Moscovium

Moscovium is a synthetic chemical element with the symbol Mc and atomic number 115. It was first synthesized in 2003 by a joint team of Russian and American scientists at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. In December 2015, it was recognized as one of four new elements by the Joint Working Party of international scientific bodies IUPAC and IUPAP. On 28 November 2016, it was officially named after the Moscow Oblast, in which the JINR is situated.[6][7][8]

Moscovium, 115Mc
Moscovium
Pronunciation/mɒsˈkviəm/ (mos-KOH-vee-əm)
Mass number[290]
Moscovium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Bi

Mc

(Uhe)
fleroviummoscoviumlivermorium
Atomic number (Z)115
Groupgroup 15 (pnictogens)
Periodperiod 7
Blockp-block
Element category  Unknown chemical properties, but probably a post-transition metal
Electron configuration[Rn] 5f14 6d10 7s2 7p3 (predicted)[1]
Electrons per shell2, 8, 18, 32, 32, 18, 5 (predicted)
Physical properties
Phase at STPsolid (predicted)[1]
Melting point670 K ​(400 °C, ​750 °F) (predicted)[1][2]
Boiling point~1400 K ​(~1100 °C, ​~2000 °F) (predicted)[1]
Density (near r.t.)13.5 g/cm3 (predicted)[2]
Heat of fusion5.90–5.98 kJ/mol (extrapolated)[3]
Heat of vaporization138 kJ/mol (predicted)[2]
Atomic properties
Oxidation states(+1), (+3) (predicted)[1][2]
Ionization energies
  • 1st: 538.3 kJ/mol (predicted)[4]
  • 2nd: 1760 kJ/mol (predicted)[2]
  • 3rd: 2650 kJ/mol (predicted)[2]
  • (more)
Atomic radiusempirical: 187 pm (predicted)[1][2]
Covalent radius156–158 pm (extrapolated)[3]
Other properties
Natural occurrencesynthetic
CAS Number54085-64-2
History
NamingAfter Moscow region
DiscoveryJoint Institute for Nuclear Research and Lawrence Livermore National Laboratory (2003)
Main isotopes of moscovium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
287Mc syn 37 ms α 283Nh
288Mc syn 164 ms α 284Nh
289Mc syn 330 ms[5] α 285Nh
290Mc syn 650 ms[5] α 286Nh
Category Category: Moscovium
| references

Moscovium is an extremely radioactive element: its most stable known isotope, moscovium-290, has a half-life of only 0.65 seconds.[9] In the periodic table, it is a p-block transactinide element. It is a member of the 7th period and is placed in group 15 as the heaviest pnictogen, although it has not been confirmed to behave as a heavier homologue of the pnictogen bismuth. Moscovium is calculated to have some properties similar to its lighter homologues, nitrogen, phosphorus, arsenic, antimony, and bismuth, and to be a post-transition metal, although it should also show several major differences from them. In particular, moscovium should also have significant similarities to thallium, as both have one rather loosely bound electron outside a quasi-closed shell. About 100 atoms of moscovium have been observed to date, all of which have been shown to have mass numbers from 287 to 290.

IntroductionEdit

 
A graphic depiction of a nuclear fusion reaction. Two nuclei fuse into one, emitting a neutron. 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.
External video
  Visualization of unsuccessful nuclear fusion, based on calculations by the Australian National University[10]

The heaviest[a] atomic nuclei are created in nuclear reactions that combine two other nuclei of unequal size[b] into one; roughly, the more unequal the two nuclei in terms of mass, 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 the beam of lighter nuclei. Two nuclei can only fuse into one if they approach each other closely enough; normally, nuclei (all positively charged) repel each other due to electrostatic repulsion. The strong interaction can overcome this repulsion but only within a very short distance from a nucleus; beam nuclei are thus greatly accelerated in order to make such repulsion insignificant compared to the velocity of the beam nucleus.[17] Coming close alone is not enough for two nuclei to fuse: when two nuclei approach each other, they usually remain together for approximately 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] If fusion does occur, the temporary merger—termed a compound nucleus—is an excited state. To lose its excitation energy and reach a more stable state, a compound nucleus either fissions or ejects one or several neutrons,[c] which carry away the energy. This occurs in approximately 10−16 seconds after the initial collision.[19][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.[22] 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 a surface-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.[22] The transfer takes about 10−6 seconds; in order to be detected, the nucleus must survive this long.[25] The nucleus is recorded again once its decay is registered, and the location, the energy, and the time of the decay are measured.[22]

Stability of a nucleus is provided by the strong interaction. However, its range is very short; as nuclei become larger, its influence on the outermost nucleons (protons and neutrons) weakens. At the same time, the nucleus is torn apart by electrostatic repulsion between protons, as it has unlimited range.[26] Nuclei of the heaviest elements are thus theoretically predicted[27] and have so far been observed[28] to primarily decay via decay modes that are caused by such repulsion: alpha decay and spontaneous fission;[f] these modes are predominant for nuclei of superheavy elements. 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 determined arithmetically.[g] Spontaneous fission, however, produces various nuclei as products, so the original nuclide cannot be determined from its daughters.[h]

The information available to physicists aiming to synthesize one of the heaviest elements 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.[i]

HistoryEdit

 
A view of the famous Red Square in Moscow. The region around the city was honored by the discoverers as "the ancient Russian land that is the home of the Joint Institute for Nuclear Research" and became the namesake of moscovium.

DiscoveryEdit

The first successful synthesis of moscovium was by a joint team of Russian and American scientists in August 2003 at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. Headed by Russian nuclear physicist Yuri Oganessian, the team included American scientists of the Lawrence Livermore National Laboratory. The researchers on February 2, 2004, stated in Physical Review C that they bombarded americium-243 with calcium-48 ions to produce four atoms of moscovium. These atoms decayed by emission of alpha-particles to nihonium in about 100 milliseconds.[40][41]

243
95
Am
+ 48
20
Ca
287
115
Mc
+ 4 1
0
n
283
113
Nh
+
α

The Dubna–Livermore collaboration strengthened their claim to the discoveries of moscovium and nihonium by conducting chemical experiments on the final decay product 268Db. None of the nuclides in this decay chain were previously known, so existing experimental data was not available to support their claim. In June 2004 and December 2005, the presence of a dubnium isotope was confirmed by extracting the final decay products, measuring spontaneous fission (SF) activities and using chemical identification techniques to confirm that they behave like a group 5 element (as dubnium is known to be in group 5 of the periodic table).[1][42] Both the half-life and the decay mode were confirmed for the proposed 268Db, lending support to the assignment of the parent nucleus to moscovium.[42][43] However, in 2011, the IUPAC/IUPAP Joint Working Party (JWP) did not recognize the two elements as having been discovered, because current theory could not distinguish the chemical properties of group 4 and group 5 elements with sufficient confidence.[44] Furthermore, the decay properties of all the nuclei in the decay chain of moscovium had not been previously characterized before the Dubna experiments, a situation which the JWP generally considers "troublesome, but not necessarily exclusive".[44]

Road to confirmationEdit

Two heavier isotopes of moscovium, 289Mc and 290Mc, were discovered in 2009–2010 as daughters of the tennessine isotopes 293Ts and 294Ts; the isotope 289Mc was later also synthesized directly and confirmed to have the same properties as found in the tennessine experiments.[5] The JINR also had plans to study lighter isotopes of moscovium in 2017 by replacing the americium-243 target with the lighter isotope americium-241.[45][46] The 48Ca+243Am reaction producing moscovium is planned to be the first experiment done at the new SHE Factory in 2018 at Dubna to test the systems in preparation for attempts at synthesising elements 119 and 120.[47]

In 2011, the Joint Working Party of international scientific bodies International Union of Pure and Applied Chemistry (IUPAC) and International Union of Pure and Applied Physics (IUPAP) evaluated the 2004 and 2007 Dubna experiments, and concluded that they did not meet the criteria for discovery. Another evaluation of more recent experiments took place within the next few years, and a claim to the discovery of moscovium was again put forward by Dubna.[44] In August 2013, a team of researchers at Lund University and at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany announced they had repeated the 2004 experiment, confirming Dubna's findings.[48][49] Simultaneously, the 2004 experiment had been repeated at Dubna, now additionally also creating the isotope 289Mc that could serve as a cross-bombardment for confirming the discovery of the tennessine isotope 293Ts in 2010.[50] Further confirmation was published by the team at the Lawrence Berkeley National Laboratory in 2015.[51]

In December 2015, the IUPAC/IUPAP Joint Working Party recognized the element's discovery and assigned the priority to the Dubna-Livermore collaboration of 2009–2010, giving them the right to suggest a permanent name for it.[52] While they did not recognise the experiments synthesising 287Mc and 288Mc as persuasive due to the lack of a convincing identification of atomic number via cross-reactions, they recognised the 293Ts experiments as persuasive because its daughter 289Mc had been produced independently and found to exhibit the same properties.[50]

In May 2016, Lund University (Lund, Scania, Sweden) and GSI cast some doubt on the syntheses of moscovium and tennessine. The decay chains assigned to 289Mc, the isotope instrumental in the confirmation of the syntheses of moscovium and tennessine, were found based on a new statistical method to be too different to belong to the same nuclide with a reasonably high probability. The reported 293Ts decay chains approved as such by the JWP were found to require splitting into individual data sets assigned to different tennessine isotopes. It was also found that the claimed link between the decay chains reported as from 293Ts and 289Mc probably did not exist. (On the other hand, the chains from the non-approved isotope 294Ts were found to be congruent.) The multiplicity of states found when nuclides that are not even–even undergo alpha decay is not unexpected and contributes to the lack of clarity in the cross-reactions. This study criticized the JWP report for overlooking subtleties associated with this issue, and considered it "problematic" that the only argument for the acceptance of the discoveries of moscovium and tennessine was a link they considered to be doubtful.[53][54]

On June 8, 2017, two members of the Dubna team published a journal article answering these criticisms, analysing their data on the nuclides 293Ts and 289Mc with widely accepted statistical methods, noted that the 2016 studies indicating non-congruence produced problematic results when applied to radioactive decay: they excluded from the 90% confidence interval both average and extreme decay times, and the decay chains that would be excluded from the 90% confidence interval they chose were more probable to be observed than those that would be included. The 2017 reanalysis concluded that the observed decay chains of 293Ts and 289Mc were consistent with the assumption that only one nuclide was present at each step of the chain, although it would be desirable to be able to directly measure the mass number of the originating nucleus of each chain as well as the excitation function of the 243Am+48Ca reaction.[55]

NamingEdit

Using Mendeleev's nomenclature for unnamed and undiscovered elements, moscovium is sometimes known as eka-bismuth. In 1979 IUPAC recommended that the placeholder systematic element name ununpentium (with the corresponding symbol of Uup)[56] be used until the discovery of the element is confirmed and a permanent name is decided. Although widely used in the chemical community on all levels, from chemistry classrooms to advanced textbooks, the recommendations were mostly ignored among scientists in the field, who called it "element 115", with the symbol of E115, (115) or even simply 115.[1]

On 30 December 2015, discovery of the element was recognized by the International Union of Pure and Applied Chemistry (IUPAC).[57] According to IUPAC recommendations, the discoverer(s) of a new element has the right to suggest a name.[58] A suggested name was langevinium, after Paul Langevin.[59] Later, the Dubna team mentioned the name moscovium several times as one among many possibilities, referring to the Moscow Oblast where Dubna is located.[60][61]

In June 2016, IUPAC endorsed the latter proposal to be formally accepted by the end of the year, which it was on 28 November 2016.[8] The naming ceremony for moscovium, tennessine, and oganesson was held on 2 March 2017 at the Russian Academy of Sciences in Moscow.[62]

Predicted propertiesEdit

No properties of moscovium or its compounds have been measured; this is due to its extremely limited and expensive production[16] and the fact that it decays very quickly. Properties of moscovium remain unknown and only predictions are available.

Nuclear stability and isotopesEdit

 
The expected location of the island of stability. The dotted line is the line of beta stability.

Moscovium is expected to be within an island of stability centered on copernicium (element 112) and flerovium (element 114).[63][64] Due to the expected high fission barriers, any nucleus within this island of stability exclusively decays by alpha decay and perhaps some electron capture and beta decay.[2] Although the known isotopes of moscovium do not actually have enough neutrons to be on the island of stability, they can be seen to approach the island as in general, the heavier isotopes are the longer-lived ones.[5][42]

The hypothetical isotope 291Mc is an especially interesting case as it has only one neutron more than the heaviest known moscovium isotope, 290Mc. It could plausibly be synthesized as the daughter of 295Ts, which in turn could be made from the reaction 249Bk(48Ca,2n)295Ts.[63] Calculations show that it may have a significant electron capture or positron emission decay mode in addition to alpha decaying and also have a relatively long half-life of several seconds. This would produce 291Fl, 291Nh, and finally 291Cn which is expected to be in the middle of the island of stability and have a half-life of about 1200 years, affording the most likely hope of reaching the middle of the island using current technology. Possible drawbacks are that the cross section of the production reaction of 295Ts is expected to be low and the decay properties of superheavy nuclei this close to the line of beta stability are largely unexplored.[63]

Other possibilities to synthesize nuclei on the island of stability include quasifission (partial fusion followed by fission) of a massive nucleus.[65] Such nuclei tend to fission, expelling doubly magic or nearly doubly magic fragments such as calcium-40, tin-132, lead-208, or bismuth-209.[66] Recently it has been shown that the multi-nucleon transfer reactions in collisions of actinide nuclei (such as uranium and curium) might be used to synthesize the neutron-rich superheavy nuclei located at the island of stability,[65] although formation of the lighter elements nobelium or seaborgium is more favored.[63] One last possibility to synthesize isotopes near the island is to use controlled nuclear explosions to create a neutron flux high enough to bypass the gaps of instability at 258–260Fm and at mass number 275 (atomic numbers 104 to 108), mimicking the r-process in which the actinides were first produced in nature and the gap of instability around radon bypassed.[63] Some such isotopes (especially 291Cn and 293Cn) may even have been synthesized in nature, but would have decayed away far too quickly (with half-lives of only thousands of years) and be produced in far too small quantities (about 10−12 the abundance of lead) to be detectable as primordial nuclides today outside cosmic rays.[63]

Physical and atomicEdit

In the periodic table, moscovium is a member of group 15, the pnictogens, below nitrogen, phosphorus, arsenic, antimony, and bismuth. Every previous pnictogen has five electrons in its valence shell, forming a valence electron configuration of ns2np3. In moscovium's case, the trend should be continued and the valence electron configuration is predicted to be 7s27p3;[1] therefore, moscovium will behave similarly to its lighter congeners in many respects. However, notable differences are likely to arise; a largely contributing effect is the spin–orbit (SO) interaction—the mutual interaction between the electrons' motion and spin. It is especially strong for the superheavy elements, because their electrons move much faster than in lighter atoms, at velocities comparable to the speed of light.[67] In relation to moscovium atoms, it lowers the 7s and the 7p electron energy levels (stabilizing the corresponding electrons), but two of the 7p electron energy levels are stabilized more than the other four.[68] The stabilization of the 7s electrons is called the inert pair effect, and the effect "tearing" the 7p subshell into the more stabilized and the less stabilized parts is called subshell splitting. Computation chemists see the split as a change of the second (azimuthal) quantum number l from 1 to ​12 and ​32 for the more stabilized and less stabilized parts of the 7p subshell, respectively.[67][j] For many theoretical purposes, the valence electron configuration may be represented to reflect the 7p subshell split as 7s2
7p2
1/2
7p1
3/2
.[1] These effects cause moscovium's chemistry to be somewhat different from that of its lighter congeners.

The valence electrons of moscovium fall into three subshells: 7s (two electrons), 7p1/2 (two electrons), and 7p3/2 (one electron). The first two of these are relativistically stabilized and hence behave as inert pairs, while the last is relativistically destabilized and can easily participate in chemistry.[1] (The 6d electrons are not destabilized enough to participate chemically, although this may still be possible in the two previous elements nihonium and flerovium.)[2] Thus, the +1 oxidation state should be favored, like Tl+, and consistent with this the first ionization potential of moscovium should be around 5.58 eV, continuing the trend towards lower ionization potentials down the pnictogens.[1] Moscovium and nihonium both have one electron outside a quasi-closed shell configuration that can be delocalized in the metallic state: thus they should have similar melting and boiling points (both melting around 400 °C and boiling around 1100 °C) due to the strength of their metallic bonds being similar.[2] Additionally, the predicted ionization potential, ionic radius (1.5 Å for Mc+; 1.0 Å for Mc3+), and polarizability of Mc+ are expected to be more similar to Tl+ than its true congener Bi3+.[2] Moscovium should be a dense metal due to its high atomic weight, with a density around 13.5 g/cm3.[2] The electron of the hydrogen-like moscovium atom (oxidized so that it only has one electron, Mc114+) is expected to move so fast that it has a mass 1.82 times that of a stationary electron, due to relativistic effects. For comparison, the figures for hydrogen-like bismuth and antimony are expected to be 1.25 and 1.077 respectively.[67]

ChemicalEdit

Moscovium is predicted to be the third member of the 7p series of chemical elements and the heaviest member of group 15 in the periodic table, below bismuth. Unlike the two previous 7p elements, moscovium is expected to be a good homologue of its lighter congener, in this case bismuth.[69] In this group, each member is known to portray the group oxidation state of +5 but with differing stability. For nitrogen, the +5 state is mostly a formal explanation of molecules like N2O5: it is very difficult to have five covalent bonds to nitrogen due to the inability of the small nitrogen atom to accommodate five ligands. The +5 state is well represented for the essentially non-relativistic typical pnictogens phosphorus, arsenic, and antimony. However, for bismuth it becomes rare due to the relativistic stabilization of the 6s orbitals known as the inert pair effect, so that the 6s electrons are reluctant to bond chemically. It is expected that moscovium will have an inert pair effect for both the 7s and the 7p1/2 electrons, as the binding energy of the lone 7p3/2 electron is noticeably lower than that of the 7p1/2 electrons. Nitrogen(I) and bismuth(I) are known but rare and moscovium(I) is likely to show some unique properties,[70] probably behaving more like thallium(I) than bismuth(I).[2] Because of spin-orbit coupling, flerovium may display closed-shell or noble gas-like properties; if this is the case, moscovium will likely be typically monovalent as a result, since the cation Mc+ will have the same electron configuration as flerovium, perhaps giving moscovium some alkali metal character.[2] Calculations predict that moscovium(I) fluoride and chloride would be ionic compounds, with an ionic radius of about 109–114 pm for Mc+, although the 7p1/2 lone pair on the Mc+ ion should be highly polarisable.[71] The Mc3+ cation should behave like its true lighter homolog Bi3+.[2] The 7s electrons are too stabilized to be able to contribute chemically and hence the +5 state should be impossible and moscovium may be considered to have only three valence electrons.[2] Moscovium would be quite a reactive metal, with a standard reduction potential of −1.5 V for the Mc+/Mc couple.[2]

The chemistry of moscovium in aqueous solution should essentially be that of the Mc+ and Mc3+ ions. The former should be easily hydrolyzed and not be easily complexed with halides, cyanide, and ammonia.[2] Moscovium(I) hydroxide (McOH), carbonate (Mc2CO3), oxalate (Mc2C2O4), and fluoride (McF) should be soluble in water; the sulfide (Mc2S) should be insoluble; and the chloride (McCl), bromide (McBr), iodide (McI), and thiocyanate (McSCN) should be only slightly soluble, so that adding excess hydrochloric acid would not noticeably affect the solubility of moscovium(I) chloride.[2] Mc3+ should be about as stable as Tl3+ and hence should also be an important part of moscovium chemistry, although its closest homolog among the elements should be its lighter congener Bi3+.[2] Moscovium(III) fluoride (McF3) and thiozonide (McS3) should be insoluble in water, similar to the corresponding bismuth compounds, while moscovium(III) chloride (McCl3), bromide (McBr3), and iodide (McI3) should be readily soluble and easily hydrolyzed to form oxyhalides such as McOCl and McOBr, again analogous to bismuth.[2] Both moscovium(I) and moscovium(III) should be common oxidation states and their relative stability should depend greatly on what they are complexed with and the likelihood of hydrolysis.[2]

Like its lighter homologues ammonia, phosphine, arsine, stibine, and bismuthine, moscovine (McH3) is expected to have a trigonal pyramidal molecular geometry, with an Mc–H bond length of 195.4 pm and a H–Mc–H bond angle of 91.8° (bismuthine has bond length 181.7 pm and bond angle 91.9°; stibine has bond length 172.3 pm and bond angle 92.0°).[72] In the predicted aromatic pentagonal planar Mc
5
cluster, analogous to pentazolate (N
5
), the Mc–Mc bond length is expected to be expanded from the extrapolated value of 156–158 pm to 329 pm due to spin–orbit coupling effects.[73]

Experimental chemistryEdit

Unambiguous determination of the chemical characteristics of moscovium has yet to have been established.[74][75] In 2011, experiments were conducted to create nihonium, flerovium, and moscovium isotopes in the reactions between calcium-48 projectiles and targets of americium-243 and plutonium-244. However, the targets included lead and bismuth impurities and hence some isotopes of bismuth and polonium were generated in nucleon transfer reactions. This, while an unforeseen complication, could give information that would help in the future chemical investigation of the heavier homologs of bismuth and polonium, which are respectively moscovium and livermorium.[75] The produced nuclides bismuth-213 and polonium-212m were transported as the hydrides 213BiH3 and 212mPoH2 at 850 °C through a quartz wool filter unit held with tantalum, showing that these hydrides were surprisingly thermally stable, although their heavier congeners McH3 and LvH2 would be expected to be less thermally stable from simple extrapolation of periodic trends in the p-block.[75] Further calculations on the stability and electronic structure of BiH3, McH3, PoH2, and LvH2 are needed before chemical investigations take place. However, moscovium and livermorium are expected to be volatile enough as pure elements for them to be chemically investigated in the near future. The moscovium isotopes 288Mc, 289Mc, and 290Mc may be chemically investigated with current methods, although their short half-lives would make this challenging.[75] Moscovium is the heaviest element that has known isotopes that are long-lived enough for chemical experimentation.[76]

See alsoEdit

NotesEdit

  1. ^ In nuclear physics, an element is called heavy 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 than 103 (although there are other definitions, such as atomic number greater than 100[11] or 112;[12] sometimes, the term is presented an equivalent to the term "transactinide", which puts an upper limit before the beginning of the hypothetical superactinide 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.
  2. ^ In 2009, a team at JINR led by Oganessian published results of their attempt to create hassium in a symmetric 136Xe + 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]
  3. ^ The greater the excitation energy, the more neutrons are ejected. If the excitation energy is lower than energy binding each neutron to the rest of the nucleus, neutrons are not emitted; instead, the compound nucleus de-excites by emitting a gamma ray.[19]
  4. ^ The definition by the IUPAC/IUPAP Joint Working Party states that a chemical element can only be recognized as discovered if a nucleus of it has not decayed within 10−14 seconds. This value was chosen as an estimate of how long it takes a nucleus to acquire its outer electrons and thus display its chemical properties.[20] This figure also marks the generally accepted upper limit for lifetime of a compound nucleus.[21]
  5. ^ 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.[23] Such separation can also be aided by a time-of-flight measurement and a recoil energy measurement; a combination of the two may allow to estimate the mass of a nucleus.[24]
  6. ^ Not all decay modes are caused by electrostatic repulsion. For example, beta decay is caused by the weak interaction.[29]
  7. ^ 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 heaviest nuclei.[30] The first direct measurement of mass of a superheavy nucleus was reported in 2018 at LBNL.[31] 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).[32]
  8. ^ Spontaneous fission was discovered by Soviet physicist Georgy Flerov,[33] a leading scientist at JINR, and thus it was a "hobbyhorse" for the facility.[34] 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.[21] They thus preferred to link new isotopes to the already known ones by successive alpha decays.[33]
  9. ^ For instance, element 102 was mistakenly identified in 1957 at the Nobel Institute of Physics in Stockholm, Stockholm County, Sweden.[35] 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.[36] 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.[36] JINR insisted that they were the first to create the element and suggested a name of their own for the new element, joliotium;[37] the Soviet name was also not accepted (JINR later referred to the naming of element 102 as "hasty").[38] The name "nobelium" remained unchanged on account of its widespread usage.[39]
  10. ^ The quantum number corresponds to the letter in the electron orbital name: 0 to s, 1 to p, 2 to d, etc. See azimuthal quantum number for more information.

ReferencesEdit

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