Ununbium
Encyclopedia
Copernicium is a chemical element
with symbol Cn and atomic number
112. It is an extremely radioactive synthetic element
that on Earth can only be created in a laboratory. The most stable known isotope
, copernicium-285, has a half-life
of approximately 29 seconds, but it is possible that this copernicium isotope may have an isomer
with a longer half-life, 8.9 min. It was first created in 1996 by the . It is named after the astronomer Nicolaus Copernicus
.
In the periodic table of the elements, it is a d-block
element, which belongs to transactinide element
s. During reactions with gold
, it is shown to be a volatile metal and a group 12 element
. Copernicium is calculated to have several properties that differ between it and its lighter homologue
s, zinc
, cadmium
and mercury
; the most notable of them is withdrawing two 6d-electrons before 7s ones due to relativistic effects
, which confirm copernicium as an undisputed transition metal
. Copernicium is also calculated to show predominance of oxidation state +4, while mercury shows it in only one compound
at extreme conditions and zinc and cadmium do not show it at all. Difficulty of oxidation of copernicium from its neutral state compared to group 12 elements has also been predicted.
In total, approximately 75 atoms of copernicium have been detected using various nuclear reactions.
(GSI) in Darmstadt
, Germany, by Sigurd Hofmann, Victor Ninov
et al. This element was created by firing accelerated zinc
-70 nuclei at a target made of lead
-208 nuclei in a heavy ion accelerator. A single atom (the second was subsequently dismissed) of copernicium was produced with a mass number
of 277.
In May 2000, the GSI successfully repeated the experiment to synthesize a further atom of copernicium-277.
This reaction was repeated at RIKEN
using the Search for a Super-Heavy Element Using a Gas-Filled Recoil Separator set-up in 2004 to synthesize two further atoms and confirm the decay data reported by the GSI team.
The IUPAC
/IUPAP
Joint Working Party (JWP) assessed the claim of discovery by the GSI team in 2001 and 2003. In both cases, they found that there was insufficient evidence to support their claim. This was primarily related to the contradicting decay data for the known nuclide rutherfordium-261. However, between 2001 and 2005, the GSI team studied the reaction 248Cm(26Mg,5n)269Hs, and were able to confirm the decay data for hassium-269 and rutherfordium-261. It was found that the existing data on rutherfordium-261 was for an isomer, now designated rutherfordium-261a.
In May 2009, the JWP reported on the claims of discovery of element 112 again and officially recognized the GSI team as the discoverers of element 112. This decision was based on the confirmation of the decay properties of daughter nuclei as well as the confirmatory experiments at RIKEN.
After acknowledging their discovery, the IUPAC asked the discovery team at GSI to suggest a permanent name for ununbium. On 14 July 2009, they proposed copernicium with the element symbol Cp, after Nicolaus Copernicus
"to honor an outstanding scientist, who changed our view of the world." IUPAC delayed the official recognition of the name, pending the results of a six-month discussion period among the scientific community.
However, it was pointed out that the symbol Cp was previously associated with the name cassiopeium (cassiopium), now known as lutetium (Lu). Furthermore, the symbol Cp is also used in organometallic chemistry
to denote the cyclopentadienyl ligand
. For this reason, the IUPAC disallowed the use of Cp as a future symbol, prompting the GSI team to put forward the symbol Cn as an alternative. On 19 February 2010, the 537th anniversary of Copernicus' birth, IUPAC officially accepted the proposed name and symbol. The name was also approved by the General Assembly of the International Union of Pure and Applied Physics (IUPAP) on November 4, 2011.
s that induces fusion reactions. Whereas most of the isotopes of rutherfordium can be synthesized directly this way, some heavier ones have only been observed as decay products of elements with higher atomic number
s.
Depending on the energies involved, the former are separated into "hot" and "cold". In hot fusion reactions, very light, high-energy projectiles are accelerated toward very heavy targets such as actinide
s, giving rise to compound nuclei at high excitation energy (~40–50 MeV
) that may either fission or evaporate several (3 to 5) neutrons. In cold fusion reactions, the produced fused nuclei have a relatively low excitation energy (~10–20 MeV), which decreases the probability that these products will undergo fission reactions. As the fused nuclei cool to the ground state
, they require emission of only one or two neutrons, and thus, allows for the generation of more neutron-rich products. The latter is a distinct concept from that of where nuclear fusion claimed to be achieved at room temperature conditions (see cold fusion
).
In a review of the data in 2000, the first decay chain was retracted. In a repeat of the reaction in 2000 they were able to synthesize a further atom. They attempted to measure the 1n excitation function in 2002 but suffered from a failure of the zinc-70 beam.
The unofficial discovery of copernicium-277 was confirmed in 2004 at RIKEN
, where researchers detected a further two atoms of the isotope and were able to confirm the decay data for the entire chain.
After the successful synthesis of copernicium-277, the GSI team performed a reaction using a 68Zn projectile in 1997 in an effort to study the effect of isospin
(neutron richness) on the chemical yield.
The experiment was initiated after the discovery of a yield enhancement during the synthesis of darmstadtium
isotopes using nickel-62 and nickel-64 ions. No decay chains of copernicium-275 were detected leading to a cross section limit of 1.2 picobarns
(pb). However, the revision of the yield for the zinc-70 reaction to 0.5 pb does not rule out a similar yield for this reaction.
In 1990, after some early indications for the formation of isotopes of copernicium in the irradiation of a tungsten target with multi-GeV protons, a collaboration between GSI and the University of Jerusalem studied the foregoing reaction.
They were able to detect some spontaneous fission
(SF) activity and a 12.5 MeV alpha decay
, both of which they tentatively assigned to the radiative capture product copernicium-272 or the 1n evaporation residue copernicium-271. Both the TWG and JWP have concluded that a lot more research is required to confirm these conclusions.
The product, copernicium-283, had a claimed half-life of 5 minutes, decaying by spontaneous fission.
The long half-life of the product initiated first chemical experiments on the gas phase atomic chemistry of copernicium. In 2000, Yuri Yukashev in Dubna repeated the experiment but was unable to observe any spontaneous fission
with half-life of 5 minutes. The experiment was repeated in 2001 and an accumulation of eight fragments resulting from spontaneous fission were found in the low-temperature section, indicating that copernicium had radon-like properties. However, there is now some serious doubt about the origin of these results. To confirm the synthesis, the reaction was successfully repeated by the same team in January 2003, confirming the decay mode and half-life. They were also able to calculate an estimate of the mass of the spontaneous fission activity to ~285, lending support to the assignment.
The team at Lawrence Berkeley National Laboratory
(LBNL) in Berkeley, United States entered the debate and performed the reaction in 2002. They were unable to detect any spontaneous fission and calculated a cross section limit of 1.6 pb for the detection of a single event.
The reaction was repeated in 2003–2004 by the team at Dubna using a slightly different set-up, the Dubna Gas-Filled Recoil Separator (DGFRS). This time, copernicium-283 was found to decay by emission of a 9.53 MeV alpha-particle with a half-life of 4 seconds. copernicium-282 was also observed in the 4n channel (emitting 4 neutrons).
In 2003, the team at GSI entered the debate and performed a search for the five-minute SF activity in chemical experiments. Like the Dubna team, they were able to detect seven SF fragments in the low temperature section. However, these SF events were uncorrelated, suggesting they were not from actual direct SF of copernicium nuclei and raised doubts about the original indications for radon-like properties. After the announcement from Dubna of different decay properties for copernicium-283, the GSI team repeated the experiment in September 2004. They were unable to detect any SF events and calculated a cross section limit of ~1.6 pb for the detection of one event, not in contradiction with the reported 2.5 pb yield by Dubna.
In May 2005, the GSI performed a physical experiment and identified a single atom of 283Cn decaying by SF with a short half-time suggesting a previously unknown SF branch.
However, initial work by Dubna had detected several direct SF events but had assumed that the parent alpha decay had been missed. These results indicated that this was not the case.
The new decay data on copernicium-283 were confirmed in 2006 by a joint PSI-FLNR experiment aimed at probing the chemical properties of copernicium. Two atoms of copernicium-283 were observed in the decay of the parent ununquadium
-287 nuclei. The experiment indicated that contrary to previous experiments, copernicium behaves as a typical member of group 12, demonstrating properties of a volatile metal.
Finally, the team at GSI successfully repeated their physical experiment in January 2007, and detected three atoms of copernicium-283, confirming both the alpha and SF decay modes.
As such, the 5 minutes SF activity is still unconfirmed and unidentified. It is possible that it refers to an isomer, namely copernicium-283b, whose yield is dependent upon the exact production methods.
The team at FLNR studied this reaction in 2004. They were unable to detect any atoms of copernicium and calculated a cross section limit of 0.6 pb. The team concluded that this indicated that the neutron mass number for the compound nucleus had an effect on the yield of evaporation residues.
s between 281 and 285. Copernicium isotopes with mass numbers 281, 284 and 285 to date have only been produced by ununquadium nuclei decay.
Parent ununquadium nuclei can be themselves decay products of ununhexium
or ununoctium
. To date, no other elements have been known to decay to copernicium.
For example, in May 2006, the Dubna team (JINR
) identified copernicium-282 as a final product in the decay of ununoctium via the alpha decay sequence. It was found that the final nucleus undergoes spontaneous fission
.
In the claimed synthesis of ununoctium-293 in 1999, copernicium-281 was identified as decaying by emission of a 10.68 MeV alpha particle
with half-life 0.90 ms. The claim was retracted in 2001. This isotope was finally created in 2010 and its decay properties supported that the previous data was wrong.
The lightest isotopes were synthesized by direct fusion between two lighter nuclei and as decay products (except for copernicium-277, which is known to be a decay product), while the heavier isotopes are only known to be produced by decay of heavier nuclei. The heaviest isotope produced by direct fusion is copernicium-283; the two heavier isotopes, copernicium-284 and copernicium-285 have only been observed as decay products of elements with larger atomic numbers. In 1999, American scientists at the University of California, Berkeley, announced that they had succeeded in synthesizing three atoms of 293118. These parent nuclei were reported to have successively emitted three alpha particles to form copernicium-281 nuclei, which were claimed to have undergone an alpha decay, emitting an alpha particle with decay energy of 10.68 MeV and half-life 0.90 ms, but their claim was retracted in 2001. The isotope, however, was produced in 2010 by the same team, confirming the previous data was wrong.
Copernicium-285 has only been observed as a decay product of ununquadium-289 and ununhexium-293; during the first recorded synthesis of ununquadium, one ununquadium-289 was created, which alpha decayed to copernicium-285, which itself emitted an alpha particle in 29 seconds, releasing 9.15 or 9.03 MeV. However, the first successful experiment of ununhexium synthesis, when ununhexium-293 was created, it was shown that the created nuclide alpha decayed to ununquadium-289, decay data for which differed from the known values significantly. Although unconfirmed, it is highly possible that this is associated with an isomer. The resulted nuclide decayed to copernicium-285, which emitted an alpha article with a half-life of 8.9 minutes, releasing 8.63 MeV. Similar to its parent, it is believed to be a nuclear isomer, namely copernicium-285b.
in the periodic table, below zinc
, cadmium
and mercury
. It is predicted to differ significantly from lighter group 12 elements. Due to stabilization of 7s electronic orbitals and destabilization of 6d ones caused by relativistic effects
, Cn2+ is likely to have [Rn]5f146d87s2 electronic configuration, breaking 6d orbitals before 7s one, unlike its homologues. In water solutions, copernicium is likely to form +2 and +4 oxidation states, with the latter one being more stable. Among lighter group 12 members, for which the +2 oxidation state is the most common, only mercury can show +4 oxidation state, but it is highly uncommon, existing at only one compound (mercury(IV) fluoride
, HgF4) at extreme conditions. The analogous compound for copernicium, CnF4, is predicted to be more stable. The diatomic ion , featuring mercury in +1 oxidation state is well-known, but the ion is predicted to be unstable or even non-existent. Oxidation of copernicium from its neutral state is also likely to be harder than those of previous group 12 members.
. As such, it should behave as the heavier homologue of mercury
and form strong binary compounds with noble metals like gold. Experiments probing the reactivity of copernicium have focused on the adsorption of atoms of element 112 onto a gold surface held at varying temperatures, in order to calculate an adsorption enthalpy. Due to relativistic stabilization of the 7s electrons, copernicium shows radon
-like properties. Experiments were performed with the simultaneous formation of mercury and radon radioisotopes, allowing a comparison of adsorption characteristics.
The first experiments were conducted using the 238U(48Ca,3n)283Cn reaction. Detection was by spontaneous fission of the claimed parent isotope with half-life of 5 minutes. Analysis of the data indicated that copernicium was more volatile than mercury and had noble gas properties. However, the confusion regarding the synthesis of copernicium-283 has cast some doubt on these experimental results. Given this uncertainty, between April–May 2006 at the JINR, a FLNR-PSI team conducted experiments probing the synthesis of this isotope as a daughter in the nuclear reaction 242Pu(48Ca,3n)287Uuq. In this experiment, two atoms of copernicium-283 were unambiguously identified and the adsorption properties indicated that copernicium is a more volatile homologue of mercury, due to formation of a weak metal-metal bond with gold, placing it firmly in group 12.
In April 2007, this experiment was repeated and a further three atoms of copernicium-283 were positively identified. The adsorption property was confirmed and indicated that copernicium has adsorption properties completely in agreement with being the heaviest member of group 12.
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
with symbol Cn and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
112. It is an extremely radioactive synthetic element
Synthetic element
In chemistry, a synthetic element is a chemical element that is too unstable to occur naturally on Earth, and therefore has to be created artificially. So far 30 synthetic elements have been discovered—that is, synthesized...
that on Earth can only be created in a laboratory. The most stable known isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
, copernicium-285, has a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of approximately 29 seconds, but it is possible that this copernicium isotope may have an isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...
with a longer half-life, 8.9 min. It was first created in 1996 by the . It is named after the astronomer Nicolaus Copernicus
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....
.
In the periodic table of the elements, it is a d-block
D-block
The d-block is the portion of the periodic table that contains the element groups 3-12. These groups correspond to the filling of the atomic d-orbital subshell, with electron configurations ranging from s2d1 to s2d10...
element, which belongs to transactinide element
Transactinide element
In chemistry, transactinide elements are the chemical elements with atomic numbers greater than those of the actinides, the heaviest of which is lawrencium ....
s. During reactions with gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
, it is shown to be a volatile metal and a group 12 element
Group 12 element
A group 12 element is one of the elements in group 12 in the periodic table. This includes zinc , cadmium and mercury . The further inclusion of copernicium in group 12 is supported by recent experiments on individual Cn atoms...
. Copernicium is calculated to have several properties that differ between it and its lighter homologue
Homology (chemistry)
In chemistry, homology refers to the appearance of homologues. A homologue is a compound belonging to a series of compounds differing from each other by a repeating unit, such as a methylene group, a peptide residue, etcetera....
s, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
and mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
; the most notable of them is withdrawing two 6d-electrons before 7s ones due to relativistic effects
Relativistic quantum chemistry
Relativistic quantum chemistry invokes quantum chemical and relativistic mechanical arguments to explain elemental properties and structure, especially for heavy elements of the periodic table....
, which confirm copernicium as an undisputed transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
. Copernicium is also calculated to show predominance of oxidation state +4, while mercury shows it in only one compound
Mercury(IV) fluoride
Mercury fluoride, HgF4, is the first mercury compound to be discovered with the metal in the oxidation state IV. Mercury, like the other group 12 elements , has an s2d10 electron configuration and generally only forms bonds involving its s orbital...
at extreme conditions and zinc and cadmium do not show it at all. Difficulty of oxidation of copernicium from its neutral state compared to group 12 elements has also been predicted.
In total, approximately 75 atoms of copernicium have been detected using various nuclear reactions.
Official discovery
Copernicium was first created on February 9, 1996, at the Gesellschaft für SchwerionenforschungGesellschaft für Schwerionenforschung
The GSI Helmholtz Centre for Heavy Ion Research GmbH in the Wixhausen suburb of Darmstadt, Germany is a federally and state co-funded heavy ion research center. The current director of GSI is Horst Stöcker who succeeded Walter F...
(GSI) in Darmstadt
Darmstadt
Darmstadt is a city in the Bundesland of Hesse in Germany, located in the southern part of the Rhine Main Area.The sandy soils in the Darmstadt area, ill-suited for agriculture in times before industrial fertilisation, prevented any larger settlement from developing, until the city became the seat...
, Germany, by Sigurd Hofmann, Victor Ninov
Victor Ninov
Victor Ninov is a former researcher in the nuclear chemistry group at Lawrence Berkeley National Laboratory who was alleged to have fabricated the evidence used to claim the creation of ununoctium and ununhexium....
et al. This element was created by firing accelerated zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
-70 nuclei at a target made of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
-208 nuclei in a heavy ion accelerator. A single atom (the second was subsequently dismissed) of copernicium was produced with a mass number
Mass number
The mass number , also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion...
of 277.
- Pb + Zn → Cn → Cn + n
In May 2000, the GSI successfully repeated the experiment to synthesize a further atom of copernicium-277.
This reaction was repeated at RIKEN
RIKEN
is a large natural sciences research institute in Japan. Founded in 1917, it now has approximately 3000 scientists on seven campuses across Japan, the main one in Wako, just outside Tokyo...
using the Search for a Super-Heavy Element Using a Gas-Filled Recoil Separator set-up in 2004 to synthesize two further atoms and confirm the decay data reported by the GSI team.
The IUPAC
International Union of Pure and Applied Chemistry
The International Union of Pure and Applied Chemistry is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science . The international headquarters of IUPAC is located in Zürich,...
/IUPAP
International Union of Pure and Applied Physics
The International Union of Pure and Applied Physics is an international non-governmental organization devoted to the advancement of physics...
Joint Working Party (JWP) assessed the claim of discovery by the GSI team in 2001 and 2003. In both cases, they found that there was insufficient evidence to support their claim. This was primarily related to the contradicting decay data for the known nuclide rutherfordium-261. However, between 2001 and 2005, the GSI team studied the reaction 248Cm(26Mg,5n)269Hs, and were able to confirm the decay data for hassium-269 and rutherfordium-261. It was found that the existing data on rutherfordium-261 was for an isomer, now designated rutherfordium-261a.
In May 2009, the JWP reported on the claims of discovery of element 112 again and officially recognized the GSI team as the discoverers of element 112. This decision was based on the confirmation of the decay properties of daughter nuclei as well as the confirmatory experiments at RIKEN.
Naming
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....
"to honor an outstanding scientist, who changed our view of the world." IUPAC delayed the official recognition of the name, pending the results of a six-month discussion period among the scientific community.
However, it was pointed out that the symbol Cp was previously associated with the name cassiopeium (cassiopium), now known as lutetium (Lu). Furthermore, the symbol Cp is also used in organometallic chemistry
Organometallic chemistry
Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
to denote the cyclopentadienyl ligand
Cyclopentadienyl complex
A cyclopentadienyl complex is a metal complex with one or more cyclopentadienyl groups . Based on the type of bonding between the metals and the cyclopentadienyl]] moieties, cyclopentadienyl complexes are classified into the following three categories: a) π-complexes, b) σ-complexes, and c) ionic...
. For this reason, the IUPAC disallowed the use of Cp as a future symbol, prompting the GSI team to put forward the symbol Cn as an alternative. On 19 February 2010, the 537th anniversary of Copernicus' birth, IUPAC officially accepted the proposed name and symbol. The name was also approved by the General Assembly of the International Union of Pure and Applied Physics (IUPAP) on November 4, 2011.
Nucleosynthesis
Super-heavy elements such as copernicium are produced by bombarding lighter elements in particle acceleratorParticle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
s that induces fusion reactions. Whereas most of the isotopes of rutherfordium can be synthesized directly this way, some heavier ones have only been observed as decay products of elements with higher atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
s.
Depending on the energies involved, the former are separated into "hot" and "cold". In hot fusion reactions, very light, high-energy projectiles are accelerated toward very heavy targets such as actinide
Actinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...
s, giving rise to compound nuclei at high excitation energy (~40–50 MeV
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
) that may either fission or evaporate several (3 to 5) neutrons. In cold fusion reactions, the produced fused nuclei have a relatively low excitation energy (~10–20 MeV), which decreases the probability that these products will undergo fission reactions. As the fused nuclei cool to the ground state
Ground state
The ground state of a quantum mechanical system is its lowest-energy state; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state...
, they require emission of only one or two neutrons, and thus, allows for the generation of more neutron-rich products. The latter is a distinct concept from that of where nuclear fusion claimed to be achieved at room temperature conditions (see cold fusion
Cold fusion
Cold fusion, also called low-energy nuclear reaction , refers to the hypothesis that nuclear fusion might explain the results of a group of experiments conducted at ordinary temperatures . Both the experimental results and the hypothesis are disputed...
).
Cold fusion
The first cold fusion reaction to produce copernicium was performed by GSI in 1996, who reported the detection of two decay chains of copernicium-277.- + → +
In a review of the data in 2000, the first decay chain was retracted. In a repeat of the reaction in 2000 they were able to synthesize a further atom. They attempted to measure the 1n excitation function in 2002 but suffered from a failure of the zinc-70 beam.
The unofficial discovery of copernicium-277 was confirmed in 2004 at RIKEN
RIKEN
is a large natural sciences research institute in Japan. Founded in 1917, it now has approximately 3000 scientists on seven campuses across Japan, the main one in Wako, just outside Tokyo...
, where researchers detected a further two atoms of the isotope and were able to confirm the decay data for the entire chain.
After the successful synthesis of copernicium-277, the GSI team performed a reaction using a 68Zn projectile in 1997 in an effort to study the effect of isospin
Isospin
In physics, and specifically, particle physics, isospin is a quantum number related to the strong interaction. This term was derived from isotopic spin, but the term is confusing as two isotopes of a nucleus have different numbers of nucleons; in contrast, rotations of isospin maintain the number...
(neutron richness) on the chemical yield.
- + → + x
The experiment was initiated after the discovery of a yield enhancement during the synthesis of darmstadtium
Darmstadtium
Darmstadtium is a chemical element with the symbol Ds and atomic number 110. It is placed as the heaviest member of group 10, but no known isotope is sufficiently stable to allow chemical experiments to confirm its placing in that group...
isotopes using nickel-62 and nickel-64 ions. No decay chains of copernicium-275 were detected leading to a cross section limit of 1.2 picobarns
Barn (unit)
A barn is a unit of area. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process, and is best understood as a measure of the...
(pb). However, the revision of the yield for the zinc-70 reaction to 0.5 pb does not rule out a similar yield for this reaction.
In 1990, after some early indications for the formation of isotopes of copernicium in the irradiation of a tungsten target with multi-GeV protons, a collaboration between GSI and the University of Jerusalem studied the foregoing reaction.
- + → + x
They were able to detect some spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
(SF) activity and a 12.5 MeV alpha decay
Alpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...
, both of which they tentatively assigned to the radiative capture product copernicium-272 or the 1n evaporation residue copernicium-271. Both the TWG and JWP have concluded that a lot more research is required to confirm these conclusions.
Hot fusion
In 1998, the team at the Flerov Laboratory of Nuclear Research (FLNR) in Dubna, Russia began a research program using calcium-48 nuclei in "warm" fusion reactions leading to super-heavy elements. In March 1998, they claimed to have synthesized two atoms of the element in the following reaction.- + → + x (x=3,4)
The product, copernicium-283, had a claimed half-life of 5 minutes, decaying by spontaneous fission.
The long half-life of the product initiated first chemical experiments on the gas phase atomic chemistry of copernicium. In 2000, Yuri Yukashev in Dubna repeated the experiment but was unable to observe any spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
with half-life of 5 minutes. The experiment was repeated in 2001 and an accumulation of eight fragments resulting from spontaneous fission were found in the low-temperature section, indicating that copernicium had radon-like properties. However, there is now some serious doubt about the origin of these results. To confirm the synthesis, the reaction was successfully repeated by the same team in January 2003, confirming the decay mode and half-life. They were also able to calculate an estimate of the mass of the spontaneous fission activity to ~285, lending support to the assignment.
The team at Lawrence Berkeley National Laboratory
Lawrence Berkeley National Laboratory
The Lawrence Berkeley National Laboratory , is a U.S. Department of Energy national laboratory conducting unclassified scientific research. It is located on the grounds of the University of California, Berkeley, in the Berkeley Hills above the central campus...
(LBNL) in Berkeley, United States entered the debate and performed the reaction in 2002. They were unable to detect any spontaneous fission and calculated a cross section limit of 1.6 pb for the detection of a single event.
The reaction was repeated in 2003–2004 by the team at Dubna using a slightly different set-up, the Dubna Gas-Filled Recoil Separator (DGFRS). This time, copernicium-283 was found to decay by emission of a 9.53 MeV alpha-particle with a half-life of 4 seconds. copernicium-282 was also observed in the 4n channel (emitting 4 neutrons).
In 2003, the team at GSI entered the debate and performed a search for the five-minute SF activity in chemical experiments. Like the Dubna team, they were able to detect seven SF fragments in the low temperature section. However, these SF events were uncorrelated, suggesting they were not from actual direct SF of copernicium nuclei and raised doubts about the original indications for radon-like properties. After the announcement from Dubna of different decay properties for copernicium-283, the GSI team repeated the experiment in September 2004. They were unable to detect any SF events and calculated a cross section limit of ~1.6 pb for the detection of one event, not in contradiction with the reported 2.5 pb yield by Dubna.
In May 2005, the GSI performed a physical experiment and identified a single atom of 283Cn decaying by SF with a short half-time suggesting a previously unknown SF branch.
However, initial work by Dubna had detected several direct SF events but had assumed that the parent alpha decay had been missed. These results indicated that this was not the case.
The new decay data on copernicium-283 were confirmed in 2006 by a joint PSI-FLNR experiment aimed at probing the chemical properties of copernicium. Two atoms of copernicium-283 were observed in the decay of the parent ununquadium
Ununquadium
Ununquadium is the temporary name of a radioactive chemical element with the temporary symbol Uuq and atomic number 114. There is no proposed name yet, although flerovium has been discussed in the media.About 80 decays of atoms of...
-287 nuclei. The experiment indicated that contrary to previous experiments, copernicium behaves as a typical member of group 12, demonstrating properties of a volatile metal.
Finally, the team at GSI successfully repeated their physical experiment in January 2007, and detected three atoms of copernicium-283, confirming both the alpha and SF decay modes.
As such, the 5 minutes SF activity is still unconfirmed and unidentified. It is possible that it refers to an isomer, namely copernicium-283b, whose yield is dependent upon the exact production methods.
- + → + x
The team at FLNR studied this reaction in 2004. They were unable to detect any atoms of copernicium and calculated a cross section limit of 0.6 pb. The team concluded that this indicated that the neutron mass number for the compound nucleus had an effect on the yield of evaporation residues.
Decay products
Copernicium has been observed as decay products of ununquadium. Ununquadium currently has five known isotopes, all of which have been shown to undergo alpha decays to become a copernicium nuclei, with mass numberMass number
The mass number , also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion...
s between 281 and 285. Copernicium isotopes with mass numbers 281, 284 and 285 to date have only been produced by ununquadium nuclei decay.
Parent ununquadium nuclei can be themselves decay products of ununhexium
Ununhexium
Ununhexium is the temporary name of a synthetic superheavy element with the temporary symbol Uuh and atomic number 116. There is no proposed name yet although moscovium has been discussed in the media.It is placed as the heaviest member of group 16 although a sufficiently stable isotope is...
or ununoctium
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...
. To date, no other elements have been known to decay to copernicium.
For example, in May 2006, the Dubna team (JINR
Joint Institute for Nuclear Research
The Joint Institute for Nuclear Research, JINR , in Dubna, Moscow Oblast , Russia, is an international research centre for nuclear sciences, with 5500 staff members, 1200 researchers including 1000 Ph.D.s from eighteen member states The Joint Institute for Nuclear Research, JINR , in Dubna, Moscow...
) identified copernicium-282 as a final product in the decay of ununoctium via the alpha decay sequence. It was found that the final nucleus undergoes spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
.
- → +
- → +
- → +
In the claimed synthesis of ununoctium-293 in 1999, copernicium-281 was identified as decaying by emission of a 10.68 MeV alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
with half-life 0.90 ms. The claim was retracted in 2001. This isotope was finally created in 2010 and its decay properties supported that the previous data was wrong.
Isotopes
Copernicium has no stable or naturally-occurring isotopes. Several radioactive isotopes have been synthesized in the laboratory, either by fusing two atoms or by observing the decay of heavier elements. Six different isotopes have been reported with atomic masses from 281 to 285, and 277, two of which, copernicium-283 and copernicium-285, have known metastable states. Most of these decay predominantly through alpha decay, but some undergo spontaneous fission.Half-lives
All copernicium isotopes are extremely unstable and radioactive; in general, heavier isotopes are more stable than the lighter. The most stable isotope, copernicium-285, has a half-life of 29 seconds, although it is suspected that this isotope has an isomer with a half-life of 8.9 minutes, and copernicium-283 may have an isomer with a half-life of about 5 minutes. Other isotopes have half-lives shorter than 0.1 seconds. Copernicium-281 and copernicium-284 have half-life of 97 ms, and the other two isotopes have half-lives slightly under one millisecond.The lightest isotopes were synthesized by direct fusion between two lighter nuclei and as decay products (except for copernicium-277, which is known to be a decay product), while the heavier isotopes are only known to be produced by decay of heavier nuclei. The heaviest isotope produced by direct fusion is copernicium-283; the two heavier isotopes, copernicium-284 and copernicium-285 have only been observed as decay products of elements with larger atomic numbers. In 1999, American scientists at the University of California, Berkeley, announced that they had succeeded in synthesizing three atoms of 293118. These parent nuclei were reported to have successively emitted three alpha particles to form copernicium-281 nuclei, which were claimed to have undergone an alpha decay, emitting an alpha particle with decay energy of 10.68 MeV and half-life 0.90 ms, but their claim was retracted in 2001. The isotope, however, was produced in 2010 by the same team, confirming the previous data was wrong.
Nuclear isomerism
First experiments on the synthesis of 283Cn produced a SF activity with half-life ~5 min. This activity was also observed from the alpha decay of ununquadium-287. The decay mode and half-life were also confirmed in a repetition of the first experiment. Later, copernicium-283 was observed to undergo 9.52 MeV alpha decay and SF with a half-life of 3.9 s. It has also been found that alpha decay of copernicium-283 leads to different excited states of darmstadtium-279. These results suggest the assignment of the two activities to two different isomeric levels in copernicium-283, creating copernicium-283a and copernicium-283b.Copernicium-285 has only been observed as a decay product of ununquadium-289 and ununhexium-293; during the first recorded synthesis of ununquadium, one ununquadium-289 was created, which alpha decayed to copernicium-285, which itself emitted an alpha particle in 29 seconds, releasing 9.15 or 9.03 MeV. However, the first successful experiment of ununhexium synthesis, when ununhexium-293 was created, it was shown that the created nuclide alpha decayed to ununquadium-289, decay data for which differed from the known values significantly. Although unconfirmed, it is highly possible that this is associated with an isomer. The resulted nuclide decayed to copernicium-285, which emitted an alpha article with a half-life of 8.9 minutes, releasing 8.63 MeV. Similar to its parent, it is believed to be a nuclear isomer, namely copernicium-285b.
Extrapolated oxidation states
Copernicium is the last member of the 6d series of transition metals and the heaviest group 12 elementGroup 12 element
A group 12 element is one of the elements in group 12 in the periodic table. This includes zinc , cadmium and mercury . The further inclusion of copernicium in group 12 is supported by recent experiments on individual Cn atoms...
in the periodic table, below zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
and mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
. It is predicted to differ significantly from lighter group 12 elements. Due to stabilization of 7s electronic orbitals and destabilization of 6d ones caused by relativistic effects
Relativistic quantum chemistry
Relativistic quantum chemistry invokes quantum chemical and relativistic mechanical arguments to explain elemental properties and structure, especially for heavy elements of the periodic table....
, Cn2+ is likely to have [Rn]5f146d87s2 electronic configuration, breaking 6d orbitals before 7s one, unlike its homologues. In water solutions, copernicium is likely to form +2 and +4 oxidation states, with the latter one being more stable. Among lighter group 12 members, for which the +2 oxidation state is the most common, only mercury can show +4 oxidation state, but it is highly uncommon, existing at only one compound (mercury(IV) fluoride
Mercury(IV) fluoride
Mercury fluoride, HgF4, is the first mercury compound to be discovered with the metal in the oxidation state IV. Mercury, like the other group 12 elements , has an s2d10 electron configuration and generally only forms bonds involving its s orbital...
, HgF4) at extreme conditions. The analogous compound for copernicium, CnF4, is predicted to be more stable. The diatomic ion , featuring mercury in +1 oxidation state is well-known, but the ion is predicted to be unstable or even non-existent. Oxidation of copernicium from its neutral state is also likely to be harder than those of previous group 12 members.
Experimental atomic gas phase chemistry
Copernicium has the ground state electron configuration [Rn]5f146d107s2 and thus should belong to group 12 of the periodic table, according to Aufbau principleAufbau principle
The Aufbau principle is used to determine the electron configuration of an atom, molecule or ion. The principle postulates a hypothetical process in which an atom is "built up" by progressively adding electrons...
. As such, it should behave as the heavier homologue of mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
and form strong binary compounds with noble metals like gold. Experiments probing the reactivity of copernicium have focused on the adsorption of atoms of element 112 onto a gold surface held at varying temperatures, in order to calculate an adsorption enthalpy. Due to relativistic stabilization of the 7s electrons, copernicium shows radon
Radon
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days...
-like properties. Experiments were performed with the simultaneous formation of mercury and radon radioisotopes, allowing a comparison of adsorption characteristics.
The first experiments were conducted using the 238U(48Ca,3n)283Cn reaction. Detection was by spontaneous fission of the claimed parent isotope with half-life of 5 minutes. Analysis of the data indicated that copernicium was more volatile than mercury and had noble gas properties. However, the confusion regarding the synthesis of copernicium-283 has cast some doubt on these experimental results. Given this uncertainty, between April–May 2006 at the JINR, a FLNR-PSI team conducted experiments probing the synthesis of this isotope as a daughter in the nuclear reaction 242Pu(48Ca,3n)287Uuq. In this experiment, two atoms of copernicium-283 were unambiguously identified and the adsorption properties indicated that copernicium is a more volatile homologue of mercury, due to formation of a weak metal-metal bond with gold, placing it firmly in group 12.
In April 2007, this experiment was repeated and a further three atoms of copernicium-283 were positively identified. The adsorption property was confirmed and indicated that copernicium has adsorption properties completely in agreement with being the heaviest member of group 12.