Ununseptium
Encyclopedia
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 2009–10. 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.
of a new element with Z=117 using the reactions:
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
.
. 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
.
.
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.
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
.
The team published a scientific paper in April 2010 (first results were presented in January 2010) 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 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.
DNS = Di-nuclear system; σ = cross section
s (because of relativistic effects ). It may have some metalloid
properties, similar to astatine
.
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
with temporary symbol Uus 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...
117. Six atoms were detected by a joint Russia–US collaboration at Dubna
Dubna
Dubna is a town in Moscow Oblast, Russia. It has a status of naukograd , being home to the Joint Institute for Nuclear Research, an international nuclear physics research centre and one of the largest scientific foundations in the country. It is also home to MKB Raduga, a defence aerospace company...
, Moscow Oblast
Moscow Oblast
Moscow Oblast , or Podmoskovye , is a federal subject of Russia . Its area, at , is relatively small compared to other federal subjects, but it is one of the most densely populated regions in the country and, with the 2010 population of 7,092,941, is the second most populous federal subject...
, Russia, in 2009–10. Although it is currently placed as the heaviest member of the halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
family, there is no experimental evidence that the chemical properties of ununseptium match those of the lighter members like iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
or astatine
Astatine
Astatine is a radioactive chemical element with the symbol At and atomic number 85. It occurs on the Earth only as the result of decay of heavier elements, and decays away rapidly, so much less is known about this element than its upper neighbors in the periodic table...
and theoretical analysis suggests there may be some notable differences.
Discovery
In January 2010, scientists at the Flerov Laboratory of Nuclear Reactions announced internally that they had succeeded in detecting the decayRadioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
of a new element with Z=117 using the reactions:
- + → * → + 3
- + → * → + 4
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
Physical Review Letters
Physical Review Letters , established in 1958, is a peer reviewed, scientific journal that is published 52 times per year by the American Physical Society...
.
Naming
The element with atomic number 117 is historically known as eka-astatineAstatine
Astatine is a radioactive chemical element with the symbol At and atomic number 85. It occurs on the Earth only as the result of decay of heavier elements, and decays away rapidly, so much less is known about this element than its upper neighbors in the periodic table...
. The name ununseptium is a systematic 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...
, used as a placeholder
Placeholder name
Placeholder names are words that can refer to objects or people whose names are either temporarily forgotten, irrelevant, or unknown in the context in which they are being discussed...
until the discovery is acknowledged by the IUPAC
International Union of Pure and Applied Chemistry
The International Union of Pure and Applied Chemistry is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science . The international headquarters of IUPAC is located in Zürich,...
, 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
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
.
Current experiments
Scientists at Dubna are continuing their study of the 249Bk + 48Ca reaction in order to attempt a first chemical study of ununtriumUnuntrium
Ununtrium is the temporary name of a synthetic element with the temporary symbol Uut and atomic number 113.It is placed as the heaviest member of the group 13 elements although a sufficiently stable isotope is not known at this time that would allow chemical experiments to confirm its position...
.
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).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 | |
| 232Th | 59Co | 291Uus | |
| 238U | 55Mn | 293Uus | |
| 237Np | 54Cr | 291Uus | |
| 244Pu | 51V | 295Uus | |
| 243Am | 50Ti | 293Uus | |
| 248Cm | 45Sc | 293Uus | |
| 249Bk | 48Ca | 297Uus | |
| 249Cf | 41K | 290Uus |
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.
The expected cross-section was of the order of 2 pb
Barn (unit)
A barn is a unit of area. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process, and is best understood as a measure of the...
. The expected evaporation residues, 293Uus and 294Uus, were predicted to decay via relatively long decay chains as far as isotopes of dubnium
Dubnium
The Soviet team proposed the name nielsbohrium in honor of the Danish nuclear physicist Niels Bohr. The American team proposed that the new element should be named hahnium , in honor of the late German chemist Otto Hahn...
or lawrencium
Lawrencium
Lawrencium is a radioactive synthetic chemical element with the symbol Lr and atomic number 103. In the periodic table of the elements, it is a period 7 d-block element and the last element of actinide series...
.
The team published a scientific paper in April 2010 (first results were presented in January 2010) 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 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.
Chronology of isotope discovery
| Isotope | Year discovered | Discovery reaction |
|---|---|---|
| 294Uus | 2009 | 249Bk(48Ca,3n) |
| 293Uus | 2009 | 249Bk(48Ca,4n) |
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) | σmax | Model | Ref |
|---|---|---|---|---|---|---|
| 209Bi | 82Se | 291Uus | 1n (290Uus) | 15 fb | DNS | |
| 209Bi | 79Se | 288Uus | 1n (287Uus) | 0.2 pb | DNS | |
| 232Th | 59Co | 291Uus | 2n (289Uus) | 0.1 pb | DNS | |
| 238U | 55Mn | 293Uus | 2-3n (291,290Uus) | 70 fb | DNS | |
| 244Pu | 51V | 295Uus | 3n (292Uus) | 0.6 pb | DNS | |
| 248Cm | 45Sc | 293Uus | 4n (289Uus) | 2.9 pb | DNS | |
| 246Cm | 45Sc | 291Uus | 4n (287Uus) | 1 pb | DNS | |
| 249Bk | 48Ca | 297Uus | 3n (294Uus) | 2.1 pb ; 3 pb | DNS | |
| 247Bk | 48Ca | 295Uus | 3n (292Uus) | 0.8, 0.9 pb | DNS |
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.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 halogenHalogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
s (because of relativistic effects ). It may have some metalloid
Metalloid
Metalloid is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, each element can usually be classified as a metal or a nonmetal. However, some elements with intermediate or mixed properties can be harder to characterize...
properties, similar to astatine
Astatine
Astatine is a radioactive chemical element with the symbol At and atomic number 85. It occurs on the Earth only as the result of decay of heavier elements, and decays away rapidly, so much less is known about this element than its upper neighbors in the periodic table...
.