|Name, symbol||dubnium, Db|
|Dubnium in the periodic table|
|Atomic number (Z)||105|
|Group, block||group 5, d-block|
|Element category||transition metal|
|Standard atomic weight (Ar)|||
|Electron configuration||[Rn] 5f14 6d3 7s2 (predicted)|
|2, 8, 18, 32, 32, 11, 2 (predicted)|
|Density near r.t.||29.3 g/cm3 (predicted)|
|Oxidation states||5, (4), (3) (parenthesized oxidation states are predictions)|
|Ionization energies||1st: 664.8 kJ/mol
2nd: 1546.7 kJ/mol
3rd: 2378.4 kJ/mol
(more) (all estimated)
|Atomic radius||empirical: 139 pm (estimated)|
|Covalent radius||149 pm (estimated)|
|Crystal structure||body-centered cubic (bcc) (predicted)|
|Naming||after the town of Dubna in Russia|
|Discovery||Joint Institute for Nuclear Research (1968)|
|Most stable isotopes of dubnium|
Dubnium is a chemical element with symbol Db and atomic number 105. It is named after the town of Dubna in Russia (north of Moscow), where it was first produced. It is a synthetic element (an element that can be created in a laboratory but is not found in nature) and radioactive; the most stable known isotope, dubnium-268, has a half-life of approximately 28 hours.
In the periodic table of the elements, it is a d-block element and in the transactinide elements. It is a member of the 7th period and belongs to Group 5. Chemistry experiments have confirmed that dubnium behaves as the heavier homologue to tantalum in group 5. The chemical properties of dubnium are characterized only partly. They are similar to those of other group 5 elements.
In the 1960s and 1970s, microscopic amounts of dubnium were produced in laboratories in the Soviet Union and in California. The priority of the discovery and therefore the naming of the element was disputed between Soviet and American scientists, and it was not until 1997 that IUPAC established "dubnium" as the official name for the element.
- 1 History
- 2 Chemical properties
- 3 Nucleosynthesis history
- 4 Isotopes
- 5 References
- 6 External links
The first discovery of an element heavier than uranium, the heaviest of the naturally occurring quantity elements—neptunium—occurred in 1940 by the University of California (UC) in Berkeley, California, United States. In the coming years, the American team undoubtedly synthesized the following elements up to fermium, element 100. However, in 1956, the Joint Institute for Nuclear Research (JINR) in Dubna, Moscow Oblast, Russian SFSR, Soviet Union, was founded and became a major rival to the American team. Their rivalry, heated by the ideological and geopolitical rivalry of their countries, which itself reached its peak in the 1960s, resulted in a race for new elements and credit of their discoveries, later named the Transfermium Wars.
First report of discovery of element 105 came from the JINR in 1968. A target of americium-243 was bombarded by a beam of neon-22 ions. The scientists at Dubna reported 9.4 MeV (with the reported half-live of 0.1–3 seconds) and 9.7 MeV (t1/2 > 0.05 s) alpha activities followed by alpha activities similar to those of lawrencium-256 and lawrencium-257. The two activity lines were, based on predicted data, assigned to 261105 and 260105, accordingly:
95Am + 22
10Ne → 265−x105 + x n (x = 4, 5)
Investigation of the original reaction was continued; the research was aimed at looking for fission fragments of Z=105 isotopes. In February 1970, a following paper was published. Two activities were found, with half-lives of 14 ms and 2.2±0.5 s. The former activity was assigned to 242mfAm; the latter one was described as caused by an isotope of element 105. The idea that the latter activity could come from a transfer reaction, rather than synthesis one, was said to be diminished by the fact yield ratio for this reaction was lower than that of the 242mfAm-producing transfer reaction. The idea that this synthesis reaction was indeed a (22Ne,xn) reaction was grounded on research on the reaction of that beam with 18O; reactions producing 256Lr and 257Lr showed very little spontaneous fission (SF) activity (matching the established data), and the reaction producing heavier 258Lr and 259Lr produced no SF activity at all, falling in line with theory. A subsequent paper, released in May 1970, reported this isotope was probably 261105, though the possibility of 260105 was not excluded.
In April 1970, a team led by Albert Ghiorso working at the University of California stepped into the competition. They claimed to have synthesized the element by bombarding a californium-249 target with nitrogen-15 ions. Alpha activity with the energy of 9.1 MeV was formed; the team attempted reaction with other nuclides—bombardment of 249Cf with 14N, Pb with 15N, Hg with 15N—and stated no such activity was found in those reactions. The characteristics of the daughter nuclei correlated with those of lawrencium-256:
98Cf + 15
7N → 260105 + 4 n
These results by the Berkeley scientists did not confirm the JINR findings regarding the 9.4 MeV or 9.7 MeV alpha-decay of dubnium-260, leaving only dubnium-261 as possible produced isotope.
In May 1970, the first paper discussing chemical examination and confirmation of the supposed element 105 was published in Dubna. That work relied on the previous data from Dubna: the February 1970 paper. The thermal gradient version of the gas-chromatography method was applied to demonstrate that the chloride of what formed the SF activity in the aforementioned work nearly agreed with that of NbCl5, rather than HfCl4: therefore, this directed to an assignment to element 105. The team identified a 2.2-second spontaneous fission activity contained within a volatile chloride portraying eka-tantalum properties.
In June 1970, the Dubna team made improvements on their original experiment, providing a purer target and intensity of transfer reactions reduced by using a collimator before the catcher. This time, they were able to find 9.1 MeV alpha activities with daughter isotopes indentifiable as either 256Lr or 257Lr; thus, the original isotope was either 260105 or 261105.
The Soviet team proposed the name nielsbohrium (Ns) in honor of the Danish nuclear physicist Niels Bohr, one of the founders of the theories of the atomic structure and the quantum theory. The American team proposed that the new element should be named hahnium (Ha), in honor of the German chemist Otto Hahn, the "father of nuclear chemistry". An element naming controversy rose; consequently, hahnium was the name that most American and Western European scientists used and appears in many papers published at the time, and nielsbohrium was used in the Soviet Union and Eastern Bloc countries.
However, tensions in the late 1960s and 1970s simmered down somewhat. Both teams synthesized the next element, element 106, but decided not to suggest their names. In 1968, the Soviet team presented a report calling recognition of discovery of elements 102 and 103 by other teams "hasty". Afterwards, they suggested establishing an international committee on elaborating the discovery criteria. This proposal was accepted in 1974; however, the newly formed Committee never assembled to assess the claims. The conflict remained unsolved, and in 1979, the IUPAC published a new suggested system of systematic element names (according to which element 105 would be named unnilpentium, from the Latin roots un- and nil- and the Greek root pent- (meaning "one", "zero", and "five", accordingly, referencing the atomic number) intended to be used as placeholders until permanent names were established; the scientists ignored it, not wishing to weaken their claims by adopting a neutral naming system rather than their own.
In 1981, a third major competitor joined the race for superheavy elements—the Gesellschaft für Schwerionenforschung (GSI; English Society for Heavy Ion Research) in Darmstadt, Hesse, West Germany. They claimed to have synthesized the element 107; their report came out five years after the first report from Dubna did, but it provided further details not presented in that work. The German team joined with the Soviet team in that it suggested the name nielsbohrium for the new element, believing Bohr did deserve an element named after him, and hoping to ease the tension on the element 105 controversy. The Soviet team did not hurry to suggest a new name for element 105, stating it was more fundamental to first determine the discoverers of the element.
In 1985, the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP) formed a Joint Working Party (JWP) aimed at assessing discoveries and establishing final names for the elements in question. The party held numerous meetings with delegates from all three competing institutes; in 1990, they established criteria on recognizing an element and in 1991, they completed the work on assessing discoverer statuses and the party was disbanded. These results were published in 1993. According to the report, the first definitely successful experiment was the April 1970 experiment in Berkeley, followed closely by the June 1970 Dubna experiment; thus, credit for discovery of the element should be shared between the two competing teams.
The American team dismissed the report, saying the input from the Russian team was overrated by the review. In relation with element 105, they claimed the Dubna team was able to undoubtedly demonstrate the synthesis of element 105 no earlier than a year after they did. On the other hand, the Russian and the German teams endorsed the report. The scientists from the former JWP rejected criticisms from Berkeley.
In 1994, the IUPAC published a recommendation on naming the disputed elements following the previous reports. For element 105, they proposed the name joliotium (Jl), after the French physicist Frédéric Joliot-Curie, a significant contributor to the development of nuclear physics and chemistry; this name was originally proposed by Soviet team for element 102, which by then had long been called nobelium. (The name nielsbohrium for the element 107 transformed to bohrium to conform the practice set by all then-current elements.) This recommendation paper was generally met with criticism from the American scientists: their recommendations were scrambled (i.e. the name rutherfordium, originally suggested by Berkeley for element 104, was used for element 106); both elements 104 and 105 were named after Russian names despite earlier recognition of the Berkeley team as of an equal co-discoverer; and especially because the name seaborgium was rejected for honoring a living person, a rule that had only just been approved. These names were to be accepted on a Council meeting in 1995; following the response, the IUPAC did allow the name seaborgium for element 106, but the American team remained unsatisfied because their other proposals were not accepted.
In 1996, the IUPAC held another meeting and reconsidered all names in hand and another set of recommendations was accepted on this meeting; it was finally approved and published in 1997. Element 105 got its final name, dubnium (Db), after the Russian town of Dubna, the location of the Joint Institute for Nuclear Research. This decision was "reluctantly" approved by the American scientists. The IUPAC stated the Berkeley laboratory had already been recognized several times in the naming of elements (i.e., berkelium, californium, americium) and that the acceptance of the names rutherfordium and seaborgium for elements 104 and 106 should be offset by recognizing the Russian team's contributions to the discovery of elements 104, 105, and 106. (The matter of naming element 107 was transferred to the Royal Danish Academy of Sciences and Letters, who recommended the name bohrium to be used.)
Element 105 is projected to be the second member of the 6d series of transition metals and the heaviest member of group V in the Periodic Table, below vanadium, niobium and tantalum. Because it is positioned right below tantalum, it may also be called eka-tantalum. All the members of the group readily portray their oxidation state of +5 and the state becomes more stable as the group is descended. Thus dubnium is expected to form a stable +5 state. For this group, +4 and +3 states are also known for the heavier members and dubnium may also form these reducing oxidation states.
In an extrapolation of the chemistries from niobium and tantalum, dubnium should react with oxygen to form an inert pentoxide, Db2O5. In alkali, the formation of an orthodubnate complex, DbO3−
4, is expected. Reaction with the halogens should readily form the pentahalides, DbX5. The pentachlorides of niobium and tantalum exist as volatile solids or monomeric trigonal bipyramidal molecules in the vapour phase. Thus, DbCl5 is expected to be a volatile solid. Similarly, the pentafluoride, DbF5, should be even more volatile. Hydrolysis of the halides is known to readily form the oxyhalides, MOX3. Thus the halides DbX5 should react with water to form DbOX3. The reaction with fluoride ion is also well known for the lighter homologues and dubnium is expected to form a range of fluoro-complexes. In particular, reaction of the pentafluoride with HF should form a hexafluorodubnate ion, DbF−
6. Excess fluoride should lead to DbF2−
7 and DbOF2−
5. If eka-tantalum properties are portrayed, higher concentrations of fluoride should ultimately form DbF3−
8 since NbF3−
8 is not known.
The chemistry of dubnium has been studied for several years using gas thermochromatography. The experiments have studied the relative adsorption characteristics of isotopes of niobium, tantalum and dubnium radioisotopes. The results have indicated the formation of typical group 5 halides and oxyhalides, namely DbCl5, DbBr5, DbOCl3 and DbOBr3. Reports on these early experiments usually refer to dubnium as hahnium.
|DbCl5||dubnium pentachloride ; dubnium(V) chloride|
|DbBr5||dubnium pentabromide ; dubnium(V) bromide|
|DbOCl3||dubnium oxychloride ; dubnium(V) trichloride oxide ; dubnyl(V) chloride|
|DbOBr3||dubnium oxybromide ; dubnium(V) tribromide oxide ; dubnyl(V) bromide|
This section deals with the synthesis of nuclei of dubnium 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(50Ti,xn)259-xDb (x=1,2,3)
The first attempts to synthesise dubnium using cold fusion reactions were performed in 1976 by the team at FLNR, Dubna using the above reaction. They were able to detect a 5 s spontaneous fission (SF) activity which they assigned to 257Db. This assignment was later corrected to 258Db. In 1981, the team at GSI studied this reaction using the improved technique of correlation of genetic parent-daughter decays. They were able to positively identify 258Db, the product from the 1n neutron evaporation channel. In 1983, the team at Dubna revisited the reaction using the method of identification of a descendant using chemical separation. They succeeded in measuring alpha decays from known descendants of the decay chain beginning with 258Db. This was taken as providing some evidence for the formation of dubnium nuclei. The team at GSI revisited the reaction in 1985 and were able to detect 10 atoms of 257Db. After a significant upgrade of their facilities in 1993, in 2000 the team measured 120 decays of 257Db, 16 decays of 256Db and decay of 258Db in the measurement of the 1n, 2n and 3n excitation functions. The data gathered for 257Db allowed a first spectroscopic study of this isotope and identified an isomer, 257mDb, and a first determination of a decay level structure for 257Db. The reaction was used in spectroscopic studies of isotopes of mendelevium and einsteinium in 2003–2004.
- 209Bi(49Ti,xn)258-xDb (x=2?)
This reaction was studied by Yuri Oganessian and the team at Dubna in 1983. They observed a 2.6 s SF activity tentatively assigned to 256Db. Later results suggest a possible reassignment to 256Rf, resulting from the ~30% EC branch in 256Db.
- 209Bi(48Ti,xn)257-xDb (x=1?)
This reaction was studied by Yuri Oganessian and the team at Dubna in 1983. They observed a 1.6 s activity with a ~80% alpha branch with a ~20% SF branch. The activity was tentatively assigned to 255Db. Later results suggest a reassignment to 256Db.
- 208Pb(51V,xn)259-xDb (x=1,2)
The team at Dubna also studied this reaction in 1976 and were again able to detect the 5 s SF activity, first tentatively assigned to 257Db and later to 258Db. In 2006, the team at LBNL reinvestigated this reaction as part of their odd-Z projectile program. They were able to detect 258Db and 257Db in their measurement of the 1n and 2n neutron evaporation channels.
The team at Dubna also studied this reaction in 1976 but this time they were unable to detect the 5 s SF activity, first tentatively assigned to 257Db and later to 258Db. Instead, they were able to measure a 1.5 s SF activity, tentatively assigned to 255Db.
- 205Tl(54Cr,xn)259-xDb (x=1?)
The team at Dubna also studied this reaction in 1976 and were again able to detect the 5 s SF activity, first tentatively assigned to 257Db and later to 258Db.
This section deals with the synthesis of nuclei of dubnium 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.
- 232Th(31P,xn)263-xDb (x=5)
There are very limited reports that this rare reaction using a P-31 beam was studied in 1989 by Andreyev et al. at the FLNR. One source suggests that no atoms were detected whilst a better source from the Russians themselves indicates that 258Db was synthesised in the 5n channel with a yield of 120 pb.
- 238U(27Al,xn)265-xDb (x=4,5)
In 2006, as part of their study of the use of uranium targets in superheavy element synthesis, the LBNL team led by Ken Gregorich studied the excitation functions for the 4n and 5n channels in this new reaction.
- 236U(27Al,xn)263-xDb (x=5,6)
This reaction was first studied by Andreyev et al. at the FLNR, Dubna in 1992. They were able to observe 258Db and 257Db in the 5n and 6n exit channels with yields of 450 pb and 75 pb, respectively.
- 243Am(22Ne,xn)265-xDb (x=5)
The first attempts to synthesise dubnium were performed in 1968 by the team at the Flerov Laboratory of Nuclear Reactions (FLNR) in Dubna, Russia. They observed two alpha lines which they tentatively assigned to 261Db and 260Db. They repeated their experiment in 1970 looking for spontaneous fission. They found a 2.2 s SF activity which they assigned to 261Db. In 1970, the Dubna team began work on using gradient thermochromatography in order to detect dubnium in chemical experiments as a volatile chloride. In their first run they detected a volatile SF activity with similar adsorption properties to NbCl5 and unlike HfCl4. This was taken to indicate the formation of nuclei of dvi-niobium as DbCl5. In 1971, they repeated the chemistry experiment using higher sensitivity and observed alpha decays from an dvi-niobium component, taken to confirm the formation of 260Db. The method was repeated in 1976 using the formation of bromides and obtained almost identical results, indicating the formation of a volatile, dvi-niobium-like DbBr5.
- 241Am(22Ne,xn)263-xDb (x=4,5)
In 2000, Chinese scientists at the Institute of Modern Physics (IMP), Lanzhou, announced the discovery of the previously unknown isotope 259Db formed in the 4n neutron evaporation channel. They were also able to confirm the decay properties for 258Db.
- 248Cm(19F,xn)267-xDb (x=4,5)
This reaction was first studied in 1999 at the Paul Scherrer Institute (PSI) in order to produce 262Db for chemical studies. Just 4 atoms were detected with a cross section of 260 pb. Japanese scientists at JAERI studied the reaction further in 2002 and determined yields for the isotope 262Db during their efforts to study the aqueous chemistry of dubnium.
- 249Bk(18O,xn)267-xDb (x=4,5)
Following from the discovery of 260Db by Albert Ghiorso in 1970 at the University of California (UC), the same team continued in 1971 with the discovery of the new isotope 262Db. They also observed an unassigned 25 s SF activity, probably associated with the now-known SF branch of 263Db. In 1990, a team led by Kratz at LBNL definitively discovered the new isotope 263Db in the 4n neutron evaporation channel. This reaction has been used by the same team on several occasions in order to attempt to confirm an electron capture (EC) branch in 263Db leading to long-lived 263Rf (see rutherfordium).
- 249Bk(16O,xn)265-xDb (x=4)
Following from the discovery of 260Db by Albert Ghiorso in 1970 at the University of California (UC), the same team continued in 1971 with the discovery of the new isotope 261Db.
- 250Cf(15N,xn)265-xDb (x=4)
Following from the discovery of 260Db by Ghiorso in 1970 at LBNL, the same team continued in 1971 with the discovery of the new isotope 261Db.
- 249Cf(15N,xn)264-xDb (x=4)
In 1970, the team at the Lawrence Berkeley National Laboratory (LBNL) studied this reaction and identified the isotope 260Db in their discovery experiment. They used the modern technique of correlation of genetic parent-daughter decays to confirm their assignment. In 1977, the team at Oak Ridge repeated the experiment and were able to confirm the discovery by the identification of K X-rays from the daughter lawrencium.
In 1988, scientists as the Lawrence Livermore National Laboratory (LLNL) used the asymmetric hot fusion reaction with an einsteinium-254 target to search for the new nuclides 264Db and 263Db. Due to the low sensitivity of the experiment caused by the small Es-254 target,they were unable to detect any evaporation residues (ER).
Decay of heavier nuclides
Isotopes of dubnium have also been identified in the decay of heavier elements. Observations to date are summarised in the table below:
|Evaporation Residue||Observed dubnium isotope|
|Isotope||Year discovered||discovery reaction|
Recent data on the decay of 272Rg has revealed that some decay chains continue through 260Db with extraordinary longer life-times than expected. These decays have been linked to an isomeric level decaying by alpha decay with a half-life of ~19 s. Further research is required to allow a definite assignment.
Evidence for an isomeric state in 258Db has been gathered from the study of the decay of 266Mt and 262Bh. It has been noted that those decays assigned to an electron capture (EC) branch has a significantly different half-life to those decaying by alpha emission. This has been taken to suggest the existence of an isomeric state decaying by EC with a half-life of ~20 s. Further experiments are required to confirm this assignment.
A study of the formation and decay of 257Db has proved the existence of an isomeric state. Initially, 257Db was taken to decay by alpha emission with energies 9.16,9.07 and 8.97 MeV. A measurement of the correlations of these decays with those of 253Lr have shown that the 9.16 MeV decay belongs to a separate isomer. Analysis of the data in conjunction with theory have assigned this activity to a meta stable state, 257mDb. The ground state decays by alpha emission with energies 9.07 and 8.97 MeV. Spontaneous fission of 257m,gDb was not confirmed in recent experiments.
Spectroscopic decay level schemes
In 1983, scientists at Dubna carried out a series of supportive experiments in their quest for the discovery of bohrium. In two such experiments, they claimed they had detected a ~1.5 s spontaneous fission activity from the reactions 207Pb(51V,xn) and 209Bi(48Ti,xn). The activity was assigned to 255Db. Later research suggested that the assignment should be changed to 256Db. As such, the isotope 255Db is currently not recognised on the chart of radionuclides and further research is required to confirm this isotope.
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