Seaborgium is a synthetic
chemical elementA 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 the symbol
Sg and
atomic numberIn 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...
106.
Seaborgium is a
synthetic elementIn 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...
whose most stable
isotopeIsotopes 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...
271Sg has a
half-lifeHalf-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 1.9
minuteA minute is a unit of measurement of time or of angle. The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute on rare occasions has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units...
s. A new isotope
269Sg has a potentially slightly longer half-life (ca. 2.1 min) based on the observation of a single decay. Chemistry experiments with seaborgium have firmly placed it in group 6 as a heavier homologue to
tungstenTungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
.
Discovery
Element 106, now known as seaborgium, was first created in 1974 at the Super HILAC accelerator at the Lawrence Berkeley Laboratory by a joint Lawrence Berkeley/Lawrence Livermore collaboration led by Albert Ghiorso and E. Kenneth Hulet. They produced the new nuclide
263Sg by bombarding a target of
249Cf with
18O ions. This nuclide decays by α emission with a half-life of 0.9 ± 0.2 sec.
Proposed names
The Berkeley/Livermore collaboration suggested the name
seaborgium (Sg) to honor the American chemist
Glenn T. SeaborgGlenn Theodore Seaborg was an American scientist who won the 1951 Nobel Prize in Chemistry for "discoveries in the chemistry of the transuranium elements", contributed to the discovery and isolation of ten elements, and developed the actinide concept, which led to the current arrangement of the...
credited as a member of the American group in recognition of his participation in the discovery of several other actinides. The name selected by the team became controversial. The IUPAC adopted
unnilhexium (symbol
Unh) as a temporary,
systematic element nameA systematic element name is the temporary name and symbol assigned to newly synthesized and not yet synthesized chemical elements. In chemistry, a transuranic element receives a permanent name and symbol only after its synthesis has been confirmed. In some cases, this has been a protracted and...
. In 1994 a committee of IUPAC recommended that element 106 be named
rutherfordium and adopted a rule that no element can be named after a living person. This ruling was fiercely objected to by the
American Chemical SocietyThe American Chemical Society is a scientific society based in the United States that supports scientific inquiry in the field of chemistry. Founded in 1876 at New York University, the ACS currently has more than 161,000 members at all degree-levels and in all fields of chemistry, chemical...
. Critics pointed out that a precedent had been set in the naming of
einsteiniumEinsteinium is a synthetic element with the symbol Es and atomic number 99. It is the seventh transuranic element, and an actinide.Einsteinium was discovered in the debris of the first hydrogen bomb explosion in 1952, and named after Albert Einstein...
during
Albert EinsteinAlbert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...
's life and a survey indicated that chemists were not concerned with the fact that Seaborg was still alive. In 1997, as part of a compromise involving elements 104 to 108, the name
seaborgium for element 106 was recognized internationally.
Oxidation states
Seaborgium is projected to be the third member of the 6d series of transition metals and the heaviest member of group 6 in the Periodic Table, below
chromiumChromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
,
molybdenumMolybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
and
tungstenTungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
. All the members of the group readily portray their group oxidation state of +6 and the state becomes more stable as the group is descended. Thus seaborgium is expected to form a stable +6 state. For this group, stable +5 and +4 states are well represented for the heavier members and the +3 state is known but reducing, except for chromium(III).
Chemistry
Much seaborgium chemical behavior is predicted by extrapolation from its lighter cogeners molybdenum and tungsten. Molybdenum and tungsten readily form stable trioxides MO
3, so seaborgium should form SgO
3. The oxides MO
3 are soluble in alkali with the formation of oxyanions, so seaborgium should form a seaborgate ion, SgO
42−. In addition, WO
3 reacts with acid, suggesting similar amphotericity for SgO
3. Molybdenum oxide, MoO
3, also reacts with moisture to form a hydroxide MoO
2(OH)
2, so SgO
2(OH)
2 is also feasible. The heavier homologues readily form the volatile, reactive hexahalides MX
6 (X=Cl,F). Only tungsten forms the unstable hexabromide, WBr
6. Therefore, the compounds SgF
6 and SgCl
6 are predicted, and "eka-tungsten character" may show itself in increased stability of the hexabromide, SgBr
6. These halides are unstable to oxygen and moisture and readily form volatile oxyhalides, MOX
4 and MO
2X
2. Therefore SgOX
4 (X=F,Cl) and SgO
2X
2 (X=F,Cl) should be possible. In aqueous solution, a variety of anionic oxyfluoro-complexes are formed with fluoride ion, examples being MOF
5− and MO
3F
33−. Similar seaborgium complexes are expected.
Gas phase chemistry
Initial experiments aiming at probing the chemistry of seaborgium focused on the gas thermochromatography of a volatile oxychloride. Seaborgium atoms were produced in the reaction
248Cm(
22Ne,4n)
266Sg, thermalised, and reacted with an O
2/HCl mixture. The adsorption properties of the resulting oxychloride were measured and compared with those of molybdenum and tungsten compounds. The results indicated that seaborgium formed a volatile oxychloride akin to those of the other group 6 elements:
- Sg + + 2 HCl → +
In 2001, a team continued the study of the gas phase chemistry of seaborgium by reacting the element with O
2 in a H
2O environment. In a manner similar to the formation of the oxychloride, the results of the experiment indicated the formation of seaborgium oxide hydroxide, a reaction well known among the lighter group 6 homologues.
- 2 Sg + 3 → 2
- + →
Aqueous phase chemistry
In its aqueous chemistry, seaborgium has been shown to resemble its lighter homologues molybdenum and tungsten, forming a stable +6 oxidation state. Seaborgium was eluted from cation exchange resin using a HNO
3/HF solution, most likely as neutral SgO
2F
2 or the anionic complex ion [SgO
2F
3]
−. In contrast, in 0.1 M HNO
3, seaborgium does not elute, unlike Mo and W, indicating that the hydrolysis of [Sg(H
2O)
6]
6+ only proceeds as far as the cationic complex [Sg(OH)
5(H
2O)]
+.
Summary of investigated compounds and complex ions
| Formula |
Names(s) |
| SgO2Cl2 |
seaborgium oxychloride ; seaborgium(VI) dioxide dichloride ; seaborgyl dichloride |
| SgO2F2 |
seaborgium oxyfluoride ; seaborgium(VI) dioxide difluoride ; seaborgyl difluoride |
| SgO3 |
seaborgium oxide ; seaborgium(VI) oxide ; seaborgium trioxide |
| SgO2(OH)2 |
seaborgium oxide hydroxide ; seaborgium(VI) dioxide dihydroxide |
| [SgO2F3]− |
trifluorodioxoseaborgate(VI) |
| [Sg(OH)5(H2O)]+ |
aquapentahydroxyseaborgium(VI) |
History of synthesis of isotopes by cold fusion
This section deals with the synthesis of nuclei of seaborgium 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(54Cr,xn)262-xSg (x=1,2,3)
The first attempt to synthesise seaborgium in cold fusion reactions was performed in September 1974 by a
SovietThe Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
team led by G. N. Flerov at the
Joint Institute for Nuclear ResearchThe 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...
at
DubnaDubna is a town in Moscow Oblast, Russia. It has a status of naukograd , being home to the Joint Institute for Nuclear Research, an international nuclear physics research centre and one of the largest scientific foundations in the country. It is also home to MKB Raduga, a defence aerospace company...
. They reported producing a 0.48 s spontaneous fission (SF) activity which they assigned to the isotope
259Sg. Based on later evidence it was suggested that the team most likely measured the decay of
260Sg and its daughter
256Rf. The TWG concluded that, at the time, the results were insufficiently convincing.
The Dubna team revisited this problem in 1983-1984 and were able to detect a 5 ms SF activity assigned directly to
260Sg.
The team at GSI studied this reaction for the first time in 1985 using the improved method of correlation of genetic parent-daughter decays. They were able to detect
261Sg (x=1) and
260Sg and measured a partial 1n neutron evaporation excitation function.
In December 2000, the reaction was studied by a team at GANIL, France and were able to detect 10 atoms of
261Sg and 2 atoms of
260Sg to add to previous data on the reaction.
After a facility upgrade, the GSI team measured the 1n excitation function in 2003 using a metallic lead target. Of significance, in May 2003, the team successfully replaced the lead-208 target with more resistant lead(II) sulfide targets (PbS) which will allow more intense beams to be used in the future. They were able to measure the 1n,2n and 3n excitation functions and performed the first detailed alpha-gamma spectroscopy on the isotope
261Sg. They detected ~1600 atoms of the isotope and identified new alpha lines as well as measuring a more accurate half-life and new EC and SF branchings. Furthermore, they were able to detect the K X-rays from the daughter
rutherfordiumRutherfordium is a chemical element with symbol Rf and atomic number 104, named in honor of New Zealand physicist Ernest Rutherford. It is a synthetic element and radioactive; the most stable known isotope, 267Rf, has a half-life of approximately 1.3 hours.In the periodic table of the elements,...
element for the first time. They were also able to provide improved data for
260Sg, including the tentative observation of an isomeric level. The study was continued in September 2005 and March 2006. The accumulated work on
261Sg was published in 2007.
Work in September 2005 also aimed to begin spectroscopic studies on
260Sg.
The team at the LBNL recently restudied this reaction in an effort to look at the spectroscopy of the isotope
261Sg. They were able to detect a new isomer,
261mSg, decaying by internal conversion into the ground state. In the same experiment, they were also able to confirm a K-isomer in the daughter
257Rf, namely
257m2Rf.
207Pb(54Cr,xn)261-xSg (x=1,2)
The team at Dubna also studied this reaction in 1974 with identical results as for their first experiments with a Pb-208 target. The SF activities were first assigned to
259Sg and later to
260Sg and/or
256Rf. Further work in 1983-1984 also detected a 5 ms SF activity assigned to the parent
260Sg.
The GSI team studied this reaction for the first time in 1985 using the method of correlation of genetic parent-daughter decays. They were able to positively identify
259Sg as a product from the 2n neutron evaporation channel.
The reaction was further used in March 2005 using PbS targets to begin a spectroscopic study of the even-even isotope
260Sg.
206Pb(54Cr,xn)260-xSg
This reaction was studied in 1974 by the team at Dubna. It was used to assist them in their assignment of the observed SF activities in reactions using Pb-207 and Pb-208 targets. They were unable to detect any SF, indicating the formation of isotopes decaying primarily by alpha decay.
208Pb(52Cr,xn)260-xSg (x=1,2)
The team at Dubna also studied this reaction in their series of cold fusion reactions performed in 1974. Once again they were unable to detect any SF activities. The reaction was revisited in 2006 by the team at LBNL as part of their studies on the effect of the isospin of the projectile and hence the mass number of the compound nucleus on the yield of evaporation residues. They were able to identify
259Sg and
258Sg in their measurement of the 1n excitation function.
209Bi(51V,xn)260-xSg (x=2)
The team at Dubna also studied this reaction in their series of cold fusion reactions performed in 1974. Once again they were unable to detect any SF activities.
In 1994, the synthesis of seaborgium was revisited using this reaction by the GSI team, in order to study the new even-even isotope
258Sg. Ten atoms of
258Sg were detected and decayed by spontaneous fission.
History of synthesis of isotopes by hot fusion
This section deals with the synthesis of nuclei of seaborgium 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 and quasi-fission. The excited nucleus then decays to the ground state via the emission of 3-5 neutrons.
238U(30Si,xn)268-xSg (x=3,4,5,6)
This reaction was first studied by Japanese scientists at the Japan Atomic Energy Research Institute (JAERI) in 1998. They detected a
spontaneous fissionSpontaneous 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...
activity which they tentatively assigned to the new isotope
264Sg or
263Db, formed by EC of
263Sg.
In 2006, the teams at GSI and LBNL both studied this reaction using the method of correlation of genetic parent-daughter decays. The LBNL team measured an excitation function for the 4n,5n and 6n channels, whilst the GSI team were able to observe an additional 3n activity. Both teams were able to identify the new isotope
264Sg which decayed with a short lifetime by
spontaneous fissionSpontaneous 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...
.
248Cm(22Ne,xn)270-xSg (x=4?,5)
In 1993, at Dubna, Yuri Lazarev and his team announced the discovery of long-lived
266Sg and
265Sg produced in the 4n and 5n channels of this nuclear reaction following the search for seaborgium isotopes suitable for a first chemical study.
It was announced that
266Sg decayed by 8.57 MeV alpha-particle emission with a projected half-life of ~20 s, lending strong support to the stabilising effect of the Z=108,N=162 closed shells.
This reaction was studied further in 1997 by a team at GSI and the yield, decay mode and half-lives for
266Sg and
265Sg have been confirmed, although there are still some discrepancies. In the recent synthesis of
270Hs (see
hassiumHassium is a synthetic element with the symbol Hs and atomic number 108. It is the heaviest member of the group 8 elements. The element was first observed in 1984...
),
266Sg was found to undergo exclusively SF with a short half-life (T
SF = 360 ms). It is possible that this is the ground state, (
266gSg) and that the other activity, produced directly, belongs to a high spin K-isomer,
266mSg, but further results are required to confirm this.
A recent re-evaluation of the decay characteristics of
265Sg and
266Sg has suggested that all decays to date in this reaction were in fact from
265Sg, which exists in two isomeric forms. The first,
265aSg has a principal alpha-line at 8.85 MeV and a calculated half-life of 8.9 s, whilst
265bSg has a decay energy of 8.70 MeV and a half-life of 16.2 s. Both isomeric levels are populated when produced directly. Data from the decay of
269Hs indicates that
265bSg is produced during the decay of
269Hs and that
265bSg decays into the shorter-lived
261gRf isotope. This means that the observation of
266Sg as a long-lived alpha emitter is retracted and that it does indeed undergo fission in a short time.
Regardless of these assignments, the reaction has been successfully used in the recent attempts to study the chemistry of seaborgium (see below).
249Cf(18O,xn)267-xSg (x=4)
The synthesis of seaborgium was first realized in 1974 by the LBNL/LLNL team. In their discovery experiment, they were able to apply the new method of correlation of genetic parent-daughter decays to identify the new isotope
263Sg. In 1975, the team at Oak Ridge were able to confirm the decay data but were unable to identify coincident X-rays in order to prove that seaborgium was produced. In 1979, the team at Dubna studied the reaction by detection of SF activities. In comparison with data from Berkeley, they calculated a 70% SF branching for
263Sg. The original synthesis and discovery reaction was confirmed in 1994 by a different team at LBNL.
Synthesis of isotopes as decay products
Isotopes of seaborgium have also been observed in the decay of heavier elements. Observations to date are summarised in the table below:
| Evaporation Residue |
Observed Sg isotope |
| 291Uuh, 287Uuq, 283Cn |
271Sg |
| 285Uuq |
269Sg |
| 271Hs |
267Sg |
| 270Hs |
266Sg |
| 277Cn, 273Ds, 269Hs |
265Sg |
| 271Ds, 267Ds |
263Sg |
| 270Ds |
262Sg |
| 269Ds, 265Hs |
261Sg |
| 264Hs |
260Sg |
Chronology of isotope discovery
| Isotope |
Year discovered |
discovery reaction |
| 258Sg |
1994 |
209Bi(51V,2n) |
| 259Sg |
1985 |
207Pb(54Cr,2n) |
| 260Sg |
1985 |
208Pb(54Cr,2n) |
| 261gSg |
1985 |
208Pb(54Cr,n) |
| 261mSg |
2009 |
208Pb(54Cr,n) |
| 262Sg |
2001 |
207Pb(64Ni,n) |
| 263Sgm |
1974 |
249Cf(18O,4n) |
| 263Sgg |
1994 |
208Pb(64Ni,n) |
| 264Sg |
2006 |
238U(30Si,4n) |
| 265Sg |
1993 |
248Cm(22Ne,5n) |
| 266Sg |
2004 |
248Cm(26Mg,4n) |
| 267Sg |
2004 |
248Cm(26Mg,3n) |
| 268Sg |
unknown |
|
| 269Sg |
2010 |
242Pu(48Ca,5n) |
| 270Sg |
unknown |
|
| 271Sg |
2003 |
242Pu(48Ca,3n) |
Isotopes
There are 12 known isotopes of seaborgium (excluding meta-stable and K-spin isomers). The longest-lived is currently
269Sg which decays through
alpha decayAlpha 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...
and
spontaneous fissionSpontaneous 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 a half-life of around 2.1 minutes. The shortest-lived isotope is
258Sg which also decays through alpha decay and spontaneous fission. It has a half-life of 2.9 ms.
266Sg
Initial work identified an 8.63 MeV alpha-decaying activity with a half-life of ~21s and assigned to the ground state of
266Sg. Later work identified a nuclide decaying by 8.52 and 8.77 MeV alpha emission with a half-life of ~21s, which is unusual for an even-even nuclide. Recent work on the synthesis of
270Hs identified
266Sg decaying by SF with a short 360 ms half-life. The recent work on
277Cn and
269Hs has provided new information on the decay of
265Sg and
261Rf. This work suggested that the initial 8.77 MeV activity should be reassigned to
265Sg. Therefore the current information suggests that the SF activity is the ground state and the 8.52 MeV activity is a high spin K-isomer. Further work is required to confirm these assignments. A recent re-evaluation of the data has suggested that the 8.52 MeV activity should be associated with
265Sg and that
266Sg only undergoes fission.
265Sg
The recent direct synthesis of
265Sg resulted in four alpha-lines at 8.94,8.84,8.76 and 8.69 MeV with a half-life of 7.4 seconds. The observation of the decay of
265Sg from the decay of
277Cn and
269Hs indicated that the 8.69 MeV line may be associated with an isomeric level with an associated half-life of ~ 20 s. It is plausible that this level is causing confusion between assignments of
266Sg and
265Sg since both can decay to fissioning rutherfordium isotopes.
A recent re-evaluation of the data has indicated that there are indeed two isomers, one with a principal decay energy of 8.85 MeV with a half-life of 8.9 s, and a second isomer which decays with energy 8.70 MeV with a half-life of 16.2 s.
263Sg
The discovery synthesis of
263Sg resulted in an alpha-line at 9.06 MeV. Observation of this nuclide by decay of
271gDs,
271mDs and
267Hs has confirmed an isomer decaying by 9.25 MeV alpha emission. The 9.06 MeV decay was also confirmed. The 9.06 MeV activity has been assigned to the ground state isomer with an associated half-life of 0.3 s. The 9.25 MeV activity has been assigned to an isomeric level decaying with a half-life of 0.9 s.
Recent work on the synthesis of
271g,mDs was resulted in some confusing data regarding the decay of
267Hs. In one such decay,
267Hs decayed to
263Sg which decayed by alpha emission with a half-life of ~ 6 s. This activity has not yet been positively assigned to an isomer and further research is required.
261Sg
269Sg
In the claimed synthesis of
293Uuo in 1999 the isotope
269Sg was identified as a daughter product. It decayed by 8.74 MeV alpha emission with a half-life of 22 s. The claim was retracted in 2001. This isotope was finally created in 2010.
Cold fusion
The table below provides cross-sections and excitation energies for cold fusion reactions producing seaborgium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.
| Projectile |
Target |
CN |
1n |
2n |
3n |
| 54Cr |
207Pb |
261Sg |
|
|
|
| 54Cr |
208Pb |
262Sg |
4.23 nb, 13.0 MeV |
500 pb |
10 pb |
| 51V |
209Bi |
260Sg |
|
38 pb, 21.5 MeV |
|
| 52Cr |
208Pb |
260Sg |
281 pb, 11.0 MeV |
|
|
Hot fusion
The table below provides cross-sections and excitation energies for hot fusion reactions producing seaborgium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.
| Projectile |
Target |
CN |
3n |
4n |
5n |
6n |
| 30Si |
238U |
268Sg |
+ |
9 pb, 40.0 |
~ 80 pb, 51.0 MeV |
~30 pb, 58.0 MeV |
| 22Ne |
248Cm |
270Sg |
|
~25 pb |
~250 pb |
|
| 18O |
249Cf |
267Sg |
|
+ |
|
|
External links
- WebElements.com - Seaborgium
- Chemistry in its element podcast (MP3) from the Royal Society of Chemistry
The Royal Society of Chemistry is a learned society in the United Kingdom with the goal of "advancing the chemical sciences." It was formed in 1980 from the merger of the Chemical Society, the Royal Institute of Chemistry, the Faraday Society and the Society for Analytical Chemistry with a new...
's Chemistry WorldChemistry World is a monthly chemistry news magazine published by the Royal Society of Chemistry. The magazine addresses current events in world of chemistry including research, international business news and government policy as it affects the chemical science community, plus the best product...
: Seaborgium