A graphic depiction of anuclear fusion reaction. Two nuclei fuse into one, emitting aneutron. Reactions that created new elements to this moment were similar, with the only possible difference that several singular neutrons sometimes were released, or none at all.
A superheavy[b]atomic nucleus is created in a nuclear reaction that combines two other nuclei of unequal size[c] into one; roughly, the more unequal the two nuclei in terms ofmass, the greater the possibility that the two react.[18] The material made of the heavier nuclei is made into a target, which is then bombarded by thebeam of lighter nuclei. Two nuclei can onlyfuse into one if they approach each other closely enough; normally, nuclei (all positively charged) repel each other due toelectrostatic repulsion. Thestrong interaction can overcome this repulsion but only within a very short distance from a nucleus; beam nuclei are thus greatlyaccelerated in order to make such repulsion insignificant compared to the velocity of the beam nucleus.[19] The energy applied to the beam nuclei to accelerate them can cause them to reach speeds as high as one-tenth of thespeed of light. However, if too much energy is applied, the beam nucleus can fall apart.[19]
Coming close enough alone is not enough for two nuclei to fuse: when two nuclei approach each other, they usually remain together for about 10−20 seconds and then part ways (not necessarily in the same composition as before the reaction) rather than form a single nucleus.[19][20] This happens because during the attempted formation of a single nucleus, electrostatic repulsion tears apart the nucleus that is being formed.[19] Each pair of a target and a beam is characterized by itscross section—the probability that fusion will occur if two nuclei approach one another expressed in terms of the transverse area that the incident particle must hit in order for the fusion to occur.[d] This fusion may occur as a result of the quantum effect in which nuclei cantunnel through electrostatic repulsion. If the two nuclei can stay close past that phase, multiple nuclear interactions result in redistribution of energy and an energy equilibrium.[19]
The resulting merger is anexcited state[23]—termed acompound nucleus—and thus it is very unstable.[19] To reach a more stable state, the temporary merger mayfission without formation of a more stable nucleus.[24] Alternatively, the compound nucleus may eject a fewneutrons, which would carry away the excitation energy; if the latter is not sufficient for a neutron expulsion, the merger would produce agamma ray. This happens in about 10−16 seconds after the initial nuclear collision and results in creation of a more stable nucleus.[24] The definition by theIUPAC/IUPAP Joint Working Party (JWP) states that achemical element can only be recognized as discovered if a nucleus of it has notdecayed within 10−14 seconds. This value was chosen as an estimate of how long it takes a nucleus to acquireelectrons and thus display its chemical properties.[25][e]
The beam passes through the target and reaches the next chamber, the separator; if a new nucleus is produced, it is carried with this beam.[27] In the separator, the newly produced nucleus is separated from other nuclides (that of the original beam and any other reaction products)[f] and transferred to asurface-barrier detector, which stops the nucleus. The exact location of the upcoming impact on the detector is marked; also marked are its energy and the time of the arrival.[27] The transfer takes about 10−6 seconds; in order to be detected, the nucleus must survive this long.[30] The nucleus is recorded again once its decay is registered, and the location, theenergy, and the time of the decay are measured.[27]
Stability of a nucleus is provided by the strong interaction. However, its range is very short; as nuclei become larger, its influence on the outermostnucleons (protons and neutrons) weakens. At the same time, the nucleus is torn apart by electrostatic repulsion between protons, and its range is not limited.[31] Totalbinding energy provided by the strong interaction increases linearly with the number of nucleons, whereas electrostatic repulsion increases with the square of the atomic number, i.e. the latter grows faster and becomes increasingly important for heavy and superheavy nuclei.[32][33] Superheavy nuclei are thus theoretically predicted[34] and have so far been observed[35] to predominantly decay via decay modes that are caused by such repulsion:alpha decay andspontaneous fission.[g] Almost all alpha emitters have over 210 nucleons,[37] and the lightest nuclide primarily undergoing spontaneous fission has 238.[38] In both decay modes, nuclei are inhibited from decaying by correspondingenergy barriers for each mode, but they can be tunneled through.[32][33]
Scheme of an apparatus for creation of superheavy elements, based on the Dubna Gas-Filled Recoil Separator set up in theFlerov Laboratory of Nuclear Reactions in JINR. The trajectory within the detector and the beam focusing apparatus changes because of adipole magnet in the former andquadrupole magnets in the latter.[39]
Alpha particles are commonly produced in radioactive decays because the mass of an alpha particle per nucleon is small enough to leave some energy for the alpha particle to be used as kinetic energy to leave the nucleus.[40] Spontaneous fission is caused by electrostatic repulsion tearing the nucleus apart and produces various nuclei in different instances of identical nuclei fissioning.[33] As the atomic number increases, spontaneous fission rapidly becomes more important: spontaneous fission partial half-lives decrease by 23 orders of magnitude fromuranium (element 92) tonobelium (element 102),[41] and by 30 orders of magnitude fromthorium (element 90) tofermium (element 100).[42] The earlierliquid drop model thus suggested that spontaneous fission would occur nearly instantly due to disappearance of thefission barrier for nuclei with about 280 nucleons.[33][43] The laternuclear shell model suggested that nuclei with about 300 nucleons would form anisland of stability in which nuclei will be more resistant to spontaneous fission and will primarily undergo alpha decay with longer half-lives.[33][43] Subsequent discoveries suggested that the predicted island might be further than originally anticipated; they also showed that nuclei intermediate between the long-lived actinides and the predicted island are deformed, and gain additional stability from shell effects.[44] Experiments on lighter superheavy nuclei,[45] as well as those closer to the expected island,[41] have shown greater than previously anticipated stability against spontaneous fission, showing the importance of shell effects on nuclei.[h]
Alpha decays are registered by the emitted alpha particles, and the decay products are easy to determine before the actual decay; if such a decay or a series of consecutive decays produces a known nucleus, the original product of a reaction can be easily determined.[i] (That all decays within a decay chain were indeed related to each other is established by the location of these decays, which must be in the same place.)[27] The known nucleus can be recognized by the specific characteristics of decay it undergoes such as decay energy (or more specifically, thekinetic energy of the emitted particle).[j] Spontaneous fission, however, produces various nuclei as products, so the original nuclide cannot be determined from its daughters.[k]
The information available to physicists aiming to synthesize a superheavy element is thus the information collected at the detectors: location, energy, and time of arrival of a particle to the detector, and those of its decay. The physicists analyze this data and seek to conclude that it was indeed caused by a new element and could not have been caused by a different nuclide than the one claimed. Often, provided data is insufficient for a conclusion that a new element was definitely created and there is no other explanation for the observed effects; errors in interpreting data have been made.[l]
Element 107 was originally proposed to be named afterNiels Bohr, a Danish nuclear/theoretical physicist, with the namenielsbohrium (Ns). This name was later changed byIUPAC tobohrium (Bh).
Two groups claimeddiscovery of the element. Evidence of bohrium was first reported in 1976 by a Soviet research team led byYuri Oganessian, in which targets ofbismuth-209 andlead-208 were bombarded with accelerated nuclei ofchromium-54 andmanganese-55, respectively.[56] Two activities, one with a half-life of one to two milliseconds, and the other with an approximately five-second half-life, were seen. Since the ratio of the intensities of these two activities was constant throughout the experiment, it was proposed that the first was from the isotopebohrium-261 and that the second was from its daughterdubnium-257. Later, the dubnium isotope was corrected todubnium-258, which indeed has a five-second half-life (dubnium-257 has a one-second half-life); however, the half-life observed for its parent is much shorter than the half-lives later observed in the definitive discovery of bohrium atDarmstadt in 1981. TheIUPAC/IUPAP Transfermium Working Group (TWG) concluded that whiledubnium-258 was probably seen in this experiment, the evidence for the production of its parentbohrium-262 was not convincing enough.[57]
This discovery was further substantiated by their detailed measurements of the alpha decay chain of the produced bohrium atoms to previously known isotopes offermium andcalifornium. TheIUPAC/IUPAP Transfermium Working Group (TWG) recognised the GSI collaboration as official discoverers in their 1992 report.[57]
In September 1992, the German group suggested the namenielsbohrium with symbolNs to honor the Danish physicistNiels Bohr. The Soviet scientists at theJoint Institute for Nuclear Research inDubna, Russia had suggested this name be given to element 105 (which was finally called dubnium) and the German team wished to recognise both Bohr and the fact that the Dubna team had been the first to propose the cold fusion reaction, and simultaneously help to solve the controversial problem of the naming of element 105. The Dubna team agreed with the German group's naming proposal for element 107.[59]
There was anelement naming controversy as to what the elements from 104 to 106 were to be called; theIUPAC adoptedunnilseptium (symbolUns) as a temporary,systematic element name for this element.[60] In 1994 a committee of IUPAC recommended that element 107 be namedbohrium, notnielsbohrium, since there was no precedent for using a scientist's complete name in the naming of an element.[60][61] This was opposed by the discoverers as there was some concern that the name might be confused withboron and in particular the distinguishing of the names of their respectiveoxyanions,bohrate andborate. The matter was handed to the Danish branch of IUPAC which, despite this, voted in favour of the namebohrium, and thus the namebohrium for element 107 was recognized internationally in 1997;[60] the names of the respective oxyanions of boron and bohrium remain unchanged despite their homophony.[62]
Bohrium has no stable or naturally occurring isotopes. Several radioactive isotopes have been synthesized in the laboratory, either by fusing two atoms or by observing the decay of heavier elements. Twelve different isotopes of bohrium have been reported with atomic masses 260–262, 264–267, 270–272, 274, and 278, one of which, bohrium-262, has a knownmetastable state. All of these but the unconfirmed278Bh decay only through alpha decay, although some unknown bohrium isotopes are predicted to undergo spontaneous fission.[71]
The lighter isotopes usually have shorter half-lives; half-lives of under 100 ms for260Bh,261Bh,262Bh, and262mBh were observed.264Bh,265Bh,266Bh, and271Bh are more stable at around 1 s, and267Bh and272Bh have half-lives of about 10 s. The heaviest isotopes are the most stable, with270Bh and274Bh having measured half-lives of about 2.4 min and 40 s respectively, and the even heavier unconfirmed isotope278Bh appearing to have an even longer half-life of about 11.5 minutes.
The most proton-rich isotopes with masses 260, 261, and 262 were directly produced by cold fusion, those with mass 262 and 264 were reported in the decay chains of meitnerium and roentgenium, while the neutron-rich isotopes with masses 265, 266, 267 were created in irradiations of actinide targets. The five most neutron-rich ones with masses 270, 271, 272, 274, and 278 (unconfirmed) appear in the decay chains of282Nh,287Mc,288Mc,294Ts, and290Fl respectively. The half-lives of bohrium isotopes range from about ten milliseconds for262mBh to about one minute for270Bh and274Bh, extending to about 11.5 minutes for the unconfirmed278Bh, which may have one of the longest half-lives among reported superheavy nuclides.[72]
Very few properties of bohrium or its compounds have been measured; this is due to its extremely limited and expensive production[73] and the fact that bohrium (and its parents) decays very quickly. A few singular chemistry-related properties have been measured, but properties of bohrium metal remain unknown and only predictions are available.
Bohrium is the fifth member of the 6d series of transition metals and the heaviest member ofgroup 7 in the periodic table, belowmanganese,technetium andrhenium. All the members of the group readily portray their group oxidation state of +7 and the state becomes more stable as the group is descended. Thus bohrium is expected to form a stable +7 state. Technetium also shows a stable +4 state whilst rhenium exhibits stable +4 and +3 states. Bohrium may therefore show these lower states as well.[74] The higher +7 oxidation state is more likely to exist in oxyanions, such as perbohrate,BhO− 4, analogous to the lighterpermanganate,pertechnetate, andperrhenate. Nevertheless, bohrium(VII) is likely to be unstable in aqueous solution, and would probably be easily reduced to the more stable bohrium(IV).[4]
The lighter group 7 elements are known to form volatile heptoxidesM2O7 (M = Mn, Tc, Re), so bohrium should also form the volatile oxideBh2O7. The oxide should dissolve in water to form perbohric acid,HBhO4.[75]Rhenium and technetium form a range of oxyhalides from the halogenation of the oxide. The chlorination of the oxide forms the oxychlorides MO3Cl, so BhO3Cl should be formed in this reaction. Fluorination results inMO3F andMO2F3 for the heavier elements in addition to the rhenium compounds ReOF5 and ReF7. Therefore, oxyfluoride formation for bohrium may help to indicate eka-rhenium properties.[76] Since the oxychlorides are asymmetrical, and they should have increasingly largedipole moments going down the group, they should become less volatile in the order TcO3Cl > ReO3Cl > BhO3Cl: this was experimentally confirmed in 2000 by measuring theenthalpies ofadsorption of these three compounds. The values are for TcO3Cl and ReO3Cl are −51 kJ/mol and −61 kJ/mol respectively; the experimental value for BhO3Cl is −77.8 kJ/mol, very close to the theoretically expected value of −78.5 kJ/mol.[4]
Bohrium is expected to be a solid under normal conditions and assume ahexagonal close-packed crystal structure (c/a = 1.62), similar to its lightercongener rhenium.[5] Early predictions by Fricke estimated its density at 37.1 g/cm3,[4] but newer calculations predict a somewhat lower value of 26–27 g/cm3.[6][7]
The atomic radius of bohrium is expected to be around 128 pm.[4] Due to the relativistic stabilization of the 7s orbital and destabilization of the 6d orbital, the Bh+ ion is predicted to have an electron configuration of [Rn] 5f14 6d4 7s2, giving up a 6d electron instead of a 7s electron, which is the opposite of the behavior of its lighter homologues manganese and technetium. Rhenium, on the other hand, follows its heavier congener bohrium in giving up a 5d electron before a 6s electron, as relativistic effects have become significant by the sixth period, where they cause among other things the yellow color ofgold and the low melting point ofmercury. The Bh2+ ion is expected to have an electron configuration of [Rn] 5f14 6d3 7s2; in contrast, the Re2+ ion is expected to have a [Xe] 4f14 5d5 configuration, this time analogous to manganese and technetium.[4] The ionic radius of hexacoordinate heptavalent bohrium is expected to be 58 pm (heptavalent manganese, technetium, and rhenium having values of 46, 57, and 53 pm respectively). Pentavalent bohrium should have a larger ionic radius of 83 pm.[4]
In 1995, the first report on attempted isolation of the element was unsuccessful, prompting new theoretical studies to investigate how best to investigate bohrium (using its lighter homologs technetium and rhenium for comparison) and removing unwanted contaminating elements such as the trivalentactinides, thegroup 5 elements, andpolonium.[77]
In 2000, it was confirmed that although relativistic effects are important, bohrium behaves like a typical group 7 element.[78] A team at thePaul Scherrer Institute (PSI) conducted a chemistry reaction using six atoms of267Bh produced in the reaction between249Bk and22Ne ions. The resulting atoms were thermalised and reacted with a HCl/O2 mixture to form a volatile oxychloride. The reaction also produced isotopes of its lighter homologues, technetium (as108Tc) and rhenium (as169Re). The isothermal adsorption curves were measured and gave strong evidence for the formation of a volatile oxychloride with properties similar to that of rhenium oxychloride. This placed bohrium as a typical member of group 7.[79] The adsorption enthalpies of the oxychlorides of technetium, rhenium, and bohrium were measured in this experiment, agreeing very well with the theoretical predictions and implying a sequence of decreasing oxychloride volatility down group 7 of TcO3Cl > ReO3Cl > BhO3Cl.[4]
2 Bh + 3O 2 + 2 HCl → 2BhO 3Cl +H 2
The longer-lived heavy isotopes of bohrium, produced as the daughters of heavier elements, offer advantages for future radiochemical experiments. Although the heavy isotope274Bh requires a rare and highly radioactiveberkelium target for its production, the isotopes272Bh,271Bh, and270Bh can be readily produced as daughters of more easily producedmoscovium andnihonium isotopes.[80]
^The most stable isotope of bohrium cannot be determined based on existing data due to uncertainty that arises from the low number of measurements. The half-life of270Bh corresponding to twostandard deviations is, based on existing data,2.4+8.8 −1.8 minutes[1], whereas that of274Bh is44+68 −26 seconds; these measurements have overlappingconfidence intervals. It is also possible that the unconfirmed278Bh is more stable than both of these, with its half-life being 11.5 minutes.[2]
^Innuclear physics, an element is calledheavy if its atomic number is high;lead (element 82) is one example of such a heavy element. The term "superheavy elements" typically refers to elements with atomic number greater than103 (although there are other definitions, such as atomic number greater than100[13] or112;[14] sometimes, the term is presented an equivalent to the term "transactinide", which puts an upper limit before the beginning of the hypotheticalsuperactinide series).[15] Terms "heavy isotopes" (of a given element) and "heavy nuclei" mean what could be understood in the common language—isotopes of high mass (for the given element) and nuclei of high mass, respectively.
^In 2009, a team at the JINR led by Oganessian published results of their attempt to create hassium in a symmetric136Xe + 136Xe reaction. They failed to observe a single atom in such a reaction, putting the upper limit on the cross section, the measure of probability of a nuclear reaction, as 2.5 pb.[16] In comparison, the reaction that resulted in hassium discovery,208Pb +58Fe, had a cross section of ~20 pb (more specifically, 19+19 -11 pb), as estimated by the discoverers.[17]
^The amount of energy applied to the beam particle to accelerate it can also influence the value of cross section. For example, in the28 14Si +1 0n →28 13Al +1 1p reaction, cross section changes smoothly from 370 mb at 12.3 MeV to 160 mb at 18.3 MeV, with a broad peak at 13.5 MeV with the maximum value of 380 mb.[21]
^This figure also marks the generally accepted upper limit for lifetime of a compound nucleus.[26]
^This separation is based on that the resulting nuclei move past the target more slowly then the unreacted beam nuclei. The separator contains electric and magnetic fields whose effects on a moving particle cancel out for a specific velocity of a particle.[28] Such separation can also be aided by atime-of-flight measurement and a recoil energy measurement; a combination of the two may allow to estimate the mass of a nucleus.[29]
^It was already known by the 1960s that ground states of nuclei differed in energy and shape as well as that certain magic numbers of nucleons corresponded to greater stability of a nucleus. However, it was assumed that there was no nuclear structure in superheavy nuclei as they were too deformed to form one.[41]
^Since mass of a nucleus is not measured directly but is rather calculated from that of another nucleus, such measurement is called indirect. Direct measurements are also possible, but for the most part they have remained unavailable for superheavy nuclei.[46] The first direct measurement of mass of a superheavy nucleus was reported in 2018 at LBNL.[47] Mass was determined from the location of a nucleus after the transfer (the location helps determine its trajectory, which is linked to the mass-to-charge ratio of the nucleus, since the transfer was done in presence of a magnet).[48]
^If the decay occurred in a vacuum, then since total momentum of an isolated system before and after the decaymust be preserved, the daughter nucleus would also receive a small velocity. The ratio of the two velocities, and accordingly the ratio of the kinetic energies, would thus be inverse to the ratio of the two masses. The decay energy equals the sum of the known kinetic energy of the alpha particle and that of the daughter nucleus (an exact fraction of the former).[37] The calculations hold for an experiment as well, but the difference is that the nucleus does not move after the decay because it is tied to the detector.
^Spontaneous fission was discovered by Soviet physicistGeorgy Flerov,[49] a leading scientist at JINR, and thus it was a "hobbyhorse" for the facility.[50] In contrast, the LBL scientists believed fission information was not sufficient for a claim of synthesis of an element. They believed spontaneous fission had not been studied enough to use it for identification of a new element, since there was a difficulty of establishing that a compound nucleus had only ejected neutrons and not charged particles like protons or alpha particles.[26] They thus preferred to link new isotopes to the already known ones by successive alpha decays.[49]
^For instance, element 102 was mistakenly identified in 1957 at the Nobel Institute of Physics inStockholm,Stockholm County,Sweden.[51] There were no earlier definitive claims of creation of this element, and the element was assigned a name by its Swedish, American, and British discoverers,nobelium. It was later shown that the identification was incorrect.[52] The following year, RL was unable to reproduce the Swedish results and announced instead their synthesis of the element; that claim was also disproved later.[52] JINR insisted that they were the first to create the element and suggested a name of their own for the new element,joliotium;[53] the Soviet name was also not accepted (JINR later referred to the naming of the element 102 as "hasty").[54] This name was proposed to IUPAC in a written response to their ruling on priority of discovery claims of elements, signed 29 September 1992.[54] The name "nobelium" remained unchanged on account of its widespread usage.[55]
^Different sources give different values for half-lives; the most recently published values are listed.
^abcHofmann, 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.
^Johnson, E.; Fricke, B.; Jacob, T.; Dong, C. Z.; Fritzsche, S.; Pershina, V. (2002). "Ionization potentials and radii of neutral and ionized species of elements 107 (bohrium) and 108 (hassium) from extended multiconfiguration Dirac–Fock calculations".The Journal of Chemical Physics.116 (5):1862–1868.Bibcode:2002JChPh.116.1862J.doi:10.1063/1.1430256.
^abcdefghijkHoffman, Darleane C.; Lee, Diana M.; Pershina, Valeria (2006). "Transactinides and the future elements". In Morss; Edelstein, Norman M.; Fuger, Jean (eds.).The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands:Springer Science+Business Media.ISBN978-1-4020-3555-5.
^abGyanchandani, Jyoti; Sikka, S. K. (10 May 2011). "Physical properties of the 6 d -series elements from density functional theory: Close similarity to lighter transition metals".Physical Review B.83 (17) 172101.doi:10.1103/PhysRevB.83.172101.
^abKratz; Lieser (2013).Nuclear and Radiochemistry: Fundamentals and Applications (3rd ed.). p. 631.
^"Популярная библиотека химических элементов. Сиборгий (экавольфрам)" [Popular library of chemical elements. Seaborgium (eka-tungsten)].n-t.ru (in Russian). Retrieved2020-01-07. Reprinted from"Экавольфрам" [Eka-tungsten].Популярная библиотека химических элементов. Серебро – Нильсборий и далее [Popular library of chemical elements. Silver through nielsbohrium and beyond] (in Russian).Nauka. 1977.
^Yu; Demin, A. G.; Danilov, N. A.; Flerov, G. N.; Ivanov, M. P.; Iljinov, A. S.; Kolesnikov, N. N.; Markov, B. N.; Plotko, V. M.; Tretyakova, S. P. (1976). "On spontaneous fission of neutron-deficient isotopes of elements".Nuclear Physics A.273:505–522.doi:10.1016/0375-9474(76)90607-2.
^Münzenberg, G.; Armbruster, P.; Hofmann, S.; Heßberger, F. P.; Folger, H.; Keller, J. G.; Ninov, V.; Poppensieker, K.; et al. (1989). "Element 107".Zeitschrift für Physik A.333 (2): 163.Bibcode:1989ZPhyA.333..163M.doi:10.1007/BF01565147.S2CID186231905.
^Hofmann, S.; Ninov, V.; Heßberger, F. P.; Armbruster, P.; Folger, H.; Münzenberg, G.; Schött, H. J.; Popeko, A. G.; Yeremin, A. V.; Andreyev, A. N.; Saro, S.; Janik, R.; Leino, M. (1995). "The new element 111".Zeitschrift für Physik A.350 (4): 281.Bibcode:1995ZPhyA.350..281H.doi:10.1007/BF01291182.S2CID18804192.
^abcOganessian, Yu. Ts. (2007). "Heaviest Nuclei Produced in 48Ca-induced Reactions (Synthesis and Decay Properties)". In Penionzhkevich, Yu. E.; Cherepanov, E. A. (eds.).AIP Conference Proceedings: International Symposium on Exotic Nuclei. Vol. 912. p. 235.doi:10.1063/1.2746600.ISBN978-0-7354-0420-5.
^Sonzogni, Alejandro."Interactive Chart of Nuclides". National Nuclear Data Center: Brookhaven National Laboratory. Archived fromthe original on 2019-04-02. Retrieved2008-06-06.
^Münzenberg, G.; Gupta, M. (2011). "Production and Identification of Transactinide Elements". In Vértes, Attila; Nagy, Sándor; Klencsár, Zoltán; Lovas, Rezső G.; Rösch, Frank (eds.).Handbook of Nuclear Chemistry: Production and Identification of Transactinide Elements. p. 877.doi:10.1007/978-1-4419-0720-2_19.ISBN978-1-4419-0719-6.
^Hans Georg Nadler "Rhenium and Rhenium Compounds" Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2000.doi:10.1002/14356007.a23_199
^Malmbeck, R.; Skarnemark, G.; Alstad, J.; Fure, K.; Johansson, M.; Omtvedt, J. P. (2000). "Chemical Separation Procedure Proposed for Studies of Bohrium".Journal of Radioanalytical and Nuclear Chemistry.246 (2): 349.Bibcode:2000JRNC..246..349M.doi:10.1023/A:1006791027906.S2CID93640208.
^Gäggeler, H. W.; Eichler, R.; Brüchle, W.; Dressler, R.; Düllmann, Ch. E.; Eichler, B.; Gregorich, K. E.; Hoffman, D. C.; et al. (2000). "Chemical characterization of bohrium (element 107)".Nature.407 (6800):63–5.Bibcode:2000Natur.407...63E.doi:10.1038/35024044.PMID10993071.S2CID4398253.
^Moody, Ken (2013-11-30). "Synthesis of Superheavy Elements". In Schädel, Matthias; Shaughnessy, Dawn (eds.).The Chemistry of Superheavy Elements (2nd ed.). Springer Science & Business Media. pp. 24–8.ISBN978-3-642-37466-1.
