Définitions et usages de : Ununseptium - Dictionnaire de anglais sensagent

Ununseptium is the temporary name of a superheavy artificial chemical element with temporary symbol Uus and atomic number 117. Six atoms were detected by a joint Russia–US collaboration at Dubna, Moscow Oblast, Russia, in November 2010.^[3]^[4] Although it is currently placed as the heaviest member of the halogen family, there is no experimental evidence that the chemical properties of ununseptium match those of the lighter members like iodine or astatine and theoretical analysis suggests there may be some notable differences.

1 History
2 Isotopes and nuclear properties
- 2.1 Nucleosynthesis
  - 2.1.1 Hot fusion
  - 2.1.2 Chronology of isotope discovery
- 2.2 Theoretical calculations
  - 2.2.1 Evaporation residue cross sections
  - 2.2.2 Decay characteristics
3 Chemical properties
- 3.1 Extrapolated chemical properties
4 See also
5 References
6 External links

History

Discovery

In January 2010, scientists at the Flerov Laboratory of Nuclear Reactions announced internally^[4] that they had succeeded in detecting the decay of a new element with Z=117 using the reactions:

48
20Ca + 249
97Bk → 297
117Uus* → 294
117Uus + 3 1
0n

48
20Ca + 249
97Bk → 297
117Uus* → 293
117Uus + 4 1
0n

Just six atoms were synthesized of two neighbouring isotopes, neither of which decayed to known isotopes of lighter elements. Their results were published on 9 April 2010 in the journal Physical Review Letters.^[5]

Naming

The element with atomic number 117 is historically known as eka-astatine. The name ununseptium is a systematic element name, used as a placeholder until the discovery is acknowledged by the IUPAC, and the IUPAC decides on a name. Usually, the name suggested by the discoverer(s) is chosen.

According to current guidelines from IUPAC, the ultimate name for all new elements should end in "-ium", which means the name for ununseptium may end in -ium, not -ine, even if ununseptium turns out to be a halogen.^[6]

The name Dunwoodium was suggested by a small number of scientists in training.

Future experiments

The team at the GSI in Darmstadt, recently acknowledged as the discoverers of copernicium, have begun experiments aimed towards a synthesis of ununseptium. The GSI have indicated that if they are unable to acquire any ²⁴⁹Bk from the United States, which is likely given the situation regarding the attempt in Russia, they will study the reaction ²⁴⁴Pu(⁵¹V,xn) instead, or possibly ²⁴³Am(⁵⁰Ti,xn).^[7]

Isotopes and nuclear properties

Nucleosynthesis

Target-projectile combinations leading to Z=117 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with atomic number 117.

Target	Projectile	CN	Attempt result
²⁰⁸Pb	⁸¹Br	²⁸⁹Uus	Reaction yet to be attempted
²⁰⁹Bi	⁷⁹Se	²⁸⁸Uus	Reaction yet to be attempted
²⁰⁹Bi	⁸²Se	²⁹¹Uus	Reaction yet to be attempted
²²⁶Ra	⁶³Cu	²⁸⁹Uus	Reaction yet to be attempted
²²⁶Ra	⁶⁵Cu	²⁹¹Uus	Reaction yet to be attempted
²³²Th	⁵⁹Co	²⁹¹Uus	Reaction yet to be attempted
²³⁸U	⁵⁵Mn	²⁹³Uus	Reaction yet to be attempted
²³⁷Np	⁵⁴Cr	²⁹¹Uus	Reaction yet to be attempted
²⁴⁴Pu	⁵¹V	²⁹⁵Uus	Reaction yet to be attempted
²⁴³Am	⁵⁰Ti	²⁹³Uus	Reaction yet to be attempted
²⁴⁸Cm	⁴⁵Sc	²⁹³Uus	Reaction yet to be attempted
²⁴⁹Bk	⁴⁸Ca	²⁹⁷Uus	Successful reaction
²⁴⁹Cf	⁴¹K	²⁹⁰Uus	Reaction yet to be attempted

Hot fusion

²⁴⁹Bk (⁴⁸Ca, xn)^297-xUus (x=3,4)

Between July 2009 and February 2010, the team at the JINR (Flerov Laboratory of Nuclear Reactions) ran a 7-month-long experiment to synthesize ununseptium using the reaction above.^[8] The expected cross-section was of the order of 2 pb. The expected evaporation residues, ²⁹³Uus and ²⁹⁴Uus, were predicted to decay via relatively long decay chains as far as isotopes of dubnium or lawrencium.

Calculated decay chains from the parent nuclei ²⁹³Uus and ²⁹⁴ Uus^[9]
Calculated excitation function for the production of the compound nucleus ²⁹⁷Uus from the reaction ²⁴⁹Bk( ⁴⁸Ca,xn) ^[9]

The team published a scientific paper in April 2010 (first results were presented in January 2010^[4]) that six atoms of the neighbouring isotopes ²⁹⁴Uus (one atom) and ²⁹³Uus (five atoms) were detected. The heavier isotope decayed by the successive emission of six alpha particles down as far as the new isotope ²⁷⁰Db which underwent apparent spontaneous fission. On the other hand, the lighter odd-even isotope decayed by the emission of just three alpha particles, as far as ²⁸¹Rg, which underwent spontaneous fission. The reaction was run at two different excitation energies of 35 MeV (dose 2x10¹⁹) and 39 MeV (dose 2.4×10¹⁹). Initial decay data was published as a preliminary presentation on the JINR website.^[10]

A further experiment in May 2010, looking at the chemistry of one of the decay products, ununtrium, identified a further two atoms derived from ²⁹⁴117.

Chronology of isotope discovery

Isotope	Year discovered	Discovery reaction
²⁹⁴Uus	2009	²⁴⁹Bk(⁴⁸Ca,3n)
²⁹³Uus	2009	²⁴⁹Bk(⁴⁸Ca,4n)

Theoretical calculations

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
²⁰⁹Bi	⁸²Se	²⁹¹Uus	1n (²⁹⁰Uus)	15 fb	DNS	^[11]
²⁰⁹Bi	⁷⁹Se	²⁸⁸Uus	1n (²⁸⁷Uus)	0.2 pb	DNS	^[11]
²³²Th	⁵⁹Co	²⁹¹Uus	2n (²⁸⁹Uus)	0.1 pb	DNS	^[11]
²³⁸U	⁵⁵Mn	²⁹³Uus	2-3n (^291,290Uus)	70 fb	DNS	^[11]
²⁴⁴Pu	⁵¹V	²⁹⁵Uus	3n (²⁹²Uus)	0.6 pb	DNS	^[11]
²⁴⁸Cm	⁴⁵Sc	²⁹³Uus	4n (²⁸⁹Uus)	2.9 pb	DNS	^[11]
²⁴⁶Cm	⁴⁵Sc	²⁹¹Uus	4n (²⁸⁷Uus)	1 pb	DNS	^[11]
²⁴⁹Bk	⁴⁸Ca	²⁹⁷Uus	3n (²⁹⁴Uus)	2.1 pb ; 3 pb	DNS	^[11]^[12]
²⁴⁷Bk	⁴⁸Ca	²⁹⁵Uus	3n (²⁹²Uus)	0.8, 0.9 pb	DNS	^[11]^[12]

Decay characteristics

Theoretical calculations in a quantum tunneling model with mass estimates from a macroscopic-microscopic model predict the alpha-decay half-lives of isotopes of ununseptium (namely, ^289–303Uus) to be around 0.1–40 ms.^[13]^[14]^[15]

Chemical properties

Extrapolated chemical properties

Certain chemical properties, such as bond lengths, are predicted to differ from what one would expect based on periodic trends from the lighter halogens (because of relativistic effects). It may have some metalloid properties, similar to astatine.^[16] For example, solid ununseptium should resemble astatine in its metallic appearance, and it is expected that ununseptium will show dominant +1 and +3 oxidation states instead of the −1 oxidation state common to all the natural halogens.^[17]