In theperiodic table, it is ad-block element and the second of the fourth-rowtransition elements. It is inperiod 7 and is agroup 4 element. Chemistry experiments have confirmed that rutherfordium behaves as the heavierhomolog tohafnium in group 4. The chemical properties of rutherfordium are characterized only partly. They compare well with the other group 4 elements, even though some calculations had indicated that the element might show significantly different properties due torelativistic effects.
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[a]atomic nucleus is created in a nuclear reaction that combines two other nuclei of unequal size[b] into one; roughly, the more unequal the two nuclei in terms ofmass, the greater the possibility that the two react.[16] 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.[17] 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.[17]
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.[17][18] This happens because during the attempted formation of a single nucleus, electrostatic repulsion tears apart the nucleus that is being formed.[17] 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.[c] 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.[17]
The resulting merger is anexcited state[21]—termed acompound nucleus—and thus it is very unstable.[17] To reach a more stable state, the temporary merger mayfission without formation of a more stable nucleus.[22] 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.[22] 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.[23][d]
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.[25] In the separator, the newly produced nucleus is separated from other nuclides (that of the original beam and any other reaction products)[e] 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.[25] The transfer takes about 10−6 seconds; in order to be detected, the nucleus must survive this long.[28] The nucleus is recorded again once its decay is registered, and the location, theenergy, and the time of the decay are measured.[25]
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.[29] 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.[30][31] Superheavy nuclei are thus theoretically predicted[32] and have so far been observed[33] to predominantly decay via decay modes that are caused by such repulsion:alpha decay andspontaneous fission.[f] Almost all alpha emitters have over 210 nucleons,[35] and the lightest nuclide primarily undergoing spontaneous fission has 238.[36] In both decay modes, nuclei are inhibited from decaying by correspondingenergy barriers for each mode, but they can be tunneled through.[30][31]
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.[37]
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.[38] Spontaneous fission is caused by electrostatic repulsion tearing the nucleus apart and produces various nuclei in different instances of identical nuclei fissioning.[31] 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),[39] and by 30 orders of magnitude fromthorium (element 90) tofermium (element 100).[40] 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.[31][41] 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.[31][41] 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.[42] Experiments on lighter superheavy nuclei,[43] as well as those closer to the expected island,[39] have shown greater than previously anticipated stability against spontaneous fission, showing the importance of shell effects on nuclei.[g]
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.[h] (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.)[25] 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).[i] Spontaneous fission, however, produces various nuclei as products, so the original nuclide cannot be determined from its daughters.[j]
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.[k]
In 1966–1969, the experiment was repeated. This time, the reaction products by gradient thermochromatography after conversion to chlorides by interaction withZrCl4. The team identifiedspontaneous fission activity contained within a volatile chloride portraying eka-hafnium properties.[54]
242 94Pu +22 10Ne →264−x104 →264−x104Cl4
The researchers considered the results to support the 0.3 second half-life. Although it is now known that there is no isotope of element 104 with such a half-life, the chemistry does fit that of element 104, as chloride volatility is much greater in group 4 than in group 3 (or the actinides).[54]
They were unable to confirm the 0.3-second half-life for260104, and instead found a 10–30 millisecond half-life for this isotope, agreeing with the modern value of 21 milliseconds. In 1970, the American team chemically identified element 104 using the ion-exchange separation method, proving it to be a group 4 element and the heavier homologue of hafnium.[56]
The American synthesis was independently confirmed in 1973 and secured the identification of rutherfordium as the parent by the observation ofK-alphaX-rays in the elemental signature of the257104 decay product, nobelium-253.[57]
Element 104 was eventually named afterErnest RutherfordIgor Kurchatov
As a consequence of the initial competing claims of discovery, anelement naming controversy arose. Since the Soviets claimed to have first detected the new element they suggested the namekurchatovium (Ku) in honor ofIgor Kurchatov (1903–1960), former head ofSoviet nuclear research. This name had been used in books of theSoviet Bloc as the official name of the element. The Americans, however, proposedrutherfordium (Rf) for the new element to honorNew Zealand physicistErnest Rutherford, who is known as the "father" ofnuclear physics.[58] In 1992, theIUPAC/IUPAP Transfermium Working Group (TWG) assessed the claims of discovery and concluded that both teams provided contemporaneous evidence to the synthesis of element 104 in 1969, and that credit should be shared between the two groups. In particular, this involved the TWG performing a new retrospective reanalysis of the Russian work in the face of the later-discovered fact that there is no 0.3-second isotope of element 104: they reinterpreted the Dubna results as having been caused by a spontaneous fission branch of259104.[54]
The American group wrote a scathing response to the findings of the TWG, stating that they had given too much emphasis on the results from the Dubna group. In particular they pointed out that the Russian group had altered the details of their claims several times over a period of 20 years, a fact that the Russian team does not deny. They also stressed that the TWG had given too much credence to the chemistry experiments performed by the Russians, considered the TWG's retrospective treatment of the Russian work based on unpublished documents to have been "highly irregular", noted that there was no proof that259104 had a spontaneous fission branch at all[56] (as of 2021 there still is not),[6] and accused the TWG of not having appropriately qualified personnel on the committee. The TWG responded by saying that this was not the case and having assessed each point raised by the American group said that they found no reason to alter their conclusion regarding priority of discovery.[56]
The International Union of Pure and Applied Chemistry (IUPAC) adoptedunnilquadium (Unq) as a temporary,systematic element name, derived from the Latin names for digits 1, 0, and 4. In 1994, IUPAC suggested a set of names for elements 104 through 109, in whichdubnium (Db) became element 104 andrutherfordium became element 106.[59] This recommendation was criticized by the American scientists for several reasons. Firstly, their suggestions were scrambled: the namesrutherfordium andhahnium, originally suggested by Berkeley for elements 104 and 105, were respectively reassigned to elements 106 and 108. Secondly, elements 104 and 105 were given names favored by JINR, despite earlier recognition of LBL as an equal co-discoverer for both of them. Thirdly and most importantly, IUPAC rejected the nameseaborgium for element 106, having just approved a rule that an element could not be named after a living person, even though the IUPAC had given the LBNL team the sole credit for its discovery.[60] In 1997, IUPAC renamed elements 104 to 109, and gave elements 104 and 106 the Berkeley proposalsrutherfordium andseaborgium. The namedubnium was given to element 105 at the same time. The 1997 names were accepted by researchers and became the standard.[61]
Rutherfordium 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. Seventeen different isotopes have been reported with atomic masses from 252 to 270 (with the exceptions of 264 and 269). Most of these decay predominantly through spontaneous fission, particularly isotopes witheven neutron numbers, while some of the lighter isotopes with odd neutron numbers also have significant alpha decay branches.[7][62]
Out of isotopes whose half-lives are known, the lighter isotopes usually have shorter half-lives. The three lightest known isotopes have half-lives of under 50 μs, with the lightest reported isotope252Rf having a half-life shorter than one microsecond.[63][64] The isotopes256Rf,258Rf,260Rf are more stable at around 10 ms;255Rf,257Rf,259Rf, and262Rf live between 1 and 5 seconds; and261Rf,265Rf, and263Rf are more stable, at around 1.1, 1.5, and 10 minutes respectively. The most stable known isotope,267Rf, is one of the heaviest, and has a half-life of about 48 minutes.[65] Rutherfordium isotopes with an odd neutron number tend to have longer half-lives than their even–even neighbors because the odd neutron provides additional hindrance against spontaneous fission.
The lightest isotopes were synthesized by direct fusion between two lighter nuclei and as decay products. The heaviest isotope produced by direct fusion is262Rf; heavier isotopes have only been observed as decay products of elements with larger atomic numbers. The heavy isotopes266Rf and268Rf have also been reported aselectron capture daughters of thedubnium isotopes266Db and268Db, but have short half-lives tospontaneous fission. It seems likely that the same is true for270Rf, a possible daughter of270Db.[66] These three isotopes remain unconfirmed.
In 1999, American scientists at the University of California, Berkeley, announced that they had succeeded in synthesizing three atoms of293Og.[67] These parent nuclei were reported to have successively emitted seven alpha particles to form265Rf nuclei, but their claim was retracted in 2001.[68] This isotope was later discovered in 2010 as the final product in the decay chain of285Fl.[8][69]
Very few properties of rutherfordium or its compounds have been measured; this is due to its extremely limited and expensive production[70] and the fact that rutherfordium (and its parents) decays very quickly. A few singular chemistry-related properties have been measured, but properties of rutherfordium metal remain unknown and only predictions are available.
Rutherfordium is the firsttransactinide element and the second member of the 6d series of transition metals. Calculations on itsionization potentials,atomic radius, as well as radii, orbital energies, and ground levels of its ionized states are similar to that ofhafnium and very different from that oflead. Therefore, it was concluded that rutherfordium's basic properties will resemble those of othergroup 4 elements, belowtitanium,zirconium, and hafnium.[71][72] Some of its properties were determined by gas-phase experiments and aqueous chemistry. The oxidation state +4 is the only stable state for the latter two elements and therefore rutherfordium should also exhibit a stable +4 state.[72] In addition, rutherfordium is also expected to be able to form a less stable +3 state.[2] Thestandard reduction potential of the Rf4+/Rf couple is predicted to be higher than −1.7 V.[73]
Initial predictions of the chemical properties of rutherfordium were based on calculations which indicated that the relativistic effects on the electron shell might be strong enough that the7p orbitals would have a lower energy level than the6d orbitals, giving it avalence electron configuration of 6d1 7s2 7p1 or even 7s2 7p2, therefore making the element behave more likelead than hafnium. With better calculation methods and experimental studies of the chemical properties of rutherfordium compounds it could be shown that this does not happen and that rutherfordium instead behaves like the rest of thegroup 4 elements.[2][72] Later it was shown in ab initio calculations with the high level of accuracy[74][75][76] that the Rf atom has the ground state with the 6d2 7s2 valence configuration and the low-lying excited 6d1 7s2 7p1 state with the excitation energy of only 0.3–0.5 eV.
In an analogous manner to zirconium and hafnium, rutherfordium is projected to form a very stable,refractory oxide, RfO2. It reacts with halogens to form tetrahalides, RfX4, which hydrolyze on contact with water to form oxyhalides RfOX2. The tetrahalides are volatile solids existing as monomeric tetrahedral molecules in the vapor phase.[72]
In the aqueous phase, the Rf4+ ion hydrolyzes less than titanium(IV) and to a similar extent as zirconium and hafnium, thus resulting in the RfO2+ ion. Treatment of the halides with halide ions promotes the formation of complex ions. The use of chloride and bromide ions produces the hexahalide complexesRfCl2− 6 andRfBr2− 6. For the fluoride complexes, zirconium and hafnium tend to form hepta- and octa- complexes. Thus, for the larger rutherfordium ion, the complexesRfF2− 6,RfF3− 7 andRfF4− 8 are possible.[72]
Rutherfordium is expected to be a solid under normal conditions and have ahexagonal close-packed crystal structure (c/a = 1.61), similar to its lightercongener hafnium.[5] It should be a metal withdensity ~17 g/cm3.[3][4] The atomic radius of rutherfordium is expected to be ~150 pm. Due to relativistic stabilization of the 7s orbital and destabilization of the 6d orbital, Rf+ and Rf2+ ions are predicted to give up 6d electrons instead of 7s electrons, which is the opposite of the behavior of its lighter homologs.[2] When under high pressure (variously calculated as 72 or ~50GPa), rutherfordium is expected to transition tobody-centered cubic crystal structure; hafnium transforms to this structure at 71±1 GPa, but has an intermediate ω structure that it transforms to at 38±8 GPa that should be lacking for rutherfordium.[77]
Early work on the study of the chemistry of rutherfordium focused on gas thermochromatography and measurement of relative deposition temperature adsorption curves. The initial work was carried out at Dubna in an attempt to reaffirm their discovery of the element. Recent work is more reliable regarding the identification of the parent rutherfordium radioisotopes. The isotope261mRf has been used for these studies,[72] though the long-lived isotope267Rf (produced in the decay chain of291Lv,287Fl, and283Cn) may be advantageous for future experiments.[78] The experiments relied on the expectation that rutherfordium would be a 6d element in group 4 and should therefore form a volatile molecular tetrachloride, that would be tetrahedral in shape.[72][79][80] Rutherfordium(IV) chloride is more volatile than its lighter homologuehafnium(IV) chloride (HfCl4) because its bonds are morecovalent.[2]
A series of experiments confirmed that rutherfordium behaves as a typical member of group 4, forming a tetravalent chloride (RfCl4) and bromide (RfBr4) as well as an oxychloride (RfOCl2). A decreased volatility was observed forRfCl 4 whenpotassium chloride is provided as the solid phase instead of gas, highly indicative of the formation of nonvolatileK 2RfCl 6 mixed salt.[71][72][81]
Rutherfordium is expected to have the electron configuration [Rn]5f14 6d2 7s2 and therefore behave as the heavier homologue ofhafnium in group 4 of the periodic table. It should therefore readily form a hydrated Rf4+ ion in strong acid solution and should readily form complexes inhydrochloric acid,hydrobromic orhydrofluoric acid solutions.[72]
The most conclusive aqueous chemistry studies of rutherfordium have been performed by the Japanese team atJapan Atomic Energy Research Institute using the isotope261mRf. Extraction experiments from hydrochloric acid solutions using isotopes of rutherfordium, hafnium, zirconium, as well as the pseudo-group 4 elementthorium have proved a non-actinide behavior for rutherfordium. A comparison with its lighter homologues placed rutherfordium firmly in group 4 and indicated the formation of a hexachlororutherfordate complex in chloride solutions, in a manner similar to hafnium and zirconium.[72][82]
261m Rf4+ + 6Cl− →[261mRfCl 6]2−
Very similar results were observed in hydrofluoric acid solutions. Differences in the extraction curves were interpreted as a weaker affinity for fluoride ion and the formation of the hexafluororutherfordate ion, whereas hafnium and zirconium ions complex seven or eight fluoride ions at the concentrations used:[72]
261m Rf4+ + 6F− →[261mRfF 6]2−
Experiments performed in mixed sulfuric and nitric acid solutions shows that rutherfordium has a much weaker affinity towards forming sulfate complexes than hafnium. This result is in agreement with predictions, which expect rutherfordium complexes to be less stable than those of zirconium and hafnium because of a smaller ionic contribution to the bonding. This arises because rutherfordium has a larger ionic radius (76 pm) than zirconium (71 pm) and hafnium (72 pm), and also because of relativistic stabilisation of the 7s orbital and destabilisation and spin–orbit splitting of the 6d orbitals.[83]
Coprecipitation experiments performed in 2021 studied rutherfordium's behaviour in basic solution containingammonia orsodium hydroxide, using zirconium, hafnium, and thorium as comparisons. It was found that rutherfordium does not strongly coordinate with ammonia and instead coprecipitates out as a hydroxide, which is probably Rf(OH)4.[84]
^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[11] or112;[12] sometimes, the term is presented an equivalent to the term "transactinide", which puts an upper limit before the beginning of the hypotheticalsuperactinide series).[13] 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.[14] 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.[15]
^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.[19]
^This figure also marks the generally accepted upper limit for lifetime of a compound nucleus.[24]
^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.[26] 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.[27]
^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.[39]
^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.[44] The first direct measurement of mass of a superheavy nucleus was reported in 2018 at LBNL.[45] 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).[46]
^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).[35] 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,[47] a leading scientist at JINR, and thus it was a "hobbyhorse" for the facility.[48] 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.[24] They thus preferred to link new isotopes to the already known ones by successive alpha decays.[47]
^For instance, element 102 was mistakenly identified in 1957 at the Nobel Institute of Physics inStockholm,Stockholm County,Sweden.[49] 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.[50] 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.[50] JINR insisted that they were the first to create the element and suggested a name of their own for the new element,joliotium;[51] the Soviet name was also not accepted (JINR later referred to the naming of the element 102 as "hasty").[52] This name was proposed to IUPAC in a written response to their ruling on priority of discovery claims of elements, signed 29 September 1992.[52] The name "nobelium" remained unchanged on account of its widespread usage.[53]
^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.Bibcode:2011PhRvB..83q2101G.doi:10.1103/PhysRevB.83.172101.
^abKratz; Lieser (2013).Nuclear and Radiochemistry: Fundamentals and Applications (3rd ed.). p. 631.
^abSonzogni, Alejandro."Interactive Chart of Nuclides". National Nuclear Data Center: Brookhaven National Laboratory. Retrieved2008-06-06.
^abUtyonkov, V. K.; Brewer, N. T.; Oganessian, Yu. Ts.; Rykaczewski, K. P.; Abdullin, F. Sh.; Dimitriev, S. N.; Grzywacz, R. K.; Itkis, M. G.; Miernik, K.; Polyakov, A. N.; Roberto, J. B.; Sagaidak, R. N.; Shirokovsky, I. V.; Shumeiko, M. V.; Tsyganov, Yu. S.; Voinov, A. A.; Subbotin, V. G.; Sukhov, A. M.; Karpov, A. V.; Popeko, A. G.; Sabel'nikov, A. V.; Svirikhin, A. I.; Vostokin, G. K.; Hamilton, J. H.; Kovrinzhykh, N. D.; Schlattauer, L.; Stoyer, M. A.; Gan, Z.; Huang, W. X.; Ma, L. (30 January 2018). "Neutron-deficient superheavy nuclei obtained in the240Pu+48Ca reaction".Physical Review C.97 (14320): 014320.Bibcode:2018PhRvC..97a4320U.doi:10.1103/PhysRevC.97.014320.
^Oganessian, Yu. Ts.; Utyonkov, V. K.; Ibadullayev, D.; et al. (2022). "Investigation of48Ca-induced reactions with242Pu and238U targets at the JINR Superheavy Element Factory".Physical Review C.106 (24612): 024612.Bibcode:2022PhRvC.106b4612O.doi:10.1103/PhysRevC.106.024612.S2CID251759318.
^"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.
^Khuyagbaatar, J.; Mosat, P.; Ballof, J.; et al. (2025). "Stepping into the sea of instability: The new sub-𝜇s superheavy nucleus252Rf".Physical Review Letters.134 (22501): 022501.arXiv:2501.08955.doi:10.1103/PhysRevLett.134.022501.
^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.
^Türler, A.; Buklanov, G. V.; Eichler, B.; Gäggeler, H. W.; Grantz, M.; Hübener, S.; Jost, D. T.; Lebedev, V. Ya.; et al. (1998). "Evidence for relativistic effects in the chemistry of element 104".Journal of Alloys and Compounds.271–273: 287.doi:10.1016/S0925-8388(98)00072-3.
^Li, Z. J.; Toyoshima, A.; Asai, M.; et al. (2012). "Sulfate complexation of element 104, Rf, in H2SO4/HNO3 mixed solution".Radiochimica Acta.100 (3):157–164.doi:10.1524/ract.2012.1898.S2CID100852185.
