Dubnium is a chemical element with symbol Db and atomic number 105. A transactinide element, dubnium is highly radioactive: the most stable known isotope, dubnium-268, has a half-life of just above a day. This greatly limits the extent of possible research on dubnium.
|Pronunciation||// ( listen)
|Mass number||268 (most stable isotope)|
|Dubnium in the periodic table|
|Atomic number (Z)||105|
|Group, period||group 5, period 7|
|Element category||transition metal|
|Electron configuration||[Rn] 5f14 6d3 7s2|
Electrons per shell
|2, 8, 18, 32, 32, 11, 2|
|Phase (at STP)||solid (predicted)|
|Density (near r.t.)||29.3 g/cm3 (predicted)|
|Oxidation states||5, (4), (3) (parenthesized oxidation states are predictions)|
|Atomic radius||empirical: 139 pm (estimated)|
|Covalent radius||149 pm (estimated)|
|Crystal structure||body-centered cubic (bcc) (predicted)|
|Naming||after Dubna, Moscow Oblast, Russia, site of the Joint Institute for Nuclear Research|
|Discovery||independently by the University of California and the Joint Institute for Nuclear Research (1970)|
|Main isotopes of dubnium|
Dubnium does not occur naturally on Earth and is produced artificially. The first discovery of the element was claimed by the Soviet Joint Institute for Nuclear Research (JINR) in 1968, followed in 1970 by the American University of California. Both teams proposed a name for the new element, and used it without formal approval. The long-standing dispute was resolved in 1993 by an official investigation of the discovery claims by the IUPAC/IUPAP Joint Working Party, resulting in credit for discovery being officially shared between both teams. The element was officially named dubnium in 1997 after Dubna, the site of the JINR.
In the periodic table of the elements, dubnium is located in the d-block of period 7, thus being a transactinide element. Dubnium belongs to group 5 as the third member of the 6d series of transition metals. Limited investigation of dubnium chemistry has demonstrated that dubnium behaves as a typical group 5 element and the heavier homologue to tantalum; however, some deviations from periodic trends occur due to relativistic effects.
Uranium, element 92, is the heaviest of the elements that occur significantly in nature; heavier elements can only practically be produced by synthesis. The first synthesis of a new element—neptunium, element 93—occurred in 1940 by a team of scientists in the United States. In the coming years, American scientists undoubtedly synthesized the following elements up to mendelevium, element 101, in 1955. However, starting with element 102, discovery priority was contested between American and Soviet physicists. Their rivalry resulted in a race for new elements and credit of their discoveries, later named the Transfermium Wars.
The first report of discovery of element 105 came from the Joint Institute for Nuclear Research (JINR) in Dubna, Moscow Oblast, Russian SFSR, Soviet Union, in 1968. A target of 243Am was bombarded by a beam of 22Ne ions. The scientists at Dubna reported 9.4 MeV (with the reported half-life of 0.1–3 seconds) and 9.7 MeV (t1/2 > 0.05 s) alpha activities followed by alpha activities similar to those of 256103 and 257103. The two activity lines were, based on predicted data, assigned to 261105 and 260105, accordingly.
→ 265−x105 + x
(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 having been caused by an isotope of element 105. The idea that the latter activity could come from a transfer reaction and thus not be from element 105 was said to be diminished by the fact that the 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 256103 and 257103 showed very little spontaneous fission (SF) activity (matching the established data), and the reaction producing heavier 258103 and 259103 produced no SF activity at all, falling in line with theory. A subsequent paper, released in May 1970, reported that this isotope was probably 261105, though the possibility of it being 260105 was not excluded.
In April 1970, a team led by Albert Ghiorso working at the University of California (Berkeley, California, United States) 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 256103, implying the assignment of the parent to 260105.
→ 260105 + 4
These results by the Berkeley scientists did not confirm the JINR findings regarding the 9.4 MeV or 9.7 MeV alpha-decay of 260105, leaving only 261105 as a possibly 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 identifiable as either 256103 or 257103; 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". Thus, an element naming controversy arose.
However, tensions in the late 1960s and 1970s somewhat simmered down. 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, including the American team, "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. Neither team was particularly excited about having to resolve the conflict via the means of a third party, and the leading scientists of the LBL—Albert Ghiorso and Glenn Seaborg—traveled to Dubna in 1975 and had a meeting with the leader of the Soviet team, Georgy Flerov, in an attempt to resolve the conflict internally and render the neutral joint group unnecessary; however, the meeting was unsuccessful. 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", respectively, referencing the decimal digits of 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 (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. In an open response, they proclaimed that the input from the Russian team was overrated by the review. In addition, they claimed the Dubna team was able to undoubtedly demonstrate the synthesis of element 105 no earlier than a year after they did. 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 the Soviet team for element 102, which by then had long been called nobelium. (The name nielsbohrium for element 107 was transformed to bohrium to conform with the practice set by all then-named elements.) This recommendation paper was generally met with criticism from the American scientists: their recommendations were scrambled (the names rutherfordium and hahnium, originally suggested by Berkeley for elements 104 and 105, were used for elements 106 and 108, respectively); both elements 104 and 105 were given names suggested by the Russian team despite earlier recognition of the Berkeley team as of an equal co-discoverer; and especially because the name seaborgium for element 106 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.
After a new term of negotiations between the parties, IUPAC decided to allow the name seaborgium for element 106 and changed the name of element 102 to flerovium after Georgy Flerov following the recognition by the 1993 report that the element had been first convincingly synthesized in Dubna. However, this compromise was also rejected by the American scientists and the decision was retracted. The name flerovium was later used for element 114.
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.)
Dubnium with its atomic number 105 is a superheavy element; like all elements of such high atomic number, it is highly unstable. The most stable known isotope of dubnium, 268Db, has a half-life of around a day. Thus, even if it had once existed on Earth, it would have decayed completely long ago and can only be obtained by artificial production.[a]
The short half-life of dubnium limits the scope of experimentation. This is amplified by the neutron-to-proton ratio of the most stable isotopes of an element growing with the atomic number, a trend that is expected to continue to the superheavy elements; this complicates synthesis of the most stable isotopes as the isotopes in question will have more neutrons per proton than both the target and beam nuclei that could be employed. (Although a different technique based on rapid neutron capture is being considered, the ones based on collision of a big and a small nucleus dominate research in the area nowadays.)
By 2016, only a few atoms of 268Db could be produced in each experiment, and thus the measured half-lives changed significantly during the process. During three experiments, 23 atoms were created in total, with a resulting half-life of 28+11
−4 hours. The second most stable isotope, 270Db, has been produced in even smaller quanitites: three atoms in total, with lifetimes of 33.4 h, 1.3 h, and 1.6 h. These two are the heaviest isotopes of dubnium to date, and both were produced as a result of decay of the heavier nuclei 288Mc and 294Ts rather than directly. The reason for this is that the experiments that yielded them were originally designed in Dubna for 48Ca beams. For its mass, 48Ca has by far the greatest neutron excess of all practically stable nuclei, both quantitative and relative, which correspondingly helps synthesize superheavy nuclei with more neutrons. However, this gain is compensated by decreased likelihood of fusion for high atomic numbers.
While it yet remains to be seen if there are principally more stable isotopes, there has not any theoretical, let alone practical, suggestion this could be the case. In a 2012 calculation from Dubna, it was suggested that the half-lives of all dubnium isotopes, synthesized or not, would not significantly exceed a day.[b]
According to the periodic law, dubnium should belong to group 5, under vanadium, niobium, and tantalum. Several studies investigated the properties of element 105 and found a general agreement with the predictions from the periodic law. Significant deviations may nevertheless occur, due to relativistic effects, which dramatically change physical properties on both atomic and macroscopic scales. (Relativistic effects arise when an object moves on velocities comparable to the speed of light; in heavy atoms, the quickly moving objects are electrons revolving around the nucleus.) These properties have remained challenging to measure: studies have only been performed on single atoms, and generally confirm the assignment of dubnium to the position under tantalum in the periodic table.
Atomic and physicalEdit
A direct relativistic effect is that as atomic numbers of elements increase, the innermost electrons begin to revolve faster around the nucleus as a result of the increase of the electromagnetic attraction between an electron and a nucleus. Similar effects have been found for s orbitals (and p1/2 ones, though this is not quite applicable for dubnium): for example, the 7s orbital is contracted by 25% in size and stabilized by 2.6 eV.
A more indirect effect would be that the contracted s and p1/2 orbitals shield (take on themselves) the charge of the nucleus more effectively, leaving even less for the outer d and f electrons, which therefore move on larger orbitals. Dubnium is greatly affected by this: unlike the previous group 5 members, its 7s electrons are more difficult to extract from an atom than the 6d electrons, though these energy levels remain close to each other.
A third effect is the spin–orbit (SO) interaction, particularly the SO splitting, which in application to dubnium splits the 6d subshell—the azimuthal quantum number ℓ for a d shell is 2—into two subshells, with four of the ten orbitals having their ℓ lowered to 3/2 and six raised to 5/2. While all ten energy levels are actually raised (lowered in absolute values), making them less stable energetically, four of them are more stable than the other six. (The three 6d electrons normally assume the energy levels of lowest energy, 6d3/2.)
While the remaining valence electrons in a singly ionized dubnium ion (Db+) organize themselves in a 6d27s2 configuration, the doubly (Db2+) or triply (Db3+) ionized atoms eliminate the 7s electrons, the opposite order to that of its lighter homologs. Despite the changes, however, dubnium is still expected to use five electrons as its valence electrons; 7p energy levels have not been shown to influence dubnium and its properties. As the 6d orbitals are further destabilized compared to 5d ones of tantalum, and Db3+ is expected to have two d, rather than s, electrons remaining, the resulting oxidation state is expected to be unstable and even rarer than that of tantalum. The ionization potential of dubnium in its maximum oxidation state should be slightly lower than that of tantalum and the ionic radius of dubnium should increase compared to tantalum; this has a significant effect on dubnium's chemistry (see below).
Dubnium atoms, when in quantity and in a free state, should arrange themselves in a body-centered cubic configuration, like the previous group 5 elements. The predicted density of dubnium is 29 g/cm3.
The simplest case for computational chemistry is the gas-phase chemistry, in which a substance is treated as if it was a gas to eliminate the necessity of taking interactions between molecules in account. Research by multiple authors has been undertaken on the expected highest chloride of dubnium, DbCl5: it has been calculated to be consistent with the periodic laws by exhibiting properties of a compound of a d-block element. For example, the molecular orbital levels indicate dubnium uses three 6d electron levels as expected. One property DbCl5 is expected to show is its increased (compared to TaCl5) covalence: a decrease in the effective charge on an atom and an increase in the overlap population (between orbitals of dubnium and chlorine).
Calculations for solution chemistry indicate that again, the maximum oxidation state, +5, will be more stable than that of niobium and tantalum, and the +3 state will be less stable than those of niobium and tantalum. Hydrolysis of cations of +5 is expected to continue to decrease within group 5; however, it is still expected to be quite rapid. Complexation of dubnium is expected to follow group 5 trends in its richness. Calculations for hydroxo-chlorido- complexes have been conducted; they show reversal in the trends of complex formation and extraction of group 5 elements, with dubnium being more prone to do so than tantalum.
Early experimental results of studies of the chemistry of dubnium date back to 1974 and 1976. Dubna researchers used a thermochromatographic system, and concluded that the volatility of dubnium bromide was less than that of niobium bromide and about the same as that of hafnium bromide. It is not certain, however, that the detected fission products confirmed that the parent was indeed element 105. This may imply that the new element behaved more like hafnium than niobium.
Further studies of the chemistry of dubnium were reported over a decade later, in 1988. Studies at Berkeley examined whether the most stable oxidation state of dubnium in aqueous solution is +5. Sorption of dubnium on glass cover slips after fuming twice and washing with concentrated nitric acid was compared with that of tracers of the group 5 elements niobium and tantalum and the group 4 elements zirconium and hafnium produced on‐line under similar conditions. The group 5 elements are known to sorb on glass surfaces while the group 4 elements do not. Dubnium was confirmed as a group 5 member. However, it was surprising that extraction behavior into methyl isobutyl ketone from mixed HNO3/HF solutions differed between dubnium, tantalum, and niobium. Dubnium did not extract and its behavior resembled niobium more closely than tantalum, indicating that details of complexing behavior cannot be predicted based only on simple extrapolations of trends within a group in the periodic table.
This prompted further exploration of the chemical behavior of complexes of dubnium. Thousands of repetitive chromatographic experiments were performed jointly in various labs between 1988 and 1993. All group 5 elements and protactinium were extracted from concentrated hydrochloric acid; at lower concentrations of HCl, small amounts of HF were added to start selective re-extraction. Dubnium showed a behavior unlike tantalum at concentrations of HCl below 12 M, following the behavior of niobium and the pseudohomolog protactinium. Because of this similarity to these two elements, the research suggested that the formed complex was either DbOX−
4 or [Db(OH)
. After extraction experiments of Db from HBr into diisobutyl carbinol (2,6-dimethylheptan-4-ol), a specific extractant for protactinium, with subsequent elutions with mixed HCl/HF and HCl, the obtained extraction sequence Pa > Nb > Db was determined. It was explained as an increasing tendency to form non‐extractable complexes of multiple negative charges. Further experiments in 1992 confirmed the stability of the +5 state: Db(V) was shown to be extractable from cation‐exchange columns with α‐hydroxyisobutyrate, similarly to other group 5 elements and protactinium; Db(III) and Db(IV) were not. In 1998 and 1999, new predictions yielded the sequence Pa >> Nb ≥ Db > Ta for extraction from halide solutions, which was later confirmed.
The first isothermal gas chromatography experiments were performed in 1992 with 262Db (t1/2 = 35 s). The volatilities for niobium and tantalum were similar within error limits, but dubnium appeared to be significantly less volatile. It was postulated that traces of oxygen in the system might have led to formation of DbOBr
3, which was predicted to be less volatile than DbBr
5. Later experiments in 1996 showed that group 5 chlorides were more volatile than the corresponding bromides, with the exception of tantalum, presumably due to formation of TaOCl
3. Later volatility studies of chlorides of dubnium and niobium as a function of controlled partial pressures of oxygen showed that formation of oxychlorides and general volatility are dependent on concentrations of oxygen. The oxychlorides were shown to be less volatile than the chlorides.
In 2004–05, researchers from Dubna and Livermore identified dubnium as a fivefold alpha decay product of the newly created element 115 which they found to be stable enough to allow chemical experiments a year earlier. In the 2004 experiment, a thin layer was removed from the surface of the target (with dubnium on it), dissolved in aqua regia with tracers and lanthanum carrier, from which precipitated various +3, +4, and +5 species on adding NH
4OH. The precipitate was washed and dissolved in HCl, in which it was converted to nitrate form then dried on a film and counted. It mostly contained a +5 species, which was immediately assigned to dubnium, but also a +4 species, and the team decided that additional chemical separation was needed. In 2005, the experiment was repeated, with the final product being hydroxide rather than nitrate precipitate, which was processed further at either Livermore (based on reverse phase chromatography) or Dubna (based on anion exchange chromatography). The +5 species was effectively isolated; dubnium in that experiment appeared three times in Ta-only fractions and not even once in Nb-only fractions. However, it was noted that these experiments were insufficient to draw conclusions about the general chemical profile of dubnium.
In 2009, another anion-exchange experiment was conducted in Japan at the JAEA tandem accelerator. Dubnium was processed to a nitric acid/hydrofluoric acid solution, with concentrations at which Nb forms NbOF−
4 and Ta forms TaF−
6. Dubnium's behavior was close to that of Nb but not Ta; thus, it was deduced that it formed DbOF−
4. It was concluded that the information available then showed that Db often behaved like Nb, sometimes like Pa, but rarely as Ta.
- While the modern theory of the atomic nucleus does not suggest a long-lived isotope of dubnium, claims were raised in the past that unknown isotopes of superheavy elements actually existed primordially on the Earth: for example, such a claim was raised for 267108 of half-life of 400 to 500 million years in 1963 or 292122 of half-life of over 100 million years in 2009; however, neither claim gained acceptance.
- While this does not conform with the current experimental value of 28+11
−4 hours for 268Db, it must be noted that the statistical law of large numbers, on which relies the regular determination of half-lives, cannot be directly applied due to a very limited number of experiments (decays). The range of uncertainty is an indication of that the half-life period lies within this range with the probability of the standard figure of 95%, which has been arbitrarily chosen to represent the probability of a true event.
- Hoffman, Darleane C.; Lee, Diana M.; Pershina, Valeria (2006). "Transactinides and the future elements". In Morss; Edelstein, Norman M.; Fuger, Jean. The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands: Springer Science+Business Media. ISBN 1-4020-3555-1.
- Östlin, A.; Vitos, L. (2011). "First-principles calculation of the structural stability of 6d transition metals". Physical Review B. 84 (11). Bibcode:2011PhRvB..84k3104O. doi:10.1103/PhysRevB.84.113104.
- Fricke, Burkhard (1975). "Superheavy elements: a prediction of their chemical and physical properties". Recent Impact of Physics on Inorganic Chemistry. 21: 89–144. doi:10.1007/BFb0116498. Retrieved 4 October 2013.
- Chemical Data. Dubnium - Db, Royal Chemical Society
- Münzenberg, G.; Gupta, M. (2011). "Production and Identification of Transactinide Elements": 877. doi:10.1007/978-1-4419-0720-2_19.
- Six New Isotopes of the Superheavy Elements Discovered. Berkeley Lab. News center. October 26, 2010
- Oganessian, Yuri Ts.; Abdullin, F. Sh.; Bailey, P. D.; et al. (2010-04-09). "Synthesis of a New Element with Atomic Number Z=117". Physical Review Letters. American Physical Society. 104 (142502). Bibcode:2010PhRvL.104n2502O. PMID 20481935. doi:10.1103/PhysRevLett.104.142502.
- Choppin, Gregory R.; Liljenzin, Jan-Olov; Rydberg, Jan (2002). Radiochemistry and Nuclear Chemistry. Elsevier. p. 416. ISBN 978-0-7506-7463-8.
- Hoffman, Darleane C. (1996). The Transuranium Elements: From Neptunium and Plutonium to Element 112 (PDF) (Report). Lawrence Livermore National Laboratory.
- Zvara, Ivo J. (2003). "Dubnium". Chemical and Engineering News. 81 (36).
- "Discovery of the Transfermium elements" (PDF). Pure and Applied Chemistry. 65 (8). 1993. Retrieved 2016-09-07.
- Fontani, Marco; Costa, Mariagrazia; Orna, Mary Virginia (October 1, 2014). The Lost Elements: The Periodic Table's Shadow Side. Oxford University Press. p. 386. ISBN 978-0-19-938335-1.
- Hoffmann, Klaus (1987). Можно ли сделать золото? Мошенники, обманщики и ученые в истории химических элементов [Can one make gold? Swindlers, deceivers and scientists from the history of the chemical elements] (in Russian). Nauka. pp. 180–181. Translation from Hoffmann, Klaus (1979). Kann man Gold machen? Gauner, Gaukler und Gelehrte. Aus der Geschichte der chemischen Elemente [Can one make gold? Swindlers, deceivers and scientists. From the history of the chemical elements] (in German). Urania.
- "Responses on the report 'Discovery of the Transfermium elements' followed by reply to the responses by Transfermium Working Group" (PDF). Pure and Applied Chemistry. 65 (8): 1815–1824. 1993. Retrieved 2016-09-07.
- "An Attempt to Solve the Controversies Over Elements 104 and 105: A Meeting in Russia, 23 September 1975". Bulletin of the American Physical Society. Volume 62, Number 1. 2017-01-28.
- Öhrström, Lars; Holden, Norman E. (2016). "The Three-letter Element Symbols:". Chemistry International. 38 (2). ISSN 1365-2192. doi:10.1515/ci-2016-0204.
- "Names and symbols of transfermium elements (IUPAC Recommendations 1994)" (PDF). Pure and Applied Chemistry. 66 (12): 2419–2421. 1994. Retrieved 2016-09-07.
- "Seaborgium Name for Element 106 Disputed". www2.lbl.gov. Retrieved 2016-09-07.
- Bera, Jitendra K. (1999). "Names of the Heavier Elements". Resonance. 4 (3).
- Hoffman, D. C.; Ghiorso, A.; Seaborg, Glenn T. (2000). The Transuranium People: The Inside Story. Imperial College Press. pp. 369–399. ISBN 978-1-86094-087-3.
- "Names and symbols of transfermium elements (IUPAC Recommendations 1997)". Pure and Applied Chemistry. 69 (12): 2471. 1997. doi:10.1351/pac199769122471.
- Karpov, A. V.; Zagrebaev, V. I.; Palenzuela, Y. Martinez; Greiner, Walter (2013-01-01). Greiner, Walter, ed. Exciting Interdisciplinary Physics. FIAS Interdisciplinary Science Series. Springer International Publishing. pp. 69–79. ISBN 978-3-319-00046-6. doi:10.1007/978-3-319-00047-3_6.
- Audi, G.; Kondev, F. G.; Wang, M.; Pfeiffer, B.; Sun, X.; Blachot, J.; MacCormick, M. (2012). "The NUBASE2012 evaluation of nuclear properties" (PDF). Chinese Physics C. 36 (12): 1157–1286. Bibcode:2012ChPhC..36....1A. doi:10.1088/1674-1137/36/12/001.
- Emsley, John (2011). Nature's Building Blocks: An A-Z Guide to the Elements (New ed.). New York, NY: Oxford University Press. pp. 215–217. ISBN 978-0-19-960563-7.
- Marinov, A.; Rodushkin, I.; Kolb, D.; Pape, A.; Kashiv, Y.; Brandt, R.; Gentry, R.V.; Miller, H.W. (2008). Evidence for a long-lived superheavy nucleus with atomic mass number A=292 and atomic number Z=~122 in natural Th. Bibcode:2010IJMPE..19..131M. arXiv: . doi:10.1142/S0218301310014662.
- Karpov, A. V.; Zagrebaev, V. I.; Palenzuela, Y. Martinez; Greiner, Walter (2013). "Superheavy Nuclei: Decay and Stability". Exciting Interdisciplinary Physics. FIAS Interdisciplinary Science Series. p. 69. ISBN 978-3-319-00046-6. doi:10.1007/978-3-319-00047-3_6.
- Botvina, Alexander; Mishustin, Igor; Zagrebaev, Valery; Greiner, Walter (2010-10-01). "Possibility of synthesizing superheavy elements in nuclear explosions". International Journal of Modern Physics E. 19 (10): 2063–2075. Bibcode:2010IJMPE..19.2063B. ISSN 0218-3013. arXiv: . doi:10.1142/S0218301310016521.
- Stoyer, N. J.; Landrum, J. H.; Wilk, P. A.; Moody, K. J.; Kenneally, J. M.; Shaughnessy, D. A.; Stoyer, M. A.; Wild, J. F.; Lougheed, R. W. (2007-05-01). "Chemical Identification of a Long-Lived Isotope of Dubnium, a Descendant of Element 115". Nuclear Physics A. Proceedings of the Ninth International Conference on Nucleus-Nucleus Collisions. 787 (1): 388–395. Bibcode:2007NuPhA.787..388S. doi:10.1016/j.nuclphysa.2006.12.060.
- Oganessian, Yu Ts; Abdullin, F. Sh.; Bailey, P. D.; Benker, D. E.; Bennett, M. E.; Dmitriev, S. N.; Ezold, J. G.; Hamilton, J. H.; Henderson, R. A. (2010-04-09). "Synthesis of a New Element with Atomic Number Z=117". Physical Review Letters. 104 (14): 142502. Bibcode:2010PhRvL.104n2502O. ISSN 1079-7114. PMID 20481935. doi:10.1103/PhysRevLett.104.142502.
- Khuyagbaatar, J.; Yakushev, A.; Düllmann, Ch. E.; Ackermann, D.; Andersson, L.-L.; Asai, M.; Block, M.; Boll, R. A.; Brand, H. (2014-05-01). "48Ca + 249Bk Fusion Reaction Leading to Element Z = 117: Long-Lived α-Decaying 270Db and Discovery of 266Lr". Physical Review Letters. 112 (17): 172501. Bibcode:2014PhRvL.112q2501K. PMID 24836239. doi:10.1103/PhysRevLett.112.172501.
- Wills, Stewart; Berger, Lee (2011). "Science Magazine Podcast. Transcript, 9 September 2011" (PDF). Science. Retrieved 2016-10-12.
- Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
- Stoyer, N. J.; Landrum, J. H.; Wilk, P. A.; et al. (2006). Chemical Identification of a Long-Lived Isotope of Dubnium, a Descendant of Element 115 (PDF) (Report). IX International Conference on Nucleus Nucleus Collisions.
- Nagame, Yuichiro; Kratz, Jens Volker; Schädel, Matthias (2016-01-01). "Chemical properties of rutherfordium (Rf) and dubnium (Db) in the aqueous phase". EPJ Web of Conferences. 131: 07007. ISSN 2100-014X. doi:10.1051/epjconf/201613107007.