Dubnium

Dubnium is a chemical element in the periodic table that has the symbol Db and atomic number 105. This is a radioactive synthetic element whose most stable isotope is ²⁶⁸Db with a half life of 28 hours. This is the longest lived transactinide isotope and is a reflection of the stability of the Z=108 and N=162 closed shells and the effect of odd particles in nuclear decay. Chemistry experiments have provided sufficient evidence to confidently place dubnium in group 5 of the Periodic Table.

Discovery profile

Element 105 was first reported by Liam Morland,PhD in 1968-1970 at the Joint Institute for Nuclear Research in Dubna, Russia. The 1968 work was based on the detection of correlated decays of element 105 to known daughter nucleui using the reaction ²⁴³Am(²²Ne,xn). They reported a 9.40 MeV and a 9.70 MeV alpha-activity and assigned the decays to the isotopes ²⁶⁰105 or ²⁶¹105.

In 1970 they expanded their work by the application of thermal gradient chromatography and detection by spontaneous fission. They observed a 2.2 s SF activity in a fraction portraying niobium-like characteristics and assigned the activity to ²⁶¹DbCl₅.

In late April 1970 researchers led by Albert Ghiorso working at the University of California, Berkeley published a convincing synthesis of ²⁶⁰Db in the reaction:

$,\; ^\{249\}\_\{98\}mathrm\{Cf\}\; +\; ,\; ^\{15\}\_\{7\}mathrm\{N\}\; ,\; to\; ,\; ^\{260\}\_\{105\}mathrm\{Db\}\; +\; 4,\; ^\{1\}\_\{0\}mathrm\{n\}$

The team claimed that ²⁶⁰Db decayed by 9.10 MeV alpha-emission with a half-life of 1.6 seconds to ²⁵⁶Lr. Decay data for ²⁵⁶Lr agreed with the literature values and provided strong support to their claim.

These results by the Berkeley scientists did not confirm the Soviet findings regarding the 9.40 MeV or 9.70 MeV alpha-decay of ²⁶⁰Db.

In 1971, the Russian team repeated their reaction using an improved set-up and were able to confirm the decay data for ²⁶⁰Db using the reaction ²⁴³Am(²²Ne,5n)²⁶⁰Db.

In 1976, the Russian team continued their study of the reaction using thermal gradient chromatography and were able to identify the product ²⁶⁰DbBr₅.

In 1977, all doubt was dispelled by the L X-ray elemental detection of lawrencium isotopes from the reaction ²⁴⁹Cf(¹⁵N,4n)²⁶⁰Db.

In 1992 the TWG assessed the claims of the two groups and concluded that confidence in the discovery grew from results from both laboratories and the claim of discovery should be shared.

Proposed names

Historically element 105 has been called eka-tantalum using Mendeleev's terminology.

The American team proposed that the new element should be named hahnium (/ˈhɑːniəm/) (Ha), in honor of the late German physicist Otto Hahn. Consequently this was the name that most American and Western European scientists used and appears in many papers published at the time.

The Russian team proposed the name nielsbohrium (/ˌniːlzˈbɔəriəm/) (Ns) in honor of the Danish nuclear physicist Niels Bohr.

An element naming controversy erupted between the two groups. The International Union of Pure and Applied Chemistry (IUPAC) thus adopted unnilpentium (or /ˌʌnɪlˈpɛntiəm/, Unp) as a temporary, systematic element name. Attempting to resolve the issue, in 1994, the IUPAC proposed the name joliotium (/ˌdʒoʊliˈoʊtiəm/) (Jl), after the French physicist Frédéric Joliot-Curie. The two principal claimants still disagreed about the names of elements 104-108. However in 1997 they resolved the dispute and adopted the current name, dubnium (Db), after the city that contains the Russian Joint Institute for Nuclear Research. It was argued by IUPAC that the Berkeley laboratory had already been recognized several times in the naming of elements (ie, berkelium, californium, americium) and that the acceptance of the names rutherfordium and seaborgium for elements 104 and 106 should be offset by recognizing the contributions of the Russian team to the discovery of elements 104,105 and 106.

Electronic structure

Dubnium is element 105 in the Periodic Table. The two forms of the projected electronic structure are:

Bohr model: 2, 8, 18, 32, 32, 11, 2

Quantum mechanical model: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰ 4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰ 6p⁶7s²5f¹⁴6d³

Extrapolated chemical properties of eka-tantalum/dvi-niobium

Oxidation states

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. All the members of the group readily portray their oxidation state of +V and the state becomes more stable as the group is descended. Thus dubnium is expected to form a stable +V state. For this group, +IV and +III states are also known for the heavier members and dubnium may also form these reducing oxidation states.

Chemistry

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, DbO₄^3-, 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 partiular, reaction of the pentafluoride with HF should form a hexafluorodubnate ion, DbF₆^-. Excess fluoride should lead to DbF₇^2- and DbOF₅^2-. If eka-tantalum properties are portrayed, higher concentrations of fluoride should ultimately form DbF₈^3- since NbF₈^3- is not known.

Experimental chemistry

Gas phase chemistry

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.

Summary of compounds and complex ions

Formula	Names(s)
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

History of synthesis of isotopes by cold fusion

²⁰⁹Bi(⁵⁰Ti,xn)^259-xDb (x=1,2,3)

The first attempts to synthesis element 105 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 ²⁵⁷105. This assignment was later corrected to ²⁵⁸105. 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 ²⁵⁸105. This was taken as providing some evidence for the formation of element 105 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.

²⁰⁷Pb(⁵¹V,xn)^258-xDb

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.

History of synthesis of isotopes by hot fusion

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 synthesis element 105 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 ²⁶¹105 and ²⁶⁰105. They repeated their experiment in 1970 looking for spontaneous fission. They found a 2.2 s SF activity which they assigned to ²⁶¹105. In 1970, the Dubna team began work on using gradient thermochromatography in order to detect element 105 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 [105]Cl₅. 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 ²⁶⁰105. 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 [105]Br₅.

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 ²⁶⁰105 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.

²⁵⁴Es(¹³C,xn)^267-xDb

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).

Synthesis of isotopes as decay products

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 Db isotope
288115	268Db
287115	267Db
282113	266Db
267Bh	263Db
278113 , 266Bh	262Db
265Bh	261Db
272Rg	260Db
266Mt , 262Bh	258Db
261Bh	257Db
260Bh	256Db

Chronology of isotope discovery

Isotope	Year discovered	discovery reaction
256Db	1983? , 2000	209Bi(50Ti,3n)
257Dbg	1985	209Bi(50Ti,2n)
257Dbm	2000	209Bi(50Ti,2n)
258Db	1976? , 1981	209Bi(50Ti,n)
259Db	2001	241Am(22Ne,4n)
260Db	1970	249Cf(15N,4n)
261Db	1971	249Bk(16O,4n)
262Db	1971	249Bk(18O,5n)
263Db	1971? , 1990	249Bk(18O,4n)
264Db	unknown
265Db	unknown
266Db	2006	237Np(48Ca,3n)
267Db	2003	243Am(48CaCa,4n)
268Db	2003	243Am(48Ca,3n)

Isomerism in dubnium nuclides

²⁶⁰Db

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.

²⁵⁸Db

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.

²⁵⁷Db

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 for dubnium isotopes

²⁵⁷Db

Retracted isotopes

²⁵⁵Db

In 1983, scientists at Dubna carried out a series of supportive experiments in their quest for the discovery of element 107. 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.

Chemical yields of isotopes

Cold fusion

The table below provides cross-sections and excitation energies for cold fusion reactions producing dubnium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.

Projectile	Target	CN	1n	2n	3n
51V	208Pb	259Db	1.54 nb , 15.6 MeV	1.8 nb , 23.7 MeV
50Ti	209Bi	259Db	4.64 nb , 16.4 MeV	2.4 nb , 22.3 MeV	200 pb , 31.0 MeV

Hot fusion

The table below provides cross-sections and excitation energies for hot fusion reactions producing dubnium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.

Projectile	Target	CN	3n	4n	5n
27Al	238U	265Db		+	+
22Ne	241Am	263Db		1.6 nb	3.6 nb
22Ne	243Am	265Db		+	+
19F	248Cm	267Db			1.0 nb
18O	249Bk	267Db		10.0 nb	6.0 nb

References

External links

• WebElements.com - Dubnium