Nobelium is asynthetic chemical element; it hassymbolNo andatomic number 102. It is named afterAlfred Nobel, the inventor ofdynamite and benefactor of science. Aradioactivemetal, it is the tenthtransuranium element, the second transfermium, and is the fourteenth member of theactinide series. Like all elements with atomic number over 100, nobelium can only be produced inparticle accelerators by bombarding lighter elements with charged particles. A total of twelvenobelium isotopes are known to exist; the most stable is259No with ahalf-life of 58 minutes, but the shorter-lived255No (half-life 3.1 minutes) is most commonly used in chemistry because it can be produced on a larger scale.
Chemistry experiments have confirmed that nobelium behaves as a heavierhomolog toytterbium in the periodic table. The chemical properties of nobelium are not completely known: they are mostly only known inaqueous solution. Before nobelium's discovery, it was predicted that it would show a stable +2oxidation state as well as the +3 state characteristic of the otheractinides; these predictions were later confirmed, as the +2 state is much more stable than the +3 state inaqueous solution and it is difficult to keep nobelium in the +3 state.
In the 1950s and 1960s, many claims of the discovery of nobelium were made from laboratories inSweden, theSoviet Union, and theUnited States. Although the Swedish scientists soon retracted their claims, the priority of the discovery and therefore thenaming of the element was disputed between Soviet and American scientists. It was not until 1992 that theInternational Union of Pure and Applied Chemistry (IUPAC) credited the Soviet team with the discovery. Even so, nobelium, the Swedish proposal, was retained as the name of the element due to its long-standing use in the literature.
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.[12] 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.[13] 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.[13]
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.[13][14] This happens because during the attempted formation of a single nucleus, electrostatic repulsion tears apart the nucleus that is being formed.[13] 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.[13]
The resulting merger is anexcited state[17]—termed acompound nucleus—and thus it is very unstable.[13] To reach a more stable state, the temporary merger mayfission without formation of a more stable nucleus.[18] 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.[18] 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.[19][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.[21] 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.[21] The transfer takes about 10−6 seconds; in order to be detected, the nucleus must survive this long.[24] The nucleus is recorded again once its decay is registered, and the location, theenergy, and the time of the decay are measured.[21]
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.[25] 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.[26][27] Superheavy nuclei are thus theoretically predicted[28] and have so far been observed[29] 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,[31] and the lightest nuclide primarily undergoing spontaneous fission has 238.[32] In both decay modes, nuclei are inhibited from decaying by correspondingenergy barriers for each mode, but they can be tunneled through.[26][27]
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.[33]
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.[34] Spontaneous fission is caused by electrostatic repulsion tearing the nucleus apart and produces various nuclei in different instances of identical nuclei fissioning.[27] 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) to nobelium (element 102),[35] and by 30 orders of magnitude fromthorium (element 90) tofermium (element 100).[36] 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.[27][37] 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.[27][37] 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.[38] Experiments on lighter superheavy nuclei,[39] as well as those closer to the expected island,[35] 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.)[21] 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]
The first announcement of the discovery of element 102 was announced by physicists at the Nobel Institute for Physics in Sweden in 1957. The team reported that they had bombarded acurium target withcarbon-13 ions for twenty-five hours in half-hour intervals. Between bombardments,ion-exchange chemistry was performed on the target. Twelve out of the fifty bombardments contained samples emitting (8.5 ± 0.1) MeValpha particles, which were in drops which eluted earlier thanfermium (atomic numberZ = 100) andcalifornium (Z = 98). Thehalf-life reported was 10 minutes and was assigned to either251102 or253102, although the possibility that the alpha particles observed were from a presumably short-livedmendelevium (Z = 101) isotope created from the electron capture of element 102 was not excluded.[50] The team proposed the namenobelium (No) for the new element,[51][52] which was immediately approved by IUPAC,[53] a decision which the Dubna group characterized in 1968 as being hasty.[54]
In 1958, scientists at theLawrence Berkeley National Laboratory repeated the experiment. The Berkeley team, consisting ofAlbert Ghiorso,Glenn T. Seaborg,John R. Walton andTorbjørn Sikkeland, used the new heavy-ionlinear accelerator (HILAC) to bombard a curium target (95%244Cm and 5%246Cm) with13C and12C ions. They were unable to confirm the 8.5 MeV activity claimed by the Swedes but were instead able to detect decays from fermium-250, supposedly the daughter of254102 (produced from the curium-246), which had an apparenthalf-life of ~3 s. Probably this assignment was also wrong, as later 1963 Dubna work showed that the half-life of254No is significantly longer (about 50 s). It is more likely that the observed alpha decays did not come from element 102, but rather from250mFm.[50]
In 1959, the Swedish team attempted to explain the Berkeley team's inability to detect element 102 in 1958, maintaining that they did discover it. However, later work has shown that no nobelium isotopes lighter than259No (no heavier isotopes could have been produced in the Swedish experiments) with a half-life over 3 minutes exist, and that the Swedish team's results are most likely fromthorium-225, which has a half-life of 8 minutes and quickly undergoes triple alpha decay topolonium-213, which has a decay energy of 8.53612 MeV. This hypothesis is lent weight by the fact that thorium-225 can easily be produced in the reaction used and would not be separated out by the chemical methods used. Later work on nobelium also showed that the divalent state is more stable than the trivalent one and hence that the samples emitting the alpha particles could not have contained nobelium, as the divalent nobelium would not have eluted with the other trivalent actinides.[50] Thus, the Swedish team later retracted their claim and associated the activity to background effects.[53]
In 1959, the team continued their studies and claimed that they were able to produce an isotope that decayed predominantly by emission of an 8.3 MeV alpha particle, with ahalf-life of 3 s with an associated 30%spontaneous fission branch. The activity was initially assigned to254102 but later changed to252102. However, they also noted that it was not certain that element 102 had been produced due to difficult conditions.[50] The Berkeley team decided to adopt the proposed name of the Swedish team, "nobelium", for the element.[53]
244 96Cm +12 6C →256 102No* →252 102No + 41 0n
Meanwhile, in Dubna, experiments were carried out in 1958 and 1960 aiming to synthesize element 102 as well. The first 1958 experiment bombardedplutonium-239 and-241 withoxygen-16 ions. Some alpha decays with energies just over 8.5 MeV were observed, and they were assigned to251,252,253102, although the team wrote that formation of isotopes fromlead orbismuth impurities (which would not produce nobelium) could not be ruled out. While later 1958 experiments noted that new isotopes could be produced frommercury,thallium, lead, or bismuth impurities, the scientists still stood by their conclusion that element 102 could be produced from this reaction, mentioning a half-life of under 30 seconds and a decay energy of (8.8 ± 0.5) MeV. Later 1960 experiments proved that these were background effects. 1967 experiments also lowered the decay energy to (8.6 ± 0.4) MeV, but both values are too high to possibly match those of253No or254No.[50] The Dubna team later stated in 1970 and again in 1987 that these results were not conclusive.[50]
In 1961, Berkeley scientists claimed the discovery ofelement 103 in the reaction of californium withboron and carbon ions. They claimed the production of the isotope257103, and also claimed to have synthesized an alpha decaying isotope of element 102 that had a half-life of 15 s and alpha decay energy 8.2 MeV. They assigned this to255102 without giving a reason for the assignment. The values do not agree with those now known for255No, although they do agree with those now known for257No, and while this isotope probably played a part in this experiment, its discovery was inconclusive.[50]
Work on element 102 also continued in Dubna, and in 1964, experiments were carried out there to detect alpha-decay daughters of element 102 isotopes by synthesizing element 102 from the reaction of auranium-238 target withneon ions. The products were carried along asilver catcher foil and purified chemically, and the isotopes250Fm and252Fm were detected. The yield of252Fm was interpreted as evidence that its parent256102 was also synthesized: as it was noted that252Fm could also be produced directly in this reaction by the simultaneous emission of an alpha particle with the excess neutrons, steps were taken to ensure that252Fm could not go directly to the catcher foil. The half-life detected for256102 was 8 s, which is much higher than the more modern 1967 value of (3.2 ± 0.2) s.[50] Further experiments were conducted in 1966 for254102, using the reactions243Am(15N,4n)254102 and238U(22Ne,6n)254102, finding a half-life of (50 ± 10) s: at that time the discrepancy between this value and the earlier Berkeley value was not understood, although later work proved that the formation of the isomer250mFm was less likely in the Dubna experiments than at the Berkeley ones. In hindsight, the Dubna results on254102 were probably correct and can be now considered a conclusive detection of element 102.[50]
One more very convincing experiment from Dubna was published in 1966 (though it was submitted in 1965), again using the same two reactions, which concluded that254102 indeed had a half-life much longer than the 3 seconds claimed by Berkeley.[50] Later work in 1967 at Berkeley and 1971 at theOak Ridge National Laboratory fully confirmed the discovery of element 102 and clarified earlier observations.[53] In December 1966, the Berkeley group repeated the Dubna experiments and fully confirmed them, and used this data to finally assign correctly the isotopes they had previously synthesized but could not yet identify at the time. Thus they claimed to have discovered nobelium in 1958 to 1961.[53]
In 1969, the Dubna team carried out chemical experiments on element 102 and concluded that it behaved as the heavier homologue ofytterbium. The Russian scientists proposed the namejoliotium (Jo) for the new element afterIrène Joliot-Curie, who had recently died, creating anelement naming controversy that would not be resolved for several decades, with each group using its own proposed names.[53][55]
In 1992, theIUPAC-IUPAP Transfermium Working Group (TWG) reassessed the claims of discovery and concluded that only the Dubna work from 1966 correctly detected and assigned decays to nuclei with atomic number 102 at the time. The Dubna team are therefore officially recognised as the discoverers of nobelium, although it is possible that it was detected at Berkeley in 1959.[50] This decision was criticized by Berkeley the following year, calling the reopening of the cases of elements 101 to 103 a "futile waste of time", while Dubna agreed with IUPAC's decision.[54]
In 1994, as part of an attempted resolution to the element naming controversy, IUPAC ratified names for elements 101–109. For element 102, it ratified the namenobelium (No) on the basis that it had become entrenched in the literature over the course of 30 years and thatAlfred Nobel should be commemorated in this fashion.[56] Because of outcry over the 1994 names, which mostly did not respect the choices of the discoverers, a comment period ensued, and in 1995 IUPAC named element 102flerovium (Fl) as part of a new proposal, after eitherGeorgy Flyorov or his eponymousFlerov Laboratory of Nuclear Reactions.[57] This proposal was also not accepted, and in 1997 the namenobelium was restored.[56] Today the nameflerovium, with the same symbol, refers toelement 114.[58]
Energy required to promote an f electron to the d subshell for the f-block lanthanides and actinides. Above around 210 kJ/mol, this energy is too high to be provided for by the greatercrystal energy of the trivalent state and thus einsteinium, fermium, and mendelevium form divalent metals like the lanthanideseuropium andytterbium. Nobelium is also expected to form a divalent metal, but this has not yet been confirmed.[59]
In theperiodic table, nobelium is located to the right of the actinidemendelevium, to the left of the actinidelawrencium, and below the lanthanideytterbium. Nobelium metal has not yet been prepared in bulk quantities, and bulk preparation is currently impossible.[60] Nevertheless, a number of predictions and some preliminary experimental results have been done regarding its properties.[60]
The lanthanides and actinides, in the metallic state, can exist as either divalent (such aseuropium andytterbium) or trivalent (most other lanthanides) metals. The former have fns2 configurations, whereas the latter have fn−1d1s2 configurations. In 1975, Johansson and Rosengren examined the measured and predicted values for thecohesive energies (enthalpies of crystallization) of the metalliclanthanides andactinides, both as divalent and trivalent metals.[61][62] The conclusion was that the increased binding energy of the [Rn]5f136d17s2 configuration over the [Rn]5f147s2 configuration for nobelium was not enough to compensate for the energy needed to promote one 5f electron to 6d, as is true also for the very late actinides: thuseinsteinium,fermium,mendelevium, and nobelium were expected to be divalent metals, although for nobelium this prediction has not yet been confirmed.[61] The increasing predominance of the divalent state well before the actinide series concludes is attributed to therelativistic stabilization of the 5f electrons, which increases with increasing atomic number: an effect of this is that nobelium is predominantly divalent instead of trivalent, unlike all the other lanthanides and actinides.[63] In 1986, nobelium metal was estimated to have anenthalpy of sublimation between 126 kJ/mol, a value close to the values for einsteinium, fermium, and mendelevium and supporting the theory that nobelium would form a divalent metal.[60] Like the other divalent late actinides (except the once again trivalent lawrencium), metallic nobelium should assume aface-centered cubic crystal structure.[2] Divalent nobelium metal should have ametallic radius of around 197 pm.[60] Nobelium's melting point has been predicted to be 800 °C, the same value as that estimated for the neighboring element mendelevium.[64] Its density is predicted to be around 9.9 ± 0.4 g/cm3.[2]
The chemistry of nobelium is incompletely characterized and is known only in aqueous solution, in which it can take on the +3 or +2oxidation states, the latter being more stable.[51] It was largely expected before the discovery of nobelium that in solution, it would behave like the other actinides, with the trivalent state being predominant; however, Seaborg predicted in 1949 that the +2 state would also be relatively stable for nobelium, as the No2+ ion would have the ground-state electron configuration [Rn]5f14, including the stable filled 5f14 shell. It took nineteen years before this prediction was confirmed.[65]
In 1967, experiments were conducted to compare nobelium's chemical behavior to that ofterbium,californium, andfermium. All four elements were reacted withchlorine and the resulting chlorides were deposited along a tube, along which they were carried by a gas. It was found that the nobelium chloride produced was stronglyadsorbed on solid surfaces, proving that it was not veryvolatile, like the chlorides of the other three investigated elements. However, both NoCl2 and NoCl3 were expected to exhibit nonvolatile behavior and hence this experiment was inconclusive as to what the preferred oxidation state of nobelium was.[65] Determination of nobelium's favoring of the +2 state had to wait until the next year, whencation-exchange chromatography andcoprecipitation experiments were carried out on around fifty thousand255No atoms, finding that it behaved differently from the other actinides and more like the divalentalkaline earth metals. This proved that in aqueous solution, nobelium is most stable in the divalent state when strongoxidizers are absent.[65] Later experimentation in 1974 showed that nobelium eluted with the alkaline earth metals, betweenCa2+ andSr2+.[65] Nobelium is the only known f-block element for which the +2 state is the most common and stable one in aqueous solution. This occurs because of the large energy gap between the 5f and 6d orbitals at the end of the actinide series.[66]
It is expected that the relativistic stabilization of the 7s subshell greatly destabilizes nobelium dihydride, NoH2, and relativistic stabilisation of the 7p1/2 spinor over the 6d3/2 spinor mean that excited states in nobelium atoms have 7s and 7p contribution instead of the expected 6d contribution. The long No–H distances in the NoH2 molecule and the significant charge transfer lead to extreme ionicity with adipole moment of 5.94 D for this molecule. In this molecule, nobelium is expected to exhibitmain-group-like behavior, specifically acting like analkaline earth metal with itsns2 valence shell configuration and core-like 5f orbitals.[67]
Nobelium'scomplexing ability withchloride ions is most similar to that ofbarium, which complexes rather weakly.[65] Its complexing ability withcitrate,oxalate, andacetate in an aqueous solution of 0.5 M ammonium nitrate is between that of calcium and strontium, although it is somewhat closer to that of strontium.[65]
Thestandard reduction potential of theE°(No3+→No2+) couple was estimated in 1967 to be between +1.4 and +1.5 V;[65] it was later found in 2009 to be only about +0.75 V.[68] The positive value shows that No2+ is more stable than No3+ and that No3+ is a good oxidizing agent. While the quoted values for theE°(No2+→No0) andE°(No3+→No0) vary among sources, the accepted standard estimates are −2.61 and −1.26 V.[65] It has been predicted that the value for theE°(No4+→No3+) couple would be +6.5 V.[65] TheGibbs energies of formation for No3+ and No2+ are estimated to be −342 and −480 kJ/mol, respectively.[65]
A nobelium atom has 102 electrons. They are expected to be arranged in the configuration [Rn]5f147s2 (ground stateterm symbol1S0), although experimental verification of this electron configuration had not yet been made as of 2006. The sixteen electrons in the 5f and 7s subshells arevalence electrons.[60] In forming compounds, three valence electrons may be lost, leaving behind a [Rn]5f13 core: this conforms to the trend set by the other actinides with their [Rn]5fn electron configurations in the tripositive state. Nevertheless, it is more likely that only two valence electrons are lost, leaving behind a stable [Rn]5f14 core with a filled 5f14 shell. The firstionization potential of nobelium was measured to be at most (6.65 ± 0.07) eV in 1974, based on the assumption that the 7s electrons would ionize before the 5f ones;[69] this value has not yet been refined further due to nobelium's scarcity and high radioactivity.[70] The ionic radius ofhexacoordinate and octacoordinate No3+ had been preliminarily estimated in 1978 to be around 90 and 102 pm respectively;[65] the ionic radius of No2+ has been experimentally found to be 100 pm to twosignificant figures.[60] Theenthalpy of hydration of No2+ has been calculated as 1486 kJ/mol.[65]
Fourteen isotopes of nobelium are known, withmass numbers 248–260 and 262; all are radioactive.[6] Additionally,nuclear isomers are known for mass numbers 250, 251, 253, and 254.[71][72] Of these, the longest-lived isotope is259No with a half-life of 58 minutes, and the longest-lived isomer is251mNo with a half-life of 1.7 seconds.[71][72] However, the still undiscovered isotope261No is predicted to have a still longer half-life of 3 hours.[6] Additionally, the shorter-lived255No (half-life 3.1 minutes) is more often used in chemical experimentation because it can be produced in larger quantities from irradiation ofcalifornium-249 withcarbon-12 ions.[73] After259No and255No, the next most stable nobelium isotopes are253No (half-life 1.62 minutes),254No (51 seconds),257No (25 seconds),256No (2.91 seconds), and252No (2.57 seconds).[73][71][72] All of the remaining nobelium isotopes have half-lives that are less than a second, and the shortest-lived known nobelium isotope (248No) has a half-life of less than 2 microseconds.[6] The isotope254No is especially interesting theoretically as it is in the middle of a series ofprolate nuclei from231Pa to279Rg, and the formation of its nuclear isomers (of which two are known) is controlled byproton orbitals such as 2f5/2 which come just above the spherical proton shell; it can be synthesized in the reaction of208Pb with48Ca.[74]
The half-lives of nobelium isotopes increase smoothly from250No to253No. However, a dip appears at254No, and beyond this the half-lives ofeven-even nobelium isotopes drop sharply asspontaneous fission becomes the dominant decay mode. For example, the half-life of256No is almost three seconds, but that of258No is only 1.2 milliseconds.[73][71][72] This shows that at nobelium, the mutual repulsion of protons poses a limit to theregion of long-lived nuclei in theactinide series.[75] The even-odd nobelium isotopes mostly continue to have longer half-lives as their mass numbers increase, with a dip in the trend at257No.[73][71][72]
The isotopes of nobelium are mostly produced by bombarding actinide targets (uranium,plutonium,curium,californium, oreinsteinium), with the exception of nobelium-262, which is produced as thedaughter of lawrencium-262.[73] The most commonly used isotope,255No, can be produced from bombardingcurium-248 or californium-249 with carbon-12: the latter method is more common. Irradiating a 350 μg cm−2 target of californium-249 with three trillion 73 MeV carbon-12 ions per second for ten minutes can produce around 1200 nobelium-255 atoms.[73]
Once the nobelium-255 is produced, it can be separated out similarly as used to purify the neighboring actinide mendelevium. The recoilmomentum of the produced nobelium-255 atoms is used to bring them physically far away from the target from which they are produced, bringing them onto a thin foil of metal (usuallyberyllium,aluminium,platinum, orgold) just behind the target in a vacuum: this is usually combined by trapping the nobelium atoms in a gas atmosphere (frequentlyhelium), and carrying them along with a gas jet from a small opening in the reaction chamber. Using a longcapillary tube, and includingpotassium chloride aerosols in the helium gas, the nobelium atoms can be transported over tens ofmeters.[76] The thin layer of nobelium collected on the foil can then be removed with dilute acid without completely dissolving the foil.[76] The nobelium can then be isolated by exploiting its tendency to form the divalent state, unlike the other trivalent actinides: under typically usedelution conditions (bis-(2-ethylhexyl) phosphoric acid (HDEHP) as stationary organic phase and 0.05 M hydrochloric acid as mobile aqueous phase, or using 3 M hydrochloric acid as an eluant fromcation-exchange resin columns), nobelium will pass through the column and elute while the other trivalent actinides remain on the column.[76] However, if a direct "catcher" gold foil is used, the process is complicated by the need to separate out the gold usinganion-exchangechromatography before isolating the nobelium by elution fromchromatographic extraction columns using HDEHP.[76]
^The density is calculated from the predicted metallic radius (Silva 2008, p. 1639) and the predicted close-packed crystal structure (Fournier 1976).
^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[7] or112;[8] sometimes, the term is presented an equivalent to the term "transactinide", which puts an upper limit before the beginning of the hypotheticalsuperactinide series).[9] 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.[10] 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.[11]
^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.[15]
^This figure also marks the generally accepted upper limit for lifetime of a compound nucleus.[20]
^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.[22] 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.[23]
^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.[35]
^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.[40] The first direct measurement of mass of a superheavy nucleus was reported in 2018 at LBNL.[41] 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).[42]
^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).[31] 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,[43] a leading scientist at JINR, and thus it was a "hobbyhorse" for the facility.[44] 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.[20] They thus preferred to link new isotopes to the already known ones by successive alpha decays.[43]
^For instance, element 102 was mistakenly identified in 1957 at the Nobel Institute of Physics inStockholm,Stockholm County,Sweden.[45] 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.[46] 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.[46] JINR insisted that they were the first to create the element and suggested a name of their own for the new element,joliotium;[47] the Soviet name was also not accepted (JINR later referred to the naming of the element 102 as "hasty").[48] This name was proposed to IUPAC in a written response to their ruling on priority of discovery claims of elements, signed 29 September 1992.[48] The name "nobelium" remained unchanged on account of its widespread usage.[49]
^Pore, Jennifer L.; Gates, Jacklyn M.; Dixon, David A.; Garcia, Fatima H.; Gibson, John K.; Gooding, John A.; McCarthy, Mallory; Orford, Rodney; Shafi, Ziad; Shuh, David K.; Sprouse, Sarah (2025). "Direct identification of Ac and No molecules with an atom-at-a-time technique".Nature.644. Springer Science and Business Media LLC:376–380.doi:10.1038/s41586-025-09342-y.ISSN0028-0836.
^Dean, John A., ed. (1999).Lange's Handbook of Chemistry (15 ed.). McGraw-Hill. Section 4; Table 4.5, Electronegativities of the Elements.
^Sato, Tetsuya K.; Asai, Masato; Borschevsky, Anastasia; Beerwerth, Randolf; Kaneya, Yusuke; Makii, Hiroyuki; Mitsukai, Akina; Nagame, Yuichiro; Osa, Akihiko; Toyoshima, Atsushi; Tsukada, Kazuki; Sakama, Minoru; Takeda, Shinsaku; Ooe, Kazuhiro; Sato, Daisuke; Shigekawa, Yudai; Ichikawa, Shin-ichi; Düllmann, Christoph E.; Grund, Jessica; Renisch, Dennis; Kratz, Jens V.; Schädel, Matthias; Eliav, Ephraim; Kaldor, Uzi; Fritzsche, Stephan; Stora, Thierry (25 October 2018). "First Ionization Potentials of Fm, Md, No, and Lr: Verification of Filling-Up of 5f Electrons and Confirmation of the Actinide Series".Journal of the American Chemical Society.140 (44):14609–14613.doi:10.1021/jacs.8b09068.
^"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.
^Fields, Peter R.; Friedman, Arnold M.; Milsted, John; Atterling, Hugo; Forsling, Wilhelm; Holm, Lennart W.; Åström, Björn (1 September 1957). "Production of the New Element 102".Physical Review.107 (5):1460–1462.Bibcode:1957PhRv..107.1460F.doi:10.1103/PhysRev.107.1460.
^Johansson, Börje; Rosengren, Anders (1975). "Generalized phase diagram for the rare-earth elements: Calculations and correlations of bulk properties".Physical Review B.11 (8):2836–2857.Bibcode:1975PhRvB..11.2836J.doi:10.1103/PhysRevB.11.2836.
^Balasubramanian, Krishnan (4 December 2001). "Potential energy surfaces of Lawrencium and Nobelium dihydrides (LrH2 and NoH2)…".Journal of Chemical Physics.116 (9):3568–75.Bibcode:2002JChPh.116.3568B.doi:10.1063/1.1446029.
^Lide, David R. (editor),CRC Handbook of Chemistry and Physics, 84th Edition, CRC Press, Boca Raton (FL), 2003, section 10,Atomic, Molecular, and Optical Physics; Ionization Potentials of Atoms and Atomic Ions
