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Hassium

February 15, 2024

Hassium is a chemical element; it has symbol Hs and atomic number 108. Hassium is highly radioactive: its most stable known isotopes have half-lives of approximately ten seconds.[a] One of its isotopes, 270Hs, has magic numbers of both protons and neutrons for deformed nuclei, which gives it greater stability against spontaneous fission. Hassium is a superheavy element; it has been produced in a laboratory only in very small quantities by fusing heavy nuclei with lighter ones. Natural occurrences of the element have been hypothesised but never found.

Hassium, 108Hs
Hassium
Pronunciation/ˈhæsiəm/ ⓘ[1] ​(HASS-ee-əm)
Mass number[269] (data not decisive)[a]
Hassium 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
Os
↑
Hs
↓
(Uhb)
bohrium ← hassium → meitnerium
Atomic number (Z)108
Groupgroup 8
Periodperiod 7
Block  d-block
Electron configuration[Rn] 5f14 6d6 7s2[4]
Electrons per shell2, 8, 18, 32, 32, 14, 2
Physical properties
Phase at STPsolid (predicted)[5]
Density (near r.t.)27–29 g/cm3 (predicted)[6][7]
Atomic properties
Oxidation states(+2), (+3), (+4), (+6), +8[8][9][10] (brackets: prediction)
Ionization energies
  • 1st: 730 kJ/mol
  • 2nd: 1760 kJ/mol
  • 3rd: 2830 kJ/mol
  • (more) (predicted)[11]
Atomic radiusempirical: 126 pm (estimated)[12]
Covalent radius134 pm (estimated)[13]
Other properties
Natural occurrencesynthetic
Crystal structure ​hexagonal close-packed (hcp)

(predicted)[5]
CAS Number54037-57-9
History
Namingafter Hassia, Latin for Hesse, Germany, where it was discovered[14]
DiscoveryGesellschaft für Schwerionenforschung (1984)
Isotopes of hassium
Main isotopes[15] Decay
abun­dance half-life (t1/2) mode pro­duct
269Hs synth 12 s α 265Sg
270Hs synth 7.6 s α 266Sg
271Hs synth 12 s α 267Sg
277mHs synth 130 s SF –
 Category: Hassium
| references

In the periodic table of elements, hassium is a transactinide element, a member of the 7th period and group 8; it is thus the sixth member of the 6d series of transition metals. Chemistry experiments have confirmed that hassium behaves as the heavier homologue to osmium, reacting readily with oxygen to form a volatile tetroxide. The chemical properties of hassium have been only partly characterized, but they compare well with the chemistry of the other group 8 elements.

The principal innovation that led to the discovery of hassium was the technique of cold fusion, in which the fused nuclei did not differ by mass as much as in earlier techniques. It relied on greater stability of target nuclei, which in turn decreased excitation energy. This decreased the number of neutron ejections during synthesis, creating heavier, more stable resulting nuclei. The technique was first tested at the Joint Institute for Nuclear Research (JINR) in Dubna, Moscow Oblast, Russian SFSR, Soviet Union, in 1974. JINR used this technique to attempt synthesis of element 108 in 1978, in 1983, and in 1984; the latter experiment resulted in a claim that element 108 had been produced. Later in 1984, a synthesis claim followed from the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Hesse, West Germany. The 1993 report by the Transfermium Working Group, formed by the International Union of Pure and Applied Chemistry and the International Union of Pure and Applied Physics, concluded that the report from Darmstadt was conclusive on its own whereas that from Dubna was not, and major credit was assigned to the German scientists. GSI formally announced they wished to name the element hassium after the German state of Hesse (Hassia in Latin), home to the facility in 1992; this name was accepted as final in 1997.

Introduction to the heaviest elements edit

This section is an excerpt from Superheavy element § Introduction.[edit]

Synthesis of superheavy nuclei edit

 
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.

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 of mass, the greater the possibility that the two react.[21] 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.[22] The energy applied to the beam nuclei to accelerate them can cause them to reach speeds as high as one-tenth of the speed of light. However, if too much energy is applied, the beam nucleus can fall apart.[22]

Coming close enough 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.[22][23] This happens because during the attempted formation of a single nucleus, electrostatic repulsion tears apart the nucleus that is being formed.[22] Each pair of a target and a beam is characterized by its cross 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 can tunnel through electrostatic repulsion. If the two nuclei can stay close for past that phase, multiple nuclear interactions result in redistribution of energy and an energy equilibrium.[22]

External videos
  Visualization of unsuccessful nuclear fusion, based on calculations from the Australian National University[25]

The resulting merger is an excited state[26]—termed a compound nucleus—and thus it is very unstable.[22] To reach a more stable state, the temporary merger may fission without formation of a more stable nucleus.[27] Alternatively, the compound nucleus may eject a few neutrons, which would carry away the excitation energy; if the latter is not sufficient for a neutron expulsion, the merger would produce a gamma ray. This happens in approximately 10−16 seconds after the initial nuclear collision and results in creation of a more stable nucleus.[27] The definition by the IUPAC/IUPAP Joint Working Party (JWP) 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.[28][e]

Decay and detection edit

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.[30] 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 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.[30] The transfer takes about 10−6 seconds; in order to be detected, the nucleus must survive this long.[33] The nucleus is recorded again once its decay is registered, and the location, the energy, and the time of the decay are measured.[30]

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, and its range is not limited.[34] Total binding 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.[35][36] Superheavy nuclei are thus theoretically predicted[37] and have so far been observed[38] to predominantly decay via decay modes that are caused by such repulsion: alpha decay and spontaneous fission.[g] Almost all alpha emitters have over 210 nucleons,[40] and the lightest nuclide primarily undergoing spontaneous fission has 238.[41] In both decay modes, nuclei are inhibited from decaying by corresponding energy barriers for each mode, but they can be tunnelled through.[35][36]

 
Scheme of an apparatus for creation of superheavy elements, based on the Dubna Gas-Filled Recoil Separator set up in the Flerov Laboratory of Nuclear Reactions in JINR. The trajectory within the detector and the beam focusing apparatus changes because of a dipole magnet in the former and quadrupole magnets in the latter.[42]

Alpha particles are commonly produced in radioactive decays because 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.[43] Spontaneous fission is caused by electrostatic repulsion tearing the nucleus apart and produces various nuclei in different instances of identical nuclei fissioning.[36] As the atomic number increases, spontaneous fission rapidly becomes more important: spontaneous fission partial half-lives decrease by 23 orders of magnitude from uranium (element 92) to nobelium (element 102),[44] and by 30 orders of magnitude from thorium (element 90) to fermium (element 100).[45] The earlier liquid drop model thus suggested that spontaneous fission would occur nearly instantly due to disappearance of the fission barrier for nuclei with about 280 nucleons.[36][46] The later nuclear shell model suggested that nuclei with about 300 nucleons would form an island of stability in which nuclei will be more resistant to spontaneous fission and will primarily undergo alpha decay with longer half-lives.[36][46] 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.[47] Experiments on lighter superheavy nuclei,[48] as well as those closer to the expected island,[44] 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.)[30] The known nucleus can be recognized by the specific characteristics of decay it undergoes such as decay energy (or more specifically, the kinetic 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]

Discovery edit

See also: Discovery of the chemical elements and Timeline of chemical element discoveries
 
Scheme of an apparatus for creating superheavy elements, based on the Dubna Gas-Filled Recoil Separator set up in the Flerov Laboratory of Nuclear Reactions in JINR. The trajectory within the detector and the beam focusing apparatus changes because of a dipole magnet in the former and quadrupole magnets in the latter.[59]

Cold fusion edit

Nuclear reactions used in the 1960s resulted in high excitation energies that required expulsion of four or five neutrons; these reactions used targets made of elements with high atomic numbers to maximize the size difference between the two nuclei in a reaction. While this increased the chance of fusion due to the lower electrostatic repulsion between the target and the projectile, the formed compound nuclei often broke apart and did not survive to form a new element. Moreover, fusion processes inevitably produce neutron-poor nuclei, as heavier elements require more neutrons per proton to maximize stability;[m] therefore, the necessary ejection of neutrons results in final products with typically have shorter lifetimes. As such, light beams (six to ten protons) allowed synthesis of elements only up to 106.[62]

To advance to heavier elements, Soviet physicist Yuri Oganessian at the Joint Institute for Nuclear Research (JINR) in Dubna, Moscow Oblast, Russian SFSR, Soviet Union, proposed a different mechanism, in which the bombarded nucleus would be lead-208, which has magic numbers of protons and neutrons, or another nucleus close to it.[63] Each proton and neutron has a fixed value of rest energy; those of all protons are equal and so are those of all neutrons. In a nucleus, some of this energy is diverted to binding protons and neutrons; if a nucleus has a magic number of protons and/or neutrons, then even more of its rest energy is diverted, which gives the nuclide additional stability. This additional stability requires more energy for an external nucleus to break the existing one and penetrate it.[64] More energy diverted to binding nucleons means less rest energy, which in turn means less mass (mass is proportional to rest energy). More equal atomic numbers of the reacting nuclei result in greater electrostatic repulsion between them, but the lower mass excess of the target nucleus balances it.[63] This leaves less excitation energy for the newly created compound nucleus, which necessitates fewer neutron ejections to reach a stable state.[64] Because of this energy difference, the former mechanism became known as "hot fusion" and the latter as "cold fusion".[65]

Cold fusion was first declared successful in 1974 at JINR, when it was tested for synthesis of the yet-undiscovered element 106.[64] These new nuclei were projected to decay via spontaneous fission. The physicists at JINR concluded element 106 was produced in the experiment because no fissioning nucleus known at the time showed parameters of fission similar to what was observed during the experiment and because changing either of the two nuclei in the reactions negated the observed effects. Physicists at the Lawrence Berkeley Laboratory (LBL; originally Radiation Laboratory, RL, and later Lawrence Berkeley National Laboratory, LBNL) of the University of California in Berkeley, California, United States, also expressed great interest in the new technique.[64] When asked about how far this new method could go and if lead targets were a physics' Klondike, Oganessian responded, "Klondike may be an exaggeration [...] But soon, we will try to get elements 107 ... 108 in these reactions."[64]

Reports edit

The synthesis of element 108 was first attempted in 1978 by a research team led by Oganessian at the JINR. The team used a reaction that would generate element 108, specifically, the isotope 270108,[n] from fusion of radium (specifically, the isotope 226
88Ra
) and calcium (48
20Ca
). The researchers were uncertain in interpreting their data, and their paper did not unambiguously claim to have discovered the element.[66] The same year, another team at JINR investigated the possibility of synthesis of element 108 in reactions between lead (208
82Pb
) and iron (58
26Fe
); they were uncertain in interpreting the data, suggesting the possibility that element 108 had not been created.[67]

 
GSI's linear particle accelerator UNILAC, where hassium was discovered[68] and where its chemistry was first observed[69]

In 1983, new experiments were performed at JINR.[70] The experiments probably resulted in the synthesis of element 108; bismuth (209
83Bi
) was bombarded with manganese (55
25Mn
) to obtain 263108, lead (207
82Pb
, 208
82Pb
) was bombarded with iron (58
26Fe
) to obtain 264108, and californium (249
98Cf
) was bombarded with neon (22
10Ne
) to obtain 270108.[14] These experiments were not claimed as a discovery and Oganessian announced them in a conference rather than in a written report.[70]

In 1984, JINR researchers in Dubna performed experiments set up identically to the previous ones; they bombarded bismuth and lead targets with ions of lighter elements manganese and iron, respectively. Twenty-one spontaneous fission events were recorded; the researchers concluded they were caused by 264108.[71]

Later in 1984, a research team led by Peter Armbruster and Gottfried Münzenberg at Gesellschaft für Schwerionenforschung (GSI; Institute for Heavy Ion Research) in Darmstadt, Hesse, West Germany, attempted to create element 108. The team bombarded a lead (208
82Pb
) target with accelerated iron (58
26Fe
) nuclei.[72] GSI's experiment to create element 108 was delayed until after their creation of element 109 in 1982, as prior calculations had suggested that even–even isotopes of element 108 would have spontaneous fission half-lives of less than one microsecond, making them difficult to detect and identify.[73] The element 108 experiment finally went ahead after 266109 had been synthesized and was found to decay by alpha emission, suggesting that isotopes of element 108 would do likewise, and this was corroborated by an experiment aimed at synthesizing isotopes of element 106. GSI reported synthesis of three atoms of 265108. Two years later, they reported synthesis of one atom of the even–even 264108.[73]

Arbitration edit

In 1985, the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP) formed the Transfermium Working Group (TWG) to assess discoveries and establish final names for elements with atomic numbers greater than 100. The party held meetings with delegates from the three competing institutes; in 1990, they established criteria for recognition of an element and in 1991, they finished the work of assessing discoveries and disbanded. These results were published in 1993.[74]

According to the report, the 1984 works from JINR and GSI simultaneously and independently established synthesis of element 108. Of the two 1984 works, the one from GSI was said to be sufficient as a discovery on its own. The JINR work, which preceded the GSI one, "very probably" displayed synthesis of element 108. However, that was determined in retrospect given the work from Darmstadt; the JINR work focused on chemically identifying remote granddaughters of element 108 isotopes (which could not exclude the possibility that these daughter isotopes had other progenitors), while the GSI work clearly identified the decay path of those element 108 isotopes. The report concluded that the major credit should be awarded to GSI.[71] In written responses to this ruling, both JINR and GSI agreed with its conclusions. In the same response, GSI confirmed that they and JINR were able to resolve all conflicts between them.[75]

Naming edit

See also: Transfermium Wars

Historically, a newly discovered element was named by its discoverer. The first regulation came in 1947, when IUPAC decided naming required regulation in case there are conflicting names.[76][o] These matters were to be resolved by the Commission of Inorganic Nomenclature and the Commission of Atomic Weights. They would review the names in case of a conflict and select one; the decision would be based on a number of factors, such as usage, and would not be an indicator of priority of a claim. The two commissions would recommend a name to the IUPAC Council, which would be the final authority.[76] The discoverers held the right to name an element, but their name would be subject to approval by IUPAC.[76] The Commission of Atomic Weights distanced itself from element naming in most cases.[76]

Under Mendeleev's nomenclature for unnamed and undiscovered elements, hassium would be known as "eka-osmium", as in "the first element below osmium in the periodic table" (from Sanskrit eka meaning "one"). In 1979, IUPAC published recommendations according to which the element was to be called "unniloctium" and assigned the corresponding symbol of "Uno",[77] a systematic element name as a placeholder until the element was discovered and the discovery then confirmed, and a permanent name was decided. Although these recommendations were widely followed in the chemical community, the competing physicists in the field ignored them.[78][79] They either called it "element 108", with the symbols E108, (108) or 108, or used the proposed name "hassium".[80]

 
Coat of arms of the German state of Hesse, after which hassium is named

In 1990, in an attempt to break a deadlock in establishing priority of discovery and naming of several elements, IUPAC reaffirmed in its nomenclature of inorganic chemistry that after existence of an element was established, the discoverers could propose a name. (In addition, the Commission of Atomic Weights was excluded from the naming process.) The first publication on criteria for an element discovery, released in 1991, specified the need for recognition by TWG.[76]

Armbruster and his colleagues, the officially recognized German discoverers, held a naming ceremony for the elements 107 through 109, which had all been recognized as discovered by GSI, on 7 September 1992. For element 108, the scientists proposed the name "hassium".[81] It is derived from the Latin name Hassia for the German state of Hesse where the institute is located.[14][75] This name was proposed to IUPAC in a written response to their ruling on priority of discovery claims of elements, signed 29 September 1992.[75]

The process of naming of element 108 was a part of a larger process of naming a number of elements starting with element 101; three teams—JINR, GSI, and LBL—claimed discoveries of several elements and the right to name those elements. Sometimes, these claims clashed; since a discoverer was considered entitled to naming of an element, conflicts over priority of discovery often resulted in conflicts over names of these new elements. These conflicts became known as the Transfermium Wars.[82] Different suggestions to name the whole set of elements from 101 onward and they occasionally assigned names suggested by one team to be used for elements discovered by another.[p] However, not all suggestions were met with equal approval; the teams openly protested naming proposals on several occasions.[84]

In 1994, IUPAC Commission on Nomenclature of Inorganic Chemistry recommended that element 108 be named "hahnium" (Hn) after the German physicist Otto Hahn so elements named after Hahn and Lise Meitner (it was recommended element 109 should be named meitnerium, following GSI's suggestion) would be next to each other, honouring their joint discovery of nuclear fission;[85] IUPAC commented that they felt the German suggestion was obscure.[86] GSI protested, saying this proposal contradicted the long-standing convention of giving the discoverer the right to suggest a name;[87] the American Chemical Society supported GSI.[14] The name "hahnium", albeit with the different symbol Ha, had already been proposed and used by the American scientists for element 105, for which they had a discovery dispute with JINR; they thus protested the confusing scrambling of names.[88] Following the uproar, IUPAC formed an ad hoc committee of representatives from the national adhering organizations of the three countries home to the competing institutions; they produced a new set of names in 1995. Element 108 was again named hahnium; this proposal was also retracted.[89] The final compromise was reached in 1996 and published in 1997; element 108 was named hassium (Hs).[90] Simultaneously, the name dubnium (Db; from Dubna, the JINR location) was assigned to element 105, and the name hahnium was not used for any element.[citation needed][q]

The official justification for this naming, alongside that of darmstadtium for element 110, was that it completed a set of geographic names for the location of the GSI; this set had been initiated by 19th-century names europium and germanium. This set would serve as a response to earlier naming of americium, californium, and berkelium for elements discovered in Berkeley. Armbruster commented on this, "this bad tradition[r] was established by Berkeley. We wanted to do it for Europe."[92] Later, when commenting on the naming of element 112, Armbruster said, "I did everything to ensure that we do not continue with German scientists and German towns."[92]

Isotopes edit

Main article: Isotopes of hassium
List of hassium isotopes
Isotope Half-life[s][t] Decay
mode 		Discovery
year[94]		 Discovery
reaction[95][u]
Value ref
263Hs 760 μs [94] α, SF 2009 208Pb(56Fe,n)
264Hs 540 μs [94] α, SF 1986 207Pb(58Fe,n)
265Hs 1.96 ms [94] α, SF 1984 208Pb(58Fe,n)
265mHs 360 μs [94] α 1995 208Pb(58Fe,n)
266Hs 3.02 ms [94] α, SF 2001 270Ds(—,α)
266mHs 280 ms [94] α 2011 270mDs(—,α)
267Hs 55 ms [93] α 1995 238U(34S,5n)
267mHs 990 μs [93] α 2004 238U(34S,5n)
268Hs 1.42 s [93] α 2010 238U(34S,4n)
269Hs 16 s [93] α 1996 277Cn(—,2α)
270Hs 9 s [93] α 2003 248Cm(26Mg,4n)
271Hs 10 s[v] [96] α 2008 248Cm(26Mg,3n)
272Hs 160 ms [97] α 2022 276Ds(—,α)
273Hs 510 ms [98] α 2010 285Fl(—,3α)
275Hs 600 ms [99] α 2004 287Fl(—,3α)
277Hs 12 ms [3] α 2010 289Fl(—,3α)
277mHs 130 s[w] [3][100] SF 2012 293mLv(—,4α)

Hassium 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. As of 2019, the quantity of all hassium ever produced was on the order of hundreds of atoms.[101][102] Thirteen isotopes with mass numbers ranging from 263 to 277 (with the exceptions of 274 and 276) have been reported, four of which—hassium-265, -266, -267, and -277—have known metastable states,[103][x] although that of hassium-277 is unconfirmed.[104] Most of these isotopes decay predominantly through alpha decay; this is the most common for all isotopes for which comprehensive decay characteristics are available, the only exception being hassium-277, which undergoes spontaneous fission.[103] Lighter isotopes were usually synthesized by direct fusion between two lighter nuclei, whereas heavier isotopes were typically observed as decay products of nuclei with larger atomic numbers.[95]

Atomic nuclei have well-established nuclear shells, and the existence of these shells provides nuclei with additional stability. If a nucleus has certain numbers of protons or neutrons, called magic numbers, that complete certain nuclear shells, then the nucleus is even more stable against decay. The highest known magic numbers are 82 for protons and 126 for neutrons. This notion is sometimes expanded to include additional numbers between those magic numbers, which also provide some additional stability and indicate closure of "sub-shells". In contrast to the better-known lighter nuclei, superheavy nuclei are deformed. Until the 1960s, the liquid drop model was the dominant explanation for nuclear structure. It suggested that the fission barrier would disappear for nuclei with about 280 nucleons.[105][106] It was thus thought that spontaneous fission would occur nearly instantly before nuclei could form a structure that could stabilize them;[62] it appeared that nuclei with Z ≈ 103[y] were too heavy to exist for a considerable length of time.[107]

The later nuclear shell model suggested that nuclei with about three hundred nucleons would form an island of stability in which nuclei will be more resistant to spontaneous fission and will primarily undergo alpha decay with longer half-lives,[105][106] and the next doubly magic nucleus (having magic numbers of both protons and neutrons) is expected to lie in the center of the island of stability in the vicinity of Z = 110–114 and the predicted magic neutron number N = 184. 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.[106] The addition to the stability against the spontaneous fission should be particularly great against spontaneous fission, although increase in stability against the alpha decay would also be pronounced.[106] The center of the region on a chart of nuclides that would correspond to this stability for deformed nuclei was determined as 270Hs, with 108 expected to be a magic number for protons for deformed nuclei—nuclei that are far from spherical—and 162 a magic number for neutrons for such nuclei.[108] Experiments on lighter superheavy nuclei,[109] as well as those closer to the expected island,[62] have shown greater than previously anticipated stability against spontaneous fission, showing the importance of shell effects on nuclei.

Theoretical models predict a region of instability for some hassium isotopes to lie around A = 275[110] and N = 168–170, which is between the predicted neutron shell closures at N = 162 for deformed nuclei and N = 184 for spherical nuclei.[111] Nuclides within this region are predicted to have low fission barrier heights, resulting in short partial half-lives toward spontaneous fission. This prediction is supported by the observed eleven-millisecond half-life of 277Hs and the five-millisecond half-life of the neighbouring isobar 277Mt because the hindrance factors from the odd nucleon were shown to be much lower than otherwise expected. The measured half-lives are even lower than those originally predicted for the even–even 276Hs and 278Ds, which suggests a gap in stability away from the shell closures and perhaps a weakening of the shell closures in this region.[111]

In 1991, Polish physicists Zygmunt Patyk and Adam Sobiczewski predicted[112] that 108 is a proton magic number for deformed nuclei and 162 is a neutron magic number for such nuclei. This means such nuclei are permanently deformed in their ground state but have high, narrow fission barriers to further deformation and hence relatively long life-times toward spontaneous fission.[113][114] Computational prospects for shell stabilization for 270Hs made it a promising candidate for a deformed doubly magic nucleus.[115] Experimental data is scarce, but the existing data is interpreted by the researchers to support the assignment of N = 162 as a magic number. In particular, this conclusion was drawn from the decay data of 269Hs, 270Hs, and 271Hs.[z] In 1997, Polish physicist Robert Smolańczuk calculated that the isotope 292Hs may be the most stable superheavy nucleus against alpha decay and spontaneous fission as a consequence of the predicted N = 184 shell closure.[118][119]

Natural occurrence edit

 
Molybdenite

Hassium is not known to occur naturally on Earth; the half-lives of all its known isotopes are short enough that no primordial hassium would have survived to the present day. This does not rule out the possibility of the existence of unknown, longer-lived isotopes or nuclear isomers, some of which could still exist in trace quantities if they are long-lived enough. As early as 1914, German physicist Richard Swinne proposed element 108 as a source of X-rays in the Greenland ice sheet. Although Swinne was unable to verify this observation and thus did not claim discovery, he proposed in 1931 the existence of "regions" of long-lived transuranic elements, including one around Z = 108.[120]

In 1963, Soviet geologist and physicist Viktor Cherdyntsev, who had previously claimed the existence of primordial curium-247,[121] claimed to have discovered element 108—specifically the 267108 isotope, which supposedly had a half-life of 400 to 500 million years—in natural molybdenite and suggested the provisional name sergenium (symbol Sg);[122][aa] this name takes its origin from the name for the Silk Road and was explained as "coming from Kazakhstan" for it.[122] His rationale for claiming that sergenium was the heavier homologue to osmium was that minerals supposedly containing sergenium formed volatile oxides when boiled in nitric acid, similarly to osmium.[123]

Cherdyntsev's findings were criticized by Soviet physicist Vladimir Kulakov on the grounds that some of the properties Cherdyntsev claimed sergenium had were inconsistent with the then-current nuclear physics. The chief questions raised by Kulakov were that the claimed alpha decay energy of sergenium was many orders of magnitude lower than expected and the half-life given was eight orders of magnitude shorter than what would be predicted for a nuclide alpha-decaying with the claimed decay energy. At the same time, a corrected half-life in the region of 1016 years would be impossible because it would imply the samples contained about a hundred milligrams of sergenium.[123] In 2003, it was suggested that the observed alpha decay with energy 4.5 MeV could be due to a low-energy and strongly enhanced transition between different hyperdeformed states of a hassium isotope around 271Hs, thus suggesting that the existence of superheavy elements in nature was at least possible, although unlikely.[124]

In 2006, Russian geologist Alexei Ivanov hypothesized that an isomer of 271Hs might have a half-life of around (2.5±0.5)×108 years, which would explain the observation of alpha particles with energies of around 4.4 MeV in some samples of molybdenite and osmiridium.[125] This isomer of 271Hs could be produced from the beta decay of 271Bh and 271Sg, which, being homologous to rhenium and molybdenum respectively, should occur in molybdenite along with rhenium and molybdenum if they occurred in nature. Because hassium is homologous to osmium, it should occur along with osmium in osmiridium if it occurs in nature. The decay chains of 271Bh and 271Sg are hypothetical and the predicted half-life of this hypothetical hassium isomer is not long enough for any sufficient quantity to remain on Earth.[125] It is possible that more 271Hs may be deposited on the Earth as the Solar System travels through the spiral arms of the Milky Way; this would explain excesses of plutonium-239 found on the ocean floors of the Pacific Ocean and the Gulf of Finland. However, minerals enriched with 271Hs are predicted to have excesses of its daughters uranium-235 and lead-207; they would also have different proportions of elements that are formed during spontaneous fission, such as krypton, zirconium, and xenon. The natural occurrence of hassium in minerals such as molybdenite and osmiride is theoretically possible, but very unlikely.[125]

In 2004, JINR started a search for natural hassium in the Modane Underground Laboratory in Modane, Auvergne-Rhône-Alpes, France; this was done underground to avoid interference and false positives from cosmic rays.[14] In 2008–09, an experiment run in the laboratory resulted in detection of several registered events of neutron multiplicity (number of emitted free neutrons after a nucleus hit has been hit by a neutron and fissioned) above three in natural osmium, and in 2012–13, these findings were reaffirmed in another experiment run in the laboratory. These results hinted natural hassium could potentially exist in nature in amounts that allow its detection by the means of analytical chemistry, but this conclusion is based on an explicit assumption that there is a long-lived hassium isotope to which the registered events could be attributed.[126]

Since 292Hs may be particularly stable against alpha decay and spontaneous fission, it was considered as a candidate to exist in nature. This nuclide, however, is predicted to be very unstable toward beta decay and any beta-stable isotopes of hassium such as 286Hs would be too unstable in the other decay channels to be observed in nature.[119] A 2012 search for 292Hs in nature along with its homologue osmium at the Maier-Leibnitz Laboratory in Garching, Bavaria, Germany, was unsuccessful, setting an upper limit to its abundance at 3×10−15 grams of hassium per gram of osmium.[127]

Predicted properties edit

Various calculations suggest hassium should be the heaviest group 8 element so far, consistently with the periodic law. Its properties should generally match those expected for a heavier homologue of osmium; as is the case for all transactinides, a few deviations are expected to arise from relativistic effects.[128]

Very few properties of hassium or its compounds have been measured; this is due to its extremely limited and expensive production[129] and the fact that hassium (and its parents) decays very quickly. A few singular chemistry-related properties have been measured, such as enthalpy of adsorption of hassium tetroxide, but properties of hassium metal remain unknown and only predictions are available.

Relativistic effects edit

Main article: Relativistic quantum chemistry
 
Energy levels of outermost orbitals of hassium and osmium atoms in electronvolts, with and without taking relativistic effects into account. Note the lack of spin–orbit splitting (and thus the lack of distinction between d3/2 and d5/2 orbitals) in nonrelativistic calculations.

Relativistic effects on hassium should arise due to the high charge of its nuclei, which causes the electrons around the nucleus to move faster—so fast their velocity becomes comparable to the speed of light.[130] There are three main effects: the direct relativistic effect, the indirect relativistic effect, and spin–orbit splitting. (The existing calculations do not account for Breit interactions, but those are negligible, and their omission can only result in an uncertainty of the current calculations of no more than 2%.)[131]

As atomic number increases, so does the electrostatic attraction between an electron and the nucleus. This causes the velocity of the electron to increase, which leads to an increase in its mass. This in turn leads to contraction of the atomic orbitals, most specifically the s and p1/2 orbitals. Their electrons become more closely attached to the atom and harder to pull from the nucleus. This is the direct relativistic effect. It was originally thought to be strong only for the innermost electrons, but was later established to significantly influence valence electrons as well.[132]

Since the s and p1/2 orbitals are closer to the nucleus, they take a bigger portion of the electric charge of the nucleus on themselves ("shield" it). This leaves less charge for attraction of the remaining electrons, whose orbitals therefore expand, making them easier to pull from the nucleus. This is the indirect relativistic effect.[133] As a result of the combination of the direct and indirect relativistic effects, the Hs+ ion, compared to the neutral atom, lacks a 6d electron, rather than a 7s electron. In comparison, Os+ lacks a 6s electron compared to the neutral atom.[4] The ionic radius (in oxidation state +8) of hassium is greater than that of osmium because of the relativistic expansion of the 6p3/2 orbitals, which are the outermost orbitals for an Hs8+ ion (although in practice such highly charged ions would be too polarised in chemical environments to have much reality).[134]

There are several kinds of electronic orbitals, denoted by the letters s, p, d, and f (g orbitals are expected to start being chemically active among elements after element 120). Each of these corresponds to an azimuthal quantum number l: s to 0, p to 1, d to 2, and f to 3. Every electron also corresponds to a spin quantum number s, which may equal either +1/2 or −1/2.[135] Thus, the total angular momentum quantum number j = l + s is equal to j = l ± 1/2 (except for l = 0, for which for both electrons in each orbital j = 0 + 1/2 = 1/2).[135] Spin of an electron relativistically interacts with its orbit, and this interaction leads to a split of a subshell into two with different energies (the one with j = l − 1/2 is lower in energy and thus these electrons more difficult to extract):[136] for instance, of the six 6p electrons, two become 6p1/2 and four become 6p3/2. This is the spin–orbit splitting (sometimes also referred to as subshell splitting or jj coupling).[137][ab] It is most visible with p electrons,[131] which do not play an important role in the chemistry of hassium,[11] but those for d and f electrons are within the same order of magnitude[131] (quantitatively, spin–orbit splitting in expressed in energy units, such as electronvolts).[135]

These relativistic effects are responsible for the expected increase of the ionization energy, decrease of the electron affinity, and increase of stability of the +8 oxidation state compared to osmium; without them, the trends would be reversed.[139] Relativistic effects decrease the atomization energies of the compounds of hassium because the spin–orbit splitting of the d orbital lowers binding energy between electrons and the nucleus and because relativistic effects decrease ionic character in bonding.[139]

Physical and atomic edit

The previous members of group 8 have relatively high melting points: Fe, 1538 °C; Ru, 2334 °C; Os, 3033 °C. Much like them, hassium is predicted to be a solid at room temperature[5] although its melting point has not been precisely calculated. Hassium should crystallize in the hexagonal close-packed structure (c/a = 1.59),[5] similarly to its lighter congener osmium.[5] Pure metallic hassium is calculated[5][140] to have a bulk modulus (resistance to uniform compression) of 450 GPa, comparable with that of diamond, 442 GPa.[141] Hassium is expected to be one of the densest of the 118 known elements, with a predicted density of 27–29 g/cm3 vs. the 22.59 g/cm3 measured for osmium.[6][7]

The atomic radius of hassium is expected to be around 126 pm.[12] Due to the relativistic stabilization of the 7s orbital and destabilization of the 6d orbital, the Hs+ ion is predicted to have an electron configuration of [Rn] 5f14 6d5 7s2, giving up a 6d electron instead of a 7s electron, which is the opposite of the behaviour of its lighter homologues. The Hs2+ ion is expected to have an electron configuration of [Rn] 5f14 6d5 7s1, analogous to that calculated for the Os2+ ion.[4] In chemical compounds, hassium is calculated to display bonding characteristic for a d-block element, whose bonding will be primarily executed by 6d3/2 and 6d5/2 orbitals; compared to the elements from the previous periods, 7s, 6p1/2, 6p3/2, and 7p1/2 orbitals should be more important.[142]

Chemical edit

Stable oxidation states in group 8[143]
Element Stable oxidation states
iron      +6 +3 +2
ruthenium +8 +6 +5 +4 +3 +2
osmium +8 +6 +5 +4 +3 +2

Hassium is the sixth member of the 6d series of transition metals and is expected to be much like the platinum group metals.[144] Some of these properties were confirmed by gas-phase chemistry experiments.[145][146][147] The group 8 elements portray a wide variety of oxidation states but ruthenium and osmium readily portray their group oxidation state of +8; this state becomes more stable down the group.[143][148][149] This oxidation state is extremely rare: among stable elements, only ruthenium, osmium, and xenon are able to attain it in reasonably stable compounds.[ac] Hassium is expected to follow its congeners and have a stable +8 state,[146] but like them it should show lower stable oxidation states such as +6, +4, +3, and +2.[12][10] Hassium(IV) is expected to be more stable than hassium(VIII) in aqueous solution.[152] Hassium should be a rather noble metal.[153] The standard reduction potential for the Hs4+/Hs couple is expected to be 0.4 V.[12]

The group 8 elements show a distinctive oxide chemistry. All the lighter members have known or hypothetical tetroxides, MO4.[154] Their oxidizing power decreases as one descends the group. FeO4 is not known due to its extraordinarily large electron affinity—the amount of energy released when an electron is added to a neutral atom or molecule to form a negative ion[155]—which results in the formation of the well-known oxyanion ferrate(VI), FeO2−
4.[156] Ruthenium tetroxide, RuO4, which is formed by oxidation of ruthenium(VI) in acid, readily undergoes reduction to ruthenate(VI), RuO2−
4.[157][158] Oxidation of ruthenium metal in air forms the dioxide, RuO2.[159] In contrast, osmium burns to form the stable tetroxide, OsO4,[160][161] which complexes with the hydroxide ion to form an osmium(VIII) -ate complex, [OsO4(OH)2]2−.[162] Therefore, hassium should behave as a heavier homologue of osmium by forming of a stable, very volatile tetroxide HsO4,[14][145][147][148][163] which undergoes complexation with hydroxide to form a hassate(VIII), [HsO4(OH)2]2−.[164] Ruthenium tetroxide and osmium tetroxide are both volatile due to their symmetrical tetrahedral molecular geometry and because they are charge-neutral; hassium tetroxide should similarly be a very volatile solid. The trend of the volatilities of the group 8 tetroxides is experimentally known to be RuO4 < OsO4 > HsO4, which confirms the calculated results. In particular, the calculated enthalpies of adsorption—the energy required for the adhesion of atoms, molecules, or ions from a gas, liquid, or dissolved solid to a surface—of HsO4, −(45.4 ± 1) kJ/mol on quartz, agrees very well with the experimental value of −(46 ± 2) kJ/mol.[165]

Experimental chemistry edit

 
In ferrocene, the cyclopentadienyl rings are in a staggered conformation.
 
In ruthenocene and osmocene, the cyclopentadienyl rings are in an eclipsed conformation. Hassocene is also predicted to have this structure.

The first goal for chemical investigation was the formation of the tetroxide; it was chosen because ruthenium and osmium form volatile tetroxides, being the only transition metals to display a stable compound in the +8 oxidation state.[166] Despite this selection for gas-phase chemical studies being clear from the beginning,[148] chemical characterization of hassium was considered a difficult task for a long time.[148] Although hassium isotopes were first synthesized in 1984, it was not until 1996 that a hassium isotope long-lived enough to allow chemical studies was synthesized. Unfortunately, this hassium isotope, 269Hs, was synthesized indirectly from the decay of 277Cn;[148] not only are indirect synthesis methods not favourable for chemical studies,[167] but the reaction that produced the isotope 277Cn had a low yield—its cross section was only 1 pb[148]—and thus did not provide enough hassium atoms for a chemical investigation.[144] Direct synthesis of 269Hs and 270Hs in the reaction 248Cm(26Mg,xn)274−xHs (x = 4 or 5) appeared more promising because the cross section for this reaction was somewhat larger at 7 pb.[148] This yield was still around ten times lower than that for the reaction used for the chemical characterization of bohrium.[148] New techniques for irradiation, separation, and detection had to be introduced before hassium could be successfully characterized chemically.[148]

Ruthenium and osmium have very similar chemistry due to the lanthanide contraction but iron shows some differences from them; for example, although ruthenium and osmium form stable tetroxides in which the metal is in the +8 oxidation state, iron does not.[148][154] In preparation for the chemical characterization of hassium, research focused on ruthenium and osmium rather than iron[148] because hassium was expected to be similar to ruthenium and osmium, as the predicted data on hassium closely matched that of those two.[168][169]

The first chemistry experiments were performed using gas thermochromatography in 2001, using the synthetic osmium radioisotopes 172Os and 173Os as a reference. During the experiment, seven hassium atoms were synthesized using the reactions 248Cm(26Mg,5n)269Hs and 248Cm(26Mg,4n)270Hs. They were then thermalized and oxidized in a mixture of helium and oxygen gases to form hassium tetroxide molecules.[145][147][170]

Hs + 2 O2 → HsO4

The measured deposition temperature of hassium tetroxide was higher than that of osmium tetroxide, which indicated the former was the less volatile one, and this placed hassium firmly in group 8.[145][147][171] The enthalpy of adsorption for HsO4 measured, −46±2 kJ/mol, was significantly lower than the predicted value, −36.7±1.5 kJ/mol, indicating OsO4 is more volatile than HsO4, contradicting earlier calculations that implied they should have very similar volatilities. For comparison, the value for OsO4 is −39±1 kJ/mol.[172] (The calculations that yielded a closer match to the experimental data came after the experiment, in 2008.)[165] It is possible hassium tetroxide interacts differently with silicon nitride than with silicon dioxide, the chemicals used for the detector; further research is required to establish whether there is a difference between such interactions and whether it has influenced the measurements. Such research would include more accurate measurements of the nuclear properties of 269Hs and comparisons with RuO4 in addition to OsO4.[171]

In 2004, scientists reacted hassium tetroxide and sodium hydroxide to form sodium hassate(VIII), a reaction that is well known with osmium. This was the first acid-base reaction with a hassium compound, forming sodium hassate(VIII):[164]

HsO
4 + 2 NaOH → Na
2[HsO
4(OH)
2]

The team from the University of Mainz planned in 2008 to study the electrodeposition of hassium atoms using the new TASCA facility at GSI. Their aim was to use the reaction 226Ra(48Ca,4n)270Hs.[173] Scientists at GSI were hoping to use TASCA to study the synthesis and properties of the hassium(II) compound hassocene, Hs(C5H5)2, using the reaction 226Ra(48Ca,xn). This compound is analogous to the lighter compounds ferrocene, ruthenocene, and osmocene, and is expected to have the two cyclopentadienyl rings in an eclipsed conformation like ruthenocene and osmocene and not in a staggered conformation like ferrocene.[10] Hassocene, which is expected to be a stable and highly volatile compound, was chosen because it has hassium in the low formal oxidation state of +2—although the bonding between the metal and the rings is mostly covalent in metallocenes—rather than the high +8 state that had previously been investigated, and relativistic effects were expected to be stronger in the lower oxidation state. The highly symmetrical structure of hassocene and its low number of atoms make relativistic calculations easier.[10] As of 2021, there are no experimental reports of hassocene.[174]

Notes edit

  1. ^ a b The most stable isotope of hassium cannot be determined based on existing data due to uncertainty that arises from the low number of measurements. The confidence interval of half-life of 269Hs corresponding to one standard deviation is, based on existing data, 16±6 seconds, whereas that of 270Hs is 9±4 seconds. It is also possible that 277mHs is more stable than both of these, with its half-life likely being 110±70 seconds, but only one event of decay of this isotope has been registered as of 2016.[2][3]
  2. ^ 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[16] or 112;[17] sometimes, the term is presented an equivalent to the term "transactinide", which puts an upper limit before the beginning of the hypothetical superactinide series).[18] 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.
  3. ^ In 2009, a team at the 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.[19] 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.[20]
  4. ^ The amount of energy applied to the beam particle to accelerate it can also influence the value of cross section. For example, in the 28
    14    Si
     + 1
    0    n
     → 28
    13    Al
     + 1
    1    p
     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.[24]
  5. ^ This figure also marks the generally accepted upper limit for lifetime of a compound nucleus.[29]
  6. ^ 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.[31] 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.[32]
  7. ^ Not all decay modes are caused by electrostatic repulsion. For example, beta decay is caused by the weak interaction.[39]
  8. ^ 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.[44]
  9. ^ 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.[49] The first direct measurement of mass of a superheavy nucleus was reported in 2018 at LBNL.[50] 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).[51]
  10. ^ If the decay occurred in a vacuum, then since total momentum of an isolated system before and after the decay must 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).[40] 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.
  11. ^ Spontaneous fission was discovered by Soviet physicist Georgy Flerov,[52] a leading scientist at JINR, and thus it was a "hobbyhorse" for the facility.[53] 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.[29] They thus preferred to link new isotopes to the already known ones by successive alpha decays.[52]
  12. ^ For instance, element 102 was mistakenly identified in 1957 at the Nobel Institute of Physics in Stockholm, Stockholm County, Sweden.[54] 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.[55] 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.[55] JINR insisted that they were the first to create the element and suggested a name of their own for the new element, joliotium;[56] the Soviet name was also not accepted (JINR later referred to the naming of the element 102 as "hasty").[57] This name was proposed to IUPAC in a written response to their ruling on priority of discovery claims of elements, signed 29 September 1992.[57] The name "nobelium" remained unchanged on account of its widespread usage.[58]
  13. ^ Generally, heavier nuclei require more neutrons because as the number of protons increases, so does electrostatic repulsion between them. This repulsion is balanced by the binding energy generated by the strong interaction between quarks within nucleons; it is enough to hold the quarks together in a nucleon together and some of it is left for binding of different nucleons. The more nucleons there are in a nucleus, the more energy there is for binding the nucleons (note that greater total binding energy does not necessarily correspond to greater binding energy per nucleon).[60] However, having too many neutrons per proton, while decreasing electrostatic repulsion per nucleon that negates the binding energy, results in beta decay.[61]
  14. ^ The superscript number to the left of a chemical symbol refers to the mass of a given nuclide; for instance, 48Ca is the notation for calcium-48. In superheavy element research, elements that have not been assigned a name and a symbol, are often referred to by their atomic numbers in lieu of symbols; if a symbol has been assigned and the number is to be displayed, it is written in subscript to the left of the symbol. 270108 would be 270Hs or 270
    108    Hs
     in modern nomenclature (or hassium-270 if spelled out).
  15. ^ This was intended to resolve not only any future conflicts, but also a number of ones that existed back then: beryllium/glucinium, niobium/columbium, lutecium/cassiopeium, hafnium/celtium, tungsten/wolfram, and protoactinium/brevium.[76]
  16. ^ For example, Armbruster suggested element 107 be named nielsbohrium; JINR used this name for element 105 which they claimed to have discovered. This was meant to honor Oganessian's technique of cold fusion; GSI had asked JINR for permission.[83]
  17. ^ American physicist Glenn T. Seaborg suggested that name for element 110 on behalf of LBNL in November 1997 after IUPAC surveyed the three main collaborations (GSI, JINR/LLNL, and LBNL) on how they thought the element should be named.[91]
  18. ^ Similarly, there are names of ruthenium, moscovium, and dubnium for JINR. The only element discovered by RIKEN in Wakō, Saitama Prefecture, Japan, is named nihonium after a Japanese name of Japan.
  19. ^ Different sources give different values for half-lives; the most recently published values are listed.
  20. ^ Few nuclei of each hassium isotope have been synthesized, and thus half-lives of these isotopes cannot be determined very precisely. Therefore, a half-life may be given as the most likely value alongside a confidence interval that corresponds to one standard deviation (such an interval based on future experiments, whose result is yet unknown, contains the true value with a probability of ~68.3%): for example, the value of 1.42 s in the isotope table obtained for 268Hs was listed in the source as 1.42 ±1.13 s, and this value is a modification of the value of 0.38+1.8
    −0.17     s    .[93]
  21. ^ The notation 208Pb(56Fe,n)263Hs denotes a nuclear reaction between a nucleus of 208Pb that was bombarded with a nucleus of 56Fe; the two fused, and after a single neutron had been emitted, the remaining nucleus was 263Hs. Another notation for this reaction would be 208Pb + 56Fe → 263Hs + n.
  22. ^ Half-life of this isotope is estimated from trends across nuclides with the same number of protons and neutrons rather than measured directly.
  23. ^ Only one event of decay of this isotope has been registered.
  24. ^ Metastable nuclides are denoted by the letter "m" immediately the mass number, such as in "hassium-277m".
  25. ^ The symbol Z refers to the atomic number—number of protons in an atomic nucleus. The symbol N refers to the neutron number—number of neutrons in a nucleus. The symbol A refers to the mass number—number of neutrons and protons in a nucleus combined.
  26. ^ In particular, the low decay energy for 270Hs matches calculations.[114] The conclusion for 269Hs was made after its decay data was compared to that of 273Ds; the decay of the latter into the former has an energy sufficiently greater than the decay of the former (11.2 MeV and 9.2 MeV, respectively). The great value of the former energy was explained as a right-to-left crossing of N = 162 (273Ds has 163 neutrons and 269Hs has 161).[116] A similar observation and conclusion were made after measurement of decay energy of 271Hs and 267Sg.[117]
  27. ^ At the time, this symbol had not yet been taken by seaborgium.
  28. ^ The spin–orbit interaction is the interaction between the magnetic field caused by the spin of an electron and the effective magnetic field caused by the electric field of a nucleus and movement of an electron orbiting it. (According to the special theory of relativity, electric and magnetic fields are both occurrences of common electromagnetic fields that can be seen as more or less electric and more or less magnetic depending on the reference frame. The effective magnetic field from the reference frame of the electron is obtained from the nucleus's electric field after a relativistic transformation from the reference frame of the nucleus.) The splitting occurs because depending on the spin of an electron, it may be either attracted to or repealed by the nucleus; this attraction or repulsion is significantly weaker the electrostatic attraction between them and it can thus only somewhat affect the electron overall.[138]
  29. ^ While iridium is known to show a +8 state in iridium tetroxide, as well as a unique +9 state in the iridium tetroxide cation IrO+
    4    , the former is known only in matrix isolation and the latter in the gas phase, and no iridium compounds in such high oxidation states have been synthesized in macroscopic amounts.[150][151]

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External links edit

  •   Media related to Hassium at Wikimedia Commons

February 15, 2024
hassium, chemical, element, symbol, atomic, number, highly, radioactive, most, stable, known, isotopes, have, half, lives, approximately, seconds, isotopes, 270hs, magic, numbers, both, protons, neutrons, deformed, nuclei, which, gives, greater, stability, aga. Hassium is a chemical element it has symbol Hs and atomic number 108 Hassium is highly radioactive its most stable known isotopes have half lives of approximately ten seconds a One of its isotopes 270Hs has magic numbers of both protons and neutrons for deformed nuclei which gives it greater stability against spontaneous fission Hassium is a superheavy element it has been produced in a laboratory only in very small quantities by fusing heavy nuclei with lighter ones Natural occurrences of the element have been hypothesised but never found Hassium 108HsHassiumPronunciation ˈ h ae s i e m 1 wbr HASS ee em Mass number 269 data not decisive a Hassium in the periodic tableHydrogen HeliumLithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine NeonSodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine ArgonPotassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine KryptonRubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine XenonCaesium 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 RadonFrancium 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 Os Hs Uhb bohrium hassium meitneriumAtomic number Z 108Groupgroup 8Periodperiod 7Block d blockElectron configuration Rn 5f14 6d6 7s2 4 Electrons per shell2 8 18 32 32 14 2Physical propertiesPhase at STPsolid predicted 5 Density near r t 27 29 g cm3 predicted 6 7 Atomic propertiesOxidation states 2 3 4 6 8 8 9 10 brackets prediction Ionization energies1st 730 kJ mol2nd 1760 kJ mol3rd 2830 kJ mol more predicted 11 Atomic radiusempirical 126 pm estimated 12 Covalent radius134 pm estimated 13 Other propertiesNatural occurrencesyntheticCrystal structure hexagonal close packed hcp predicted 5 CAS Number54037 57 9HistoryNamingafter Hassia Latin for Hesse Germany where it was discovered 14 DiscoveryGesellschaft fur Schwerionenforschung 1984 Isotopes of hassiumveMain isotopes 15 Decayabun dance half life t1 2 mode pro duct269Hs synth 12 s a 265Sg270Hs synth 7 6 s a 266Sg271Hs synth 12 s a 267Sg277mHs synth 130 s SF Category Hassiumviewtalkedit referencesIn the periodic table of elements hassium is a transactinide element a member of the 7th period and group 8 it is thus the sixth member of the 6d series of transition metals Chemistry experiments have confirmed that hassium behaves as the heavier homologue to osmium reacting readily with oxygen to form a volatile tetroxide The chemical properties of hassium have been only partly characterized but they compare well with the chemistry of the other group 8 elements The principal innovation that led to the discovery of hassium was the technique of cold fusion in which the fused nuclei did not differ by mass as much as in earlier techniques It relied on greater stability of target nuclei which in turn decreased excitation energy This decreased the number of neutron ejections during synthesis creating heavier more stable resulting nuclei The technique was first tested at the Joint Institute for Nuclear Research JINR in Dubna Moscow Oblast Russian SFSR Soviet Union in 1974 JINR used this technique to attempt synthesis of element 108 in 1978 in 1983 and in 1984 the latter experiment resulted in a claim that element 108 had been produced Later in 1984 a synthesis claim followed from the Gesellschaft fur Schwerionenforschung GSI in Darmstadt Hesse West Germany The 1993 report by the Transfermium Working Group formed by the International Union of Pure and Applied Chemistry and the International Union of Pure and Applied Physics concluded that the report from Darmstadt was conclusive on its own whereas that from Dubna was not and major credit was assigned to the German scientists GSI formally announced they wished to name the element hassium after the German state of Hesse Hassia in Latin home to the facility in 1992 this name was accepted as final in 1997 Contents 1 Introduction to the heaviest elements 1 1 Synthesis of superheavy nuclei 1 2 Decay and detection 2 Discovery 2 1 Cold fusion 2 2 Reports 2 3 Arbitration 2 4 Naming 3 Isotopes 4 Natural occurrence 5 Predicted properties 5 1 Relativistic effects 5 2 Physical and atomic 5 3 Chemical 6 Experimental chemistry 7 Notes 8 References 9 Bibliography 10 External linksIntroduction to the heaviest elements editThis section is an excerpt from Superheavy element Introduction edit Synthesis of superheavy nuclei edit nbsp 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 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 of mass the greater the possibility that the two react 21 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 22 The energy applied to the beam nuclei to accelerate them can cause them to reach speeds as high as one tenth of the speed of light However if too much energy is applied the beam nucleus can fall apart 22 Coming close enough 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 22 23 This happens because during the attempted formation of a single nucleus electrostatic repulsion tears apart the nucleus that is being formed 22 Each pair of a target and a beam is characterized by its cross 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 can tunnel through electrostatic repulsion If the two nuclei can stay close for past that phase multiple nuclear interactions result in redistribution of energy and an energy equilibrium 22 External videos nbsp Visualization of unsuccessful nuclear fusion based on calculations from the Australian National University 25 The resulting merger is an excited state 26 termed a compound nucleus and thus it is very unstable 22 To reach a more stable state the temporary merger may fission without formation of a more stable nucleus 27 Alternatively the compound nucleus may eject a few neutrons which would carry away the excitation energy if the latter is not sufficient for a neutron expulsion the merger would produce a gamma ray This happens in approximately 10 16 seconds after the initial nuclear collision and results in creation of a more stable nucleus 27 The definition by the IUPAC IUPAP Joint Working Party JWP 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 28 e Decay and detection edit 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 30 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 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 30 The transfer takes about 10 6 seconds in order to be detected the nucleus must survive this long 33 The nucleus is recorded again once its decay is registered and the location the energy and the time of the decay are measured 30 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 and its range is not limited 34 Total binding 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 35 36 Superheavy nuclei are thus theoretically predicted 37 and have so far been observed 38 to predominantly decay via decay modes that are caused by such repulsion alpha decay and spontaneous fission g Almost all alpha emitters have over 210 nucleons 40 and the lightest nuclide primarily undergoing spontaneous fission has 238 41 In both decay modes nuclei are inhibited from decaying by corresponding energy barriers for each mode but they can be tunnelled through 35 36 nbsp Scheme of an apparatus for creation of superheavy elements based on the Dubna Gas Filled Recoil Separator set up in the Flerov Laboratory of Nuclear Reactions in JINR The trajectory within the detector and the beam focusing apparatus changes because of a dipole magnet in the former and quadrupole magnets in the latter 42 Alpha particles are commonly produced in radioactive decays because 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 43 Spontaneous fission is caused by electrostatic repulsion tearing the nucleus apart and produces various nuclei in different instances of identical nuclei fissioning 36 As the atomic number increases spontaneous fission rapidly becomes more important spontaneous fission partial half lives decrease by 23 orders of magnitude from uranium element 92 to nobelium element 102 44 and by 30 orders of magnitude from thorium element 90 to fermium element 100 45 The earlier liquid drop model thus suggested that spontaneous fission would occur nearly instantly due to disappearance of the fission barrier for nuclei with about 280 nucleons 36 46 The later nuclear shell model suggested that nuclei with about 300 nucleons would form an island of stability in which nuclei will be more resistant to spontaneous fission and will primarily undergo alpha decay with longer half lives 36 46 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 47 Experiments on lighter superheavy nuclei 48 as well as those closer to the expected island 44 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 30 The known nucleus can be recognized by the specific characteristics of decay it undergoes such as decay energy or more specifically the kinetic 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 Discovery editSee also Discovery of the chemical elements and Timeline of chemical element discoveries nbsp Scheme of an apparatus for creating superheavy elements based on the Dubna Gas Filled Recoil Separator set up in the Flerov Laboratory of Nuclear Reactions in JINR The trajectory within the detector and the beam focusing apparatus changes because of a dipole magnet in the former and quadrupole magnets in the latter 59 Cold fusion edit Nuclear reactions used in the 1960s resulted in high excitation energies that required expulsion of four or five neutrons these reactions used targets made of elements with high atomic numbers to maximize the size difference between the two nuclei in a reaction While this increased the chance of fusion due to the lower electrostatic repulsion between the target and the projectile the formed compound nuclei often broke apart and did not survive to form a new element Moreover fusion processes inevitably produce neutron poor nuclei as heavier elements require more neutrons per proton to maximize stability m therefore the necessary ejection of neutrons results in final products with typically have shorter lifetimes As such light beams six to ten protons allowed synthesis of elements only up to 106 62 To advance to heavier elements Soviet physicist Yuri Oganessian at the Joint Institute for Nuclear Research JINR in Dubna Moscow Oblast Russian SFSR Soviet Union proposed a different mechanism in which the bombarded nucleus would be lead 208 which has magic numbers of protons and neutrons or another nucleus close to it 63 Each proton and neutron has a fixed value of rest energy those of all protons are equal and so are those of all neutrons In a nucleus some of this energy is diverted to binding protons and neutrons if a nucleus has a magic number of protons and or neutrons then even more of its rest energy is diverted which gives the nuclide additional stability This additional stability requires more energy for an external nucleus to break the existing one and penetrate it 64 More energy diverted to binding nucleons means less rest energy which in turn means less mass mass is proportional to rest energy More equal atomic numbers of the reacting nuclei result in greater electrostatic repulsion between them but the lower mass excess of the target nucleus balances it 63 This leaves less excitation energy for the newly created compound nucleus which necessitates fewer neutron ejections to reach a stable state 64 Because of this energy difference the former mechanism became known as hot fusion and the latter as cold fusion 65 Cold fusion was first declared successful in 1974 at JINR when it was tested for synthesis of the yet undiscovered element 106 64 These new nuclei were projected to decay via spontaneous fission The physicists at JINR concluded element 106 was produced in the experiment because no fissioning nucleus known at the time showed parameters of fission similar to what was observed during the experiment and because changing either of the two nuclei in the reactions negated the observed effects Physicists at the Lawrence Berkeley Laboratory LBL originally Radiation Laboratory RL and later Lawrence Berkeley National Laboratory LBNL of the University of California in Berkeley California United States also expressed great interest in the new technique 64 When asked about how far this new method could go and if lead targets were a physics Klondike Oganessian responded Klondike may be an exaggeration But soon we will try to get elements 107 108 in these reactions 64 Reports edit The synthesis of element 108 was first attempted in 1978 by a research team led by Oganessian at the JINR The team used a reaction that would generate element 108 specifically the isotope 270108 n from fusion of radium specifically the isotope 22688 Ra and calcium 4820 Ca The researchers were uncertain in interpreting their data and their paper did not unambiguously claim to have discovered the element 66 The same year another team at JINR investigated the possibility of synthesis of element 108 in reactions between lead 20882 Pb and iron 5826 Fe they were uncertain in interpreting the data suggesting the possibility that element 108 had not been created 67 nbsp GSI s linear particle accelerator UNILAC where hassium was discovered 68 and where its chemistry was first observed 69 In 1983 new experiments were performed at JINR 70 The experiments probably resulted in the synthesis of element 108 bismuth 20983 Bi was bombarded with manganese 5525 Mn to obtain 263108 lead 20782 Pb 20882 Pb was bombarded with iron 5826 Fe to obtain 264108 and californium 24998 Cf was bombarded with neon 2210 Ne to obtain 270108 14 These experiments were not claimed as a discovery and Oganessian announced them in a conference rather than in a written report 70 In 1984 JINR researchers in Dubna performed experiments set up identically to the previous ones they bombarded bismuth and lead targets with ions of lighter elements manganese and iron respectively Twenty one spontaneous fission events were recorded the researchers concluded they were caused by 264108 71 Later in 1984 a research team led by Peter Armbruster and Gottfried Munzenberg at Gesellschaft fur Schwerionenforschung GSI Institute for Heavy Ion Research in Darmstadt Hesse West Germany attempted to create element 108 The team bombarded a lead 20882 Pb target with accelerated iron 5826 Fe nuclei 72 GSI s experiment to create element 108 was delayed until after their creation of element 109 in 1982 as prior calculations had suggested that even even isotopes of element 108 would have spontaneous fission half lives of less than one microsecond making them difficult to detect and identify 73 The element 108 experiment finally went ahead after 266109 had been synthesized and was found to decay by alpha emission suggesting that isotopes of element 108 would do likewise and this was corroborated by an experiment aimed at synthesizing isotopes of element 106 GSI reported synthesis of three atoms of 265108 Two years later they reported synthesis of one atom of the even even 264108 73 Arbitration edit In 1985 the International Union of Pure and Applied Chemistry IUPAC and the International Union of Pure and Applied Physics IUPAP formed the Transfermium Working Group TWG to assess discoveries and establish final names for elements with atomic numbers greater than 100 The party held meetings with delegates from the three competing institutes in 1990 they established criteria for recognition of an element and in 1991 they finished the work of assessing discoveries and disbanded These results were published in 1993 74 According to the report the 1984 works from JINR and GSI simultaneously and independently established synthesis of element 108 Of the two 1984 works the one from GSI was said to be sufficient as a discovery on its own The JINR work which preceded the GSI one very probably displayed synthesis of element 108 However that was determined in retrospect given the work from Darmstadt the JINR work focused on chemically identifying remote granddaughters of element 108 isotopes which could not exclude the possibility that these daughter isotopes had other progenitors while the GSI work clearly identified the decay path of those element 108 isotopes The report concluded that the major credit should be awarded to GSI 71 In written responses to this ruling both JINR and GSI agreed with its conclusions In the same response GSI confirmed that they and JINR were able to resolve all conflicts between them 75 Naming edit See also Transfermium Wars Historically a newly discovered element was named by its discoverer The first regulation came in 1947 when IUPAC decided naming required regulation in case there are conflicting names 76 o These matters were to be resolved by the Commission of Inorganic Nomenclature and the Commission of Atomic Weights They would review the names in case of a conflict and select one the decision would be based on a number of factors such as usage and would not be an indicator of priority of a claim The two commissions would recommend a name to the IUPAC Council which would be the final authority 76 The discoverers held the right to name an element but their name would be subject to approval by IUPAC 76 The Commission of Atomic Weights distanced itself from element naming in most cases 76 Under Mendeleev s nomenclature for unnamed and undiscovered elements hassium would be known as eka osmium as in the first element below osmium in the periodic table from Sanskrit eka meaning one In 1979 IUPAC published recommendations according to which the element was to be called unniloctium and assigned the corresponding symbol of Uno 77 a systematic element name as a placeholder until the element was discovered and the discovery then confirmed and a permanent name was decided Although these recommendations were widely followed in the chemical community the competing physicists in the field ignored them 78 79 They either called it element 108 with the symbols E108 108 or 108 or used the proposed name hassium 80 nbsp Coat of arms of the German state of Hesse after which hassium is namedIn 1990 in an attempt to break a deadlock in establishing priority of discovery and naming of several elements IUPAC reaffirmed in its nomenclature of inorganic chemistry that after existence of an element was established the discoverers could propose a name In addition the Commission of Atomic Weights was excluded from the naming process The first publication on criteria for an element discovery released in 1991 specified the need for recognition by TWG 76 Armbruster and his colleagues the officially recognized German discoverers held a naming ceremony for the elements 107 through 109 which had all been recognized as discovered by GSI on 7 September 1992 For element 108 the scientists proposed the name hassium 81 It is derived from the Latin name Hassia for the German state of Hesse where the institute is located 14 75 This name was proposed to IUPAC in a written response to their ruling on priority of discovery claims of elements signed 29 September 1992 75 The process of naming of element 108 was a part of a larger process of naming a number of elements starting with element 101 three teams JINR GSI and LBL claimed discoveries of several elements and the right to name those elements Sometimes these claims clashed since a discoverer was considered entitled to naming of an element conflicts over priority of discovery often resulted in conflicts over names of these new elements These conflicts became known as the Transfermium Wars 82 Different suggestions to name the whole set of elements from 101 onward and they occasionally assigned names suggested by one team to be used for elements discovered by another p However not all suggestions were met with equal approval the teams openly protested naming proposals on several occasions 84 In 1994 IUPAC Commission on Nomenclature of Inorganic Chemistry recommended that element 108 be named hahnium Hn after the German physicist Otto Hahn so elements named after Hahn and Lise Meitner it was recommended element 109 should be named meitnerium following GSI s suggestion would be next to each other honouring their joint discovery of nuclear fission 85 IUPAC commented that they felt the German suggestion was obscure 86 GSI protested saying this proposal contradicted the long standing convention of giving the discoverer the right to suggest a name 87 the American Chemical Society supported GSI 14 The name hahnium albeit with the different symbol Ha had already been proposed and used by the American scientists for element 105 for which they had a discovery dispute with JINR they thus protested the confusing scrambling of names 88 Following the uproar IUPAC formed an ad hoc committee of representatives from the national adhering organizations of the three countries home to the competing institutions they produced a new set of names in 1995 Element 108 was again named hahnium this proposal was also retracted 89 The final compromise was reached in 1996 and published in 1997 element 108 was named hassium Hs 90 Simultaneously the name dubnium Db from Dubna the JINR location was assigned to element 105 and the name hahnium was not used for any element citation needed q The official justification for this naming alongside that of darmstadtium for element 110 was that it completed a set of geographic names for the location of the GSI this set had been initiated by 19th century names europium and germanium This set would serve as a response to earlier naming of americium californium and berkelium for elements discovered in Berkeley Armbruster commented on this this bad tradition r was established by Berkeley We wanted to do it for Europe 92 Later when commenting on the naming of element 112 Armbruster said I did everything to ensure that we do not continue with German scientists and German towns 92 Isotopes editMain article Isotopes of hassium List of hassium isotopes vte Isotope Half life s t Decaymode Discoveryyear 94 Discoveryreaction 95 u Value ref263Hs 760 ms 94 a SF 2009 208Pb 56Fe n 264Hs 540 ms 94 a SF 1986 207Pb 58Fe n 265Hs 1 96 ms 94 a SF 1984 208Pb 58Fe n 265mHs 360 ms 94 a 1995 208Pb 58Fe n 266Hs 3 02 ms 94 a SF 2001 270Ds a 266mHs 280 ms 94 a 2011 270mDs a 267Hs 55 ms 93 a 1995 238U 34S 5n 267mHs 990 ms 93 a 2004 238U 34S 5n 268Hs 1 42 s 93 a 2010 238U 34S 4n 269Hs 16 s 93 a 1996 277Cn 2a 270Hs 9 s 93 a 2003 248Cm 26Mg 4n 271Hs 10 s v 96 a 2008 248Cm 26Mg 3n 272Hs 160 ms 97 a 2022 276Ds a 273Hs 510 ms 98 a 2010 285Fl 3a 275Hs 600 ms 99 a 2004 287Fl 3a 277Hs 12 ms 3 a 2010 289Fl 3a 277mHs 130 s w 3 100 SF 2012 293mLv 4a Hassium 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 As of 2019 the quantity of all hassium ever produced was on the order of hundreds of atoms 101 102 Thirteen isotopes with mass numbers ranging from 263 to 277 with the exceptions of 274 and 276 have been reported four of which hassium 265 266 267 and 277 have known metastable states 103 x although that of hassium 277 is unconfirmed 104 Most of these isotopes decay predominantly through alpha decay this is the most common for all isotopes for which comprehensive decay characteristics are available the only exception being hassium 277 which undergoes spontaneous fission 103 Lighter isotopes were usually synthesized by direct fusion between two lighter nuclei whereas heavier isotopes were typically observed as decay products of nuclei with larger atomic numbers 95 Atomic nuclei have well established nuclear shells and the existence of these shells provides nuclei with additional stability If a nucleus has certain numbers of protons or neutrons called magic numbers that complete certain nuclear shells then the nucleus is even more stable against decay The highest known magic numbers are 82 for protons and 126 for neutrons This notion is sometimes expanded to include additional numbers between those magic numbers which also provide some additional stability and indicate closure of sub shells In contrast to the better known lighter nuclei superheavy nuclei are deformed Until the 1960s the liquid drop model was the dominant explanation for nuclear structure It suggested that the fission barrier would disappear for nuclei with about 280 nucleons 105 106 It was thus thought that spontaneous fission would occur nearly instantly before nuclei could form a structure that could stabilize them 62 it appeared that nuclei with Z 103 y were too heavy to exist for a considerable length of time 107 The later nuclear shell model suggested that nuclei with about three hundred nucleons would form an island of stability in which nuclei will be more resistant to spontaneous fission and will primarily undergo alpha decay with longer half lives 105 106 and the next doubly magic nucleus having magic numbers of both protons and neutrons is expected to lie in the center of the island of stability in the vicinity of Z 110 114 and the predicted magic neutron number N 184 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 106 The addition to the stability against the spontaneous fission should be particularly great against spontaneous fission although increase in stability against the alpha decay would also be pronounced 106 The center of the region on a chart of nuclides that would correspond to this stability for deformed nuclei was determined as 270Hs with 108 expected to be a magic number for protons for deformed nuclei nuclei that are far from spherical and 162 a magic number for neutrons for such nuclei 108 Experiments on lighter superheavy nuclei 109 as well as those closer to the expected island 62 have shown greater than previously anticipated stability against spontaneous fission showing the importance of shell effects on nuclei Theoretical models predict a region of instability for some hassium isotopes to lie around A 275 110 and N 168 170 which is between the predicted neutron shell closures at N 162 for deformed nuclei and N 184 for spherical nuclei 111 Nuclides within this region are predicted to have low fission barrier heights resulting in short partial half lives toward spontaneous fission This prediction is supported by the observed eleven millisecond half life of 277Hs and the five millisecond half life of the neighbouring isobar 277Mt because the hindrance factors from the odd nucleon were shown to be much lower than otherwise expected The measured half lives are even lower than those originally predicted for the even even 276Hs and 278Ds which suggests a gap in stability away from the shell closures and perhaps a weakening of the shell closures in this region 111 In 1991 Polish physicists Zygmunt Patyk and Adam Sobiczewski predicted 112 that 108 is a proton magic number for deformed nuclei and 162 is a neutron magic number for such nuclei This means such nuclei are permanently deformed in their ground state but have high narrow fission barriers to further deformation and hence relatively long life times toward spontaneous fission 113 114 Computational prospects for shell stabilization for 270Hs made it a promising candidate for a deformed doubly magic nucleus 115 Experimental data is scarce but the existing data is interpreted by the researchers to support the assignment of N 162 as a magic number In particular this conclusion was drawn from the decay data of 269Hs 270Hs and 271Hs z In 1997 Polish physicist Robert Smolanczuk calculated that the isotope 292Hs may be the most stable superheavy nucleus against alpha decay and spontaneous fission as a consequence of the predicted N 184 shell closure 118 119 Natural occurrence edit nbsp MolybdeniteHassium is not known to occur naturally on Earth the half lives of all its known isotopes are short enough that no primordial hassium would have survived to the present day This does not rule out the possibility of the existence of unknown longer lived isotopes or nuclear isomers some of which could still exist in trace quantities if they are long lived enough As early as 1914 German physicist Richard Swinne proposed element 108 as a source of X rays in the Greenland ice sheet Although Swinne was unable to verify this observation and thus did not claim discovery he proposed in 1931 the existence of regions of long lived transuranic elements including one around Z 108 120 In 1963 Soviet geologist and physicist Viktor Cherdyntsev who had previously claimed the existence of primordial curium 247 121 claimed to have discovered element 108 specifically the 267108 isotope which supposedly had a half life of 400 to 500 million years in natural molybdenite and suggested the provisional name sergenium symbol Sg 122 aa this name takes its origin from the name for the Silk Road and was explained as coming from Kazakhstan for it 122 His rationale for claiming that sergenium was the heavier homologue to osmium was that minerals supposedly containing sergenium formed volatile oxides when boiled in nitric acid similarly to osmium 123 Cherdyntsev s findings were criticized by Soviet physicist Vladimir Kulakov on the grounds that some of the properties Cherdyntsev claimed sergenium had were inconsistent with the then current nuclear physics The chief questions raised by Kulakov were that the claimed alpha decay energy of sergenium was many orders of magnitude lower than expected and the half life given was eight orders of magnitude shorter than what would be predicted for a nuclide alpha decaying with the claimed decay energy At the same time a corrected half life in the region of 1016 years would be impossible because it would imply the samples contained about a hundred milligrams of sergenium 123 In 2003 it was suggested that the observed alpha decay with energy 4 5 MeV could be due to a low energy and strongly enhanced transition between different hyperdeformed states of a hassium isotope around 271Hs thus suggesting that the existence of superheavy elements in nature was at least possible although unlikely 124 In 2006 Russian geologist Alexei Ivanov hypothesized that an isomer of 271Hs might have a half life of around 2 5 0 5 108 years which would explain the observation of alpha particles with energies of around 4 4 MeV in some samples of molybdenite and osmiridium 125 This isomer of 271Hs could be produced from the beta decay of 271Bh and 271Sg which being homologous to rhenium and molybdenum respectively should occur in molybdenite along with rhenium and molybdenum if they occurred in nature Because hassium is homologous to osmium it should occur along with osmium in osmiridium if it occurs in nature The decay chains of 271Bh and 271Sg are hypothetical and the predicted half life of this hypothetical hassium isomer is not long enough for any sufficient quantity to remain on Earth 125 It is possible that more 271Hs may be deposited on the Earth as the Solar System travels through the spiral arms of the Milky Way this would explain excesses of plutonium 239 found on the ocean floors of the Pacific Ocean and the Gulf of Finland However minerals enriched with 271Hs are predicted to have excesses of its daughters uranium 235 and lead 207 they would also have different proportions of elements that are formed during spontaneous fission such as krypton zirconium and xenon The natural occurrence of hassium in minerals such as molybdenite and osmiride is theoretically possible but very unlikely 125 In 2004 JINR started a search for natural hassium in the Modane Underground Laboratory in Modane Auvergne Rhone Alpes France this was done underground to avoid interference and false positives from cosmic rays 14 In 2008 09 an experiment run in the laboratory resulted in detection of several registered events of neutron multiplicity number of emitted free neutrons after a nucleus hit has been hit by a neutron and fissioned above three in natural osmium and in 2012 13 these findings were reaffirmed in another experiment run in the laboratory These results hinted natural hassium could potentially exist in nature in amounts that allow its detection by the means of analytical chemistry but this conclusion is based on an explicit assumption that there is a long lived hassium isotope to which the registered events could be attributed 126 Since 292Hs may be particularly stable against alpha decay and spontaneous fission it was considered as a candidate to exist in nature This nuclide however is predicted to be very unstable toward beta decay and any beta stable isotopes of hassium such as 286Hs would be too unstable in the other decay channels to be observed in nature 119 A 2012 search for 292Hs in nature along with its homologue osmium at the Maier Leibnitz Laboratory in Garching Bavaria Germany was unsuccessful setting an upper limit to its abundance at 3 10 15 grams of hassium per gram of osmium 127 Predicted properties editVarious calculations suggest hassium should be the heaviest group 8 element so far consistently with the periodic law Its properties should generally match those expected for a heavier homologue of osmium as is the case for all transactinides a few deviations are expected to arise from relativistic effects 128 Very few properties of hassium or its compounds have been measured this is due to its extremely limited and expensive production 129 and the fact that hassium and its parents decays very quickly A few singular chemistry related properties have been measured such as enthalpy of adsorption of hassium tetroxide but properties of hassium metal remain unknown and only predictions are available Relativistic effects edit Main article Relativistic quantum chemistry nbsp Energy levels of outermost orbitals of hassium and osmium atoms in electronvolts with and without taking relativistic effects into account Note the lack of spin orbit splitting and thus the lack of distinction between d3 2 and d5 2 orbitals in nonrelativistic calculations Relativistic effects on hassium should arise due to the high charge of its nuclei which causes the electrons around the nucleus to move faster so fast their velocity becomes comparable to the speed of light 130 There are three main effects the direct relativistic effect the indirect relativistic effect and spin orbit splitting The existing calculations do not account for Breit interactions but those are negligible and their omission can only result in an uncertainty of the current calculations of no more than 2 131 As atomic number increases so does the electrostatic attraction between an electron and the nucleus This causes the velocity of the electron to increase which leads to an increase in its mass This in turn leads to contraction of the atomic orbitals most specifically the s and p1 2 orbitals Their electrons become more closely attached to the atom and harder to pull from the nucleus This is the direct relativistic effect It was originally thought to be strong only for the innermost electrons but was later established to significantly influence valence electrons as well 132 Since the s and p1 2 orbitals are closer to the nucleus they take a bigger portion of the electric charge of the nucleus on themselves shield it This leaves less charge for attraction of the remaining electrons whose orbitals therefore expand making them easier to pull from the nucleus This is the indirect relativistic effect 133 As a result of the combination of the direct and indirect relativistic effects the Hs ion compared to the neutral atom lacks a 6d electron rather than a 7s electron In comparison Os lacks a 6s electron compared to the neutral atom 4 The ionic radius in oxidation state 8 of hassium is greater than that of osmium because of the relativistic expansion of the 6p3 2 orbitals which are the outermost orbitals for an Hs8 ion although in practice such highly charged ions would be too polarised in chemical environments to have much reality 134 There are several kinds of electronic orbitals denoted by the letters s p d and f g orbitals are expected to start being chemically active among elements after element 120 Each of these corresponds to an azimuthal quantum number l s to 0 p to 1 d to 2 and f to 3 Every electron also corresponds to a spin quantum number s which may equal either 1 2 or 1 2 135 Thus the total angular momentum quantum number j l s is equal to j l 1 2 except for l 0 for which for both electrons in each orbital j 0 1 2 1 2 135 Spin of an electron relativistically interacts with its orbit and this interaction leads to a split of a subshell into two with different energies the one with j l 1 2 is lower in energy and thus these electrons more difficult to extract 136 for instance of the six 6p electrons two become 6p1 2 and four become 6p3 2 This is the spin orbit splitting sometimes also referred to as subshell splitting or jj coupling 137 ab It is most visible with p electrons 131 which do not play an important role in the chemistry of hassium 11 but those for d and f electrons are within the same order of magnitude 131 quantitatively spin orbit splitting in expressed in energy units such as electronvolts 135 These relativistic effects are responsible for the expected increase of the ionization energy decrease of the electron affinity and increase of stability of the 8 oxidation state compared to osmium without them the trends would be reversed 139 Relativistic effects decrease the atomization energies of the compounds of hassium because the spin orbit splitting of the d orbital lowers binding energy between electrons and the nucleus and because relativistic effects decrease ionic character in bonding 139 Physical and atomic edit The previous members of group 8 have relatively high melting points Fe 1538 C Ru 2334 C Os 3033 C Much like them hassium is predicted to be a solid at room temperature 5 although its melting point has not been precisely calculated Hassium should crystallize in the hexagonal close packed structure c a 1 59 5 similarly to its lighter congener osmium 5 Pure metallic hassium is calculated 5 140 to have a bulk modulus resistance to uniform compression of 450 GPa comparable with that of diamond 442 GPa 141 Hassium is expected to be one of the densest of the 118 known elements with a predicted density of 27 29 g cm3 vs the 22 59 g cm3 measured for osmium 6 7 The atomic radius of hassium is expected to be around 126 pm 12 Due to the relativistic stabilization of the 7s orbital and destabilization of the 6d orbital the Hs ion is predicted to have an electron configuration of Rn 5f14 6d5 7s2 giving up a 6d electron instead of a 7s electron which is the opposite of the behaviour of its lighter homologues The Hs2 ion is expected to have an electron configuration of Rn 5f14 6d5 7s1 analogous to that calculated for the Os2 ion 4 In chemical compounds hassium is calculated to display bonding characteristic for a d block element whose bonding will be primarily executed by 6d3 2 and 6d5 2 orbitals compared to the elements from the previous periods 7s 6p1 2 6p3 2 and 7p1 2 orbitals should be more important 142 Chemical edit Stable oxidation states in group 8 143 Element Stable oxidation statesiron 6 3 2ruthenium 8 6 5 4 3 2osmium 8 6 5 4 3 2 Hassium is the sixth member of the 6d series of transition metals and is expected to be much like the platinum group metals 144 Some of these properties were confirmed by gas phase chemistry experiments 145 146 147 The group 8 elements portray a wide variety of oxidation states but ruthenium and osmium readily portray their group oxidation state of 8 this state becomes more stable down the group 143 148 149 This oxidation state is extremely rare among stable elements only ruthenium osmium and xenon are able to attain it in reasonably stable compounds ac Hassium is expected to follow its congeners and have a stable 8 state 146 but like them it should show lower stable oxidation states such as 6 4 3 and 2 12 10 Hassium IV is expected to be more stable than hassium VIII in aqueous solution 152 Hassium should be a rather noble metal 153 The standard reduction potential for the Hs4 Hs couple is expected to be 0 4 V 12 The group 8 elements show a distinctive oxide chemistry All the lighter members have known or hypothetical tetroxides MO4 154 Their oxidizing power decreases as one descends the group FeO4 is not known due to its extraordinarily large electron affinity the amount of energy released when an electron is added to a neutral atom or molecule to form a negative ion 155 which results in the formation of the well known oxyanion ferrate VI FeO2 4 156 Ruthenium tetroxide RuO4 which is formed by oxidation of ruthenium VI in acid readily undergoes reduction to ruthenate VI RuO2 4 157 158 Oxidation of ruthenium metal in air forms the dioxide RuO2 159 In contrast osmium burns to form the stable tetroxide OsO4 160 161 which complexes with the hydroxide ion to form an osmium VIII ate complex OsO4 OH 2 2 162 Therefore hassium should behave as a heavier homologue of osmium by forming of a stable very volatile tetroxide HsO4 14 145 147 148 163 which undergoes complexation with hydroxide to form a hassate VIII HsO4 OH 2 2 164 Ruthenium tetroxide and osmium tetroxide are both volatile due to their symmetrical tetrahedral molecular geometry and because they are charge neutral hassium tetroxide should similarly be a very volatile solid The trend of the volatilities of the group 8 tetroxides is experimentally known to be RuO4 lt OsO4 gt HsO4 which confirms the calculated results In particular the calculated enthalpies of adsorption the energy required for the adhesion of atoms molecules or ions from a gas liquid or dissolved solid to a surface of HsO4 45 4 1 kJ mol on quartz agrees very well with the experimental value of 46 2 kJ mol 165 Experimental chemistry edit nbsp In ferrocene the cyclopentadienyl rings are in a staggered conformation nbsp In ruthenocene and osmocene the cyclopentadienyl rings are in an eclipsed conformation Hassocene is also predicted to have this structure The first goal for chemical investigation was the formation of the tetroxide it was chosen because ruthenium and osmium form volatile tetroxides being the only transition metals to display a stable compound in the 8 oxidation state 166 Despite this selection for gas phase chemical studies being clear from the beginning 148 chemical characterization of hassium was considered a difficult task for a long time 148 Although hassium isotopes were first synthesized in 1984 it was not until 1996 that a hassium isotope long lived enough to allow chemical studies was synthesized Unfortunately this hassium isotope 269Hs was synthesized indirectly from the decay of 277Cn 148 not only are indirect synthesis methods not favourable for chemical studies 167 but the reaction that produced the isotope 277Cn had a low yield its cross section was only 1 pb 148 and thus did not provide enough hassium atoms for a chemical investigation 144 Direct synthesis of 269Hs and 270Hs in the reaction 248Cm 26Mg xn 274 xHs x 4 or 5 appeared more promising because the cross section for this reaction was somewhat larger at 7 pb 148 This yield was still around ten times lower than that for the reaction used for the chemical characterization of bohrium 148 New techniques for irradiation separation and detection had to be introduced before hassium could be successfully characterized chemically 148 Ruthenium and osmium have very similar chemistry due to the lanthanide contraction but iron shows some differences from them for example although ruthenium and osmium form stable tetroxides in which the metal is in the 8 oxidation state iron does not 148 154 In preparation for the chemical characterization of hassium research focused on ruthenium and osmium rather than iron 148 because hassium was expected to be similar to ruthenium and osmium as the predicted data on hassium closely matched that of those two 168 169 The first chemistry experiments were performed using gas thermochromatography in 2001 using the synthetic osmium radioisotopes 172Os and 173Os as a reference During the experiment seven hassium atoms were synthesized using the reactions 248Cm 26Mg 5n 269Hs and 248Cm 26Mg 4n 270Hs They were then thermalized and oxidized in a mixture of helium and oxygen gases to form hassium tetroxide molecules 145 147 170 Hs 2 O2 HsO4The measured deposition temperature of hassium tetroxide was higher than that of osmium tetroxide which indicated the former was the less volatile one and this placed hassium firmly in group 8 145 147 171 The enthalpy of adsorption for HsO4 measured 46 2 kJ mol was significantly lower than the predicted value 36 7 1 5 kJ mol indicating OsO4 is more volatile than HsO4 contradicting earlier calculations that implied they should have very similar volatilities For comparison the value for OsO4 is 39 1 kJ mol 172 The calculations that yielded a closer match to the experimental data came after the experiment in 2008 165 It is possible hassium tetroxide interacts differently with silicon nitride than with silicon dioxide the chemicals used for the detector further research is required to establish whether there is a difference between such interactions and whether it has influenced the measurements Such research would include more accurate measurements of the nuclear properties of 269Hs and comparisons with RuO4 in addition to OsO4 171 In 2004 scientists reacted hassium tetroxide and sodium hydroxide to form sodium hassate VIII a reaction that is well known with osmium This was the first acid base reaction with a hassium compound forming sodium hassate VIII 164 HsO4 2 NaOH Na2 HsO4 OH 2 The team from the University of Mainz planned in 2008 to study the electrodeposition of hassium atoms using the new TASCA facility at GSI Their aim was to use the reaction 226Ra 48Ca 4n 270Hs 173 Scientists at GSI were hoping to use TASCA to study the synthesis and properties of the hassium II compound hassocene Hs C5H5 2 using the reaction 226Ra 48Ca xn This compound is analogous to the lighter compounds ferrocene ruthenocene and osmocene and is expected to have the two cyclopentadienyl rings in an eclipsed conformation like ruthenocene and osmocene and not in a staggered conformation like ferrocene 10 Hassocene which is expected to be a stable and highly volatile compound was chosen because it has hassium in the low formal oxidation state of 2 although the bonding between the metal and the rings is mostly covalent in metallocenes rather than the high 8 state that had previously been investigated and relativistic effects were expected to be stronger in the lower oxidation state The highly symmetrical structure of hassocene and its low number of atoms make relativistic calculations easier 10 As of 2021 update there are no experimental reports of hassocene 174 Notes edit a b The most stable isotope of hassium cannot be determined based on existing data due to uncertainty that arises from the low number of measurements The confidence interval of half life of 269Hs corresponding to one standard deviation is based on existing data 16 6 seconds whereas that of 270Hs is 9 4 seconds It is also possible that 277mHs is more stable than both of these with its half life likely being 110 70 seconds but only one event of decay of this isotope has been registered as of 2016 update 2 3 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 16 or 112 17 sometimes the term is presented an equivalent to the term transactinide which puts an upper limit before the beginning of the hypothetical superactinide series 18 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 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 19 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 20 The amount of energy applied to the beam particle to accelerate it can also influence the value of cross section For example in the 2814 Si 10 n 2813 Al 11 p 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 24 This figure also marks the generally accepted upper limit for lifetime of a compound nucleus 29 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 31 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 32 Not all decay modes are caused by electrostatic repulsion For example beta decay is caused by the weak interaction 39 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 44 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 49 The first direct measurement of mass of a superheavy nucleus was reported in 2018 at LBNL 50 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 51 If the decay occurred in a vacuum then since total momentum of an isolated system before and after the decay must 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 40 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 physicist Georgy Flerov 52 a leading scientist at JINR and thus it was a hobbyhorse for the facility 53 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 29 They thus preferred to link new isotopes to the already known ones by successive alpha decays 52 For instance element 102 was mistakenly identified in 1957 at the Nobel Institute of Physics in Stockholm Stockholm County Sweden 54 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 55 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 55 JINR insisted that they were the first to create the element and suggested a name of their own for the new element joliotium 56 the Soviet name was also not accepted JINR later referred to the naming of the element 102 as hasty 57 This name was proposed to IUPAC in a written response to their ruling on priority of discovery claims of elements signed 29 September 1992 57 The name nobelium remained unchanged on account of its widespread usage 58 Generally heavier nuclei require more neutrons because as the number of protons increases so does electrostatic repulsion between them This repulsion is balanced by the binding energy generated by the strong interaction between quarks within nucleons it is enough to hold the quarks together in a nucleon together and some of it is left for binding of different nucleons The more nucleons there are in a nucleus the more energy there is for binding the nucleons note that greater total binding energy does not necessarily correspond to greater binding energy per nucleon 60 However having too many neutrons per proton while decreasing electrostatic repulsion per nucleon that negates the binding energy results in beta decay 61 The superscript number to the left of a chemical symbol refers to the mass of a given nuclide for instance 48Ca is the notation for calcium 48 In superheavy element research elements that have not been assigned a name and a symbol are often referred to by their atomic numbers in lieu of symbols if a symbol has been assigned and the number is to be displayed it is written in subscript to the left of the symbol 270108 would be 270Hs or 270108 Hs in modern nomenclature or hassium 270 if spelled out This was intended to resolve not only any future conflicts but also a number of ones that existed back then beryllium glucinium niobium columbium lutecium cassiopeium hafnium celtium tungsten wolfram and protoactinium brevium 76 For example Armbruster suggested element 107 be named nielsbohrium JINR used this name for element 105 which they claimed to have discovered This was meant to honor Oganessian s technique of cold fusion GSI had asked JINR for permission 83 American physicist Glenn T Seaborg suggested that name for element 110 on behalf of LBNL in November 1997 after IUPAC surveyed the three main collaborations GSI JINR LLNL and LBNL on how they thought the element should be named 91 Similarly there are names of ruthenium moscovium and dubnium for JINR The only element discovered by RIKEN in Wakō Saitama Prefecture Japan is named nihonium after a Japanese name of Japan Different sources give different values for half lives the most recently published values are listed Few nuclei of each hassium isotope have been synthesized and thus half lives of these isotopes cannot be determined very precisely Therefore a half life may be given as the most likely value alongside a confidence interval that corresponds to one standard deviation such an interval based on future experiments whose result is yet unknown contains the true value with a probability of 68 3 for example the value of 1 42 s in the isotope table obtained for 268Hs was listed in the source as 1 42 1 13 s and this value is a modification of the value of 0 38 1 8 0 17 s 93 The notation 208Pb 56Fe n 263Hs denotes a nuclear reaction between a nucleus of 208Pb that was bombarded with a nucleus of 56Fe the two fused and after a single neutron had been emitted the remaining nucleus was 263Hs Another notation for this reaction would be 208Pb 56Fe 263Hs n Half life of this isotope is estimated from trends across nuclides with the same number of protons and neutrons rather than measured directly Only one event of decay of this isotope has been registered Metastable nuclides are denoted by the letter m immediately the mass number such as in hassium 277m The symbol Z refers to the atomic number number of protons in an atomic nucleus The symbol N refers to the neutron number number of neutrons in a nucleus The symbol A refers to the mass number number of neutrons and protons in a nucleus combined In particular the low decay energy for 270Hs matches calculations 114 The conclusion for 269Hs was made after its decay data was compared to that of 273Ds the decay of the latter into the former has an energy sufficiently greater than the decay of the former 11 2 MeV and 9 2 MeV respectively The great value of the former energy was explained as a right to left crossing of N 162 273Ds has 163 neutrons and 269Hs has 161 116 A similar observation and conclusion were made after measurement of decay energy of 271Hs and 267Sg 117 At the time this symbol had not yet been taken by seaborgium The spin orbit interaction is the interaction between the magnetic field caused by the spin of an electron and the effective magnetic field caused by the electric field of a nucleus and movement of an electron orbiting it According to the special theory of relativity electric and magnetic fields are both occurrences of common electromagnetic fields that can be seen as more or less electric and more or less magnetic depending on the reference frame The effective magnetic field from the reference frame of the electron is obtained from the nucleus s electric field after a relativistic transformation from the reference frame of the nucleus The splitting occurs because depending on the spin of an electron it may be either attracted to or repealed by the nucleus this attraction or repulsion is significantly weaker the electrostatic attraction between them and it can thus only somewhat affect the electron overall 138 While iridium is known to show a 8 state in iridium tetroxide as well as a unique 9 state in the iridium tetroxide cation IrO 4 the former is known only in matrix isolation and the latter in the gas phase and no iridium compounds in such high oxidation states have been synthesized in macroscopic amounts 150 151 References edit Hassium The Periodic Table of Videos University of Nottingham 28 January 2011 Retrieved 19 October 2012 Radioactive Elements Commission on Isotopic Abundances and Atomic Weights 2018 Retrieved 20 September 2020 a b c Audi et al 2017 p 030001 136 a b c Hoffman Lee amp Pershina 2006 p 1672 a b c d e f Ostlin A 2013 Transition metals Electronic Structure Studies and Method Development for Complex Materials PDF Licentiate pp 15 16 Retrieved 24 October 2019 a b Gyanchandani Jyoti Sikka S K 10 May 2011 Physical properties of the 6 d series elements from density functional theory Close similarity to lighter transition metals Physical Review B 83 17 172101 doi 10 1103 PhysRevB 83 172101 a b Kratz Lieser 2013 Nuclear and Radiochemistry Fundamentals and Applications 3rd ed p 631 Hoffman 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 p 1691 ISBN 978 1 4020 3555 5 Fricke Burkhard 1975 Superheavy elements a prediction of their chemical and physical properties Recent Impact of Physics on Inorganic Chemistry Structure and Bonding 21 89 144 doi 10 1007 BFb0116498 ISBN 978 3 540 07109 9 Retrieved 4 October 2013 a 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11 March 2020 Retrieved 30 June 2019 Maria L Marcalo J Gibson J K 2019 Evans W J Hanusa T P eds The Heaviest Metals Science and Technology of the Actinides and Beyond John Wiley amp Sons p 260 ISBN 978 1 119 30408 1 Bibliography editAudi G Kondev F G Wang M et al 2017 The NUBASE2016 evaluation of nuclear properties PDF Chinese Physics C 41 3 030001 Bibcode 2017ChPhC 41c0001A doi 10 1088 1674 1137 41 3 030001 S2CID 126750783 Archived from the original PDF on 1 August 2020 Barber R C Greenwood N N Hrynkiewicz A Z et al 1993 Discovery of the Transfermium elements PDF Pure and Applied Chemistry 65 8 1757 1814 doi 10 1351 pac199365081757 S2CID 195819585 Archived PDF from the original on 20 September 2016 Retrieved 7 September 2016 Beiser A 2003 Concepts of modern physics 6th ed McGraw Hill ISBN 978 0 07 244848 1 OCLC 48965418 Greenwood N N Earnshaw A 1997 Chemistry of the Elements 2nd ed Butterworth Heinemann ISBN 978 0 08 037941 8 Hoffman D C Ghiorso A Seaborg G T 2000 The Transuranium People The Inside Story World Scientific ISBN 978 1 78 326244 1 Hoffman D C Lee D M Pershina V 2006 Transactinides and the future elements In Morss L R Edelstein N M Fuger J eds The Chemistry of the Actinide and Transactinide Elements 3rd ed Springer Science Business Media pp 1652 1752 ISBN 978 1 4020 3555 5 Kragh H 2018 From Transuranic to Superheavy Elements A Story of Dispute and Creation Springer ISBN 978 3 319 75813 8 Lide D R 2004 Handbook of chemistry and physics 84th ed CRC Press ISBN 978 0 8493 0566 5 Zagrebaev V Karpov A Greiner W 2013 Future of superheavy element research Which nuclei could be synthesized within the next few years Journal of Physics Conference Series 420 1 012001 arXiv 1207 5700 Bibcode 2013JPhCS 420a2001Z doi 10 1088 1742 6596 420 1 012001 ISSN 1742 6588 S2CID 55434734 External links edit nbsp Media related to Hassium at Wikimedia Commons Retrieved from https en wikipedia org w index php title Hassium amp oldid 1199992034, wikipedia, wiki, book, books, 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