Isotopes of dubnium

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 identify²⁵⁸Db, the product from the 1n neutron evaporation channel.^[17] 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.^[18] After a significant upgrade of their facilities in 1993, in 2000 the team measured 120 decays of ²⁵⁷Db, 16 decays of ²⁵⁶Db and decay of²⁵⁸Db 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.^[19] The reaction was used in spectroscopic studies of isotopes of mendelevium and einsteinium in 2003–2004.^[20]

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?,2)

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. In 2005, the team at the University of Jyväskylä studied this reaction. They observed three atoms of ²⁵⁵Db with a cross section of 40 pb.^[7]

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 to²⁵⁸Db. 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.^[21]

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.

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 reaction using a phosphorus-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.^[22]

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.^[23]

²⁴³Am(²²Ne,xn)^265−xDb (x=5)

The first attempts to synthesis 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 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 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.^[24]

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.^[25] 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.^[26]

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.^[27] In 1990, a team led by Kratz at LBNL definitively discovered the new isotope ²⁶³Db in the 4n neutron evaporation channel.^[28] 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).^[29]

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.^[27]

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.^[27]

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.^[30] 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.^[31]

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 ²⁵⁴Es target, they were unable to detect any evaporation residues (ER).

Isotopes of dubnium have also been identified in the decay of heavier elements. Observations to date are summarised in the table below:

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.

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.

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.

• Isotope masses from:
  • M. Wang; G. Audi; A. H. Wapstra; F. G. Kondev; M. MacCormick; X. Xu; et al. (2012). "The AME2012 atomic mass evaluation (II). Tables, graphs and references" (PDF). Chinese Physics C. 36 (12): 1603–2014. Bibcode:2012ChPhC..36....3M. doi:10.1088/1674-1137/36/12/003. hdl:11858/00-001M-0000-0010-23E8-5. S2CID 250839471.
  • 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
• Half-life, spin, and isomer data selected from the following sources.
  • G. Audi; F. G. Kondev; M. Wang; B. Pfeiffer; X. Sun; J. Blachot; M. MacCormick (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. Archived from the original (PDF) on 22 February 2014.
  • 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
  • National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
  • Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.
  • GSI (2011). "Superheavy Element Research at GSI" (PDF). GSI. Retrieved 20 August 2012.