Hassium
Encyclopedia
Hassium is a synthetic element
with the symbol Hs and atomic number
108. It is the heaviest member of the group 8 (VIII) elements. The element was first observed in 1984. Experiments have confirmed that hassium is a typical member of group 8 showing a stable +8 oxidation state, analogous to osmium
.
Several isotopes are known, with 269Hs being the longest-lived with a half-life
of ~10 s.
More than 100 atoms of hassium have been synthesized to date in various cold and hot fusion reactions, both as a parent nucleus and decay product.
and Gottfried Münzenberg
at the Institute for Heavy Ion Research
(Gesellschaft für Schwerionenforschung) in Darmstadt
. The team bombarded a lead target with 58Fe nuclei to produce 3 atoms of 265Hs in the reaction:
The IUPAC/IUPAP Transfermium Working Group (TWG) recognised the GSI collaboration as official discoverers in their 1992 report.
. During the period of controversy over the names of the elements (see element naming controversy
) IUPAC adopted unniloctium (symbol Uno) as a temporary element name
for this element.
The name hassium was proposed by the officially recognised German discoverers in 1992, derived from the Latin name for the German state of Hesse
where the institute is located .
In 1994 a committee of IUPAC recommended that element 108 be named hahnium (Hn), in spite of the long-standing convention to give the discoverer the right to suggest a name.
After protests from the German discoverers, the name hassium (Hs) was adopted internationally in 1997.
In addition, they also hope to study the spectroscopy of 269Hs, 265Sg and 261Rf, using the reaction 248Cm(26Mg,5n) or 226Ra(48Ca,5n). This will allow them to determine the level structure in 265Sg and 261Rf and attempt to give spin and parity assignments to the various proposed isomers.
In addition, scientists at the GSI are hoping to utilize the new TASCA facility to study the synthesis and properties of the hassium(II) compound, hassocene, Hs(Cp)2 using the reaction 226Ra(48Ca,xn).
Important future experiments will involve the attempted synthesis of hassium isotopes in this symmetric reaction using the fission fragments.
This reaction was carried out at Dubna in 2007 but no atoms were detected, leading to a cross section limit of 1 pb. If confirmed, this would indicate that such symmetric fusion reactions should be modelled as 'hot fusion' reactions rather than 'cold fusion' ones, as first suggested. This would indicate that such reactions will unfortunately have limited use in the synthesis of superheavy elements.
This reaction was performed in May 2002 at the GSI. Unfortunately, the experiment was cut short due to a failure of the zinc-70 beam.
This reaction was first reported in 1978 by the team at Dubna. In a later experiment in 1984, using the rotating drum technique, they were able to detect a spontaneous fission activity assigned to 260Sg, daughter of 264Hs.
In a repeat experiment in the same year, they applied the method of chemical identification of a descendant to provide support to the synthesis of element 108. They were able to detect several alpha decays of 253Es and 253Fm, descendants of 265Hs.
In the official discovery of the element in 1984, the team at GSI studied the reaction using the alpha decay genetic correlation method. They were able to positively identify 3 atoms of 265Hs. After an upgrade of their facilities in 1993, the team repeated the experiment in 1994 and detected 75 atoms of 265Hs and 2 atoms of 264Hs, during the measurement of a partial excitation function for the 1n neutron evaporation channel. The maximum of the 1n channel was measured as 69 pb in a further run in late 1997 in which a further 20 atoms were detected.
The discovery experiment was successfully repeated in 2002 at RIKEN
(10 atoms) and in 2003 at GANIL (7 atoms).
The team at RIKEN further studied the reaction in 2008 in order to conduct first spectroscopic studies of the even-even nucleus 264Hs. They were also able to detect a further 29 atoms of 265Hs.
The use of a Pb-207 target was first used in 1984 at Dubna. They were able to detect the same SF activity as observed in the Pb-208 run and once again assigned it to 260Sg, daughter of 264Hs. The team at GSI
first studied the reaction in 1986 using the method of correlation of genetic alpha decays and identified a single atom of 264Hs with a cross section of 3.2 pb. The reaction was repeated in 1994 and the team were able to measure both alpha decay
and spontaneous fission
for 264Hs.
This reaction was studied in 2008 at RIKEN in order to conduct first spectrscopic studies of the even-even nucleus 264Hs. The team detected 11 atoms of the isotope.
This reaction was studied for the first time in 2008 by the team at LBNL. They were able to produce and identify 6 atoms of the new isotope 263Hs. A few months later, the RIKEN team also published their results on the same reaction.
This reaction was studied for the first time in 2008 by the team at RIKEN. They were able to identify 8 atoms of the new isotope 263Hs.
First attempts to synthesise nuclei of hassium were performed using this reaction by the team at Dubna in 1983. Using the rotating drum technique, they were able to detect a spontaneous fission activity assigned to 255Rf, descendant of the 263Hs decay chain. Identical results were measured in a repeat run in 1984.
In a subsequent experiment in 1983, they applied the method of chemical identification of a descendant to provide support to the synthesis of hassium. They were able to detect alpha decays from fermium isotopes, assigned as descendants of the decay of 262Hs. This reaction has not been tried since and 262Hs is currently unconfirmed.
This reaction was reportedly first studied in 1978 by the team at the Flerov Laboratory of Nuclear Reactions (FLNR) under the leadership of Yuri Oganessian. However, results are not available in the literature.
The reaction was repeated at the FLNR in June 2008 and results show that the 4 atoms of the isotope 270Hs were detected with a yield of 9 pb. The decay data for the recently discovered isotope was confirmed, although the alpha energy was slightly higher. In Jan 2009, the team repeated the experiment and a further 2 atoms of 270Hs were detected.
This reaction was first studied at Dubna in 1987. Detection was by spontaneous fission and no activities were found leading to a calculated cross section limit of 2 pb.
This reaction with the rare and expensive 36S isotope was conducted at the GSI in April–May 2008. Preliminary results show that a single atom of 270Hs was detected with a yield of 0.8 pb. The data confirms the decay properties of 270Hs and 266Sg.
In March 1994, the team at Dubna led by the late Yuri Lazerev announced the detection of 3 atoms of 267Hs from the 5n neutron evaporation channel.
The decay properties was confirmed by the team at GSI in their simultaneous study of element 110.
The reaction was repeated at the GSI in Jan-Feb 2009 in order to search for the new isotope 268Hs. The team, led by Prof. Nishio, detected a single atom of both 268Hs and 267Hs. The new isotope underwent alpha-decay to the previously known isotope 264Sg.
Most recently, a GSI-PSI collaboration has studied the nuclear reaction of curium-248 with magnesium-26 ions. Between May 2001 and August 2005, the team has studied the excitation function of the 3n, 4n, and 5n evaporation channels leading to 269Hs, 270Hs, and 271Hs. The synthesis of the important isotope 270Hs was published in December 2006 by the team of scientists from the Technical University of Munich
. It was reported that this isotope decayed by emission of an alpha-particle with an energy of 8.83 MeV and a projected half-life of ~22 s, assuming a 0+ to 0+ ground state decay to 266Sg using the Viola-Seaborg equation.
This new reaction was studied at the GSI in July–August 2006 in a search for the new isotope 268Hs. They were unable to detect any atoms from neutron evaporation and calculated a cross section limit of 1 pb.
The team at Dubna studied this reaction in 1983 using detection by spontaneous fission
(SF). Several short SF activities were found indicating the formation of nuclei of hassium.
In addition, N=162 has been calculated as a deformed neutron magic number and hence the nucleus 270Hs has promise as a deformed doubly magic nucleus. Experimental data from the decay of Z=110 isotopes 271Ds and 273Ds, provides strong evidence for the magic nature of the N=162 sub-shell. The recent synthesis of 269Hs, 270Hs, and 271Hs also fully support the assignment of N=162 as a magic closed shell. In particular, the low decay energy for 270Hs is in complete agreement with calculations.
For SF, it is necessary to measure the half-lives for the isotonic nuclei 268Sg, 270Hs and 272Ds. Since the seaborgium
and darmstadtium
isotopes are not known at this time, and fission of 270Hs has not been measured, this method can be used to date to confirm the stabilizing nature of the Z=108 shell.
However, good evidence for the magicity of the Z=108 can be deemed from the large differences in the alpha decay energies measured for 270Hs, 271Ds and 273Ds. More conclusive evidence would come from the determination of the decay energy for the nucleus 272Ds.
s that produce isotopes of hassium directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.
DNS = Di-nuclear system ; σ = cross section
, ruthenium
and osmium
. The latter two members of the group readily portray their group oxidation state of +8 and this state becomes more stable as the group is descended. Thus hassium is expected to form a stable +8 state. Osmium also shows stable +5, +4 and +3 states with the +4 state the most stable. For ruthenium, the +6, +5 and +3 states are stable with the +3 state being the most stable. Hassium is therefore expected to also show other stable lower oxidation states.
chemistry which allows facile extrapolations to be made for hassium. All the lighter members have known or hypothetical tetroxides, MO4. The oxidising power decreases as one descends the group such that FeO4
is not known due to an extraordinary electron affinity
which results in the formation of the well-known oxo-ion ferrate(VI), FeO42−. Ruthenium tetroxide, RuO4, formed by oxidation of ruthenium(VI) in acid
, readily undergoes reduction to ruthenate(VI), RuO42−. Oxidation of ruthenium metal in air forms the dioxide, RuO2. In contrast, osmium burns to form the stable tetroxide, OsO4, which complexes with hydroxide ion to form an osmium(VIII) -ate complex, [OsO4(OH)2]2−. Therefore, eka-osmium properties for hassium should be demonstrated by the formation of a volatile tetroxide HsO4, which undergoes complexation with hydroxide to form a hassate(VIII), [HsO4(OH)2]2−.
The first chemistry experiments were performed using gas thermochromatography in 2001, using 172Os as a reference. During the experiment, 5 hassium atoms were detected using the reaction 248Cm(26Mg,5n)269Hs. The resulting atoms were thermalized and oxidized in a He/O2 mixture to form the oxide.
The measured deposition temperature indicated that hassium(VIII) oxide is less volatile than osmium tetroxide, OsO4, and places hassium firmly in group 8.
In order to further probe the chemistry of hassium, scientists decided to assess the reaction between hassium tetroxide and sodium hydroxide to form sodium hassate(VIII), a reaction well-known with osmium. In 2004, scientists announced that they had succeeded in carrying out the first acid-base reaction with a hassium compound:
Synthetic element
In chemistry, a synthetic element is a chemical element that is too unstable to occur naturally on Earth, and therefore has to be created artificially. So far 30 synthetic elements have been discovered—that is, synthesized...
with the symbol Hs and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
108. It is the heaviest member of the group 8 (VIII) elements. The element was first observed in 1984. Experiments have confirmed that hassium is a typical member of group 8 showing a stable +8 oxidation state, analogous to osmium
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...
.
Several isotopes are known, with 269Hs being the longest-lived with a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of ~10 s.
More than 100 atoms of hassium have been synthesized to date in various cold and hot fusion reactions, both as a parent nucleus and decay product.
Official discovery
Hassium was first synthesized in 1984 by a German research team led by Peter ArmbrusterPeter Armbruster
Peter Armbruster is a physicist at the Gesellschaft für Schwerionenforschung facility in Darmstadt, Germany, and is credited with co-discovering elements 107 , 108 , 109 , 110 , 111 , and 112 with research partner Gottfried Münzenberg.He studied physics at the Technical...
and Gottfried Münzenberg
Gottfried Münzenberg
Gottfried Münzenberg is a German physicist.He studied physics at Justus-Liebig-Universität in Giessen and Leopold-Franzens-Universität Innsbruck and completed his studies with a Ph.D. at the University of Giessen, Germany, in 1971...
at the Institute for Heavy Ion Research
Gesellschaft für Schwerionenforschung
The GSI Helmholtz Centre for Heavy Ion Research GmbH in the Wixhausen suburb of Darmstadt, Germany is a federally and state co-funded heavy ion research center. The current director of GSI is Horst Stöcker who succeeded Walter F...
(Gesellschaft für Schwerionenforschung) in Darmstadt
Darmstadt
Darmstadt is a city in the Bundesland of Hesse in Germany, located in the southern part of the Rhine Main Area.The sandy soils in the Darmstadt area, ill-suited for agriculture in times before industrial fertilisation, prevented any larger settlement from developing, until the city became the seat...
. The team bombarded a lead target with 58Fe nuclei to produce 3 atoms of 265Hs in the reaction:
- + → +
The IUPAC/IUPAP Transfermium Working Group (TWG) recognised the GSI collaboration as official discoverers in their 1992 report.
Naming
Hassium has historically been known as eka-osmiumMendeleev's predicted elements
Professor Dmitri Mendeleev published the first Periodic Table of the Atomic Elements in 1869 based on properties which appeared with some regularity as he laid out the elements from lightest to heaviest....
. During the period of controversy over the names of the elements (see element naming controversy
Element naming controversy
The names for the chemical elements 104 to 106 were the subject of a major controversy starting in the 1960s, described by some nuclear chemists as the Transfermium Wars because it concerned the elements following fermium on the periodic table....
) IUPAC adopted unniloctium (symbol Uno) as a temporary element name
Systematic element name
A systematic element name is the temporary name and symbol assigned to newly synthesized and not yet synthesized chemical elements. In chemistry, a transuranic element receives a permanent name and symbol only after its synthesis has been confirmed. In some cases, this has been a protracted and...
for this element.
The name hassium was proposed by the officially recognised German discoverers in 1992, derived from the Latin name for the German state of Hesse
Hesse
Hesse or Hessia is both a cultural region of Germany and the name of an individual German state.* The cultural region of Hesse includes both the State of Hesse and the area known as Rhenish Hesse in the neighbouring Rhineland-Palatinate state...
where the institute is located .
In 1994 a committee of IUPAC recommended that element 108 be named hahnium (Hn), in spite of the long-standing convention to give the discoverer the right to suggest a name.
After protests from the German discoverers, the name hassium (Hs) was adopted internationally in 1997.
Spectroscopy
Scientists at the GSI are planning to search for K-isomers in 270Hs using the reaction 226Ra(48Ca,4n) in 2010. They will use the new TASISpec method developed alongside the introduction of the new TASCA facility at the GSI.In addition, they also hope to study the spectroscopy of 269Hs, 265Sg and 261Rf, using the reaction 248Cm(26Mg,5n) or 226Ra(48Ca,5n). This will allow them to determine the level structure in 265Sg and 261Rf and attempt to give spin and parity assignments to the various proposed isomers.
Chemistry
The team from the universität Mainz are planning to study the electrodeposition of hassium atoms using TASCA at the GSI. The current aim is to use the reaction 226Ra(48Ca,4n)270Hs.In addition, scientists at the GSI are hoping to utilize the new TASCA facility to study the synthesis and properties of the hassium(II) compound, hassocene, Hs(Cp)2 using the reaction 226Ra(48Ca,xn).
Cold fusion
This section deals with the synthesis of nuclei of hassium by so-called "cold" fusion reactions. These are processes which create compound nuclei at low excitation energy (~10-20 MeV, hence "cold"), leading to a higher probability of survival from fission. The excited nucleus then decays to the ground state via the emission of one or two neutrons only.136Xe(136Xe,xn)272−xHs
Important future experiments will involve the attempted synthesis of hassium isotopes in this symmetric reaction using the fission fragments.
This reaction was carried out at Dubna in 2007 but no atoms were detected, leading to a cross section limit of 1 pb. If confirmed, this would indicate that such symmetric fusion reactions should be modelled as 'hot fusion' reactions rather than 'cold fusion' ones, as first suggested. This would indicate that such reactions will unfortunately have limited use in the synthesis of superheavy elements.
198Pt(70Zn,xn)268−xHs
This reaction was performed in May 2002 at the GSI. Unfortunately, the experiment was cut short due to a failure of the zinc-70 beam.
208Pb(58Fe,xn)266−xHs (x=1,2)
This reaction was first reported in 1978 by the team at Dubna. In a later experiment in 1984, using the rotating drum technique, they were able to detect a spontaneous fission activity assigned to 260Sg, daughter of 264Hs.
In a repeat experiment in the same year, they applied the method of chemical identification of a descendant to provide support to the synthesis of element 108. They were able to detect several alpha decays of 253Es and 253Fm, descendants of 265Hs.
In the official discovery of the element in 1984, the team at GSI studied the reaction using the alpha decay genetic correlation method. They were able to positively identify 3 atoms of 265Hs. After an upgrade of their facilities in 1993, the team repeated the experiment in 1994 and detected 75 atoms of 265Hs and 2 atoms of 264Hs, during the measurement of a partial excitation function for the 1n neutron evaporation channel. The maximum of the 1n channel was measured as 69 pb in a further run in late 1997 in which a further 20 atoms were detected.
The discovery experiment was successfully repeated in 2002 at RIKEN
RIKEN
is a large natural sciences research institute in Japan. Founded in 1917, it now has approximately 3000 scientists on seven campuses across Japan, the main one in Wako, just outside Tokyo...
(10 atoms) and in 2003 at GANIL (7 atoms).
The team at RIKEN further studied the reaction in 2008 in order to conduct first spectroscopic studies of the even-even nucleus 264Hs. They were also able to detect a further 29 atoms of 265Hs.
207Pb(58Fe,xn)265−xHs (x=1)
The use of a Pb-207 target was first used in 1984 at Dubna. They were able to detect the same SF activity as observed in the Pb-208 run and once again assigned it to 260Sg, daughter of 264Hs. The team at GSI
Gesellschaft für Schwerionenforschung
The GSI Helmholtz Centre for Heavy Ion Research GmbH in the Wixhausen suburb of Darmstadt, Germany is a federally and state co-funded heavy ion research center. The current director of GSI is Horst Stöcker who succeeded Walter F...
first studied the reaction in 1986 using the method of correlation of genetic alpha decays and identified a single atom of 264Hs with a cross section of 3.2 pb. The reaction was repeated in 1994 and the team were able to measure both alpha decay
Alpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...
and spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
for 264Hs.
This reaction was studied in 2008 at RIKEN in order to conduct first spectrscopic studies of the even-even nucleus 264Hs. The team detected 11 atoms of the isotope.
208Pb(56Fe,xn)264−xHs (x=1)
This reaction was studied for the first time in 2008 by the team at LBNL. They were able to produce and identify 6 atoms of the new isotope 263Hs. A few months later, the RIKEN team also published their results on the same reaction.
206Pb(58Fe,xn)264−xHs (x=1)
This reaction was studied for the first time in 2008 by the team at RIKEN. They were able to identify 8 atoms of the new isotope 263Hs.
209Bi(55Mn,xn)264−xHs
First attempts to synthesise nuclei of hassium were performed using this reaction by the team at Dubna in 1983. Using the rotating drum technique, they were able to detect a spontaneous fission activity assigned to 255Rf, descendant of the 263Hs decay chain. Identical results were measured in a repeat run in 1984.
In a subsequent experiment in 1983, they applied the method of chemical identification of a descendant to provide support to the synthesis of hassium. They were able to detect alpha decays from fermium isotopes, assigned as descendants of the decay of 262Hs. This reaction has not been tried since and 262Hs is currently unconfirmed.
Hot fusion
This section deals with the synthesis of nuclei of hassium by so-called "hot" fusion reactions. These are processes which create compound nuclei at high excitation energy (~40-50 MeV, hence "hot"), leading to a reduced probability of survival from fission and quasi-fission. The excited nucleus then decays to the ground state via the emission of 3-5 neutrons.226Ra(48Ca,xn)274−xHs (x=4)
This reaction was reportedly first studied in 1978 by the team at the Flerov Laboratory of Nuclear Reactions (FLNR) under the leadership of Yuri Oganessian. However, results are not available in the literature.
The reaction was repeated at the FLNR in June 2008 and results show that the 4 atoms of the isotope 270Hs were detected with a yield of 9 pb. The decay data for the recently discovered isotope was confirmed, although the alpha energy was slightly higher. In Jan 2009, the team repeated the experiment and a further 2 atoms of 270Hs were detected.
232Th(40Ar,xn)272−xHs
This reaction was first studied at Dubna in 1987. Detection was by spontaneous fission and no activities were found leading to a calculated cross section limit of 2 pb.
238U(36S,xn)274−xHs (x=4)
This reaction with the rare and expensive 36S isotope was conducted at the GSI in April–May 2008. Preliminary results show that a single atom of 270Hs was detected with a yield of 0.8 pb. The data confirms the decay properties of 270Hs and 266Sg.
238U(34S,xn)272−xHs (x=4,5)
In March 1994, the team at Dubna led by the late Yuri Lazerev announced the detection of 3 atoms of 267Hs from the 5n neutron evaporation channel.
The decay properties was confirmed by the team at GSI in their simultaneous study of element 110.
The reaction was repeated at the GSI in Jan-Feb 2009 in order to search for the new isotope 268Hs. The team, led by Prof. Nishio, detected a single atom of both 268Hs and 267Hs. The new isotope underwent alpha-decay to the previously known isotope 264Sg.
248Cm(26Mg,xn)274−xHs (x=3,4,5)
Most recently, a GSI-PSI collaboration has studied the nuclear reaction of curium-248 with magnesium-26 ions. Between May 2001 and August 2005, the team has studied the excitation function of the 3n, 4n, and 5n evaporation channels leading to 269Hs, 270Hs, and 271Hs. The synthesis of the important isotope 270Hs was published in December 2006 by the team of scientists from the Technical University of Munich
Technical University of Munich
The Technische Universität München is a research university with campuses in Munich, Garching, and Weihenstephan...
. It was reported that this isotope decayed by emission of an alpha-particle with an energy of 8.83 MeV and a projected half-life of ~22 s, assuming a 0+ to 0+ ground state decay to 266Sg using the Viola-Seaborg equation.
248Cm(25Mg,xn)273−xHs
This new reaction was studied at the GSI in July–August 2006 in a search for the new isotope 268Hs. They were unable to detect any atoms from neutron evaporation and calculated a cross section limit of 1 pb.
249Cf(22Ne,xn)271−xHs
The team at Dubna studied this reaction in 1983 using detection by spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
(SF). Several short SF activities were found indicating the formation of nuclei of hassium.
Chronology of isotope discovery
| Isotope | Year discovered | Discovery reaction |
|---|---|---|
| 263Hs | 2008 | 208Pb(56Fe,n) |
| 264Hs | 1986 | 207Pb(58Fe,n) |
| 265Hs | 1984 | 208Pb(58Fe,n) |
| 266Hs | 2000 | 207Pb(64Ni,n) |
| 267Hs | 1995 | 238U(34S,5n) |
| 268Hs | 2009 | 238U(34S,4n) |
| 269Hs | 1996 | 208Pb(70Zn,n) |
| 270Hs | 2004 | 248Cm(26Mg,4n) |
| 271Hs | 2004 | 248Cm(26Mg,3n) |
| 272Hs | unknown | |
| 273Hs | 2010 | |242Pu(48Ca,5n) |
| 274Hs | unknown | |
| 275Hs | 2003 | 242Pu(48Ca,3n) |
| 276Hs | unknown | |
| 277aHs | 2009 | 244Pu(48Ca,3n) |
| 277bHs? | 1999 | 244Pu(48Ca,3n) |
277bHs
An isotope assigned to 277Hs has been observed on one occasion decaying by SF with a long half-life of ~11 minutes. The isotope is not observed in the decay of the most common isotope of 281Ds but is observed in the decay from a rare, as yet unconfirmed isomeric level, namely 281bDs . The half-life is very long for the ground state and it is possible that it belongs to an isomeric level in 277Hs. Furthermore, in 2009, the team at the GSI observed a small alpha decay branch for 281aDs producing an isotope of 277Hs decaying by SF in a short lifetime. The measured half-life is close to the expected value for ground state isomer, 277aHs. Further research is required to confirm the production of the isomer.273Hs
The claimed synthesis of element 118 by LBNL in 1999 involved the intermediate 273Hs. This isotope was claimed to decay by 9.78 and 9.47 MeV alpha emission with a half-life of 1.2 s. The claim to discovery of 293118 was retracted in 2001. This isotope was finally created in 2010 and the data confirmed the fabrication of previous data.270Hs: prospects for a deformed doubly magic nucleus
According to macroscopic-microscopic (MM) theory, Z=108 is a deformed proton magic number, in combination with the neutron shell at N=162. This means that such nuclei are permanently deformed in their ground state but have high, narrow fission barriers to further deformation and hence relatively long SF partial half-lives. The SF half-lives in this region are typically reduced by a factor of 109 in comparison with those in the vicinity of the spherical doubly magic nucleus 298114, caused by an increase in the probability of barrier penetration by quantum tunnelling, due to the narrower fission barrier.In addition, N=162 has been calculated as a deformed neutron magic number and hence the nucleus 270Hs has promise as a deformed doubly magic nucleus. Experimental data from the decay of Z=110 isotopes 271Ds and 273Ds, provides strong evidence for the magic nature of the N=162 sub-shell. The recent synthesis of 269Hs, 270Hs, and 271Hs also fully support the assignment of N=162 as a magic closed shell. In particular, the low decay energy for 270Hs is in complete agreement with calculations.
Evidence for the Z=108 deformed proton shell
Evidence for the magicity of the Z=108 proton shell can be deemed from two sources:- the variation in the partial spontaneous fissionSpontaneous fissionSpontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
half-lives for isotones - the large gap in Qα for isotonic pairs between Z=108 and Z=110.
For SF, it is necessary to measure the half-lives for the isotonic nuclei 268Sg, 270Hs and 272Ds. Since the seaborgium
Seaborgium
Seaborgium is a synthetic chemical element with the symbol Sg and atomic number 106.Seaborgium is a synthetic element whose most stable isotope 271Sg has a half-life of 1.9 minutes. A new isotope 269Sg has a potentially slightly longer half-life based on the observation of a single decay...
and darmstadtium
Darmstadtium
Darmstadtium is a chemical element with the symbol Ds and atomic number 110. It is placed as the heaviest member of group 10, but no known isotope is sufficiently stable to allow chemical experiments to confirm its placing in that group...
isotopes are not known at this time, and fission of 270Hs has not been measured, this method can be used to date to confirm the stabilizing nature of the Z=108 shell.
However, good evidence for the magicity of the Z=108 can be deemed from the large differences in the alpha decay energies measured for 270Hs, 271Ds and 273Ds. More conclusive evidence would come from the determination of the decay energy for the nucleus 272Ds.
269Hs
The direct synthesis of 269Hs has resulted in three alpha lines at 9.21, 9.10, and 8.94 MeV. In the decay of 277112, only 9.21 MeV 269Hs alpha decays have been observed indicating that this decay occurs from an isomeric level. Further research is required to confirm this.267Hs
The decay of 267Hs is known to occur by alpha decay with three alpha lines at 9.88, 9.83, and 9.75 MeV and a half-life of 52 ms. In the recent syntheses of 271m,gDs additional activities have been observed. A .94ms activity decaying by 9.83 MeV alpha emission has been observed in addition to longer lived ~.8 s and ~6.0 s activities. Each of these is currently not assigned and confirmed and further research is required to positively identify them.265Hs
The synthesis of 265Hs has also provided evidence for two levels. The ground state decays by 10.30 MeV alpha emission with a half-life of 2.0 ms. The isomeric state is placed at 300 keV above the ground state and decays by 10.57 MeV alpha emission with a half-life of .75 ms.Physical production yields
The tables below provides cross-sections and excitation energies for nuclear reactionNuclear reaction
In nuclear physics and nuclear chemistry, a nuclear reaction is semantically considered to be the process in which two nuclei, or else a nucleus of an atom and a subatomic particle from outside the atom, collide to produce products different from the initial particles...
s that produce isotopes of hassium directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.
Cold fusion
| Projectile | Target | CN | 1n | 2n | 3n |
|---|---|---|---|---|---|
| 58Fe | 208Pb | 266Hs | 69 pb, 13.9 MeV | 4.5 pb | |
| 58Fe | 207Pb | 265Hs | 3.2 pb |
Hot fusion
| Projectile | Target | CN | 3n | 4n | 5n |
|---|---|---|---|---|---|
| 48Ca | 226Ra | 274Hs | 9.0 pb | ||
| 36S | 238U | 274Hs | 0.8 pb | ||
| 34S | 238U | 272Hs | 2.5 pb, 50.0 MeV | ||
| 26Mg | 248Cm | 274Hs | 2.5 pb | 3.0 pb | 7.0 pb |
Evaporation residue cross sections
The below table contains various targets-projectile combinations for which calculations have provided estimates for cross section yields from various neutron evaporation channels. The channel with the highest expected yield is given.DNS = Di-nuclear system ; σ = cross section
| Target | Projectile | CN | Channel (product) | σ max | Model | Ref |
|---|---|---|---|---|---|---|
| 136Xe | 136Xe | 272Hs | 1-4n (271-268Hs) | 10−6 pb | DNS | |
| 238U | 34S | 272Hs | 4n (268Hs) | 10 pb | DNS |
Occurrence
Hassium has been postulated to exist in nature through a long-lived isotope hassium-271.Oxidation states
Hassium is projected to be the fifth member of the 6d series of transition metals and the heaviest member of group VIII in the Periodic Table, below ironIron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, ruthenium
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...
and osmium
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...
. The latter two members of the group readily portray their group oxidation state of +8 and this state becomes more stable as the group is descended. Thus hassium is expected to form a stable +8 state. Osmium also shows stable +5, +4 and +3 states with the +4 state the most stable. For ruthenium, the +6, +5 and +3 states are stable with the +3 state being the most stable. Hassium is therefore expected to also show other stable lower oxidation states.
Chemistry
The group VIII elements show a very distinctive oxideOxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
chemistry which allows facile extrapolations to be made for hassium. All the lighter members have known or hypothetical tetroxides, MO4. The oxidising power decreases as one descends the group such that FeO4
is not known due to an extraordinary electron affinity
Electron affinity
The Electron affinity of an atom or molecule is defined as the amount of energy released when an electron is added to a neutral atom or molecule to form a negative ion....
which results in the formation of the well-known oxo-ion ferrate(VI), FeO42−. Ruthenium tetroxide, RuO4, formed by oxidation of ruthenium(VI) in acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
, readily undergoes reduction to ruthenate(VI), RuO42−. Oxidation of ruthenium metal in air forms the dioxide, RuO2. In contrast, osmium burns to form the stable tetroxide, OsO4, which complexes with hydroxide ion to form an osmium(VIII) -ate complex, [OsO4(OH)2]2−. Therefore, eka-osmium properties for hassium should be demonstrated by the formation of a volatile tetroxide HsO4, which undergoes complexation with hydroxide to form a hassate(VIII), [HsO4(OH)2]2−.
Gas phase chemistry
Hassium is expected to have the electron configuration [Rn]5f14 6d6 7s2 and thus behave as the heavier homolog of osmium (Os). As such, it should form a volatile tetroxide, HsO4, due to the tetrahedral shape of the molecule.The first chemistry experiments were performed using gas thermochromatography in 2001, using 172Os as a reference. During the experiment, 5 hassium atoms were detected using the reaction 248Cm(26Mg,5n)269Hs. The resulting atoms were thermalized and oxidized in a He/O2 mixture to form the oxide.
- + 2 →
The measured deposition temperature indicated that hassium(VIII) oxide is less volatile than osmium tetroxide, OsO4, and places hassium firmly in group 8.
In order to further probe the chemistry of hassium, scientists decided to assess the reaction between hassium tetroxide and sodium hydroxide to form sodium hassate(VIII), a reaction well-known with osmium. In 2004, scientists announced that they had succeeded in carrying out the first acid-base reaction with a hassium compound:
- + 2 NaOH →
Summary of compounds and complex ions
| Formula | Names(s) |
|---|---|
| HsO4 | hassium tetroxide; hassium(VIII) oxide |
| |sodium hassate(VIII); disodium dihydroxytetraoxohassate(VIII) |