Darmstadtium

iso	NA	half-life	DM	DE (MeV)	DP
^281aDs	syn	11 s	94% SF
^281aDs	syn	11 s	6% α	8.67	^277aHs
^281bDs ?	syn	3.7 m	α	8.77	^277bHs ?
²⁷⁹Ds	syn	0.20 s	10% α	9.70	²⁷⁵Hs
²⁷⁹Ds	syn	0.20 s	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

Darmstadtium (pronounced /dɑrmˈʃtætiəm/ ( listen) darm-SHTAT-ee-əm), formerly known as ununnilium, is a chemical element with the symbol Ds and atomic number 110. It is placed as the heaviest member of group 10 but a sufficiently stable isotope is not known which would allow chemical experiments to confirm its place. This synthetic element is one of the so-called super-heavy atoms and was first synthesized in 1994. The longest-lived and heaviest isotope known is ^281aDs with a half-life of ~10 s although a possible nuclear isomer, ^281bDs has an unconfirmed half-life of about 4 minutes.

1 History
2 Isotopes and nuclear properties
3 Chemical properties
- 3.1 Extrapolated chemical properties
  - 3.1.1 Oxidation states
  - 3.1.2 Chemistry
4 See also
5 References
6 External links

History

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: ^[1]

20882Pb + 6228Ni → 269110Ds + 10n

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: ^[2]

20882Pb + 6428Ni → 271110Ds + 10n

The IUPAC/IUPAP Joint Working Party (JWP) recognised the GSI team as discoverers in their 2001 report.^[3]

Proposed names

Element 110 was first given the temporary name ununnilium (/ˌjuːnəˈnɪliəm/ or /ˌʌnəˈnɪliəm/^[4], 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.

Future experiments

The team at GSI has scheduled experiments for Aug 27 - Oct 10 2010 in order to re-study the K-isomer of ²⁷⁰Ds formed in the reaction ²⁰⁷Pb(⁶⁴Ni,n).

The team at the HIRFL, Lanzhou, China are planning to restudy the reaction ²³⁸U(⁴⁰Ar,xn) after recent calculations indicated a measurable yield in the 4n evaporation channel, leading to the new nuclide ²⁷⁴Ds.

At the FLNR, scientists will study the new reaction ²²⁶Ra(⁵⁰Ti,xn) in order to compare the yield with that obtained using ⁴⁸Ca projectiles in order to ascertain the viability of using ⁵⁰Ti projectiles in SHE synthesis.

Isotopes and nuclear properties

Nucleosynthesis

Target-Projectile Combinations leading to Z=110 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with Z=110.

Target	Projectile	CN	Attempt result
²⁰⁸Pb	⁶⁴Ni	²⁷²Ds	Successful reaction
²⁰⁸Pb	⁶²Ni	²⁷⁰Ds	Successful reaction
²³²Th	⁴⁸Ca	²⁸⁰Ds	Failure to date
²³⁸U	⁴⁰Ar	²⁷⁸Ds	Failure to date
²⁴⁴Pu	³⁶S	²⁸⁰Ds	Reaction yet to be attempted
²⁴⁴Pu	³⁴S	²⁷⁸Ds	Successful reaction
²⁴⁸Cm	³⁰Si	²⁷⁸Ds	Reaction yet to be attempted
²⁴⁹Cf	²⁶Mg	²⁷⁵Ds	Reaction yet to be attempted

Cold fusion

This section deals with the synthesis of nuclei of darmstadtium 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.

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.^[2] This reaction was successfully repeated in 2000 by GSI (4 atoms), in 2000 ^[5] ^[6] and 2004 ^[7] ^[8] by LBNL (9 atoms in total) and in 2002 by RIKEN (14 atoms).^[9] 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. ^[10]

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.^[1] 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. ^[11]

Hot fusion

This section deals with the synthesis of nuclei of darmstadtium 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. The excited nucleus then decays to the ground state via the emission of 3-5 neutrons. Fusion reactions utilizing ⁴⁸Ca nuclei usually produce compound nuclei with intermediate excitation energies (~30-35 MeV) and are sometimes referred to as "warm" fusion reactions. This leads, in part, to relatively high yields from these reactions.

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. ^[12]

As a decay product

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
²⁹³Uuh, ²⁸⁹Uuq	²⁸¹Ds
²⁹¹Uuh, ²⁸⁷Uuq, ²⁸³Cn	²⁷⁹Ds
²⁷⁷Cn	²⁷³Ds

In some experiments, the decay of ²⁹³Uuh and ²⁸⁹Uuq 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.

Retracted isotopes

²⁸⁰Ds

The first synthesis of element 114 resulted in two atoms assigned to ²⁸⁸Uuq, decaying to the ²⁸⁰Ds which underwent spontaneous fission. The assignment was later changed to ²⁸⁹Uuq and the darmstadtium isotope to ²⁸¹Ds. Hence, ²⁸⁰Ds is currently unknown.

²⁷⁷Ds

In the claimed synthesis of ²⁹³Uuo 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.^[13]

^273mDs

In the synthesis of ²⁷⁷Cn in 1996 by GSI (see copernicium), 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 synthesize 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.

Chronology of isotope discovery

Isotope	Year discovered	Discovery reaction
²⁶⁷Ds ??	1994	²⁰⁹Bi(⁵⁹Co,n)
²⁶⁸Ds	unknown
²⁶⁹Ds	1994	²⁰⁸Pb(⁶²Ni,n)
²⁷⁰Ds^g,m	2000	²⁰⁷Pb(⁶⁴Ni,n)
²⁷¹Ds^g,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)^[14]
²⁸⁰Ds	unknown
^281aDs	1999	²⁴⁴Pu(⁴⁸Ca,3n)^[14]
^281bDs ?	1999	²⁴⁴Pu(⁴⁸Ca,3n)^[14]

Nuclear isomerism

²⁸¹Ds

The production of ²⁸¹Ds by the decay of ²⁸⁹Uuq or ²⁹³Uuh 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 an isomeric 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 processes.

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.

Spectroscopy

²⁷⁰Ds

This is the current partial decay level scheme for ²⁷⁰Ds proposed following the work of Hofmann et al. in 2000 at GSI

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 represent 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

Fission of compound nuclei with Z=110

Experiments have been performed in 2004 at the Flerov Laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nucleus ²⁸⁰Ds. The nuclear reaction used is ²³²Th+⁴⁸Ca. The result revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as ¹³²Sn (Z=50, N=82).^[15]

Theoretical calculations

Decay characteristics

Theoretical calculation in a quantum tunneling model reproduces the experimental alpha decay half live data.^[16]^[17] It also predicts that the isotope ²⁹⁴110 would have alpha decay half life of the order of 311 years.^[18]^[19]

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
²⁰⁸Pb	⁶⁴Ni	²⁷²Ds	1n (²⁷¹Ds)	10 pb	DNS	^[20]
²³²Th	⁴⁸Ca	²⁸⁰Ds	4n (²⁷⁶Ds)	0.2 pb	DNS	^[21]
²³⁰Th	⁴⁸Ca	²⁷⁸Ds	4n (²⁷⁴Ds)	1 pb	DNS	^[21]
²³⁸U	⁴⁰Ar	²⁷⁸Ds	4n (²⁷⁴Ds)	2 pb	DNS	^[21]

Chemical properties

Extrapolated chemical properties

Oxidation states

Darmstadtium 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 +6 is shown by platinum whilst the +4 state is stable for both elements. Both elements also possess a stable +2 state. Darmstadtium is therefore predicted to show oxidation states +6, +4, and +2.

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.

References

↑ ^1.0 ^1.1 Hofmann, S.; Ninov, V.; He�berger, F. P.; Armbruster, P.; Folger, H.; M�nzenberg, G.; Sch�tt, H. J.; Popeko, A. G. et al. (1995). "Production and decay of ²⁶⁹110". Zeitschrift für Physik a Hadrons and Nuclei 350: 277. doi:10.1007/BF01291181.
↑ ^2.0 ^2.1 Hofmann, S (1998). Reports on Progress in Physics 61: 639. doi:10.1088/0034-4885/61/6/002.
↑ Karol, P. J.; Nakahara, H.; Petley, B. W.; Vogt, E. (2001). "On the discovery of the elements 110-112 (IUPAC Technical Report)". Pure and Applied Chemistry 73: 959. doi:10.1351/pac200173060959.
↑ ununnilium - Definitions from Dictionary.com
↑ Ginter, T. N.; Gregorich, K.; Loveland, W.; Lee, D.; Kirbach, U.; Sudowe, R.; Folden, C.; Patin, J. et al. (2003). "Confirmation of production of element 110 by the ²⁰⁸Pb(⁶⁴Ni,n) reaction". Physical Review C 67: 064609. doi:10.1103/PhysRevC.67.064609.
↑ "Confirmation of production of element 110 by the ²⁰⁸Pb(⁶⁴Ni,n) reaction", Ginter et al., LBNL repositories. Retrieved on 2008-03-02
↑ Folden, C. M.; Gregorich, KE; Düllmann, ChE; Mahmud, H; Pang, GK; Schwantes, JM; Sudowe, R; Zielinski, PM et al. (2004). "Development of an Odd-Z-Projectile Reaction for Heavy Element Synthesis: ²⁰⁸Pb(⁶⁴Ni,n)²⁷¹Ds and ²⁰⁸Pb(⁶⁵Cu,n)²⁷²111". Physical Review Letters 93 (21): 212702. doi:10.1103/PhysRevLett.93.212702. PMID 15601003.
↑ "Development of an Odd-Z-Projectile Reaction for Heavy Element Synthesis: ²⁰⁸Pb(⁶⁴Ni,n)²⁷¹Ds and ²⁰⁸Pb(⁶⁵Cu,n)²⁷²111", Folden et al., LBNL repositories. Retrieved on 2008-03-02
↑ Morita, K.; Morimoto, K.; Kaji, D.; Haba, H.; Ideguchi, E.; Kanungo, R.; Katori, K.; Koura, H. et al. (2004). "Production and decay of the isotope ²⁷¹Ds (Z = 110)". The European Physical Journal A 21: 257. doi:10.1140/epja/i2003-10205-1.
↑ Hofmann et al; Heßberger, F.P.; Ackermann, D.; Antalic, S.; Cagarda, P.; Ćwiok, S.; Kindler, B.; Kojouharova, J. et al. (2001). "The new isotope ²⁷⁰110 and its decay products ²⁶⁶Hs and ²⁶²Sg". Eur. Phys. J. A 10: 5–10. doi:10.1007/s100500170137. http://www.dnp.fmph.uniba.sk/etext/68/text/Hofmann_et_al_EPJ_A10_(2001)_5.pdf.
↑ Ghiorso, A.; Lee, D.; Somerville, L.; Loveland, W.; Nitschke, J.; Ghiorso, W.; Seaborg, G.; Wilmarth, P. et al. (1995). "Evidence for the possible synthesis of element 110 produced by the ⁵⁹Co+²⁰⁹Bi reaction". Physical Review C 51: R2293. doi:10.1103/PhysRevC.51.R2293.
↑ Lazarev, Yu. A.; Lobanov, Yu.; Oganessian, Yu.; Utyonkov, V.; Abdullin, F.; Polyakov, A.; Rigol, J.; Shirokovsky, I. et al. (1996). "α decay of ²⁷³110: Shell closure at N=162". Physical Review C 54: 620. doi:10.1103/PhysRevC.54.620.
↑ see ununoctium
↑ ^14.0 ^14.1 ^14.2 see ununquadium
↑ see Flerov lab annual report 2004
↑ P. Roy Chowdhury, C. Samanta, and D. N. Basu (2006). "α decay half-lives of new superheavy elements". Phys. Rev. C 73: 014612. doi:10.1103/PhysRevC.73.014612.
↑ C. Samanta, P. Roy Chowdhury and D.N. Basu (2007). "Predictions of alpha decay half lives of heavy and superheavy elements". Nucl. Phys. A 789: 142–154. doi:10.1016/j.nuclphysa.2007.04.001.
↑ P. Roy Chowdhury, C. Samanta, and D. N. Basu (2008). "Search for long lived heaviest nuclei beyond the valley of stability". Phys. Rev. C 77: 044603. doi:10.1103/PhysRevC.77.044603.
↑ P. Roy Chowdhury, C. Samanta, and D. N. Basu (2008). "Nuclear half-lives for α -radioactivity of elements with 100 ≤ Z ≤ 130". At. Data & Nucl. Data Tables 94: 781. doi:10.1016/j.adt.2008.01.003.
↑ Feng, Zhao-Qing; Jin, Gen-Ming; Li, Jun-Qing; Scheid, Werner (2007). "Formation of superheavy nuclei in cold fusion reactions". Physical Review C 76: 044606. doi:10.1103/PhysRevC.76.044606. http://arxiv.org/pdf/0707.2588.
↑ ^21.0 ^21.1 ^21.2 Feng, Z; Jin, G; Li, J; Scheid, W (2009). "Production of heavy and superheavy nuclei in massive fusion reactions". Nuclear Physics A 816: 33. doi:10.1016/j.nuclphysa.2008.11.003. http://arxiv.org/pdf/0803.1117.