Darmstadtium

2008/9 Schools Wikipedia Selection. Related subjects: Chemical elements

110 meitnerium ← darmstadtium → roentgenium Pt ↑ Ds ↓ (Uhn) Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	darmstadtium, Ds, 110
Element category	transition metals
Group, Period, Block	10, 7, d
Appearance	unknown, probably silvery white or metallic gray
Standard atomic weight	[281]  g·mol−1
Electron configuration	perhaps [Rn] 5f14 6d9 7s1 (in analogy to platinum)
Electrons per shell	2, 8, 18, 32, 32, 17, 1
Phase	presumably a solid
CAS registry number	54083-77-1
Selected isotopes
Main article: Isotopes of darmstadtium iso NA half-life DM DE ( MeV) DP 281Ds syn 11 s SF 279Ds syn 0.20 s 10% α 9.70 275Hs 90% SF 273Ds syn 170 ms α 11.14 269Hs 271mDs syn 69 ms α 10.71 267Hs 271gDs syn 1.63 ms α 10.74,10.69 267Hs 270mDs syn 6 ms α 12.15,11.15,10.95 266Hs 270gDs syn 0.10 ms α 11.03 266Hs 269Ds syn 0.17 ms α 11.11 265Hs 267Ds ? syn 0.004 ms
References

Darmstadtium (pronounced /dɑrmˈʃtætiəm/), formerly known as Ununnilium, is a chemical element with the symbol Ds and atomic number 110.

This synthetic element is one of the so-called super-heavy atoms. It decays quickly: Heavier isotopes of darmstadtium have half-lives on the order of ten seconds.

Official discovery

Darmstadtium was first created on November 9, 1994 at the Gesellschaft für Schwerionenforschung (GSI) in Wixhausen, a northern suburb of Darmstadt, Germany by Peter Armbruster and Gottfried Münzenberg, under the direction of professor Sigurd Hofmann. Four atoms of it were detected by a nuclear fusion reaction caused by bombarding a lead-208 target with nickel-62 ions:

In the same series of experiments, the same team also carried out the reaction using heavier nickel-64 ions. During two runs, 9 atoms of ²⁷¹Ds were convincingly detected by correlation with known daughter decay properties:

The IUPAC/IUPAP Joint Working Party (JWP) recognised the GSI team as discoverers in their 2001 report.

Proposed names

Element 110 was first given the temporary name ununnilium (/ˌjuːnəˈnɪliəm/ or /ˌʌnəˈnɪliəm/, symbol Uun). Once recognized as discoverers, the team at GSI considered the names darmstadtium (Ds) and wixhausium (Wi) for element 110. They decided on the former and named the element after the city near the place of its discovery, Darmstadt and not the suburb Wixhausen itself. The new name was officially recommended by IUPAC on August 16, 2003.

The element has also earned the nickname of policium, because the telephone number of the police is 110 within Germany.

Electronic structure

Darmstadtium is element 110 in the Periodic Table. The two forms of the projected electronic structure are:

Bohr model: 2, 8, 18, 32, 32, 17, 1

Quantum mechanical model: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰ 4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰ 6p⁶7s¹5f¹⁴6d⁹

Extrapolated chemical properties of eka-platinum/dvi-palladium

Oxidation states

Element 110 is projected to be the eighth member of the 6d series of transition metals and the heaviest member of group 10 in the Periodic Table, below nickel, palladium and platinum. The highest confirmed oxidation state of +VI is shown by platinum whilst the +IV state is stable for both elements. Both elements also possess a stable +II state. Darmstadtium is therefore predicted to show oxidation states +VI, +IV and +II.

Chemistry

High oxidation states are expected to become more stable as the group is descended, so darmstadtium is expected to form a stable hexafluoride, DsF₆, in addition to DsF₅ and DsF₄. Halogenation should result in the formation of the tetrahalides, DsCl₄, DsBr₄ and DsI₄.

Like other Group 10 elements, darmstadtium can be expected to have notable hardness and catalytic properties.

History of synthesis of isotopes by cold fusion

²⁰⁸Pb(⁶⁴Ni,xn)^272-xDs (x=1)

This reaction was first studied by scientists at GSI in 1986, without success. A cross section limit of 12 pb was calculated. After an upgrade of their facilities, they successfully detected 9 atoms of ²⁷¹Ds in two runs in 1994 as part of their discovery experiments on element 110. This reaction was successfully repeated in 2000 by GSI (4 atoms), in 2000 and 2004 by LBNL (9 atoms in total) and in 2002 by RIKEN (14 atoms). The summation of the data allowed a measurement of the 1n neutron evaporation excitation function.

²⁰⁷Pb(⁶⁴Ni,xn)^271-xDs (x=1)

In addition to the official discovery reactions, in October-November 2000, the team at GSI also studied the reaction using a Pb-207 target in order to search for the new isotope ²⁷⁰Ds. They succeeded in synthesising 8 atoms of ²⁷⁰Ds, relating to a ground state isomer, ^270gDs, and a high-spin K-isomer, ^270mDs.

²⁰⁸Pb(⁶²Ni,xn)^270-xDs (x=1)

The GSI team studied this reaction in 1994 as part of their discovery experiment. Three atoms of ²⁶⁹Ds were detected. A fourth decay chain was measured but subsequently retracted.

²⁰⁹Bi(⁵⁹Co,xn)^268-xDs

This reaction was first studied by the team at Dubna in 1986. They were unable to detect any product atoms and measured a cross section limit of 1 pb. In 1995, the team at LBNL reported that they had succeeded in detecting a single atom of ²⁶⁷Ds from the 1n neutron evaporation channel. However, several decays were missed and further research is required to confirm this discovery.

History of synthesis of isotopes by hot fusion

²³²Th(⁴⁸Ca,xn)^280-xDs

The synthesis of element 110 by hot fusion pathways was first attempted in 1986 by the team at Dubna. Using the method of detection of spontaneous fission, they were unable to measure any SF activities and calculated a cross section limit of 1 pb for the decay mode. In three separate experiments between November 1997 and October 1998, the same team re-studied this reaction as part of their new ⁴⁸Ca program on the synthesis of superheavy elements. Several SF activities with relatively long half-lives were detected and tentatively assigned to decay of the daughters ²⁶⁹Sg or ²⁶⁵Rf, with a cross section of 5 pb. These observations have not been confirmed and the results are taken as only an indication for the synthesis of darmstadtium in this reaction.

²³²Th(⁴⁴Ca,xn)^276-xDs

This reaction was attempted in 1986 and 1987 by the Dubna team. In both experiments, a 10 ms SF activities was measured and assigned to ²⁷²Ds, with a calculated cross section of 10 pb. This activity is currently not thought to be due to a darmstadtium isotope.

²³⁸U(⁴⁰Ar,xn)^278-xDs

This reaction was first attempted by the Dubna team in 1987. Only spontaneous fission from the transfer products ^240mfAm and ^242mfAm were observed and the team calculated a cross section limit of 1.6 pb. The team at GSI first studied this reaction in 1990. Once again, no atoms of element 110 could be detected. In August 2001, the GSI repeated reaction, without success, and calculated a cross section limit of 1.0 pb.

²³⁶U(⁴⁰Ar,xn)^276-xDs

This reaction was first attempted by the Dubna team in 1987. No spontaneous fission was observed.

²³⁵U(⁴⁰Ar,xn)^275-xDs

This reaction was first attempted by the Dubna team in 1987. No spontaneous fission was observed. It was further studied in 1990 by the GSI team. Once again, no atoms were detected and a cross section limit of 21 pb was calculated.

²³³U(⁴⁰Ar,xn)^273-xDs

This reaction was first studied in 1990 by the GSI team. No atoms were detected and a cross section limit of 21 pb was calculated.

²⁴⁴Pu(³⁴S,xn)^278-xDs (x=5)

In September 1994 the team at Dubna detected a single atom of ²⁷³Ds, formed in the 5n neutron evaporation channel. The measured cross section was just 400 fb.

Synthesis of isotopes as decay products

Isotopes of darmstadtium have also been detected in the decay of heavier elements. Observations to date are shown in the table below:

Evaporation Residue	Observed Ds isotope
293116 , 289114	281Ds
291116 , 287114 , 283112	279Ds
277112	273Ds

In some experiments, the decay of ²⁹³116 and ²⁸⁹114 produced an isotope of darmstadtium decaying by emission of an 8.77 MeV alpha particle with a half life of 3.7 minutes. Although unconfirmed, it is highly possible that this activity is associated with a meta-stable isomer, namely ^281mDs.

Spectroscopy of darmstadtium isotopes

²⁷⁰Ds

Chronology of isotope discovery

Isotope	Year discovered	discovery reaction
267Ds	1994?	209Bi(59Co,n)
268Ds	unknown
269Ds	1994	208Pb(62Ni,n)
270Dsg,m	2000	207Pb(64Ni,n)
271Dsg,m	1994	208Pb(64Ni,n)
272Ds	unknown
273Ds	1996	244Pu(34S,5n)
274Ds	unknown
275Ds	unknown
276Ds	unknown
277Ds	1997?	232Th(48Ca,3n)
278Ds	unknown
279Ds	2002	244Pu(48Ca,5n)
280Ds	unknown
281Ds	1999? , 2002	244Pu(48Ca,3n)

Chemical yields of isotopes

Cold fusion

The table below provides cross-sections and excitation energies for cold fusion reactions producing darmstadtium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.

Projectile	Target	CN	1n	2n	3n
62Ni	208Pb	270Ds	3.5 pb
64Ni	208Pb	272Ds	15 pb , 9.9 MeV

Isomerism in darmstadtium nuclides

²⁸¹Ds

The production of ²⁸¹Ds by the decay of ²⁸⁹114 or ²⁹³116 has produced two very conflicting decay modes. The most common and readily confirmed mode is SF with a half-life of 11 s. A much rarer and hitherto unconfirmed mode is alpha decay by emission of an 8.77 MeV alpha particle with an observed half-life of ~3.7 m. This decay is associated with a unique decay pathway from the parent nuclides and must be assigned to an isomeric level. The half-life suggests that it must be assigned to a meta-stable state but further research is required to confirm these reports.

²⁷¹Ds

Decay data from the direct synthesis of ²⁷¹Ds clearly indicates the presence of two alpha groups. The first has alpha lines at 10.74 and 10.69 MeV with a half-life of 1.63 ms. The other has a single alpha line at 10.71 MeV with a half-life of 69 ms. The first has been assigned to the ground state and the latter to an isomeric level. It has been suggested that the closeness of the alpha decay energies indicates that the isomeric level may decay primarily by delayed gamma emission to the ground state, resulting in an identical measured alpha energy and a combined half-life for the two processess.

²⁷⁰Ds

The direct production of ²⁷⁰Ds has clearly identified two alpha groups belonging to two isomeric levels. The ground state decays into the ground state of ²⁶⁶Hs by emitting an 11.03 MeV alpha particle with a half-life of 0.10 ms. The isomeric level decays by alpha emission with alpha lines at 12.15,11.15 and 10.95 MeV with a half-life of 6 ms. The 12.15 MeV has been assigned as decay into the ground state of ²⁶⁶Hs indicating that this high spin K-isomer lies at 1.12 MeV above the ground state.

Retracted isotopes

²⁸⁰Ds

The first synthesis of element 114 resulted in two atoms assigned to ²⁸⁸114, decaying to the ²⁸⁰Ds which underwent spontaneous fission. The assignment was later changed to ²⁸⁹114 and the darmstadtium isotope to ²⁸¹Ds. Hence, ²⁸⁰Ds is currently unknown.

²⁷⁷Ds

In the claimed synthesis of ²⁹³118 in 1999, the isotope ²⁷⁷Ds was identified as decaying by 10.18 MeV alpha emission with a half-life of 3.0 ms. This claim was retracted in 2001 and thus this darmstadtium isotope is currently unknown or unconfirmed.

^273mDs

In the synthesis of ²⁷⁷112 in 1996 by GSI (see ununbium), one decay chain proceeded via ²⁷³Ds which decayed by emission of a 9.73 MeV alpha particle with a lifetime of 170 ms. This would have been assigned to an isomeric level. This data could not be confirmed and thus this isotope is currently unknown or unconfirmed.

²⁷²Ds

In the first attempt to synthesise element 110, a 10 ms SF activity was assigned to ²⁷²Ds in the reaction ²³²Th(⁴4Ca,4n). Given current understanding regarding stability, this isotope has been retracted from the Table of Isotopes.

Theoretical calculation in a quantum tunneling model reproduces the experimental alpha decay half live data. It also predicts that the isotope ²⁹⁴110 would have alpha decay half life of the order of 311 years.