bohrium ← hassium → meitnerium Os ↑ Hs ↓ (Upo) 108Hs Periodic table
Appearance
unknown
General properties
Name, symbol, number	hassium, Hs, 108
Pronunciation	i/ˈhæsiəm/ HASS-ee-əm or /ˈhɑːsiəm/ HAH-see-əm
Element category	transition metal
Group, period, block	8, 7, d
Standard atomic weight	[269]
Electron configuration	[Rn] 5f14 6d6 7s2 (predicted)
Electrons per shell	2, 8, 18, 32, 32, 14, 2 (predicted) (Image)
Physical properties
Phase	solid (presumably)
Atomic properties
Oxidation states	8
Covalent radius	134 (estimated)[1] pm
Miscellanea
Crystal structure	unknown
CAS registry number	54037-57-9
Most stable isotopes
Main article: Isotopes of hassium
iso NA half-life DM DE (MeV) DP 277aHs syn 2 s SF 277bHs ? syn ~11 min[2] SF 275Hs syn 0.15 s α 9.30 271Sg 273Hs syn 0.24 s α 9.59 269Sg 271Hs syn 40# s α 9.27,9.13 267Sg 270Hs syn 3.6 s α 9.02,8.88 266Sg 269Hs syn 9.7 s α 9.21,9.10,8.97 265Sg 268Hs syn 0.36 s α 9.48 264Sg 267mHs syn 0.8 s α 9.83 263Sg 267Hs syn 52 ms α 9.99,9.87 263Sg 266Hs syn 2.3 ms α 10.18 262Sg 265mHs syn 0.75 ms α 261Sg 265Hs syn 2.0 ms α 261Sg 264Hs syn ~0.8 ms .5 α 10.43 260Sg .5 SF 263Hs syn 0.74 ms α 10.89,10.72,10.57 259Sg
v t e · r

Hassium (ⁱ/ˈhæsiəm/ HASS-ee-əm or /ˈhɑːsiəm/ HAH-see-əm)^[3] 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. Hassium is the heavier homologue of 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.

History[link]

Official discovery[link]

Hassium was first synthesized in 1984 by a German research team led by Peter Armbruster 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:

208
82Pb + 58
26Fe → 265
108Hs + n

The IUPAC/IUPAP Transfermium Working Group (TWG) recognised the GSI collaboration as official discoverers in their 1992 report. ^[4]

Naming[link]

Hassium has historically been known as eka-osmium. 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 (Latin: Hassia German: Hessen).

In 1994 a committee of IUPAC recommended that element 108 be named hahnium (Hn),^[5] 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.^[6]

Future experiments[link]

Spectroscopy[link]

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.^[7]

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.^[8]

Chemistry[link]

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.^[9]

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).^[10]

Nucleosynthesis[link]

Cold fusion[link]

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.^[11] 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. ^[12] 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.^[13] 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.^[14] 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.^[15]

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.

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.^[4] 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.^[16] 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.

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.^[17] A few months later, the RIKEN team also published their results on the same reaction.^[18]

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.^[19]

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.^[4] 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.^[4]

Hot fusion[link]

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.^[4] 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.^[20] In Jan 2009, the team repeated the experiment and a further 2 atoms of ²⁷⁰Hs were detected.^[21]

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.^[4]

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.^[22]

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. ^[23] The decay properties were confirmed by the team at GSI in their simultaneous study of darmstadtium.

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.^{[24][dead link][25][dead link]} The synthesis of the important isotope ²⁷⁰Hs was published in December 2006 by the team of scientists from the Technical University of Munich.^[26] 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 (SF). Several short SF activities were found indicating the formation of nuclei of hassium. ^[4]

Isotopes[link]

Chronology of isotope discovery

Unconfirmed isotopes[link]

^277bHs

An isotope assigned to ²⁷⁷Hs has been observed on one occasion decaying by SF with a long half-life of ~11 minutes.^[2] 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.

Retracted isotopes[link]

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.^[30]

Evidence for the Z=108 deformed proton shell[link]

Evidence for the magicity of the Z=108 proton shell can be deemed from two sources:

1. the variation in the partial spontaneous fission half-lives for isotones
2. the large gap in Q_α 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 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.

Nuclear isomerism[link]

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.

Chemical properties[link]

Extrapolated chemical properties[link]

Oxidation states[link]

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 iron, 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[link]

The group VIII elements show a very distinctive oxide 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^[31] 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⁻.

Density[link]

Hassium is predicted to have a bulk density of 41 g/cm³, the highest of any of the 118 known elements and nearly twice the density of osmium, the most dense measured element, at 22.6 g/cm³. This results from hassium's high atomic weight, the lanthanide and actinide contractions, and relativistic effects, although production of enough hassium to measure this quantity would be impractical, and the sample would quickly decay.^[32]

Experimental chemistry[link]

Gas phase chemistry[link]

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.

269
108Hs + 2 O₂ → 269
108HsO₄

The measured deposition temperature indicated that hassium(VIII) oxide is less volatile than osmium tetroxide, OsO₄, and places hassium firmly in group 8.^[33][34]

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:^[35]

HsO₄ + 2 NaOH → Na₂[HsO₄(OH)₂]

Summary of compounds and complex ions[link]

References[link]

External links[link]

• WebElements.com: Hassium

vep:Hassii

Sisely Treasure
Background information
Origin	Los Angeles, California, USA
Genres	Pop, rock, dance, electronic
Occupations	Singer, dancer
Instruments	Bass, keyboards
Years active	2002–present
Labels	Audacious, Dreamworks, Teenacide
Associated acts	Sparkids, Cooler Kids, BoygirL, The Holograms, Pussycat Dolls, Paradiso Girls, Gunn Metal Grey, Sisely and the Safety Pin-ups, Shiny Toy Guns

Sisely Treasure is an American singer, songwriter, dancer and actress, notable for the song "All Around the World" released by Dreamworks Records in July 2003 and appearing in Billboard Magazine's Top 40 Dance charts the same year.^{[citation needed]} "Morning Star", another song off the Punk Debutante album, made top ten on Billboards dance chart.^{[citation needed]} In 2008, she became one of three vocalists for the rock group Shiny Toy Guns.^{[citation needed]} In 2011, she released her solo single, "That You Like." On November 28, a preview video of a new single titled "Million Hands" was released on her official YouTube page. She was born in Long Beach, California and currently lives in Los Angeles.^{[citation needed]}

Cooler Kids[link]

Before Treasure's appearance on the Pussycat Dolls reality TV show, she formed the music group Cooler Kids with producer and performer Kaz Gamble.^{[citation needed]} Treasure had the opportunity to work with several record labels, including DreamWorks Recordings, Audacious Records and Teenacide Records, and released a debut album, entitled Punk Debutante, in which the chart-entering single "All Around the World" was published.^{[citation needed]} She has co-written and sung on songs "The Grass is Greener" and "Common Ground" by Dave Audé and Tall Paul.^[1] Sisely Treasure was also a member of all the all-girl pop-punk, j-pop-ish group The Holograms, at which time they had a chart buster on Billboard top garage Hits "Are you ready for it".^{[citation needed]}

Dancer[link]

She was among the first original crew of kids that made up the dance troupe Sparkids performing at the Forum during the LA Sparks games and Laker games.^{[citation needed]} In her early teens she was part of one of the premier young dance companies in the world, under the wing of renowned choreographer Marguerite Derricks.^{[citation needed]} She has also danced in various commercials and for several other major choreographers and dancers such as Terry Beeman, Wade Robson, Wes Veldink and Galen Hooks.^[2]

Search for the Next Doll[link]

Treasure appeared on the first season on the CW reality show The Pussycat Dolls Present: The Search For The Next Doll. Sisely was often praised by Robin Antin for her uniqueness and individuality.^{[citation needed]} On the show, she was a couple years older than the others and said she at times felt like an outsider. She was the third girl eliminated after being told her vocals were off and she didn't live up to her rock persona. She shook up the show's fanbase and fellow contestant and eventual winner Asia Nitollano when she responded to the contestants' discussion of each other's dancing abilities by stating that she thought that Asia danced "like a drag queen", shortly before she was eliminated, causing the other contestants (with the exception of Nitollano) to burst out laughing. She then very briefly joined the Paradiso Girls.^{[citation needed]}

Sisely and the Safety Pin-ups[link]

After Search for the Next Doll she joined another group named Sisely and the Safety Pin-ups and released a cover of "Do the Robot" which was voted coolest garage song by Garage Rock.^[3] She was also featured in a Yahoo article which named her the "Punkycat Doll".^[4] She was also one of the members of the Gunn Metal Grey dance group.^[5]

Shiny Toy Guns[link]

On August 12, 2008, it was announced that Sisely Treasure was the new female vocalist for the band Shiny Toy Guns, replacing Carah Faye Charnow.^{[citation needed]} Her vocals are featured on the band's second album Season of Poison, released on November 4, 2008, and the band's covers of "Burnin' for You" and "Major Tom (Coming Home)" that are played in commercials for Lincoln cars.

Early February 2011, Sisely Treasure released a single as a solo artist on her website.^[6] The single, "That You Like", is available for a free download on her website (www.siselytreasure.com).^{[citation needed]} Shiny Toy Guns confirmed that Sisely is no longer a member of the band and will not be a part of the third Shiny Toy Guns album.^{[citation needed]}

References[link]

External links[link]

• Official website
• Sisely Treasure at the Internet Movie Database
• Billboard.com, Cooler Kids biography
• http://www.laweekly.com/2006-08-31/music/the-holograms/