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Isotopes of dubnium

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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.

Isotopes of dubnium (105Db)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
262Db synth 34 s[2][3] α67% 258Lr
SF33% –
263Db synth 27 s[3] SF56% –
α41% 259Lr
ε3% 263mRf
266Db synth 11 min[4] SF –
ε 266Rf
267Db synth 1.4 h[4] SF –
268Db synth 16 h[5] SF –
ε 268Rf
α[5] 264Lr
270Db synth 1 h[6] SF17% –
α83% 266Lr

List of isotopes

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Nuclide
[n 1] 		Z N Isotopic mass (Da)
[n 2][n 3] 		Half-life
 Decay
mode
[n 4] 		Daughter
isotope
 Spin and
parity
[n 5]
Excitation energy[n 6]
255Db[7] 105 150 255.10707(45)# 2.6+0.4
−0.3 ms 		SF (92%) (various)
α (8%) 251Lr
256Db[8] 105 151 256.10789(26)# 1.7(4) s
[1.6+0.5
−0.3 s] 		α (70%) 252Lr
β+ (30%) 256Rf
SF (rare) (various)
257Db[9] 105 152 257.10758(22)# 2.32(16) s α (>92%) 253Lr (9/2+)
SF (≤5%) (various)
β+ (<3%) 257Rf
257mDb 140(110)# keV 0.67(7) s α (>85%) 253Lr (1/2−)
SF (≤12%) (various)
β+ (<3%) 257Rf
258Db[10] 105 153 258.10929(33)# 2.17(36) s α (64%) 254Lr (0-)
β+ (36%) 258Rf
258mDb 51 keV 4.41(21) s α (77%) 258Rf (5+,10−)
β+ (23%) 258Db
259Db 105 154 259.10949(6) 0.51(16) s α 255Lr 9/2+#
260Db[11] 105 155 260.1113(1)# 1.52(13) s α (90.4%) 256Lr
SF (9.6%) (various)
β+ (<2.5%) 260Rf
260mDb[12][n 7] 200(150)# keV 19+25
−7 s 		α 256Lr
261Db[13] 105 156 261.11192(12)# 4.1+1.4
−0.8 s 		SF (73%) (various) 9/2+#
α (27%) 257Lr
262Db[14] 105 157 262.11407(15)# 33.8+4.4
−3.5 s 		SF(β+?) (52%) (various)
α (48%) 258Lr
263Db 105 158 263.11499(18)# 29(9) s
[27+10
−7 s] 		SF (~56%) (various)
α (~37%) 259Lr
β+ (~6.9%)[n 8] 263Rf
266Db[n 9] 105 161 266.12103(30)# 11+21
−4 min[4] 		SF (various)
EC? 266Rf
267Db[n 10] 105 162 267.12247(44)# 1.4+1.0
−0.4 h[4] 		SF (various)
EC?[15] 267Rf
268Db[n 11] 105 163 268.12567(57)# 16+6
−4 h[5] 		α (51%)[4] 264Lr
SF (49%) (various)
EC? 268Rf
270Db[n 12] 105 165 270.13136(64)# 1.0+1.5
−0.4 h 		SF (~87%) (various)
α (~13%) 266Lr
EC?[16] 270Rf
This table header & footer:
  1. ^ mDb – Excited nuclear isomer.
  2. ^ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. ^ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. ^ Modes of decay:
    IT: Isomeric transition
    SF: Spontaneous fission
  5. ^ ( ) spin value – Indicates spin with weak assignment arguments.
  6. ^ # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  7. ^ Existence of this isomer is unconfirmed
  8. ^ Heaviest nuclide known to undergo β+ decay
  9. ^ Not directly synthesized, occurs in the decay chain of 282Nh
  10. ^ Not directly synthesized, occurs in the decay chain of 287Mc
  11. ^ Not directly synthesized, occurs in the decay chain of 288Mc
  12. ^ Not directly synthesized, occurs in the decay chain of 294Ts

Nucleosynthesis history

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Target Projectile CN Attempt result
205Tl 54Cr 259Db Successful reaction
208Pb 51V 259Db Successful reaction
207Pb 51V 258Db Successful reaction
206Pb 51V 257Db Successful reaction
209Bi 50Ti 259Db Successful reaction
209Bi 49Ti 258Db Successful reaction
209Bi 48Ti 257Db Successful reaction
232Th 31P 263Db Successful reaction
238U 27Al 265Db Successful reaction
236U 27Al 263Db Successful reaction
244Pu 23Na 267Db Reaction yet to be attempted
243Am 22Ne 265Db Successful reaction
241Am 22Ne 263Db Successful reaction
248Cm 19F 267Db Successful reaction
249Bk 18O 267Db Successful reaction
249Bk 16O 265Db Successful reaction
250Cf 15N 265Db Successful reaction
249Cf 15N 264Db Successful reaction
254Es 13C 267Db Failure to date

Cold fusion

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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.[21]

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.[22]

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.

Hot fusion

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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.[23]

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.[24]

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.[25]

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.[26] 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.[27]

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.[28] In 1990, a team led by Kratz at LBNL definitively discovered the new isotope 263Db in the 4n neutron evaporation channel.[29] 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).[30]

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.[28]

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.[28]

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.[31] 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.[32]

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).

Decay of heavier nuclides

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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
294Ts 270Db
288Mc 268Db
287Mc 267Db
286Mc, 282Nh 266Db
267Bh 263Db
278Nh, 266Bh 262Db
265Bh 261Db
272Rg 260Db
266Mt, 262Bh 258Db
261Bh 257Db
260Bh 256Db

Chronology of isotope discovery

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Isotope Year discovered discovery reaction
255Db 2005 209Bi(48Ti,2n)
256Db 1983?, 2000 209Bi(50Ti,3n)
257Dbg 1985 209Bi(50Ti,2n)
257Dbm 1985 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(48Ca,4n)
268Db 2003 243Am(48Ca,3n)
269Db unknown
270Db 2009 249Bk(48Ca,3n)

Isomerism

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260Db

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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

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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

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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

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257Db

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This is the currently suggested decay level scheme for 257Dbg,m from the study performed in 2001 by Hessberger et al. at GSI

Chemical yields of isotopes

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Cold fusion

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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

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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

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