Isotopes of bohrium
Encyclopedia
Bohrium
(Bh) 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 262Bh in 1981. There are 12 known isotopes ranging from 260Bh to 275Bh, and 1 isomer
, 262mBh. The longest-lived isotope is 274Bh with a half-life
of 0.9 minutes.
at Dubna
using this cold fusion reaction. Analysis was by detection of spontaneous fission
(SF). They discovered two SF activities, one with a 1-2 ms half-life and one with a 5 s activity. Based on the results of other cold fusion reactions, they concluded that they were due to 261Bh and 257Db respectively. However, later evidence gave a much lower SF branching for 261Bh reducing confidence in this assignment. The assignment of the dubnium activity was later changed to 258Db, presuming that the decay of bohrium was missed. The 2 ms SF activity was assigned to 258Rf resulting from the 33% EC
branch.
The GSI team studied the reaction in 1981 in their discovery experiments. Five atoms of 262Bh were detected using the method of correlation of genetic parent-daughter decays.
In 1987, an internal report from Dubna indicated that the team had been able to detect the spontaneous fission
of 261Bh directly.
The GSI team further studied the reaction in 1989 and discovered the new isotope 261Bh during the measurement of the 1n and 2n excitation functions but were unable to detect an SF branching for 261Bh.
They continued their study in 2003 using newly developed bismuth(III) fluoride (BiF3) targets, used to provide further data on the decay data for262Bh and the daughter 258Db.
The 1n excitation function was remeasured in 2005 by the team at LBNL after some doubt about the accuracy of previous data. They observed 18 atoms of 262Bh and 3 atoms of 261Bh and confirmed the two isomers of 262Bh.
In 1983, they repeated the experiment using a new technique: measurement of alpha decay from a descendant using chemical separation. The team were able to detect the alpha decay from a descendant of the 1n evaporation channel, providing some evidence for the formation of element 107 nuclei.
This reaction was later studied in detail using modern techniques by the team at LBNL. In 2005 they measured 33 decays of 262Bh and 2 atoms of261Bh, providing a 1n excitation function and some spectroscopic data of both 262Bh isomers. The 2n excitation function was further studied in a 2006 repeat of the reaction.
The team found that this reaction had a higher 1n cross section than the corresponding reaction with a Bi-209 target, contrary to expectations. Further research is required to understand the reasons.
, possibly from264Bh.
and gather more data on 266Bh. In two series of experiments, the team has measured partial excitation functions of the 3n,4n and 5n evaporation channels.
. The decay of 266Bh by the emission of 9.04 MeV alpha particles was confirmed, although lines at 9.29 MeV (see below) and 9.77 MeV (see ununtrium
) were not.
from nuclei of bohrium.
More recently, hot fusions pathways to bohrium have been re-investigated in order to allow for the synthesis of more long-lived, neutron
rich isotopes to allow a first chemical study of bohrium. In 1999, the team at LBNL claimed the discovery of long-lived 267Bh (5 atoms) and 266Bh (1 atom). In the following year, the same team attempted to confirm the synthesis and decay of 266Bh, but were unable to do so. Current research has been unable to confirm the 9.29 MeV decay claimed and the synthesis of 266Bh by this reaction is not accepted at this moment in time.
The team at the Paul Scherrer Institute (PSI) in Bern, Switzerland later synthesized 6 atoms of 267Bh in the first definitive study of the chemistry of bohrium (see below).
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...
(Bh) 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 262Bh in 1981. There are 12 known isotopes ranging from 260Bh to 275Bh, and 1 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...
, 262mBh. The longest-lived isotope is 274Bh 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 0.9 minutes.
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: 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 | |||||||
| 260Bh | 107 | 153 | 260.12197(62)# | 0.3# ms | 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... |
256Db | |
| 261Bh | 107 | 154 | 261.12166(25)# | 13(4) ms [12(+5-3) ms] |
α (95%?) | 257Db | |
| 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... (5%?) |
(various) | ||||||
| 262Bh | 107 | 155 | 262.12289(37)# | 290(160) ms | α (80%) | 258Db | |
| SF (20%) | (various) | ||||||
| 262mBh | 300(60) keV | 14(4) ms | α (70%) | 258Db | |||
| SF (30%) | (various) | ||||||
| 264BhNot directly synthesized, occurs in 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 272Rg |
107 | 157 | 264.1246(3)# | 1.3(5) s [0.44(+60-16) s] |
α | 260Db | |
| SF (rare) | (various) | ||||||
| 265Bh | 107 | 158 | 265.12515(41)# | 0.9(+7-3) s | α | 261Db | |
| 266BhNot directly synthesized, occurs in decay chain of 278Uut | 107 | 159 | 266.12694(22)# | 5(3) s | α | 262Db | |
| 267Bh | 107 | 160 | 267.12765(28)# | 22(10) s [17(+14-6) s] |
α | 263Db | |
| 270BhNot directly synthesized, occurs in decay chain of 282Uut | 107 | 163 | 270.13362(50)# | 30# s | α | 266Db | |
| 271BhNot directly synthesized, occurs in decay chain of 287Uup | 107 | 164 | 271.13518(60)# | 40# s | α | 267Db | |
| 272BhNot directly synthesized, occurs in decay chain of 288Uup | 107 | 165 | 272.13803(65)# | 10(+12-4) s | α | 268Db | |
| 274BhNot directly synthesized, occurs in decay chain of 294Uus | 107 | 167 | 274.14244(84)# | 0.9 min | α | 270Db | |
Cold fusion
This section deals with the synthesis of nuclei of bohrium 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(54Cr,xn)263-xBh (x=1,2)
The synthesis of bohrium was first attempted in 1976 by scientists at the Joint Institute for Nuclear ResearchJoint Institute for Nuclear Research
The Joint Institute for Nuclear Research, JINR , in Dubna, Moscow Oblast , Russia, is an international research centre for nuclear sciences, with 5500 staff members, 1200 researchers including 1000 Ph.D.s from eighteen member states The Joint Institute for Nuclear Research, JINR , in Dubna, Moscow...
at Dubna
Dubna
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...
using this cold fusion reaction. Analysis was by detection of 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). They discovered two SF activities, one with a 1-2 ms half-life and one with a 5 s activity. Based on the results of other cold fusion reactions, they concluded that they were due to 261Bh and 257Db respectively. However, later evidence gave a much lower SF branching for 261Bh reducing confidence in this assignment. The assignment of the dubnium activity was later changed to 258Db, presuming that the decay of bohrium was missed. The 2 ms SF activity was assigned to 258Rf resulting from the 33% EC
Electron capture
Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...
branch.
The GSI team studied the reaction in 1981 in their discovery experiments. Five atoms of 262Bh were detected using the method of correlation of genetic parent-daughter decays.
In 1987, an internal report from Dubna indicated that the team had been able to detect the 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...
of 261Bh directly.
The GSI team further studied the reaction in 1989 and discovered the new isotope 261Bh during the measurement of the 1n and 2n excitation functions but were unable to detect an SF branching for 261Bh.
They continued their study in 2003 using newly developed bismuth(III) fluoride (BiF3) targets, used to provide further data on the decay data for262Bh and the daughter 258Db.
The 1n excitation function was remeasured in 2005 by the team at LBNL after some doubt about the accuracy of previous data. They observed 18 atoms of 262Bh and 3 atoms of 261Bh and confirmed the two isomers of 262Bh.
209Bi(53Cr,xn)262-xBh
The team at Dubna studied this reaction in 1976 in order to assist in their assignments of the SF activities from their experiments with a Cr-54 beam. They were unable to detect any such activity, indicating the formation of different isotopes decaying primarily by alpha decay.209Bi(52Cr,xn)261-xBh (x=1)
This reaction was studied for the first time in 2007 by the team at LBNL to search for the lightest bohrium isotope 260Bh. The team successfully detected 8 atoms of 260Bh decaying by correlated 10.16 MeV alpha particle emission to 256Db. The alpha decay energy indicates the continued stabilising effect of the N=152 closed shell.208Pb(55Mn,xn)263-xBh (x=1)
The team at Dubna also studied this reaction in 1976 as part of their newly established cold fusion approach to new elements. As for the reaction using a Bi-209 target, they observed the same SF activities and assigned them to 261107 and 257105. Later evidence indicated that these should be reassigned to258105 and 258104 (see above).In 1983, they repeated the experiment using a new technique: measurement of alpha decay from a descendant using chemical separation. The team were able to detect the alpha decay from a descendant of the 1n evaporation channel, providing some evidence for the formation of element 107 nuclei.
This reaction was later studied in detail using modern techniques by the team at LBNL. In 2005 they measured 33 decays of 262Bh and 2 atoms of261Bh, providing a 1n excitation function and some spectroscopic data of both 262Bh isomers. The 2n excitation function was further studied in a 2006 repeat of the reaction.
The team found that this reaction had a higher 1n cross section than the corresponding reaction with a Bi-209 target, contrary to expectations. Further research is required to understand the reasons.
Hot fusion
This section deals with the synthesis of nuclei of bohrium 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.238Am(31P,xn)269-xBh (x=5?)
This reaction was first studied in 2006 at the LBNL as part of their systematic study of fusion reactions using 238U targets. Results have not been published but preliminary results appear to indicate the observation of spontaneous fissionSpontaneous 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...
, possibly from264Bh.
243Am(26Mg,xn)269-xBh (x=3,4,5)
Recently, the team at the Institute of Modern Physics (IMP), Lanzhou, have studied the nuclear reaction between americium-243 and magnesium-26 ions in order to synthesise the new isotope 265Bhand gather more data on 266Bh. In two series of experiments, the team has measured partial excitation functions of the 3n,4n and 5n evaporation channels.
248Cm(23Na,xn)271-xBh (x=4,5)
This reaction was studied for the first time in 2008 by the team at RIKEN, Japan, in order to study the decay properties of 266Bh, which is a decay product in their claimed decay chains of ununtriumUnuntrium
Ununtrium is the temporary name of a synthetic element with the temporary symbol Uut and atomic number 113.It is placed as the heaviest member of the group 13 elements although a sufficiently stable isotope is not known at this time that would allow chemical experiments to confirm its position...
. The decay of 266Bh by the emission of 9.04 MeV alpha particles was confirmed, although lines at 9.29 MeV (see below) and 9.77 MeV (see ununtrium
Ununtrium
Ununtrium is the temporary name of a synthetic element with the temporary symbol Uut and atomic number 113.It is placed as the heaviest member of the group 13 elements although a sufficiently stable isotope is not known at this time that would allow chemical experiments to confirm its position...
) were not.
249Bk(22Ne,xn)271-xBh (x=4)
The first attempts to synthesize bohrium by hot fusion pathways were performed in 1979 by the team at Dubna. The reaction was repeated in 1983. In both cases, they were unable to detect any spontaneous fissionSpontaneous 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...
from nuclei of bohrium.
More recently, hot fusions pathways to bohrium have been re-investigated in order to allow for the synthesis of more long-lived, neutron
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...
rich isotopes to allow a first chemical study of bohrium. In 1999, the team at LBNL claimed the discovery of long-lived 267Bh (5 atoms) and 266Bh (1 atom). In the following year, the same team attempted to confirm the synthesis and decay of 266Bh, but were unable to do so. Current research has been unable to confirm the 9.29 MeV decay claimed and the synthesis of 266Bh by this reaction is not accepted at this moment in time.
The team at the Paul Scherrer Institute (PSI) in Bern, Switzerland later synthesized 6 atoms of 267Bh in the first definitive study of the chemistry of bohrium (see below).
254Es(16O,xn)270-xBh
As an alternative means of producing long-lived bohrium isotopes suitable for a chemical study, the synthesis of 267Bh and 266Bh were attempted in 1995 by the team at GSI using the highly asymmetric reaction using an einsteinium-254 target. They were unable to detect any product atoms.As decay products
Isotopes of bohrium have also been detected in the decay of heavier elements. Observations to date are shown in the table below:| Evaporation Residue | Observed Bh isotope |
|---|---|
| 294Uus | 274Bh |
| 288Uup | 272Bh |
| 287Uup | 271Bh |
| 282Uut | 270Bh |
| 278Uut | 266Bh |
| 272Rg | 264Bh |
| 266Mt | 262Bh |
List of discovered isotopes
| Isotope | Year discovered | discovery reaction |
|---|---|---|
| 260Bh | 2007 | 209Bi(52Cr,n) |
| 261Bh | 1989 | 209Bi(54Cr,2n) |
| 262Bhg,m | 1981 | 209Bi(54Cr,n) |
| 263Bh | unknown | |
| 264Bh | 1994 | 209Bi(64Ni,n) |
| 265Bh | 2004 | 243Am(26Mg,4n) |
| 266Bh | 2004 | 209Bi(70Zn,n) |
| 267Bh | 2000 | 249Bk(22Ne,4n) |
| 268Bh | unknown | |
| 269Bh | unknown | |
| 270Bh | 2006 | 237Np(48Ca,3n) |
| 271Bh | unknown | |
| 272Bh | 2003 | 243Am(48Ca,3n) |
| 273Bh | unknown | |
| 274Bh | 2009 | 249Bk(48Ca,3n) |
262Bh
The only confirmed example of isomerism in bohrium is for the isotope 262Bh. Direct production populates two states, a ground state and an isomeric state. The ground state is confirmed as decaying by alpha emission with alpha lines at 10.08,9.82 and 9.76 MeV with a revised half-life of 84 ms. The excited state decays by alpha emission with lines at 10.37 and 10.24 MeV with a revised half-life of 9.6 ms.Cold Fusion
The table below provides cross-sections and excitation energies for cold fusion reactions producing bohrium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.| Projectile | Target | CN | 1n | 2n | 3n |
|---|---|---|---|---|---|
| 55Mn | 208Pb | 263Bh | 590 pb, 14.1 MeV | ~35 pb | |
| 54Cr | 209Bi | 263Bh | 510 pb, 15.8 MeV | ~50 pb | |
| 52Cr | 209Bi | 261Bh | 59 pb, 15.0 MeV |
Hot Fusion
The table below provides cross-sections and excitation energies for hot fusion reactions producing bohrium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.| Projectile | Target | CN | 3n | 4n | 5n |
|---|---|---|---|---|---|
| 26Mg | 243Am | 271Bh | + | + | + |
| 22Ne | 249Bk | 271Bh | ~96 pb | + |