Ununtrium (pronounced /juːˈnʌntriəm/ or /əˈnʌntriəm/) is the temporary name of a synthetic element in the periodic table that has the temporary symbol Uut and has the atomic number 113.

It has been synthesised both directly in "cold" and "warm" fusion reactions. It was first observed in the decay of ununpentium. Only eight atoms of ununtrium have been observed to date. Following periodic trends it is expected to be a soft, silvery metal.

The first report of ununtrium was in August 2003 when it was identified as a decay product of ununpentium. These results were published on February 1, 2004, by a team composed of Russian scientists at Dubna (Joint Institute for Nuclear Research), and American scientists at the Lawrence Livermore National Laboratory.^[1][2]

On July 23, 2004, a team of Japanese scientists at RIKEN detected a single atom of ²⁷⁸Uut using the cold fusion reaction between Bismuth-209 and zinc-70. They published their results on September 28, 2004.^[3]

Support for their claim appeared in 2004 when scientists at the Institute of Modern Physics (IMP) identified ²⁶⁶Bh as decaying with identical properties to their single event (see bohrium).

The RIKEN team produced a further atom on April 2, 2005, although the decay data was different from the first chain, and may be due to the formation of a meta-stable isomer.

The Dubna-Livermore collaboration has strengthened their claim for the discovery of ununtrium by conducting chemical experiments on the decay daughter ²⁶⁸Db. In experiments in Jun 2004 and Dec 2005, the Dubnium isotope was successfully identified by milking the Db fraction and measuring any SF activities. Both the half-life and decay mode were confirmed for the proposed ²⁶⁸Db which lends support to the assignment of Z=115 and Z=113 to the parent and daughter nuclei.^[4][5]

Theoretical estimates of alpha-decay half-lives of alpha-decay chains from element 113 are in good agreement with the experimental data.^[6]

The element with Z=113 is historically known as eka-thallium. Ununtrium (Uut) is a temporary IUPAC systematic element name. Research scientists usually refer to the element simply as element 113 (E113).

Proposed names by claimants

Claims to the discovery of element 113 have been put forward by Dmitriev of the Dubna team and Morita of the RIKEN team. The JWP will decide to whom the right to suggest a name will be given. The IUPAC have the final say on the official adoption of a name. The table below gives the names that the teams above have suggested and which can be verified by press interviews.

Group	Proposed Name	Derivation
RIKEN	Japonium	Japan - country of group claimants
RIKEN	Rikenium	RIKEN - institute of group claimants

Ununtrium is element 113 in the Periodic Table. The two forms of the projected electronic structure are:

Bohr model: 2, 8, 18, 32, 32, 18, 3

Quantum mechanical model: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰ 4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰ 6p⁶7s²5f¹⁴6d¹⁰7p¹

Oxidation states

Element 113 is projected to be the first member of the 7p series of non-metals and the heaviest member of group 13 (IIIA) in the Periodic Table, below thallium. Each of the members of this group show the group oxidation state of +III. However, thallium has a tendency to form only a stable +I state due to the "inert pair effect", explained by the relativistic stabilisation of the 7s-orbitals, resulting in a higher ionisation potentialand weaker tendency to participate in bonding.

Chemistry

Element 113 should portray eka-thallium chemical properties and should therefore from a monoxide, Uut₂O, and monohalides, UutF, UutCl, UutBr and UutI. If the +III state is accessible, it is likely that it is only possible in the oxide, Uut₂O₃, and fluoride, UutF₃.

²⁰⁹Bi(⁷⁰Zn,xn)^279-x113 (x=1)

The synthesis of element 113 was first attempted in 1998 by the team at GSI using the above cold fusion reaction. In two separate runs, they were unable to detect any atoms and calculated a cross section limit of 900 fb. They repeated the experiment in 2003 and lowered the limit further to 400 fb  In late 2003, the emerging team at RIKEN using their efficient apparatus GARIS attempted the reaction and reached a limit of 140 fb. In December 2003-August 2004, they resulted to 'brute force' and performed an eight-month-long irradiation in which they increased the sensitivity to 51 fb. They were able to detect a single atom of ²⁷⁸113.  They repeated the reaction in several runs in 2005 and were able to synthesise a second atom. They calculated a record-low 31 fb for the cross section for the 2 atoms.

²³⁷Np(⁴⁸Ca,xn)^285-x113 (x=3)

In June 2006, the Dubna-Livermore team synthesised ununtrium directly in the "warm" fusion reaction between neptunium-237 and calcium-48 nuclei. Two atoms of ²⁸²Uut were detected with a cross section of 900 fb.

Isotope	Year discovered	discovery reaction
278Uut	2004	209Bi(70Zn,n)
279Uut	unknown
280Uut	unknown
281Uut	unknown
282Uut	2006	237Np(48Ca,3n)
283Uut	2003	243Am(48Ca,4n)
284Uut	2003	243Am(48Ca,3n)

Cold fusion

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

Projectile	Target	CN	1n	2n	3n
70Zn	209Bi	279Uut	31 fb

Hot Fusion

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

Projectile	Target	CN	3n	4n	5n
48Ca	237Np	285Uut	0.9 pb , 39.1 MeV