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.
Blocks of the periodic table
(Undiscovered (theorized) elements are coloured in a lighter shade)
All of these hypothetical undiscovered elements are named by the International Union of Pure and Applied Chemistry (IUPAC) systematic element name standard which creates a generic name for use until the element has been discovered, confirmed, and an official name approved.
As of March 2011, synthesis has been attempted for only ununennium, unbinilium, unbibium, unbiquadium and unbihexium.
The positioning of the g-block in the table (to the left of the f-block, to the right, or in between) is speculative. The positions shown in the table above correspond to the assumption that the Madelung rule will continue to hold for higher atomic numbers; this assumption may or may not be true. At element 118, the orbitals 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, 5d, 5f, 6s, 6p, 6d, 7s and 7p are assumed to be filled, with the remaining orbitals unfilled. The orbitals of the eighth period are predicted to be filled in the order 8s, 5g, 6f, 7d, 8p. However, after approximately element 120, the proximity of the electron shells makes placement in a simple table problematic.
PYYKKÖ MODEL
Not all models show the higher elements following the pattern established by lighter elements. Pekka Pyykkö, for example, used computer modeling to calculate the positions of elements up to Z=172, and found that several were displaced from the Madelung rule. He predicts that the orbital shells will fill up in this order:
He also suggests that period 8 be split into three parts:
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 Qalpha 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 Qalpha 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 (TSF1/2 = 0.8 ms) and 286Uuq (TSF1/2 = 130 ms), and 284Cn (TSF = 97 ms) and 288Uuq (TSF >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 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.
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
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.
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:
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 Td configuration for UuoF4, as distinct from the square planar D4h one of XeF4 and RnF4. The Uuo–F bond will most probably be ionic rather than covalent, rendering the UuoFn 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 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.
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.
The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with an atomic number of 119.
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 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
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.
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.
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.
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.
The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with an atomic number of 120.
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 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.
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.
The below table contains various combinations of targets and projectiles which could hypothetically be used to form compound nuclei with atomic number 121.
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).
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.
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.
The table below contains various combinations of targets and projectiles which could be used to form compound nuclei with atomic number 122.
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।