Isotopes of dubnium
Encyclopedia
Dubnium
(Db) is an artificial element, and thus a standard atomic mass
cannot be given. Like all artificial elements, it has no stable isotope
s. The first isotope
to be synthesized was 261Db in 1968. There are 12 known radioisotopes from 256Db to 270Db, and 1-3 isomer
s. The longest-lived isotope is 268Db with a half-life
of 32 hours.
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?)
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 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.
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 to258Db.
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 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 [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 isotope261Db.
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.
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 daughterlawrencium
.
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).
carried out a series of supportive experiments in their quest for the discovery of Bohrium
. 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.
Dubnium
The Soviet team proposed the name nielsbohrium in honor of the Danish nuclear physicist Niels Bohr. The American team proposed that the new element should be named hahnium , in honor of the late German chemist Otto Hahn...
(Db) is an artificial element, and thus a standard atomic mass
Atomic mass
The atomic mass is the mass of a specific isotope, most often expressed in unified atomic mass units. The atomic mass is the total mass of protons, neutrons and electrons in a single atom....
cannot be given. Like all artificial elements, it has no stable isotope
Stable isotope
Stable isotopes are chemical isotopes that may or may not be radioactive, but if radioactive, have half-lives too long to be measured.Only 90 nuclides from the first 40 elements are energetically stable to any kind of decay save proton decay, in theory...
s. The first isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
to be synthesized was 261Db in 1968. There are 12 known radioisotopes from 256Db to 270Db, and 1-3 isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...
s. The longest-lived isotope is 268Db with a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 32 hours.
Table
| nuclide symbol |
Z(p Proton The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number.... ) |
N(n Neutron The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of... ) |
isotopic mass (u) |
half-life | decay mode(s)Abbreviations: EC: Electron capture Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino... IT: Isomeric transition Isomeric transition An isomeric transition is a radioactive decay process that involves emission of a gamma ray from an atom where the nucleus is in an excited metastable state, referred to in its excited state, as a nuclear isomer.... SF: Spontaneous fission Spontaneous fission Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses... |
daughter isotope(s) |
nuclear spin |
|---|---|---|---|---|---|---|---|
| excitation energy | |||||||
| 256Db | 105 | 151 | 256.10813(31)# | 1.9(4) s [1.6(+5-3) s] |
α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... (~64%) |
252Lr | |
| SF Spontaneous fission Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses... (~0.02%) |
(various) | ||||||
| β+ Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... (~36%) |
256Rf | ||||||
| 257Db | 105 | 152 | 257.10772(24)# | 1.53(17) s [1.50(+19-15) s] |
α (82%) | 253Lr | (9/2+) |
| SF (17%) | (various) | ||||||
| β+ (1%) | 257Rf | ||||||
| 257mDb | 100(100)# keV | 790(130) ms [0.76(+15-11) s] |
(1/2-) | ||||
| 258Db | 105 | 153 | 258.10923(37)# | 4.5(6) s | α (64%) | 254Lr | |
| β+ (36%) | 258Rf | ||||||
| SF (1%) | (various) | ||||||
| 258mDbExistence of this isomer is unconfirmed | 60(100)# keV | 20(10) s | EC Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino... |
258Rf | |||
| IT Isomeric transition An isomeric transition is a radioactive decay process that involves emission of a gamma ray from an atom where the nucleus is in an excited metastable state, referred to in its excited state, as a nuclear isomer.... (rare) |
258Db | ||||||
| 259Db | 105 | 154 | 259.10961(23)# | 0.51(16) s | α | 255Lr | |
| 260Db | 105 | 155 | 260.11130(25)# | 1.52(13) s | α (88%) | 256Lr | |
| SF (9.6%) | (various) | ||||||
| β+ (2%) | 260Rf | ||||||
| 260mDb | 19 s | ||||||
| 261Db | 105 | 156 | 261.11206(25)# | 1.8(4) s | SF (50%) | (various) | |
| α (50%) | 257Lr | ||||||
| 262Db | 105 | 157 | 262.11408(20)# | 35(5) s | SF (71%) | (various) | |
| α (26%) | 258Lr | ||||||
| β+ (3%) | 262Rf | ||||||
| 263Db | 105 | 158 | 263.11499(18)# | 29(9) s [27(+10-7) s] |
SF (50%) | (various) | |
| α (42%) | 259Lr | ||||||
| β+ (8%)Heaviest nuclide known to undergo β+ decay | 263Rf | ||||||
| 266DbNot directly synthesized, occurs in the decay chain Decay chain In nuclear science, the decay chain refers to the radioactive decay of different discrete radioactive decay products as a chained series of transformations... of 282Uut |
105 | 161 | 266.12103(39)# | 20# min | SF | (various) | |
| EC | 266Rf | ||||||
| 267DbNot directly synthesized, occurs in the decay chain of 287Uup | 105 | 162 | 267.12238(50)# | 73(+350-33) min | SF | (various) | |
| 268DbNot directly synthesized, occurs in the decay chain of 288Uup | 105 | 163 | 268.12545(57)# | 32(+11-7) h | SF | (various) | |
| EC Heaviest nuclide known to undergo electron capture Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino... |
268Rf | ||||||
| 270DbNot directly synthesized, occurs in the decay chain of 294Uus | 105 | 165 | 270.13071(77)# | 23.15 h | SF | (various) | |
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
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
(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
Mendelevium
Mendelevium is a synthetic element with the symbol Md and the atomic number 101. A metallic radioactive transuranic element in the actinide series, mendelevium is usually synthesized by bombarding einsteinium with alpha particles. It was named after Dmitri Ivanovich Mendeleev, who created the...
and einsteinium
Einsteinium
Einsteinium is a synthetic element with the symbol Es and atomic number 99. It is the seventh transuranic element, and an actinide.Einsteinium was discovered in the debris of the first hydrogen bomb explosion in 1952, and named after Albert Einstein...
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 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.
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 to258Db.
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 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 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
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
. 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 [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
Rutherfordium
Rutherfordium is a chemical element with symbol Rf and atomic number 104, named in honor of New Zealand physicist Ernest Rutherford. It is a synthetic element and radioactive; the most stable known isotope, 267Rf, has a half-life of approximately 1.3 hours.In the periodic table of the elements,...
).
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 isotope261Db.
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.
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 daughterlawrencium
Lawrencium
Lawrencium is a radioactive synthetic chemical element with the symbol Lr and atomic number 103. In the periodic table of the elements, it is a period 7 d-block element and the last element of actinide series...
.
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).
Decay of heavier nuclides
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 |
|---|---|
| 294Uus | 270Db |
| 288Uup | 268Db |
| 287Uup | 267Db |
| 282Uut | 266Db |
| 267Bh | 263Db |
| 278Uut, 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) |
| 269Db | unknown | |
| 270Db | 2009 | 249Bk(48Ca,3n) |
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.257Db
255Db
In 1983, scientists at DubnaDubna
Dubna is a town in Moscow Oblast, Russia. It has a status of naukograd , being home to the Joint Institute for Nuclear Research, an international nuclear physics research centre and one of the largest scientific foundations in the country. It is also home to MKB Raduga, a defence aerospace company...
carried out a series of supportive experiments in their quest for the discovery of Bohrium
Bohrium
Bohrium is a chemical element with the symbol Bh and atomic number 107 and is the heaviest member of group 7 .It is a synthetic element whose most stable known isotope, 270Bh, has a half-life of 61 seconds...
. In two such experiments, they claimed they had detected a ~1.5 s spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
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.
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 |