number of physically possible elements is unknown. The light-speed limit on electrons orbiting in ever-bigger electron shells theoretically limits neutral atoms to a Z of approximately 173, after which it would be nonsensical to assign the elements to blocks on the basis of electron configuration. However, it is likely that the periodic table actually ends much earlier, possibly soon after the island of stability, which is expected to center around Z = 126.

Additionally the extension of the periodic and nuclides tables is restricted by the proton drip line and the neutron drip line.

Bohr model breakdown

The Bohr model exhibits difficulty for atoms with atomic number greater than 137, for the speed of an electron in a 1s electron orbital, v, is given by

Where Z is the atomic number, and α is the fine structure constant, a measure of the strength of electromagnetic interactions. Under this approximation, any element with an atomic number of greater than 137 would require 1s electrons to be traveling swifter than c, the speed of light. Hence a non-relativistic model such as the Bohr model is inadequate for such calculations.

THE DIRAC EQUATION

The semi-relativistic Dirac equation also has problems for Z > 137, for the ground state energy is

Where m₀ is the rest mass of the electron. For Z > 137, the wave function of the Dirac ground state is oscillatory, rather than bound, and there is no gap between the positive and negative energy spectra, as in the Klein paradox. Richard Feynman pointed out this effect, so the last element expected under this model, 137 (untriseptium), is sometimes called feynmanium (symbol: Fy).

However, a realistic calculation has to take into account the finite extension of the nuclear-charge distribution. This results in a critical Z of ≈ 173 (unseptrium), such that neutral atoms may be limited to elements equal to or lower than this. Higher elements could only exist as ions, for example as salts.

ISLAND OF STABILITY

3-dimensional rendering of the theoretical Island of Stability: The island of stability is a term from nuclear physics that describes the possibility of elements with particularly stable magic numbers of protons and neutrons. Existing on this "island" would allow the isotopes of some trans uranium elements to be far more stable than others; that is, to decay much more slowly with half-lives of at least minutes or days as compared to seconds. Some theorists have suggested the possibility that the half-lives of these isotopes could be on the order of millions of years.

Theory and origin: The possibility of an "island of stability" was first proposed by Glenn T. Seaborg. The hypothesis is that the atomic nucleus is built up in "shells" in a manner similar to the electron shells in atoms. In both cases shells are just groups of quantum energy levels that are relatively close to each other. Energy levels from quantum states in two different shells will be separated by a relatively large energy gap. So when the number of neutrons and protons completely fill the energy levels of a given shell in the nucleus, the binding energy per nucleon will reach a local maximum and thus that particular configuration will have a longer lifetime than nearby isotopes that do not have filled shells.

A filled shell would have "magic numbers" of neutrons and protons. One possible magic number of neutrons for spherical nuclei is 184, and some possible matching proton numbers are 114, 120 and 126 – which would mean that the most stable spherical isotopes would be ununquadium-298, unbinilium-304 and unbihexium-310. Of particular note is Ubh-310, which would be "doubly magic" (both its proton number of 126 and neutron number of 184 are thought to be magic) and thus the most likely to have a very long half-life. (The next lighter doubly-magic spherical nucleus is lead-208, the heaviest stable nucleus and most stable heavy metal.)

Recent research indicates that large nuclei are deformed, causing magic numbers to shift. Hassium-270 is now believed to be a doubly-magic deformed nucleus, with deformed magic numbers 108 and 162. However, it has a half-life of only 3.6 seconds.

Isotopes have been produced with enough protons to plant them upon an island of stability but with too few neutrons to even place them upon the island's outer "shores". It is possible that these elements have unusual chemical properties and, if they have isotopes long-lived enough, various practical applications (such as targets in nuclear physics and neutron sources).

We search for the island of stability because, like Mount Everest, it is there. But, as with Everest, there is profound emotion, too, infusing the scientific search to test a hypothesis. The quest for the magic island shows us that science is far from being coldness and calculation, as many people imagine, but is shot through with passion, longing and romance. Oliver Sacks.

Half-lives of large isotopes

Periodic table with elements colored according to the half-life of their most stable isotope.

Stable elements.

Radioactive elements with half-lives of over four million years.

Half-lives between 800 and 34,000 years.

Half-lives between 1 day and 103 years.

Half-lives ranging between a minute and 1 day.

Half-lives less than a minute.

Fermium is the heaviest element that can be produced in a nuclear reactor. The "stability" (half-life of the longest-lived known isotope) of elements generally decreases from element 100 to element 118. It increases very slightly in the range of elements 110 to 113, hypothesized to be at the beginning of the island of stability. The longest-lived observed isotopes are shown in the following table.

(Note that for elements 109-118 the longest-lived known isotope is always the heaviest one discovered, making it likely that there are still longer-lived isotopes among the undiscovered heavier ones)

The half-lives of nuclei in the island of stability itself are unknown since none of the isotopes that would be "on the island" have been observed. Many physicists think they are relatively short, on the order of minutes or days. However, some theoretical calculations indicate that their half-lives may be long, on the order of 10⁹ years.

The alpha-decay half-lives of 1700 nuclei with 100 ≤ Z ≤ 130 have been calculated in a quantum tunneling model with both experimental and theoretical alpha-decay Q-values. The theoretical calculations are in good agreement with the available experimental data.

Island of relative stability

²³²Th (thorium), ²³⁵U and ²³⁸U (uranium) are the only naturally occurring isotopes beyond bismuth that are relatively stable over the current lifespan of the universe. Bismuth was found to be unstable in 2003, with an α-emission half-life of 1.9×1019

years for ²⁰⁹Bi. All other isotopes beyond bismuth are relatively or very unstable. So the main periodic table ends at bismuth, with an island at thorium and uranium. Between bismuth and thorium there is a "sea of instability", which renders such elements as astatine, radon, and francium extremely short-lived relative to all but the heaviest elements found so far.

Current theoretical investigation indicates that in the region Z=106−108 and N≈160−164, a small "island"/"peninsula" might be stable with respect to fission and beta decay, such super heavy nuclei undergoing only alpha decay. Also, ²⁹⁸Uuq is not the center of the magic island as predicted earlier. On the contrary, the nucleus with Z=110, N=183 appears to be near the center of a possible "magic island" (Z=104−116, N≈176−186). In the N≈162 region the beta-stable, fission survived ²⁶⁸Sg is predicted to have alpha-decay half-life ~3.2 hours that is greater than that (~28 s) of the deformed doubly-magic ²⁷⁰Hs. The super heavy nucleus ²⁶⁸Sg has not been produced in the laboratory as yet (2009). For super heavy nuclei with Z>116 and N≈184 the alpha-decay half-lives are predicted to be less than one second. The nuclei with Z=120, 124, 126 and N=184 are predicted to form spherical doubly-magic nuclei and be stable with respect to fission. Calculations in a quantum tunneling model show that such super heavy nuclei would undergo alpha decay within microseconds or less.

Synthesis problems

The manufacturing of nuclei in the island of stability proves to be very difficult, because the nuclei available as starting materials do not deliver the necessary sum of neutrons. For the synthesis of isotope 298 of element 114 one could use an isotope of plutonium and one of calcium, that together have a sum of at least 298 nucleons, for example calcium-50 and plutonium-248. However these and the heavier isotopes are not available in weigh-able quantities, making production in this way virtually impossible with current methods. The same problem exists for the other possible combinations of isotopes needed to generate elements on the island using target-projectile methods. It may be possible to generate the isotope 298 of element 114, if the multi-nucleon transfer reactions would work in low-energy collisions of actinide nuclei. One of these reactions may be:

²⁴⁸Cm + ²³⁸U → ²⁹⁸Uuq + ¹⁸⁶W + 2 ¹n

UNUNTRIUM

Ununtrium is the temporary name of a synthetic element with the temporary symbol Uut and atomic number 113.It is placed as the heaviest member of the group 13 (IIIA) elements although a sufficiently stable isotope is not known at this time that would allow chemical experiments to confirm its position. It was first detected in 2003 in the decay of ununpentium and was synthesized directly in 2004. Only fourteen atoms of ununtrium have been observed to date. The longest-lived isotope known is ²⁸⁶Uut with a half-life of ~20 s, allowing first chemical experiments to study its chemistry.

Discovery profile: The first report of ununtrium was in August 2003 when it was identified as a decay product of ununpentium. These results were published on February 1, 2004, by a team composed of Russian scientists at Dubna (Joint Institute for Nuclear Research), and American scientists at the Lawrence Livermore National Laboratory.

On July 23, 2004, a team of Japanese scientists at RIKEN detected a single atom of ²⁷⁸Uut using the cold fusion reaction between bismuth-209 and zinc-70. They published their results on September 28, 2004.

Support for their claim appeared in 2004 when scientists at the Institute of Modern Physics (IMP) identified ²⁶⁶Bh as decaying with identical properties to their single event

The RIKEN team produced a further atom on April 2, 2005, although the decay data were different from the first chain, and may be due to the formation of a meta-stable isomer.

The Dubna-Livermore collaboration has strengthened their claim for the discovery of ununtrium by conducting chemical experiments on the decay daughter ²⁶⁸Db. In experiments in Jun 2004 and Dec 2005, the Dubnium isotope was successfully identified by milking the Db fraction and measuring any SF activities. Both the half-life and decay mode were confirmed for the proposed ²⁶⁸Db which lends support to the assignment of Z=115 and Z=113 to the parent and daughter nuclei.

Theoretical estimates of alpha-decay half-lives of alpha-decay chains from element 113 are in good agreement with the experimental data.

Naming: The element with atomic number 113 is historically known as eka-thallium. Ununtrium (Uut) is a temporary IUPAC systematic element name. Research scientists usually refer to the element simply as element 113 (or E113).

Proposed names by claimants: Claims to the discovery of ununtrium have been put forward by Dmitriev of the Dubna team and Morita of the RIKEN team. The IUPAC/IUPAP Joint Working Party will decide to whom the right to suggest a name will be given. The IUPAC have the final say on the official adoption of a name.

The following names have been suggested by the above-mentioned teams claiming discovery:

Target-Projectile combinations leading to Z=113 compound nuclei

The below table contains various combinations of targets and projectiles (both at max no. of neutrons) which could be used to form compound nuclei with an atomic number of 113.

Cold fusion: This section deals with the synthesis of nuclei of ununtrium by so-called "cold" fusion reactions. These are processes which create compound nuclei at low excitation energy (~10-20 MeV, hence "cold"), leading to a higher probability of survival from fission. The excited nucleus then decays to the ground state via the emission of one or two neutrons only.

²⁰⁹Bi(⁷⁰Zn,xn)^279-xUut (x=1)

The synthesis of ununtrium was first attempted in 1998 by the team at GSI using the above cold fusion reaction. In two separate runs, they were unable to detect any atoms and calculated a cross section limit of 900 fb. They repeated the experiment in 2003 and lowered the limit further to 400 fb. In late 2003, the emerging team at RIKEN using their efficient apparatus GARIS attempted the reaction and reached a limit of 140 fb. In December 2003-August 2004, they resorted to 'brute force' and performed an eight-month-long irradiation in which they increased the sensitivity to 51 fb. They were able to detect a single atom of ²⁷⁸Uut. They repeated the reaction in several runs in 2005 and were able to synthesize a second atom. They calculated a record-low 31 fb for the cross section for the 2 atoms. The reaction was repeated again in 2006 with two long production runs but no further atoms were detected. This lowered the yield further to the current value of just 23 fb.

Hot fusion: This section deals with the synthesis of nuclei of ununtrium by so-called "hot" fusion reactions. These are processes which create compound nuclei at high excitation energy (~40-50 MeV, hence "hot"), leading to a reduced probability of survival from fission. The excited nucleus then decays to the ground state via the emission of 3-5 neutrons. Fusion reactions utilizing ⁴⁸Ca nuclei usually produce compound nuclei with intermediate excitation energies (~30-35 MeV) and are sometimes referred to as "warm" fusion reactions. This leads, in part, to relatively high yields from these reactions.

²³⁷Np(⁴⁸Ca,xn)^285-xUut (x=3)

In June 2006, the Dubna-Livermore team synthesised ununtrium directly in the "warm" fusion reaction between neptunium-237 and calcium-48 nuclei. Two atoms of ²⁸²Uut were detected with a cross section of 900 fb.

As a decay product: Ununtrium has also been detected in the decay of Ununpentium and Ununseptium.

CHRONOLOGY OF ISOTOPE DISCOVERY

Cold fusion: The table below provides cross-sections and excitation energies for cold fusion reactions producing ununtrium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.

Hot fusion: The table below provides cross-sections and excitation energies for hot fusion reactions producing ununtrium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.

Evaporation residue 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; σ = cross section

Chemical properties:

Oxidation states: Ununtrium is projected to be the first member of the 7p series of elements and the heaviest member of group 13 (IIIA) in the Periodic Table, below thallium. Each of the members of this group shows the group oxidation state of +III. However, thallium has a tendency to form only a stable +I state due to the "inert pair effect", explained by the relativistic stabilization of the 7s-orbitals, resulting in a higher ionisation potential and weaker tendency to participate in bonding.

Chemistry: Ununtrium should portray eka-thallium chemical properties and should therefore form a monoxide, Uut₂O, and monohalides, UutF, UutCl, UutBr, and UutI. If the +III state is accessible, it is likely that it is only possible in the oxide, Uut₂O₃, and fluoride, UutF₃. Spin-orbit splitting of the 7p orbitals may stabilize the -1 state as well, as is seen with gold(-1) (aurides).

UNUNQUADIUM

Ununquadium is the temporary name of a radioactive chemical element with the temporary symbol Uuq and atomic number 114.

About 80 decays of atoms of Ununquadium have been observed to date, 50 directly and 30 from the decay of the heavier elements Ununhexium and Ununoctium. All decays have been assigned to the five neighbouring isotopes with mass numbers 285-289. The longest-lived isotope currently known is ²⁸⁹Uuq with a half-life of ~2.6 s, although there is evidence for an isomer, ^289bUuq, with a half-life of ~66 s, that would be one of the longest-lived nuclei in the super heavy element region.

Initial chemical studies have strongly indicated that Ununquadium possesses non-'eka'-lead properties and appears to behave as the first super heavy element that portrays noble-gas-like properties due to relativistic effects. However, more recent experiments using a different set-up have indicated that Ununquadium might have metallic properties.

Discovery: In December 1998, scientists at Dubna (Joint Institute for Nuclear Research) in Russia bombarded a ²⁴⁴Pu target with ⁴⁸Ca ions. A single atom of Ununquadium, decaying by 9.67 MeV alpha-emission with a half-life of 30 s, was produced and assigned to ²⁸⁹114. This observation was subsequently published in January 1999. However, the decay chain observed has not been repeated and the exact identity of this activity is unknown, although it is possible that it is due to a meta-stable isomer, namely ^289mUuq.

In March 1999, the same team replaced the ²⁴⁴Pu target with a ²⁴²Pu one in order to produce other isotopes. This time two atoms of Ununquadium were produced, decaying by 10.29 MeV alpha-emission with a half-life of 5.5 s. They were assigned as ²⁸⁷Uuq. Once again, this activity has not been seen again and it is unclear what nucleus was produced. It is possible that it was a meta-stable isomer, namely ^287mUuq.

The now-confirmed discovery of Ununquadium was made in June 1999 when the Dubna team repeated the ²⁴⁴Pu reaction. This time, two atoms of element 114 were produced decaying by emission of 9.82 MeV alpha particles with a half-life of 2.6 s.

This activity was initially assigned to ²⁸⁸Uuq in error, due to the confusion regarding the above observations. Further work in Dec 2002 has allowed a positive reassignment to ²⁸⁹114.

_{244 48 292 289 1}

₉₄Pu + ₂₀Ca → ₁₁₄Uuq^* → ₁₁₄Uuq + 3 ₀ n

In May 2009, the Joint Working Party (JWP) of IUPAC published a report on the discovery of Copernicium in which they acknowledged the discovery of the isotope ²⁸³Cn. This therefore implies the de facto discovery of Ununquadium, from the acknowledgment of the data for the synthesis of ²⁸⁷Uuq and ²⁹¹Uuh (see below), relating to ²⁸³Cn, although this may not be determined as the first synthesis of the element. An impending report by the JWP will discuss these issues.

The discovery of Ununquadium, as ²⁸⁷Uuq and ²⁸⁶Uuq, was confirmed in January 2009 at Berkeley. This was followed by confirmation of ²⁸⁸Uuq and ²⁸⁹Uuq in July 2009 at the GSI (see section 2.1.3).

Naming: Ununquadium (Uuq) is a temporary IUPAC systematic element name. The element is often referred to as element 114, for its atomic number.

According to IUPAC recommendations, the discoverer(s) of a new element has the right to suggest a name. No naming suggestions have yet been given by the (claimant) discoverers.

Future experiments: The team at RIKEN have indicated plans to study the cold fusion reaction:

_{208 76 284}

₈₂Pb + ₃₂Ge → ₁₁₄Uuq^* →?

The FLNR have future plans to study light isotopes of Ununquadium, formed in the reaction between ²³⁹Pu and ⁴⁸Ca.

Isotopes and nuclear properties

Target-Projectile combinations leading to Z=114 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with an atomic number of 114.

Cold fusion: This section deals with the synthesis of nuclei of Ununquadium by so-called "cold" fusion reactions. These are processes which create compound nuclei at low excitation energy (~10-20 MeV, hence "cold"), leading to a higher probability of survival from fission. The excited nucleus then decays to the ground state via the emission of one or two neutrons only.

²⁰⁸Pb(⁷⁶Ge,xn)^284−xUuq

The first attempt to synthesise Ununquadium in cold fusion reactions was performed at Grand accélérateur national d'ions lourds (GANIL), France in 2003. No atoms were detected providing a yield limit of 1.2 pb.

Hot fusion: This section deals with the synthesis of nuclei of Ununquadium by so-called "hot" fusion reactions. These are processes which create compound nuclei at high excitation energy (~40-50 MeV, hence "hot"), leading to a reduced probability of survival from fission. The excited nucleus then decays to the ground state via the emission of 3-5 neutrons. Fusion reactions utilizing ⁴⁸Ca nuclei usually produce compound nuclei with intermediate excitation energies (~30-35 MeV) and are sometimes referred to as "warm" fusion reactions. This leads, in part, to relatively high yields from these reactions.

²⁴⁴Pu(⁴⁸Ca,xn)^292−xUuq (x=3,4,5)

The first experiments on the synthesis of Ununquadium were performed by the team in Dubna in November 1998. They were able to detect a single, long decay chain, assigned to ²⁸⁹Uuq. The reaction was repeated in 1999 and a further two atoms of Ununquadium were detected. The products were assigned to ²⁸⁸Uuq. The team further studied the reaction in 2002. During the measurement of the 3n, 4n, and 5n neutron evaporation excitation functions they were able to detect three atoms of ²⁸⁹Uuq, twelve atoms of the new isotope ²⁸⁸Uuq, and one atom of the new isotope ²⁸⁷Uuq. Based on these results, the first atom to be detected was tentatively reassigned to ²⁹⁰Uuq or ^289mUuq, whilst the two subsequent atoms were reassigned to ²⁸⁹Uuq and therefore belong to the unofficial discovery experiment. In an attempt to study the chemistry of Copernicium as the isotope ²⁸⁵Cn, this reaction was repeated in April 2007. Surprisingly, a PSI-FLNR directly detected two atoms of ²⁸⁸Uuq forming the basis for the first chemical studies of Ununquadium.

In June 2008, the experiment was repeated in order to further assess the chemistry of the element using the ²⁸⁹Uuq isotope. A single atom was detected seeming to confirm the noble-gas-like properties of the element.

During May–July 2009, the team at GSI studied this reaction for the first time, as a first step towards the synthesis of Ununseptium. The team were able to confirm the synthesis and decay data for ²⁸⁸Uuq and ²⁸⁹Uuq, producing nine atoms of the former isotope and four atoms of the latter.

In September 2009, the team at GSI used TASCA to study the chemistry of element 114. They were able to detect two atoms of Ununquadium and determined that the element had strong metallic character, contrary to experiments conducted at the FLNR.

²⁴²Pu(⁴⁸Ca,xn)^290−x114 (x=2,3,4,5)

The team at Dubna first studied this reaction in March–April 1999 and detected two atoms of Ununquadium, assigned to ²⁸⁷Uuq. The reaction was repeated in September 2003 in order to attempt to confirm the decay data for ²⁸⁷Uuq and ²⁸³Cn since conflicting data for ²⁸³Cn had been collected (see Copernicium). The Russian scientists were able to measure decay data for ²⁸⁸Uuq, ²⁸⁷Uuq and the new isotope ²⁸⁶Uuq from the measurement of the 2n, 3n, and 4n excitation functions.

In April 2006, a PSI-FLNR collaboration used the reaction to determine the first chemical properties of Copernicium by producing ²⁸³Cn as an overshoot product. In a confirmatory experiment in April 2007, the team was able to detect ²⁸⁷Uuq directly and therefore measure some initial data on the atomic chemical properties of Ununquadium.

The team at Berkeley, using the Berkeley gas-filled separator (BGS), continued their studies using newly acquired ²⁴²Pu targets by attempting the synthesis of Ununquadium in January 2009 using the above reaction. In September 2009, they reported that they had succeeded in detecting two atoms of Ununquadium, as ²⁸⁷Uuq and ²⁸⁶Uuq, confirming the decay properties reported at the FLNR, although the measured cross sections were slightly lower; however the statistics were of lower quality.^[12]

In April 2009, the collaboration of Paul Scherrer Institute (PSI) and Flerov Laboratory of Nuclear Reactions (FLNR) of JINR carried out another study of the chemistry of Ununquadium using this reaction. A single atom of ²⁸³112 was detected.

In December 2010, the team at the LBNL announced the synthesis of a single atom of the new isotope ²⁸⁵Uuq with the consequent observation of 5 new isotopes of daughter elements.

As a decay product: The isotopes of Ununquadium have also been observed in the decay chains of Ununhexium and Ununoctium.

Retracted isotopes

²⁸⁵Uuq

In the claimed synthesis of ²⁹³Uuo in 1999, the isotope ²⁸⁵Uuq was identified as decaying by 11.35 MeV alpha emission with a half-life of 0.58 ms. The claim was retracted in 2001. This isotope was finally created in 2010 and its decay properties supported the fabrication of the previously published decay data.

Chronology of isotope discovery

Fission of compound nuclei with an atomic number of 114

Several experiments have been performed between 2000-2004 at the Flerov Laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nucleus ²⁹²Uuq. The nuclear reaction used is ²⁴⁴Pu+⁴⁸Ca. The results have revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as ¹³²Sn (Z=50, N=82). It was also found that the yield for the fusion-fission pathway was similar between ⁴⁸Ca and ⁵⁸Fe projectiles, indicating a possible future use of ⁵⁸Fe projectiles in super heavy element formation.

NUCLEAR ISOMERISM

²⁸⁹Uuq

In the first claimed synthesis of Ununquadium, an isotope assigned as ²⁸⁹Uuq decayed by emitting a 9.71 MeV alpha particle with a lifetime of 30 seconds. This activity was not observed in repetitions of the direct synthesis of this isotope. However, in a single case from the synthesis of ²⁹³Uuh, a decay chain was measured starting with the emission of a 9.63 MeV alpha particle with a lifetime of 2.7 minutes. All subsequent decays were very similar to that observed from ²⁸⁹Uuq, presuming that the parent decay was missed. This strongly suggests that the activity should be assigned to an isomeric level. The absence of the activity in recent experiments indicates that the yield of the isomer is ~20% compared to the supposed ground state and that the observation in the first experiment was a fortunate (or not as the case history indicates). Further research is required to resolve these issues.

²⁸⁷Uuq

In a manner similar to those for ²⁸⁹Uuq, first experiments with a ²⁴²Pu target identified an isotope ²⁸⁷Uuq decaying by emission of a 10.29 MeV alpha particle with a lifetime of 5.5 seconds. The daughter spontaneously fissioned with a lifetime in accord with the previous synthesis of ²⁸³Cn. Both these activities have not been observed since (see Copernicium). However, the correlation suggests that the results are not random and are possible due to the formation of isomers whose yield is obviously dependent on production methods. Further research is required to unravel these discrepancies.

Yields of isotopes:

The tables below provide cross-sections and excitation energies for fusion reactions producing Ununquadium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.

COLD FUSION

HOT FUSION

Theoretical calculations

Evaporation residue 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.

MD = multi-dimensional; DNS = Dinuclear system; σ = cross section

Decay characteristics: Theoretical estimation of the alpha decay half-lives of the isotopes of the Ununquadium supports the experimental data. The fission-survived isotope ²⁹⁸Uuq is predicted to have alpha decay half-life around 17 days.

IN SEARCH FOR THE ISLAND OF STABILITY:

²⁹⁸Uuq

According to macroscopic-microscopic (MM) theory Z=114 is the next spherical magic number. This means that such nuclei are spherical in their ground state and should have high, wide fission barriers to deformation and hence long SF partial half-lives. In the region of Z=114, MM theory indicates that N=184 is the next spherical neutron magic number and puts forward the nucleus ²⁹⁸Uuq as a strong candidate for the next spherical doubly magic nucleus, after ²⁰⁸Pb (Z=82, N=126). ²⁹⁸Uuq is taken to be at the centre of a hypothetical ‘island of stability’. However, other calculations using relativistic mean field (RMF) theory propose Z=120, 122, and 126 as alternative proton magic numbers depending upon the chosen set of parameters. It is possible that rather than a peak at a specific proton shell, there exists a plateau of proton shell effects from Z=114–126.

It should be noted that calculations suggest that the minimum of the shell-correction energy and hence the highest fission barrier exists for ²⁹⁷Uup, caused by pairing effects. Due to the expected high fission barriers, any nucleus within this island of stability will exclusively decay by alpha-particle emission and as such the nucleus with the longest half-life is predicted to be ²⁹⁸Uuq. The expected half-life is unlikely to reach values higher than about 10 minutes, unless the N=184 neutron shell proves to be more stabilising than predicted, for which there exists some evidence. In addition, ²⁹⁷Uuq may have an even-longer half-life due to the effect of the odd neutron, creating transitions between similar Nilsson levels with lower Q_alpha values.

In either case, an island of stability does not represent nuclei with the longest half-lives but those which are significantly stabilized against fission by closed-shell effects.

Evidence for Z=114 closed proton shell

While evidence for closed neutron shells can be deemed directly from the systematic variation of Q_alpha values for ground-state to ground-state transitions, evidence for closed proton shells comes from (partial) spontaneous fission half-lives. Such data can sometimes be difficult to extract due to low production rates and weak SF branching. In the case of Z=114, evidence for the effect of this proposed closed shell comes from the comparison between the nuclei pairings ²⁸²Cn (T_SF1/2 = 0.8 ms) and ²⁸⁶Uuq (T_SF1/2 = 130 ms), and ²⁸⁴Cn (T_SF = 97 ms) and ²⁸⁸Uuq (T_SF >800 ms). Further evidence would come from the measurement of partial SF half-lives of nuclei with Z>114, such as ²⁹⁰Uuh and ²⁹²Uuo (both N=174 isotones). The extraction of Z=114 effects is complicated by the presence of a dominating N=184 effect in this region.

Difficulty of synthesis of ²⁹⁸Uuq

The direct synthesis of the nucleus ²⁹⁸Uuq by a fusion-evaporation pathway is impossible since no known combination of target and projectile can provide 184 neutrons in the compound nucleus.

It has been suggested that such a neutron-rich isotope can be formed by the quasifission (partial fusion followed by fission) of a massive nucleus. Such nuclei tend to fission with the formation of isotopes close to the closed shells Z=20/N=20 (⁴⁰Ca), Z=50/N=82 (¹³²Sn) or Z=82/N=126 (²⁰⁸Pb/²⁰⁹Bi). If Z=114 does represent a closed shell, then the hypothetical reaction below may represent a method of synthesis:

_{204 136 298 40 1}

₈₀Hg + ₅₄Xe →₁₁₄Uuq +₂₀Ca + 2 ₀ n

Recently it has been shown that the multi-nucleon transfer reactions in collisions of actinide nuclei (such as uranium and curium) might be used to synthesize the neutron rich superheavy nuclei located at the island of stability. It is also possible that ²⁹⁸Uuq can be synthesized by the alpha decay of a massive nucleus. Such a method would depend highly on the SF stability of such nuclei, since the alpha half-lives are expected to be very short. The yields for such reactions will also most likely be extremely small. One such reaction is:

_{244 96 338 298 4}

₉₄Pu(₄₀Zr, 2n) → ₁₃₄Utq → → ₁₁₄Uuq + 10 ₂He

Chemical properties

Extrapolated chemical properties

Oxidation states: Ununquadium is projected to be the second member of the 7p series of chemical elements and the heaviest member of group 14 (IVA) in the Periodic Table, below lead. Each of the members of this group show the group oxidation state of +IV and the latter members have an increasing +II chemistry due to the onset of the inert pair effect. Tin represents the point at which the stability of the +II and +IV states are similar. Lead, the heaviest member, portrays a switch from the +IV state to the +II state. Ununquadium should therefore follow this trend and a possess an oxidising +IV state and a stable +II state.

Chemistry: Ununquadium should portray eka-lead chemical properties and should therefore form a monoxide, UuqO, and dihalides, UuqF₂, UuqCl₂, UuqBr₂, and UuqI₂. If the +IV state is accessible, it is likely that it is only possible in the oxide, UuqO₂, and fluoride, UuqF₄. It may also show a mixed oxide, Uuq₃O₄, analogous to Pb₃O₄.

Some studies also suggest that the chemical behaviour of Ununquadium might in fact be closer to that of the noble gas radon, than to that of lead.

Experimental chemistry

Atomic gas phase: Two experiments were performed in April–May 2007 in a joint FLNR-PSI collaboration aiming to study the chemistry of Copernicium. The first experiment involved the reaction ²⁴²Pu(⁴⁸Ca,3n)²⁸⁷Uuq and the second the reaction ²⁴⁴Pu(⁴⁸Ca,4n)²⁸⁸Uuq. The adsorption properties of the resultant atoms on a gold surface were compared with those of radon. The first experiment allowed detection of 3 atoms of ²⁸³Cn but also seemingly detected 1 atom of ²⁸⁷Uuq. This result was a surprise given the transport time of the product atoms is ~2 s, so Ununquadium atoms should decay before adsorption. In the second reaction, 2 atoms of ²⁸⁸Uuq and possibly 1 atom of ²⁸⁹Uuq were detected. Two of the three atoms portrayed adsorption characteristics associated with a volatile, noble-gas-like element, which has been suggested but is not predicted by more recent calculations. These experiments did however provide independent confirmation for the discovery of Copernicium, Ununquadium, and Ununhexium via comparison with published decay data. Further experiments were performed in 2008 to confirm this important result and a single atom of ²⁸⁹Uuq was detected which gave data in agreement with previous data in support of Ununquadium having a noble-gas-like interaction with gold. In April 2009, the FLNR-PSI collaboration synthesized a further atom of E114. In September 2009, the GSI team using TASCA detected two atoms of E114. Most noteworthy was that these results indicated that E114 had strong metallic properties, contrary to the results above.

UNUNPENTIUM

Ununpentium is the temporary name of a synthetic superheavy element in the periodic table that has the temporary symbol Uup and has the atomic number 115.

It is placed as the heaviest member of group 15 (VA) although a sufficiently stable isotope is not known at this time that would allow chemical experiments to confirm its position. It was first observed in 2003 and only about 30 atoms of ununpentium have been synthesized to date, with just 4 direct decays of the parent element having been detected. Four consecutive isotopes are currently known, ^287-290Uup, with ²⁸⁹Uup having the longest measured half-life of ~220 ms, although the isotope ²⁹⁰Uup may well have an even longer half-life (only a single decay has been measured leading to poor accuracy).

Discovery profile: On February 2, 2004, synthesis of ununpentium was reported in Physical Review C by a team composed of Russian scientists at the Joint Institute for Nuclear Research in Dubna, and American scientists at the Lawrence Livermore National Laboratory. The team reported that they bombarded americium-243 with calcium-48 ions to produce four atoms of ununpentium. These atoms, they report, decayed by emission of alpha-particles to ununtrium in approximately 100 milliseconds.

_{48 243 291 288}

₂₀Ca + ₉₅Am → ₁₁₅Uup*→ ₁₁₅Uup

The Dubna-Livermore collaboration has strengthened their claim for the discovery of ununpentium by conducting chemical experiments on the decay daughter ²⁶⁸Db. In experiments in June 2004 and December 2005, the Dubnium isotope was successfully identified by milking the Db fraction and measuring any SF activities. Both the half-life and decay mode were confirmed for the proposed ²⁶⁸Db which lends support to the assignment of Z=115 to the parent nuclei.

Official claim of discovery of ununpentium: Sergei Dmitriev from the Flerov Laboratory of Nuclear Reactions (FLNR) in Dubna, Russia, has formally put forward their claim of discovery of ununpentium to the Joint Working Party (JWP) from IUPAC and IUPAP. The JWP are expected to publish their opinions on such claims in the near future.

Naming: Ununpentium is historically known as eka-bismuth. Ununpentium is a temporary IUPAC systematic element name. Research scientists usually refer to the element simply as element 115.

Future experiments: The team at the FLNR have scheduled further experiments on the ²⁴³Am + ⁴⁸Ca reaction to start in September 2010. The exact goals of these experiments have not been outlined. It is likely they are attempting to measure a complete excitation function. Furthermore, a primary next goal for the Dubna team is to measure the mass of the dubnium product from the above reaction, so this may also be a part of their immediate plans.

The FLNR also have future plans to study light isotopes of element 115 using the reaction ²⁴¹Am + ⁴⁸Ca.

ISOTOPES AND NUCLEAR PROPERTIES

Nucleosynthesis

Target-projectile combinations leading to Z=115 compound nuclei

The table below contains various combinations of targets and projectiles which could be used to form compound nuclei with Z=115.

Hot fusion: This section deals with the synthesis of nuclei of ununpentium by so-called "hot" fusion reactions. These are processes which create compound nuclei at high excitation energy (~40-50 MeV, hence "hot"), leading to a reduced probability of survival from fission. The excited nucleus then decays to the ground state via the emission of 3-5 neutrons. Fusion reactions utilizing ⁴⁸Ca nuclei usually produce compound nuclei with intermediate excitation energies (~30-35 MeV) and are sometimes referred to as "warm" fusion reactions. This leads, in part, to relatively high yields from these reactions.

²³⁸U(⁵¹V,xn)^289−xUup

There are strong indications that this reaction was performed in late 2004 as part of a uranium(IV) fluoride target test at the GSI. No reports have been published suggesting that no products atoms were detected, as anticipated by the team.

²⁴³Am(⁴⁸Ca,xn)^291−xUup (x=3,4)

This reaction was first performed by the team in Dubna in July–August 2003. In two separate runs they were able to detect 3 atoms of ²⁸⁸Uup and a single atom of ²⁸⁷Uup. The reaction was studied further in June 2004 in an attempt to isolate the descendant ²⁶⁸Db from the ²⁸⁸Uup decay chain. After chemical separation of a +4/+5 fraction, 15 SF decays were measured with a lifetime consistent with ²⁶⁸Db. In order to prove that the decays were from dubnium-268, the team repeated the reaction in August 2005 and separated the +4 and +5 fractions and further separated the +5 fractions into tantalum-like and niobium-like ones. Five SF activities were observed, all occurring in the +5 fractions and none in the tantalum-like fractions, proving that the product was indeed isotopes of dubnium.

Chronology of isotope discovery

Yields of isotopes

Hot fusion: The table below provides cross-sections and excitation energies for hot fusion reactions producing ununpentium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.

DECAY CHARACTERISTICS

Theoretical calculations using a quantum-tunneling model support the experimental alpha-decay half-lives.

Evaporation residue cross sections

The table below contains various target-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.

MD = multi-dimensional; DNS = Di-nuclear system; σ = cross section

Chemical properties

Extrapolated chemical properties

Oxidation states: Ununpentium is projected to be the third member of the 7p series of chemical elements and the heaviest member of group 15 (VA) in the Periodic Table, below bismuth. In this group, each member is known to portray the group oxidation state of +V but with differing stability. For nitrogen, the +V state is very difficult to achieve due to the lack of low-lying d-orbitals and the inability of the small nitrogen atom to accommodate five ligands. The +V state is well represented for phosphorus, arsenic, and antimony. However, for bismuth it is rare due to the reluctance of the 6s² electron to participate in bonding. This effect is known as the "inert pair effect" and is commonly linked to relativistic stabilisation of the 6s-orbitals. It is expected that ununpentium will continue this trend and portray only +III and +I oxidation states. Nitrogen (I) and Bismuth (I) are known but rare and Uup(I) is likely to show some unique properties. Because of spin-orbit coupling, Ununquadium may display closed-shell or noble gas-like properties; if this is the case, Uup will likely be monovalent as a result, since the cation Uup⁺ will have the same electron configuration as Uuq.

Chemistry: Ununpentium should display eka-bismuth chemical properties and should therefore form a sesquioxide, Uup₂O₃, and anologous chalcogenides, Uup₂S₃, Uup₂Se₃ and Uup₂Te₃. It should also form trihydrides and trihalides, i.e. UupH₃, UupF₃, UupCl₃, UupBr₃ and UupI₃. If the +V state is accessible, it is likely that it is only possible in the fluoride, UupF₅.^[13]

As some studies suggest that the chemical behaviour of ununquadium might in fact be closer to the noble gas radon, it is possible that ununpentium might behave like an alkali metal, showing only the +I oxidation state.^[14] If this is the case, then ununpentium may behave more like an analog to caesium and francium than bismuth.

Stability

Main article: Island of stability

All the reported above isotopes of element 115, obtained by nuclear collisions of lighter nuclei, are severely neutron-deficient, due to the fact that the proportion of neutrons to protons needed for maximum stability increases with atomic number. The most stable isotope will probably be ²⁹⁹Uup, with 184 neutrons, a known "magic" closed-shell number conferring exceptional stability, making it (with one further proton outside the "magic number" of 114 protons) both the chemical and the nuclear homolog of ²⁰⁹Bi; but the technology required to add the required neutrons presently does not exist. This is because no known combination of target and projectile can result in the required neutrons. It has been suggested that such a neutron-rich isotope could be formed by quasifission (fusion followed by fission) of a massive nucleus, multi-nucleon transfer reactions in collisions of actinide nuclei, or by the alpha decay of a massive nucleus (although this would depend on the stability of the parent nuclei towards spontaneous fission).

UNUNHEXIUM

Ununhexium is the temporary name of a synthetic superheavy element with the temporary symbol Uuh and atomic number 116.

It is placed as the heaviest member of group 16 (VIA) although a sufficiently stable isotope is not known at this time to allow chemical experiments to confirm its position as the heavier homologue to polonium.

It was first detected in 2000 and since the discovery about 30 atoms of Ununhexium have been produced, either directly or as a decay product of Ununoctium, and are associated with decays from the four neighbouring isotopes with masses 290–293. The most stable isotope to date is Uuh-293 with a half-life of ~60 ms.

Discovery profile: On July 19, 2000, scientists at Dubna (JINR) detected a single decay from an atom of Ununhexium following the irradiation of a Cm-248 target with Ca-48 ions. The results were published in December, 2000. This 10.54 MeV alpha-emitting activity was originally assigned to ²⁹²Uuh due to the correlation of the daughter to previously assigned ²⁸⁸Uuq. However, that assignment was later altered to ²⁸⁹Uuq, and hence this activity was correspondingly changed to ²⁹³Uuh. Two further atoms were reported by the institute during their second experiment between April–May 2001.

In the same experiment they also detected a decay chain which corresponded to the first observed decay of Ununquadium and assigned to ²⁸⁹Uuq. This activity has not been observed again in a repeat of the same reaction. However, its detection in this series of experiments indicates the possibility of the decay of an isomer of Ununhexium, namely ^293bUuh, or a rare decay branch of the already discovered isomer,^293aUuh, in which the first alpha particle was missed. Further research is required to positively assign this activity.

The team repeated the experiment in April–May 2005 and detected 8 atoms of Ununhexium. The measured decay data confirmed the assignment of the discovery isotope as ²⁹³Uuh. In this run, the team also observed ²⁹²Uuh in the 4n channel for the first time.

In May 2009, the Joint Working Party reported on the discovery of Copernicium and acknowledged the discovery of the isotope ²⁸³Cn This implies the de facto discovery of Ununhexium, as ²⁹¹Uuh (see below), from the acknowledgment of the data relating to the granddaughter ²⁸³Cn, although the actual discovery experiment may be determined as that above. An impending JWP report will discuss these issues further.

Naming: Ununhexium is historically known as eka-polonium. Ununhexium (Uuh) is a temporary IUPAC systematic element name. Research scientists usually refer to the element simply as element 116 (or E116).

According to IUPAC recommendations, the discoverer(s) of a new element has the right to suggest a name. The JWP has not yet officially accepted the discovery of element 116 and so the naming process has not yet begun.

Current and future experiments: The GSI were to be running an experiment (Jun 24-Jul 25 2010) to study the formation of ^293,292Uuh in the ²⁴⁸Cm(⁴⁸Ca,xn) reaction as a first step in their future program with a ²⁴⁸Cm target, aiming towards a synthesis of unbinilium.

The team at Dubna have indicated plans to synthesize Ununhexium using the reaction between plutonium-244 and titanium-50. This experiment will allow them to assess the feasibility of using projectiles with Z>20 required in the synthesis of superheavy elements with Z>118. Although initially scheduled for 2008, the reaction looking at the synthesis of evaporation residues has not been conducted to date.

There are also plans to repeat the Cm-248 reaction at different projectile energies in order to probe the 2n channel, leading to the new isotope ²⁹⁴Uuh. In addition, they have future plans to complete the excitation function of the 4n channel product, ²⁹²Uuh, which will allow them to assess the stabilizing effect of the N=184 shell on the yield of evaporation residues.

ISOTOPES AND NUCLEAR PROPERTIES

Nucleosynthesis

Target-projectile combinations leading to Z=116 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with atomic number 116.

Cold fusion

²⁰⁸Pb(⁸²Se,xn)^290−xUuh

In 1998, the team at GSI attempted the synthesis of ²⁹⁰Uuh as a radiative capture (x=0) product. No atoms were detected providing a cross section limit of 4.8 pb.

Hot fusion: This section deals with the synthesis of nuclei of ununhexium by so-called "hot" fusion reactions. These are processes which create compound nuclei at high excitation energy (~40-50 MeV, hence "hot"), leading to a reduced probability of survival from fission. The excited nucleus then decays to the ground state via the emission of 3-5 neutrons. Fusion reactions utilizing ⁴⁸Ca nuclei usually produce compound nuclei with intermediate excitation energies (~30-35 MeV) and are sometimes referred to as "warm" fusion reactions. This leads, in part, to relatively high yields from these reactions.

²³⁸U(⁵⁴Cr,xn)^292−xUuh

There are sketchy indications that this reaction was attempted by the team at GSI in 2006. There are no published results on the outcome, presumably indicating that no atoms were detected. This is expected from a study of the systematics of cross sections for ²³⁸U targets.

²⁴⁸Cm(⁴⁸Ca,xn)^296−xUuh (x=3,4)

The first attempt to synthesise Ununhexium was performed in 1977 by Ken Hulet and his team at the Lawrence Livermore National Laboratory (LLNL). They were unable to detect any atoms of Ununhexium. Yuri Oganessian and his team at the Flerov Laboratory of Nuclear Reactions (FLNR) subsequently attempted the reaction in 1978 and were met by failure. In 1985, a joint experiment between Berkeley and Peter Armbruster's team at GSI, the result was again negative with a calculated cross-section limit of 10–100 pb.

In 2000, Russian scientists at Dubna finally succeeded in detecting a single atom of Ununhexium, assigned to the isotope ²⁹²Uuh. In 2001, they repeated the reaction and formed a further 2 atoms in a confirmation of their discovery experiment. A third atom was tentatively assigned to ²⁹³Uuh on the basis of a missed parental alpha decay. In April 2004, the team ran the experiment again at higher energy and were able to detect a new decay chain, assigned to ²⁹²Uuh. On this basis, the original data were reassigned to ²⁹³Uuh. The tentative chain is therefore possibly associated with a rare decay branch of this isotope. In this reaction, 2 further atoms of ²⁹³Uuh were detected.

²⁴⁵Cm(⁴⁸Ca,xn)^293−x116 (x=2,3)

In order to assist in the assignment of isotope mass numbers for Ununhexium, in March–May 2003 the Dubna team bombarded a ²⁴⁵Cm target with ⁴⁸Ca ions. They were able to observe two new isotopes, assigned to ²⁹¹Uuh and ²⁹⁰Uuh. This experiment was successfully repeated in Feb-March 2005 where 10 atoms were created with identical decay data to those reported in the 2003 experiment.

As a decay product: Ununhexium has also been observed in the decay of Ununoctium. In October 2006 it was announced that 3 atoms of Ununoctium had been detected by the bombardment of californium-249 with calcium-48 ions, which then rapidly decayed into Ununhexium.

The observation of ²⁹⁰Uuh allowed the assignment of the product to ²⁹⁴Uuo and proved the synthesis of Ununoctium.

Fission of compound nuclei with Z=116

Several experiments have been performed between 2000-2006 at the Flerov laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nuclei ^296,294,290Uuh. Four nuclear reactions have been used, namely ²⁴⁸Cm+⁴⁸Ca, ²⁴⁶Ca+⁴⁸Ca, ²⁴⁴Pu+⁵⁰Ti and ²³²Th+⁵⁸Fe. The results have revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as ¹³²Sn (Z=50, N=82). It was also found that the yield for the fusion-fission pathway was similar between ⁴⁸Ca and ⁵⁸Fe projectiles, indicating a possible future use of ⁵⁸Fe projectiles in superheavy element formation.In addition, in comparative experiments synthesizing ²⁹⁴Uuh using ⁴⁸Ca and ⁵⁰Ti projectiles, the yield from fusion-fission was ~3x less for ⁵⁰Ti, also suggesting a future use in SHE production

RETRACTED ISOTOPES

²⁸⁹Uuh

In 1999, researchers at Lawrence Berkeley National Laboratory announced the synthesis of ²⁹³Uuo (see Ununoctium), in a paper published in Physical Review Letters. The claimed isotope ²⁸⁹Uuh decayed by 11.63 MeV alpha emission with a half-life of 0.64 ms. The following year, they published a retraction after other researchers were unable to duplicate the results. 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 the principal author Victor Ninov. As such, this isotope of Ununhexium is currently unknown.

Chronology of isotope discovery

Yields of isotopes

Hot fusion: The table below provides cross-sections and excitation energies for hot fusion reactions producing Ununhexium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.

Theoretical calculations

Decay characteristics

Theoretical calculation in a quantum tunneling model supports the experimental data relating to the synthesis of ^293,292Uuh.

Evaporation residue 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; σ = cross section

Chemical properties

Extrapolated chemical properties

Oxidation states: Ununhexium is projected to be the fourth member of the 7p series of non-metals and the heaviest member of group 16 (VIA) in the Periodic Table, below polonium. The group oxidation state of +VI is known for all the members apart from oxygen which lacks available d-orbitals for expansion and is limited to a maximum +II state, exhibited in the fluoride OF₂. The +IV is known for sulfur, selenium, tellurium, and polonium, undergoing a shift in stability from reducing for S(IV) and Se(IV) to oxidizing in Po(IV). Tellurium (IV) is the most stable for this element. This suggests a decreasing stability for the higher oxidation states as the group is descended and Ununhexium should portray an oxidizing +IV state and a more stable +II state. The lighter members are also known to form a −II state as oxide, sulfide, selenide, telluride, and polonide.

Chemistry: The possible chemistry of Ununhexium can be extrapolated from that of polonium. It should therefore undergo oxidation to a dioxide, UuhO₂, although a trioxide, UuhO₃ is plausible, but unlikely. The stability of a +II state should manifest itself in the formation of a simple monoxide, UuhO. Fluorination will likely result in a tetrafluoride, UuhF₄ and/or a difluoride, UuhF₂. Chlorination and bromination may well stop at the corresponding dihalides, UuhCl₂ and UuhBr₂. Oxidation by iodine should certainly stop at UuhI₂ and may even be inert to this element.

UNUNSEPTIUM

Ununseptium is the temporary name of the chemical element with temporary symbol Uus and atomic number 117. It is the latest element to have a claim of discovery, with six atoms having been detected by a joint Russia–US collaboration at Dubna, Moscow Oblast, Russia, in 2009–10. Although it is placed as the heaviest member of the halogen family, there is no experimental evidence that the chemical properties of Ununseptium match those of the lighter members like iodine or astatine and theoretical analysis suggests there may be some notable differences.

Discovery: In January 2010, scientists at the Flerov Laboratory of Nuclear Reactions announced internally that they had succeeded in detecting the decay of a new element with Z=117 using the reactions:

_{48 249 297 294 1}

₂₀Ca + ₉₇Bk → ₁₁₇Uus* → ₁₁₇Uus + 3 ₀n

_{48 249 297 293 1}

₂₀Ca + ₉₇Bk → ₁₁₇Uus* → ₁₁₇Uus + 4 ₀n

Just six atoms were synthesized of two neighbouring isotopes, neither of which decayed to known isotopes of lighter elements. Their results were published on 9 April 2010 in the journal Physical Review Letters.

Naming: The element with atomic number 117 is historically known as eka-astatine. The name Ununseptium is a systematic element name, used as a placeholder until the discovery is acknowledged by the IUPAC, and the IUPAC decides on a name. Usually, the name suggested by the discoverer(s) is chosen. According to current guidelines from IUPAC, the ultimate name for all new elements should end in "-ium", which means the name for Ununseptium may end in -ium, not -ine, even if Ununseptium turns out to be a halogen.

Current experiments: Scientists at Dubna are continuing their study of the ²⁴⁹Bk + ⁴⁸Ca reaction in order to attempt a first chemical study of ununtrium.

Future experiments: The team at the GSI in Darmstadt recently acknowledged as the discoverers of Copernicium have begun experiments aiming towards a synthesis of Ununseptium. The GSI have indicated that if they are unable to acquire any ²⁴⁹Bk from the United States, which is likely given the situation regarding the attempt in Russia, they will study the reaction ²⁴⁴Pu(⁵¹V,xn) instead, or possibly ²⁴³Am(⁵⁰Ti,xn).

Isotopes and nuclear properties

Target-projectile combinations leading to Z=117 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with atomic number 117.

Hot fusion

²⁴⁹Bk (⁴⁸Ca, xn)^297-xUus (x=3,4)

Between July 2009 and February 2010, the team at the JINR (Flerov Laboratory of Nuclear Reactions) ran a 7-month-long experiment to synthesize Ununseptium using the reaction above. The expected cross-section was of the order of 2 pb. The expected evaporation residues, ²⁹³Uus and ²⁹⁴Uus, were predicted to decay via relatively long decay chains as far as isotopes of Dubnium or lawrencium.

The team published a scientific paper in April 2010 (first results were presented in January 2010) that six atoms of the neighbouring isotopes ²⁹⁴Uus (one atom) and ²⁹³Uus (five atoms) were detected. The heavier isotope decayed by the successive emission of six alpha particles down as far as the new isotope ²⁷⁰Db which underwent apparent spontaneous fission. On the other hand, the lighter odd-even isotope decayed by the emission of just three alpha particles, as far ²⁸¹Rg, which underwent spontaneous fission. The reaction was run at two different excitation energies of 35 MeV (dose 2x10¹⁹) and 39 MeV (dose 2.4×10¹⁹). Initial decay data was published as a preliminary presentation on the JINR website.

CHRONOLOGY OF ISOTOPE DISCOVERY

THEORETICAL CALCULATIONS

Evaporation residue 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; σ = cross section

Decay characteristics

Theoretical calculations in a quantum tunneling model with mass estimates from a macroscopic-microscopic model predict the alpha-decay half-lives of isotopes of Ununseptium (namely, ^289–303117) to be around 0.1–40 ms.

Chemical properties

Extrapolated chemical properties

Certain chemical properties, such as bond lengths, are predicted to differ from what one would expect based on periodic trends from the lighter halogens (because of relativistic effects). It may have some metalloid properties, similar to astatine.

UNUNOCTIUM

Ununoctium is the temporary IUPAC name for the transactinide element having the atomic number 118 and temporary element symbol Uuo. It is also known as eka-radon or element 118, and on the periodic table of the elements it is a p-block element and the last one of the 7th period. Ununoctium is currently the only synthetic member of Group 18. It has the highest atomic number and highest atomic mass of all discovered elements.

The radioactive Ununoctium atom is very unstable, and since 2002, only three atoms (possibly four) of the isotope 294

Uuo have been detected. While this allowed for very little experimental characterization of its properties and possible compounds, theoretical calculations have resulted in many predictions, including some unexpected ones. For example, although Ununoctium is a member of Group 18, it may possibly not be a noble gas, unlike all the other Group 18 elements.^[1] It was formerly thought to be a gas but is now predicted to be a solid under normal conditions due to relativistic effects.^[1]

Unsuccessful attempts: In late 1998, Polish physicist Robert Smolańczuk published calculations on the fusion of atomic nuclei towards the synthesis of superheavy atoms, including Ununoctium. His calculations suggested that it might be possible to make Ununoctium by fusing lead with krypton under carefully controlled conditions.

In 1999, researchers at Lawrence Berkeley National Laboratory made use of these predictions and announced the discovery of Ununhexium and Ununoctium, in a paper published in Physical Review Letters, and very soon after the results were reported in Science. The researchers claimed to have performed the reaction

_{86 208 293}

₃₆Kr + ₈₂Pb → ₁₁₈Uuo + n.

The following year, they published a retraction after researchers at other laboratories were unable to duplicate the results and the Berkeley lab itself was unable to duplicate them as well. 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.

Discovery: The first decay of atoms of Ununoctium was discovered and observed at the Joint Institute for Nuclear Research (JINR) by Yuri Oganessian and his group in Dubna, Russia, in 2002. On October 9, 2006, researchers from JINR and Lawrence Livermore National Laboratory of California, USA, working at the JINR in Dubna, announced that they had indirectly detected a total of three (possibly four) nuclei of ununoctium-294 (one or two in 2002 and two more in 2005) produced via collisions of californium-249 atoms and calcium-48 ions:

_{249 48 294}

₉₈Cf + ₂₀Ca → ₁₁₈Uuo + 3 n.

Because of the very small fusion reaction probability (the fusion cross section is ~0.3–0.6 pb = (3–6)×10⁻⁴¹ m²) the experiment took 4 months and involved a beam dose of 4×10¹⁹ calcium ions that had to be shot at the californium target to produce the first recorded event believed to be the synthesis of Ununoctium. Nevertheless, researchers are highly confident that the results are not a false positive, since the chance that the detections were random events was estimated to be less than one part in 100,000.

In the experiments, the alpha-decay of three atoms of Ununoctium was observed. A fourth decay by direct spontaneous fission was also proposed. A half-life of 0.89 ms was calculated: ²⁹⁴Uuo decays into ²⁹⁰Uuh by alpha decay. Since there were only three nuclei, the half-life derived from observed lifetimes has a large uncertainty: 0.89^+1.07ms.

^−0.31

_{294 290 4}

₁₁₈Uuo → ₁₁₆Uuh + He

The identification of the ²⁹⁴Uuo nuclei was verified by separately creating the putative daughter nucleus ²⁹⁰Uuh by means of a bombardment of ²⁴⁵Cm with ⁴⁸Ca ions,

_{245 48 290}

₉₆Cm + ₂₀Ca → ₁₁₆Uuh + 3 n

And checking that the ²⁹⁰Uuh decay matched the decay chain of the ²⁹⁴Uuo nuclei. The daughter nucleus ²⁹⁰ Uuh is very unstable, decaying with a half-life of 14 milliseconds into ²⁸⁶Uuq, which may experience either spontaneous fission or alpha decay into ²⁸²Cn, which will undergo spontaneous fission. _+0.23 In a quantum-tunneling model, the alpha decay half-life of ²⁹⁴Uuo was predicted to be 0.66_−0.18 ms with the experimental Q-value published in 2004. Calculation with theoretical Q-values from the macroscopic-microscopic model of Muntian–Hofman–Patyk–Sobiczewski gives somewhat low but comparable results.

Following the success in obtaining Ununoctium, the discoverers have started similar experiments in the hope of creating unbinilium from ⁵⁸Fe and ²⁴⁴Pu. Isotopes of unbinilium are predicted to have alpha decay half lives of the order of micro-seconds.

Naming: Until the 1960s Ununoctium was known as eka-emanation (emanation is the old name for radon). In 1979 the IUPAC published recommendations according to which the element was to be called Ununoctium, a systematic element name, as a placeholder until the discovery of the element is confirmed and the IUPAC decides on a name.

Before the retraction in 2002, the researchers from Berkeley had intended to name the element ghiorsium (Gh), after Albert Ghiorso (a leading member of the research team).

The Russian discoverers reported their synthesis in 2006. In 2007, the head of the Russian institute stated the team were considering two names for the new element: flyorium in honor of Georgy Flyorov, the founder of the research laboratory in Dubna; and moskovium, in recognition of the Moskovskaya Oblast where Dubna is located. He also stated that although the element was discovered as an American collaboration, who provided the californium target, the element should rightly be named in honor of Russia since the Flerov Laboratory of Nuclear Reactions at JINR was the only facility in the world which could achieve this result.

CHARACTERISTICS

Nucleus stability and isotopes: There are no elements with an atomic number above 82 (after lead) that have stable isotopes. The stability of nuclei decreases with the increase in atomic number, such that all isotopes with an atomic number above 101 decay radioactively with a half-life under a day. Nevertheless, because of reasons not very well understood yet, there is a slight increased nuclear stability around atomic numbers 110–114, which leads to the appearance of what is known in nuclear physics as the "island of stability". This concept, proposed by UC Berkeley professor Glenn Seaborg, explains why superheavy elements last longer than predicted.^[36] Ununoctium is radioactive and has half-life that appears to be less than a millisecond. Nonetheless, this is still longer than some predicted values, thus giving further support to the idea of this "island of stability".Calculations using a quantum-tunneling model predict the existence of several neutron-rich isotopes of Ununoctium with alpha-decay half-lives close to 1 ms.

Theoretical calculations done on the synthetic pathways for, and the half-life of, other isotopes have shown that some could be slightly more stable than the synthesized isotope 294

Uuo, most likely ²⁹³Uuo, ²⁹⁵Uuo, ²⁹⁶Uuo, ²⁹⁷Uuo, ²⁹⁸Uuo, ³⁰⁰Uuo and ³⁰²Uuo. Of these, ²⁹⁷Uuo 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 ³¹³Uuo, could also provide longer-lived nuclei.

Calculated atomic and physical properties: Ununoctium is a member of group 18, the zero-valence elements. The members of this group are usually inert to most common chemical reactions (for example, combustion) because the outer valence shell is completely filled with eight electrons. This produces a stable, minimum energy configuration in which the outer electrons are tightly bound. It is thought that similarly, Ununoctium has a closed outer valence shell in which its valence electrons are arranged in a 7s²7p⁶ configuration.

Consequently, some expect Ununoctium to have similar physical and chemical properties to other members of its group, most closely resembling the noble gas above it in the periodic table, radon. Following the periodic trend, Ununoctium would be expected to be slightly more reactive than radon. However, theoretical calculations have shown that it could be quite reactive, so that it can probably not be considered a noble gas. In addition to being far more reactive than radon, Ununoctium may be even more reactive than elements Ununquadium and Copernicium. The reason for the apparent enhancement of the chemical activity of Ununoctium relative to radon is an energetic destabilization and a radial expansion of the last occupied 7p subshell. More precisely, considerable spin-orbit interactions between the 7p electrons with the inert 7s² electrons, effectively lead to a second valence shell closing at Ununquadium, and a significant decrease in stabilization of the closed shell of element 118. It has also been calculated that Ununoctium, unlike other noble gases, binds an electron with release of energy—or in other words, it exhibits positive electron affinity.^[44][45][46]

Ununoctium is expected to have by far the broadest polarizability of all elements before it in the periodic table, and almost twofold of radon. By extrapolating from the other noble gases, it is expected that Ununoctium has a boiling point between 320 and 380 K. This is very different from the previously estimated values of 263 K or 247 K. Even given the large uncertainties of the calculations, it seems highly unlikely that Ununoctium would be a gas under standard conditions. And as the liquid range of the other gases is very narrow, between 2 and 9 kelvins, this element should be solid at standard conditions. If ununoctium forms a gas under standard conditions nevertheless, it would be one of the densest gaseous substances at standard conditions (even if it is monatomic like the other noble gases).

Because of its tremendous polarizability, Ununoctium is expected to have an anomalously low ionization energy (similar to that of lead which is 70% of that of radon and significantly smaller than that of Ununquadium) and a standard state condensed phase.

Predicted compounds: No compounds of Ununoctium have been synthesized yet, but calculations on theoretical compounds have been performed since 1964. It is expected that if the ionization energy of the element is high enough, it will be difficult to oxidize and therefore, the most common oxidation state will be 0 (as for other noble gases).

Calculations on the dimeric molecule Uuo₂ showed a bonding interaction roughly equivalent to that calculated for Hg₂, and a dissociation energy of 6 kJ/mol, roughly 4 times of that of Rn₂. But most strikingly, it was calculated to have a bond length shorter than in Rn₂ by 0.16 Å, which would be indicative of a significant bonding interaction. On the other hand, the compound UuoH⁺ exhibits a dissociation energy (in other words proton affinity of Uuo) that is smaller than that of RnH⁺.

The bonding between Ununoctium and hydrogen in UuoH is very limp and can be regarded as a pure van der Waals interaction rather than a true chemical bond. On the other hand, with highly electronegative elements, Ununoctium seems to form more stable compounds than for example element 112 or element 114. The stable oxidation states +2 and +4 have been predicted to exist in the fluorinated compounds UuoF₂ and UuoF₄. This is a result of the same spin-orbit interactions that make Ununoctium unusually reactive. For example, it was shown that the reaction of Uuo with F₂ to form the compound UuoF₂, would release energy of 106 kcal/mol of which about 46 kcal/mol come from these interactions. For comparison, the spin-orbit interaction for the similar molecule RnF₂ is about 10 kcal/mol out of a formation energy of 49 kcal/mol. The same interaction stabilizes the tetrahedral T_d configuration for UuoF₄, as distinct from the square planar D_4h one of XeF₄ and RnF₄. The Uuo–F bond will most probably be ionic rather than covalent, rendering the UuoF_n compounds non-volatile. Unlike the other noble gases, Ununoctium was predicted to be sufficiently electropositive to form a Uuo–Cl bond with chlorine.

Since no more than four atoms of Ununoctium have been produced, it currently has no uses outside of basic scientific research.

UNUNENNIUM

Ununennium also known as eka-francium or element 119, is the temporary name of a hypothetical chemical element in the periodic table that has the temporary symbol Uue and has the atomic number 119. To date, attempted syntheses of this element have been unsuccessful. Since it is below the alkali metals it might have properties similar to those of francium or caesium. Like other alkali metals, it should be extremely reactive with water and air. A predicted oxidation state is 1. Ununennium would be the first element in the eighth period of the periodic table and the seventh alkali metal.

UNSUCCESSFUL ATTEMPTS AT SYNTHESIS

The synthesis of ununennium was attempted in 1985 by bombarding a target of einsteinium-254 with calcium-48 ions at the superHILAC accelerator at Berkeley, California. No atoms were identified, leading to a limiting yield of 300 nb.

It is highly unlikely that this reaction will be useful given the extremely difficult task of making sufficient amounts of Es-254 to make a large enough target to increase the sensitivity of the experiment to the required level, due to the rarity of the element, and extreme rarity of the isotope.

Predicted decay characteristics

The alpha-decay half-lives of 1700 nuclei with 100 ≤ Z ≤ 130 have been calculated in a quantum tunneling model with alpha-decay Q-values from different mass estimates. The alpha-decay half-lives predicted for ^291-307119 are of the order of micro-seconds. The highest value of the alpha-decay half-life predicted in the quantum tunneling model with the mass estimates from a macroscopic-microscopic model is ~485 microseconds for the isotope ²⁹⁴119. For ³⁰²119 it is ~163 microseconds.

Target-projectile combinations leading to Z=119 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with an atomic number of 119.

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; σ = cross section

UNBINILIUM

Unbinilium also called eka-radium or element 120, is the temporary, systematic element name of a hypothetical chemical element in the periodic table that has the temporary symbol Ubn and has the atomic number 120. Since unbinilium is placed below the alkaline earth metals it possibly has properties similar to those of radium or barium.

Attempts to date to synthesize the element using fusion reactions at low excitation energy have met with failure, although there are reports that the fission of nuclei of unbinilium at very high excitation has been successfully measured, indicating a strong shell effect at Z=120.

ATTEMPTS AT SYNTHESIS

Neutron evaporation:

In March–April 2007, the synthesis of unbinilium was attempted at the Flerov Laboratory of Nuclear Reactions in Dubna by bombarding a plutonium-244 target with iron-58 ions. Initial analysis revealed that no atoms of element 120 were produced providing a limit of 400 fb for the cross section at the energy studied.

The Russian team is planning to upgrade their facilities before attempting the reaction again.

In April 2007, the team at GSI attempted to create unbinilium using uranium-238 and nickel-64:

No atoms were detected providing a limit of 1.6 pb on the cross section at the energy provided. The GSI repeated the experiment with higher sensitivity in three separate runs from April–May 2007, Jan–March 2008, and Sept–Oct 2008, all with negative results and providing a cross section limit of 90 fb.

Compound nucleus fission:

Unbinilium is of interest because it is part of the hypothesized island of stability, with the compound nucleus ³⁰²Ubn being the most stable of those that can be created directly by current methods. It has been calculated that Z=120 may in fact be the next proton magic number, rather than at Z=114 or 126.

Several experiments have been performed between 2000–2008 at the Flerov laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nucleus ³⁰²Ubn. Two nuclear reactions have been used, namely ²⁴⁴Pu+⁵⁸Fe and ²³⁸U+⁶⁴Ni. The results have revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as ¹³²Sn (Z=50, N=82). It was also found that the yield for the fusion-fission pathway was similar between ⁴⁸Ca and ⁵⁸Fe projectiles, indicating a possible future use of ⁵⁸Fe projectiles in superheavy element formation.

In 2008, the team at GANIL, France, described the results from a new technique which attempts to measure the fission half-life of a compound nucleus at high excitation energy, since the yields are significantly higher than from neutron evaporation channels. It is also a useful method for probing the effects of shell closures on the survivability of compound nuclei in the super-heavy region, which can indicate the exact position of the next proton shell (Z=114, 120, 124, or 126). The team studied the nuclear fusion reaction between uranium ions and a target of natural nickel:

The results indicated that nuclei of unbinilium were produced at high (~70 MeV) excitation energy which underwent fission with measurable half-lives > 10⁻¹⁸s. Although very short, the ability to measure such a process indicates a strong shell effect at Z=120. At lower excitation energy (see neutron evaporation), the effect of the shell will be enhanced and ground-state nuclei can be expected to have relatively long half-lives. This result could partially explain the relatively long half-life of ²⁹⁴Uuo measured in experiments at Dubna. Similar experiments have indicated a similar phenomenon at Z=124 (see unbiquadium) but not for ununquadium, suggesting that the next proton shell does in fact lie at Z>120.

Future reactions:

The GSI have plans to start up a program utilizing ²⁴⁸Cm targets for superheavy element production and will most likely attempt this reaction in 2011.

Likewise, the team at RIKEN have also begun a program utilizing ²⁴⁸Cm targets and have indicated future experiments to probe the possibility of Z=120 being the next magic number using the aforementioned nuclear reactions to form ³⁰²Ubn.

Calculated decay characteristics:

In a quantum tunneling model with mass estimates from a macroscopic-microscopic model, the alpha-decay half-lives of several isotopes of unbinilium (namely, ^292-304Ubn) have been predicted to be around 1–20 microseconds.

Extrapolated reactivity

Unbinilium should be highly reactive, according to periodic trends, as this element is a member of alkaline earth metals. It would be much more reactive than any other lighter elements of this group. If group reactivity is followed, this element would react violently in air to form an oxide (UbnO) and in water to form the hydroxide, which would be a strong base and highly explosive in terms of flammability.It is also possible that, due to relativistic effects, the element has noble gas character, which may be also the case for Ununquadium. A predicted oxidation state is II.

Target-projectile combinations leading to Z=120 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with an atomic number of 120.

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.

MD = multi-dimensional; DNS = dinuclear system; AS = advanced statistical; σ = cross section

UNBIUNIUM

Unbiunium also known as eka-actinium or element 121, is the temporary name of a hypothetical chemical element in the periodic table that has the temporary symbol Ubu and has the atomic number 121. It would be the first element in the g-block of the periodic table. As of November 2010, no attempt has been made to synthesize Unbiunium.

Naming: The name unbiunium is a systematic element name, used as a placeholder until it is confirmed by other research groups and the IUPAC decides on a name. Usually, the name suggested by the discoverer(s) is chosen.

Electronic configurations:

Unbiunium is the first element whose ground state electron configuration may contain an electron in a g subshell, which would make it the first element in the g-block. However, neither lanthanum nor actinium show such a predicted ground state for the f-block, and lie in the transition metals, so unbiunium's third electron should also hang up. Other elements have access to their g subshells, though not in their ground states. Computations have indicated that the ground state of the element would be 8s²8p¹.

Isotopes: Calculations have shown that ³²⁰Ubu would be the most stable isotope.

Target-projectile combinations leading to Z=121 compound nuclei

The below table contains various combinations of targets and projectiles which could hypothetically be used to form compound nuclei with atomic number 121.

UNBIBIUM

Unbibium also referred to as eka-thorium or element 122, is the temporary name of a currently unknown chemical element in the periodic table that has the temporary symbol Ubb and the atomic number 122.

In 2008, it was claimed to have been discovered in natural thorium samples but that claim has now been dismissed by recent repetitions of the experiment using more accurate techniques.

Extrapolated reactivity:

If group reactivity is followed, unbibium should be a reactive metal, more reactive than cerium or thorium. It would most likely form the dioxide, UbbO₂, and trihalides, such as UbbF₃ and UbbCl₃. The predicted oxidation states are III and IV (and perhaps II).

HISTORY

Neutron evaporation:

The first attempt to synthesize unbibium was performed in 1972 by Flerov et al. at JINR, using the hot fusion reaction:

No atoms were detected and a yield limit of 5 mb (5,000,000 pb) was measured. Current results (see Ununquadium) have shown that the sensitivity of this experiment was too low by at least 6 orders of magnitude.

In 2000, the Gesellschaft für Schwerionenforschung performed a very similar experiment with much higher sensitivity:

These results indicate that the synthesis of such heavier elements remains a significant challenge and further improvements of beam intensity and experimental efficiency is required. The sensitivity should be increased to 1 fb.

Compound nucleus fission

Several experiments have been performed between 2000-2004 at the Flerov laboratory of Nuclear Reactions studying the fission characteristics of the compound nucleus ³⁰⁶Ubb. Two nuclear reactions have been used, namely ²⁴⁸Cm+⁵⁸Fe and ²⁴²Pu+⁶⁴Ni. The results have revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as ¹³²Sn (Z=50, N=82). It was also found that the yield for the fusion-fission pathway was similar between ⁴⁸Ca and ⁵⁸Fe projectiles, indicating a possible future use of ⁵⁸Fe projectiles in superheavy element formation.

Target-projectile combinations leading to Z=122 compound nuclei

The table below contains various combinations of targets and projectiles which could be used to form compound nuclei with atomic number 122.

Claimed discovery as a naturally occurring element

On April 24, 2008, a group led by Amnon Marinov at the Hebrew University of Jerusalem claimed to have found single atoms of unbibium in naturally occurring thorium deposits at an abundance of between 10⁻¹¹ and 10⁻¹², relative to thorium. The claim of Marinov et al. was criticized by a part of the scientific community, and Marinov says he has submitted the article to the journals Nature and Nature Physics but both turned it down without sending it for peer review.

A criticism of the technique, previously used in purportedly identifying lighter thorium isotopes by mass spectrometry, was published in Physical Review C in 2008. A rebuttal by the Marinov group was published in Physical Review C after the published comment.

A repeat of the thorium-experiment using the superior method of Accelerator Mass Spectrometry (AMS) failed to confirm the results, despite a 100-fold better sensitivity. This result throws considerable doubt on the results of the Marinov collaboration with regards to their claims of long-lived isotopes of thorium, Roentgenium and unbibium.

প্রকৃতিতে প্রথম অতিভারী মৌল

মাধ্যমিক পর্যায়ের রসায়ন বইয়েই আমরা সবাই পড়ে থাকি যে, সর্বমোট মৌলিক পদার্থের সংখ্যা ১০৯ টি যার মধ্যে ৯২টি প্রকৃতিতে পাওয়া যায় এবং বাকি ১৭টি নিউক্লীয় চুল্লীতে কৃত্রিমভাবে উৎপাদন করতে হয়। তখন পর্যন্ত পর্যায় সারণী১০৯ মৌলেই সীমাবদ্ধ ছিল। কিন্তু বর্তমানে তা প্রায় ১১৮ পর্যন্ত বিস্তৃত হয়েছে। বিজ্ঞানীরা ১১১ থেকে ১১৮ পারমাণবিক সংখ্যাবিশিষ্ট মৌলগুলো গবেষণাগারে কৃত্রিমভাবে উৎপাদন করেছেন। ৯০ থেকে ১০৯ পর্যন্ত মৌলগুলোকে ভারী মৌল বললে, ১০৯ এর পরের গুলোকে স্বাভাবিক কারণেই অতিভারী মৌল বলা যেতে পারে।

সমস্যা হল অতিভারী মৌলগুলো প্রকৃতিতে পাওয়া যায় না। কৃত্রিমভাবে তৈরী করা হলেও তারা হয় ক্ষণস্থায়ী। কিন্তু মজার বিষয় হচ্ছে, খুব বেশিদিন টিকে না থাকলেও তাদের জীবনকাল একেবারে কম নয়। অর্থাৎ তৈরীর পর বেশ কিছু সময় টিকে থাকে তারা। এটাই প্রমাণ করে যে, প্রকৃতিতে অতিভারী মৌলগুলো স্বাভাবিক অবস্থায় থাকতে পারে। যদি থেকেই থাকে তাহলে আমরা তাদের খুঁজে পাচ্ছি না কেন? এই প্রশ্নই ছিল সবার মনে। এখন মনে হচ্ছে, আমরা সেই অতিভারী মৌলখুঁজে পেয়েছি।

হিব্রু ইউনিভার্সিটি অফ জেরাজালেমের বিজ্ঞানী আম্‌নন মারিনভ এবং তার গবেষণা দল একটি অতিভারী মৌল খুঁজে পেয়েছেন। এতোদিন ধরে এই পৃথিবীতেই ছিল, কিন্তু আমাদের খুঁজে পেতে দেরী হয়েছে। ভারী থোরিয়াম ধাতুর মধ্যকার রাসায়নিক উপাদানগুলো খুঁটিয়ে খুঁটিয়ে পরীক্ষা করতে গিয়ে তারা নতুন এই মৌলের সন্ধান পেয়েছেন।

তারা যা করেছেন তা হল একটার পর একটা থোরিয়াম কেন্দ্রিনকে ভর বর্ণালিবীক্ষণ যন্ত্রের মধ্যে দিয়ে অতিক্রম করিয়েছেন। এর মাধ্যমে তারা দেখেছেন কোন কেন্দ্রিনের মধ্যে কি আছে। থোরিয়ামের পারমাণবিক সংখ্যা ৯০ এবং এর দুইটি সমাণুক রয়েছে যাদের পারমাণবিক ভর যথাক্রমে ২৩০ ও ২৩২। তারা মূলত থোরিয়ামই পেয়েছেন। সাথে এদের কিছু অক্সাইড ও হাইড্রাইড অণু পাওয়া গেছে। কৌশলগত কারণে অন্যান্য কিছু জিনিসও পাওয়া গেছে যেগুলো খুব একটা গুরুত্বপূর্ণ না।

সবশেষে তারা এক অবিস্মরণীয় মৌলের সন্ধান পেলেন। এই অতিভারী মৌলটির পরমাণবিক সংখ্যা ১২২ বলে ধারণা করা হচ্ছে। আর এর পারমাণবিক ভর ২৯২। এতোদিন ধরে প্রকৃতিতেই তা বিরাজমান ছিল, আমরা খোঁজ পাইনি। এই অতিভারী মৌলের অর্ধায়ু প্রায় ১০০ মিলিয়ন বছর এবং এর প্রাকৃতিক প্রাচুর্যতা থোরিয়ামের তুলনায় ১ থেকে ১০*১০ই-১২ এর মধ্যে। থোরিয়াম বেশ সহজলভ্য মৌল যার প্রাচুর্য সীসার কাছাকাছি।

এই নতুন মৌল বিজ্ঞান জগতে নতুন দিগন্তের উন্মোচন ঘটিয়েছে। প্রমাণ করেছে, প্রকৃতিতে আরও অতিভারী মৌল থাকতে পারে। আমাদের সেগুলো খুঁজে নিতে হবে। ইতোমধ্যে পর্যায় সারণীতে একে স্থান দেয়া হয়ে গেছে। সারণীতে এর অবস্থানহবে অষ্টম পর্যায়ের তৃতীয় বিশেষ শ্রেণীতে। এটাই অষ্টম পর্যায়ের প্রথম মৌল। একটা নামও ঠিক করা হয়েছে মিস্টার ১২২ এর জন্য: একা-থোরিয়াম বা আনবিবিয়াম।

আনবিবিয়ামকে আমাদের জগতে স্বাগতম জানাই।এখন থেকে অতিভারী মৌলের সন্ধান কয়েকগুণ বেড়ে যাবে। পরবর্তী টার্গেট অবশ্যই হবে ইউরেনিয়াম। কারণ অতিভারী অ্যাক্টিনাইডের পরবর্তী স্থানগুলো ইউরেনিয়াম থেকে পাওয়া কোন মৌলই দখল করতে পারে।

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