Bohrium (107Bh) is anartificial element. Like all artificial elements, it has nostable isotopes, and astandard atomic weight cannot be given. The firstisotope to be synthesized was262Bh in 1981. There are 11 known isotopes ranging from260Bh to274Bh, and 1isomer,262mBh. The longest-lived isotope is270Bh with ahalf-life of 2.4 minutes, although the unconfirmed278Bh may have an even longer half-life of about 11.5 minutes.
^( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
^# – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
Superheavy elements such as bohrium are produced by bombarding lighter elements inparticle accelerators that inducefusion reactions. Whereas most of the isotopes of bohrium can be synthesized directly this way, some heavier ones have only been observed as decay products of elements with higheratomic numbers.[8]
Depending on the energies involved, the former are separated into "hot" and "cold". In hot fusion reactions, very light, high-energy projectiles are accelerated toward very heavy targets (actinides), giving rise to compound nuclei at high excitation energy (~40–50−MeV) that may either fission or evaporate several (3 to 5) neutrons.[9] In cold fusion reactions, the produced fused nuclei have a relatively low excitation energy (~10–20 MeV), which decreases the probability that these products will undergo fission. As the fused nuclei cool to theground state, they require emission of only one or two neutrons, thus allowing for the generation of more neutron-rich products.[8] The latter is a distinct concept from that of where nuclear fusion claimed to be achieved at room temperature conditions (seecold fusion).[10]
The table below contains various combinations of targets and projectiles which could be used to form compound nuclei withZ = 107.
Before the first successful synthesis of hassium in 1981 by the GSI team, the synthesis of bohrium was first attempted in 1976 by scientists at theJoint Institute for Nuclear Research atDubna using this cold fusion reaction. They detected twospontaneous fission activities, one with ahalf-life of 1–2 ms and one with a half-life of 5 s. Based on the results of other cold fusion reactions, they concluded that they were due to261Bh and257Db respectively. However, later evidence gave a much lower SF branching for261Bh reducing confidence in this assignment. The assignment of the dubnium activity was later changed to258Db, presuming that the decay of bohrium was missed. The 2 ms SF activity was assigned to258Rf resulting from the 33%EC branch. The GSI team studied the reaction in 1981 in their discovery experiments. Five atoms of262Bh were detected using the method of correlation of genetic parent-daughter decays.[11] In 1987, an internal report from Dubna indicated that the team had been able to detect thespontaneous fission of261Bh directly. The GSI team further studied the reaction in 1989 and discovered the new isotope261Bh during the measurement of the 1n and 2n excitation functions but were unable to detect an SF branching for261Bh.[12] They continued their study in 2003 using newly developedbismuth(III) fluoride (BiF3) targets, used to provide further data on the decay data for262Bh and the daughter258Db. The 1n excitation function was remeasured in 2005 by the team at theLawrence Berkeley National Laboratory (LBNL) after some doubt about the accuracy of previous data. They observed 18 atoms of262Bh and 3 atoms of261Bh and confirmed the two isomers of262Bh.[13]
In 2007, the team at LBNL studied the analogous reaction with chromium-52 projectiles for the first time to search for the lightest bohrium isotope260Bh:
The team successfully detected 8 atoms of260Bh decaying byalpha decay to256Db, emitting alpha particles with energy 10.16 MeV. The alpha decay energy indicates the continued stabilizing effect of theN=152 closed shell.[14]
The team at Dubna also studied the reaction between lead-208 targets and manganese-55 projectiles in 1976 as part of their newly established cold fusion approach to new elements:
They observed the same spontaneous fission activities as those observed in the reaction between bismuth-209 and chromium-54 and again assigned them to261Bh and257Db. Later evidence indicated that these should be reassigned to258Db and258Rf (see above). In 1983, they repeated the experiment using a new technique: measurement of alpha decay from adecay product that had been separated out chemically. The team were able to detect the alpha decay from a decay product of262Bh, providing some evidence for the formation of bohrium nuclei. This reaction was later studied in detail using modern techniques by the team at LBNL. In 2005 they measured 33 decays of262Bh and 2 atoms of261Bh, providing anexcitation function for the reaction emitting oneneutron and some spectroscopic data of both262Bh isomers. The excitation function for the reaction emitting two neutrons was further studied in a 2006 repeat of the reaction. The team found that the reaction emitting one neutron had a highercross section than the corresponding reaction with a209Bi target, contrary to expectations. Further research is required to understand the reasons.[15][16]
The reaction betweenuranium-238 targets andphosphorus-31 projectiles was first studied in 2006 at the LBNL as part of their systematic study of fusion reactions using uranium-238 targets:
Results have not been published but preliminary results appear to indicate the observation ofspontaneous fission, possibly from264Bh.[17]
In 2004, the team at theInstitute of Modern Physics (IMP),Lanzhou, have studied the nuclear reaction betweenamericium-243 targets and accelerated nuclei ofmagnesium-26 in order to synthesise the new isotope265Bh and gather more data on266Bh:
In two series of experiments, the team measured partial excitation functions for the reactions emitting three, four, and five neutrons.[18]
The reaction between targets ofcurium-248 and accelerated nuclei ofsodium-23 was studied for the first time in 2008 by the team at RIKEN, Japan, in order to study the decay properties of266Bh, which is a decay product in their claimed decay chains ofnihonium:[19]
The decay of266Bh by the emission of alpha particles with energies of 9.05–9.23 MeV was further confirmed in 2010.[20]
The first attempts to synthesize bohrium by hot fusion pathways were performed in 1979 by the team at Dubna, using the reaction between accelerated nuclei ofneon-22 and targets ofberkelium-249:
The reaction was repeated in 1983. In both cases, they were unable to detect anyspontaneous fission from nuclei of bohrium. More recently,[when?] 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-lived267Bh (5 atoms) and266Bh (1 atom).[21] Later, both of these were confirmed.[22] The team at thePaul Scherrer Institute (PSI) inBern, Switzerland later synthesized 6 atoms of267Bh in the first definitive study of the chemistry of bohrium.[23]
Bohrium has been detected in the decay chains of elements with a higheratomic number, such asmeitnerium. Meitnerium currently has seven isotopes that are known to undergo alpha decays to become bohrium nuclei, with mass numbers between 262 and 274. Parent meitnerium nuclei can be themselves decay products ofroentgenium,nihonium,flerovium,moscovium,livermorium, ortennessine.[29] For example, in January 2010, the Dubna team (JINR) identified bohrium-274 as a product in the decay of tennessine via an alpha decay sequence:[24]
The only confirmed example of isomerism in bohrium is in the isotope262Bh. Direct synthesis of262Bh results in two states, aground state and anisomeric state. The ground state is confirmed to decay by alpha decay, emitting alpha particles with energies of 10.08, 9.82, and 9.76 MeV, and has a revised half-life of 84 ms. The excited state also decays by alpha decay, emitting alpha particles with energies of 10.37 and 10.24 MeV, and has a revised half-life of 9.6 ms.[11]
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.
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.
^abHofmann, S.; Heinz, S.; Mann, R.; Maurer, J.; Münzenberg, G.; Antalic, S.; Barth, W.; Burkhard, H. G.; Dahl, L.; Eberhardt, K.; Grzywacz, R.; Hamilton, J. H.; Henderson, R. A.; Kenneally, J. M.; Kindler, B.; Kojouharov, I.; Lang, R.; Lommel, B.; Miernik, K.; Miller, D.; Moody, K. J.; Morita, K.; Nishio, K.; Popeko, A. G.; Roberto, J. B.; Runke, J.; Rykaczewski, K. P.; Saro, S.; Scheidenberger, C.; Schött, H. J.; Shaughnessy, D. A.; Stoyer, M. A.; Thörle-Popiesch, P.; Tinschert, K.; Trautmann, N.; Uusitalo, J.; Yeremin, A. V. (2016). "Review of even element super-heavy nuclei and search for element 120".The European Physics Journal A.2016 (52).Bibcode:2016EPJA...52..180H.doi:10.1140/epja/i2016-16180-4.Cite error: The named reference "Hofmann2016" was defined multiple times with different content (see thehelp page).
^Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*".Chinese Physics C.45 (3) 030003.doi:10.1088/1674-1137/abddaf.
^Fleischmann, Martin; Pons, Stanley (1989). "Electrochemically induced nuclear fusion of deuterium".Journal of Electroanalytical Chemistry and Interfacial Electrochemistry.261 (2):301–308.doi:10.1016/0022-0728(89)80006-3.
^abcOganessian, Yu. Ts.; Penionzhkevich, Yu. E.; Cherepanov, E. A. (2007). "Heaviest Nuclei Produced in 48Ca-induced Reactions (Synthesis and Decay Properties)".AIP Conference Proceedings. Vol. 912. pp. 235–246.doi:10.1063/1.2746600.
^abMorita, Kosuke; Morimoto, Kouji; Kaji, Daiya; Akiyama, Takahiro; Goto, Sin-ichi; Haba, Hiromitsu; Ideguchi, Eiji; Kanungo, Rituparna; Katori, Kenji; Koura, Hiroyuki; Kudo, Hisaaki; Ohnishi, Tetsuya; Ozawa, Akira; Suda, Toshimi; Sueki, Keisuke; Xu, HuShan; Yamaguchi, Takayuki; Yoneda, Akira; Yoshida, Atsushi; Zhao, YuLiang (2004). "Experiment on the Synthesis of Element 113 in the Reaction209Bi(70Zn,n)278113".Journal of the Physical Society of Japan.73 (10):2593–2596.Bibcode:2004JPSJ...73.2593M.doi:10.1143/JPSJ.73.2593.
^Münzenberg, G.; Armbruster, P.; Heßberger, F. P.; Hofmann, S.; Poppensieker, K.; Reisdorf, W.; Schneider, J. H. R.; Schneider, W. F. W.; Schmidt, K.-H.; Sahm, C.-C.; Vermeulen, D. (1982). "Observation of one correlated α-decay in the reaction58Fe on209Bi→267109".Zeitschrift für Physik A.309 (1):89–90.Bibcode:1982ZPhyA.309...89M.doi:10.1007/BF01420157.S2CID120062541.
^Sonzogni, Alejandro."Interactive Chart of Nuclides". National Nuclear Data Center: Brookhaven National Laboratory. Archived fromthe original on 2019-04-02. Retrieved2008-06-06.
Half-life, spin, and isomer data selected from the following sources.
