Dubnium (105Db) is a synthetic element, thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 261Db in 1968. Thirteen radioisotopes are known, ranging from 255Db to 270Db (except 264Db, 265Db, and 269Db), along with one isomer (257mDb); two more isomers have been reported but are unconfirmed. The longest-lived known isotope is 268Db with a half-life of 16 hours.
List of isotopes
Nucleosynthesis history
Cold fusion 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. 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 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. 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?,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.
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.
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.
206Pb(51V,xn)257−xDb (x=2) This reaction was studied in 2024; 255Db was observed.
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.
Hot fusion 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.
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 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.
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