Meitnerium
Encyclopedia
Meitnerium is a chemical element
with the symbol Mt and atomic number
109. It is placed as the heaviest member of group 9 (or VIII) in the periodic table but a sufficiently stable isotope is not known at this time which would allow chemical experiments to confirm its position, unlike its lighter neighbours.
It was first synthesized in 1982 and several isotopes are currently known. The heaviest and the most stable isotope known is 278Mt, with a half-life
of ~8 s.
and Gottfried Münzenberg
at the Institute for Heavy Ion Research
(Gesellschaft für Schwerionenforschung) in Darmstadt
. The team bombarded a target of bismuth
-209 with accelerated nuclei of iron
-58 and detected a single atom of the isotope
meitnerium-266:
Historically, meitnerium has been referred to as eka
-iridium
.
The name meitnerium (Mt) was suggested in honor of the Austrian physicist Lise Meitner
. In 1997, the name was officially adopted by the IUPAC.
See more on Cold Fusion
The first success in this reaction was in 1982 by the GSI
team in their discovery experiment with the identification of a single atom of 266Mt in the 1n neutron evaporation channel. The GSI team used the parent-daughter correlation technique.
After an initial failure in 1983, in 1985 the team at the FLNR, Dubna, observed alpha decays from the descendant 246Cf indicating the formation of meitnerium.
The GSI synthesised a further 2 atoms of 266Mt in 1988 and continued in 1997 with the detection of 12 atoms during the measurement of the 1n excitation function.
This reaction was first studied in 1985 by the team in Dubna. They were able to detect the alpha decay of the descendant 246Cf nuclei indicating the formation of meitnerium atoms.
In 2007, in a continuation of their study of the effect of odd-Z projectiles on yields of evaporation residues in cold fusion reactions, the team at LBNL synthesised 266Mt and were able to correlate the decay with known daughters.
There are indications that this cold fusion reaction using a tantalum
target was attempted in August 2001 at the GSI. No details can be found suggesting that no atoms of meitnerium were detected.
In 2002–2003, the team at LBNL attempted the above reaction in order to search for the isotope 271Mt with hope that it may be sufficiently stable to allow a first study of the chemical properties of meitnerium. Unfortunately, no atoms were detected and a cross section limit of 1.5 pb was measured for the 4n channel at the projectile energy used.
Attempts to produce long-living isotopes of meitnerium were first performed by Ken Hulet at the Lawrence Livermore National Laboratory
(LLNL) in 1988 using the asymmetric hot fusion reaction above. They were unable to detect any product atoms and established a cross section limit of 1 nb.
HIVAP = heavy-ion vaporisation statistical-evaporation model; σ = cross section
around 30 g/cm3 (Co: 8.9, Rh: 12.5, Ir: 22.5) and a high melting point around 2600–2900°C (Co: 1480, Rh: 1966, Ir: 2454). It should be very corrosion-resistant; even more so than Ir which is currently the most corrosion-resistant metal known.
, rhodium
and iridium
. This group of transition metal
s is the first to show lower oxidation states and the +9 state is not known. The latter two members of the group show a maximum oxidation state of +6, whilst the most stable states are +4 and +3 for iridium and +3 for rhodium. Meitnerium is therefore expected to form a stable +3 state but may also portray stable +4 and +6 states.
In combination with oxygen, rhodium forms Rh2O3 whereas iridium is oxidised to the +4 state in IrO2. Meitnerium may therefore show a dioxide, MtO2, if eka-iridium reactivity is shown.
The +3 state in group 9 is common in the trihalides (except fluorides) formed by direct reaction with halogen
s. Meitnerium should therefore form MtCl3, MtBr3 and MtI3 in an analogous manner to iridium.
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 the symbol Mt 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...
109. It is placed as the heaviest member of group 9 (or VIII) in the periodic table but a sufficiently stable isotope is not known at this time which would allow chemical experiments to confirm its position, unlike its lighter neighbours.
It was first synthesized in 1982 and several isotopes are currently known. The heaviest and the most stable isotope known is 278Mt, with a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of ~8 s.
Official discovery
Meitnerium was first synthesized on August 29, 1982 by a German research team led by Peter ArmbrusterPeter Armbruster
Peter Armbruster is a physicist at the Gesellschaft für Schwerionenforschung facility in Darmstadt, Germany, and is credited with co-discovering elements 107 , 108 , 109 , 110 , 111 , and 112 with research partner Gottfried Münzenberg.He studied physics at the Technical...
and Gottfried Münzenberg
Gottfried Münzenberg
Gottfried Münzenberg is a German physicist.He studied physics at Justus-Liebig-Universität in Giessen and Leopold-Franzens-Universität Innsbruck and completed his studies with a Ph.D. at the University of Giessen, Germany, in 1971...
at the Institute for Heavy Ion Research
Gesellschaft für Schwerionenforschung
The GSI Helmholtz Centre for Heavy Ion Research GmbH in the Wixhausen suburb of Darmstadt, Germany is a federally and state co-funded heavy ion research center. The current director of GSI is Horst Stöcker who succeeded Walter F...
(Gesellschaft für Schwerionenforschung) in Darmstadt
Darmstadt
Darmstadt is a city in the Bundesland of Hesse in Germany, located in the southern part of the Rhine Main Area.The sandy soils in the Darmstadt area, ill-suited for agriculture in times before industrial fertilisation, prevented any larger settlement from developing, until the city became the seat...
. The team bombarded a target of bismuth
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
-209 with accelerated nuclei of iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
-58 and detected a single atom of the isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
meitnerium-266:
- + → +
Naming
Meitnerium was formerly known as Unnilennium, bearing the symbol Une.Historically, meitnerium has been referred to as eka
Mendeleev's predicted elements
Professor Dmitri Mendeleev published the first Periodic Table of the Atomic Elements in 1869 based on properties which appeared with some regularity as he laid out the elements from lightest to heaviest....
-iridium
Iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
.
The name meitnerium (Mt) was suggested in honor of the Austrian physicist Lise Meitner
Lise Meitner
Lise Meitner FRS was an Austrian-born, later Swedish, physicist who worked on radioactivity and nuclear physics. Meitner was part of the team that discovered nuclear fission, an achievement for which her colleague Otto Hahn was awarded the Nobel Prize...
. In 1997, the name was officially adopted by the IUPAC.
Target-projectile combinations leading to Z=109 compound nuclei
The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with Z=109.| Target | Projectile | CN | Attempt result |
|---|---|---|---|
| 208Pb | 59Co | 267Mt | |
| 209Bi | 58Fe | 267Mt | |
| 232Th | 41K | 273Mt | |
| 231Pa | 40Ar | 271Mt | |
| 238U | 37Cl | 275Mt | |
| 237Np | 36S | 275Mt | |
| 244Pu | 31P | 275Mt | |
| 242Pu | 31P | 273Mt | |
| 243Am | 30Si | 273Mt | |
| 248Cm | 27Al | 275Mt | |
| 249Bk | 26Mg | 275Mt | |
| 249Cf | 23Na | 272Mt | |
| 254Es | 22Ne | 276Mt |
Cold fusion
This section deals with the synthesis of nuclei of meitnerium 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.See more on Cold Fusion
Cold fusion
Cold fusion, also called low-energy nuclear reaction , refers to the hypothesis that nuclear fusion might explain the results of a group of experiments conducted at ordinary temperatures . Both the experimental results and the hypothesis are disputed...
209Bi(58Fe,xn)267-xMt (x=1)
The first success in this reaction was in 1982 by the GSI
Gesellschaft für Schwerionenforschung
The GSI Helmholtz Centre for Heavy Ion Research GmbH in the Wixhausen suburb of Darmstadt, Germany is a federally and state co-funded heavy ion research center. The current director of GSI is Horst Stöcker who succeeded Walter F...
team in their discovery experiment with the identification of a single atom of 266Mt in the 1n neutron evaporation channel. The GSI team used the parent-daughter correlation technique.
After an initial failure in 1983, in 1985 the team at the FLNR, Dubna, observed alpha decays from the descendant 246Cf indicating the formation of meitnerium.
The GSI synthesised a further 2 atoms of 266Mt in 1988 and continued in 1997 with the detection of 12 atoms during the measurement of the 1n excitation function.
208Pb(59Co,xn)267-xMt (x=1)
This reaction was first studied in 1985 by the team in Dubna. They were able to detect the alpha decay of the descendant 246Cf nuclei indicating the formation of meitnerium atoms.
In 2007, in a continuation of their study of the effect of odd-Z projectiles on yields of evaporation residues in cold fusion reactions, the team at LBNL synthesised 266Mt and were able to correlate the decay with known daughters.
181Ta(86Kr,xn)267-xMt
There are indications that this cold fusion reaction using a tantalum
Tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as tantalium, the name comes from Tantalus, a character in Greek mythology. Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion resistant. It is part of the refractory...
target was attempted in August 2001 at the GSI. No details can be found suggesting that no atoms of meitnerium were detected.
238U(37Cl,xn)275-xMt
In 2002–2003, the team at LBNL attempted the above reaction in order to search for the isotope 271Mt with hope that it may be sufficiently stable to allow a first study of the chemical properties of meitnerium. Unfortunately, no atoms were detected and a cross section limit of 1.5 pb was measured for the 4n channel at the projectile energy used.
254Es(22Ne,xn)276-xMt
Attempts to produce long-living isotopes of meitnerium were first performed by Ken Hulet at the Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...
(LLNL) in 1988 using the asymmetric hot fusion reaction above. They were unable to detect any product atoms and established a cross section limit of 1 nb.
As a decay product
Isotopes of meitnerium have also been detected in the decay of heavier elements. Observations to date are shown in the table below:| Evaporation residue | Observed Mt isotope |
|---|---|
| 294Uus | 278Mt |
| 288Uup | 276Mt |
| 287Uup | 275Mt |
| 282Uut | 274Mt |
| 278Uut | 270Mt |
| 272Rg | 268Mt |
Chronology of isotope discovery
| Isotope | Year discovered | Discovery reaction |
|---|---|---|
| 266Mt | 1982 | 209Bi(58Fe,n) |
| 267Mt | unknown | |
| 268Mt | 1994 | 209Bi(64Ni,n) |
| 269Mt | unknown | |
| 270Mt | 2004 | 209Bi(70Zn,n) |
| 271Mt | unknown | |
| 272Mt | unknown | |
| 273Mt | unknown | |
| 274Mt | 2006 | 237Np(48Ca,3n) |
| 275Mt | 2003 | 243Am(48Ca,4n) |
| 276Mt | 2003 | 243Am(48Ca,3n) |
| 277Mt | unknown | |
| 278Mt | 2009 | 249Bk(48Ca,3n) |
270Mt
Two atoms of 270Mt have been identified in the decay chains of 278Uut. The two decays have very different lifetimes and decay energies and are also produced from two apparently different isomers in 274Rg. The first isomer decays by emission of an 10.03 MeV alpha particle with a lifetime 7.2 ms. The other decays by emitting an alpha particle with a lifetime of 1.63 s. An assignment to specific levels is not possible with the limited data available. Further research is required.268Mt
The alpha decay spectrum for 268Mt appears to be complicated from the results of several experiments. Alpha lines of 10.28,10.22 and 10.10 MeV have been observed. Half-lives of 42 ms, 21 ms and 102 ms have been determined. The long-lived decay is associated with alpha particles of energy 10.10 MeV and must be assigned to an isomeric level. The discrepancy between the other two half-lives has yet to be resolved. An assignment to specific levels is not possible with the data available and further research is required.Cold fusion
The table below provides cross-sections and excitation energies for cold fusion reactions producing meitnerium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.| Projectile | Target | CN | 1n | 2n | 3n |
|---|---|---|---|---|---|
| 58Fe | 209Bi | 267Mt | 7.5 pb | ||
| 59Co | 208Pb | 267Mt | 2.6 pb, 14.9 MeV |
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.HIVAP = heavy-ion vaporisation statistical-evaporation model; σ = cross section
| Target | Projectile | CN | Channel (product) | σmax | Model | Ref |
|---|---|---|---|---|---|---|
| 243Am | 30Si | 273Mt | 3n (270Mt) | 22 pb | HIVAP | |
| 243Am | 28Si | 271Mt | 4n (267Mt) | 3 pb | HIVAP | |
| 249Bk | 26Mg | 275Mt | 4n (271Mt) | 9.5 pb | HIVAP | |
| 254Es | 22Ne | 276Mt | 4n (272Mt) | 8 pb | HIVAP | |
| 254Es | 20Ne | 274Mt | 4-5n (270,269Mt) | 3 pb | HIVAP |
Physical properties
Mt should be a very heavy metal with a densityDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
around 30 g/cm3 (Co: 8.9, Rh: 12.5, Ir: 22.5) and a high melting point around 2600–2900°C (Co: 1480, Rh: 1966, Ir: 2454). It should be very corrosion-resistant; even more so than Ir which is currently the most corrosion-resistant metal known.
Oxidation states
Meitnerium is projected to be the sixth member of the 6d series of transition metals and the heaviest member of group 9 in the Periodic Table, below cobaltCobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
, rhodium
Rhodium
Rhodium is a chemical element that is a rare, silvery-white, hard and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. It is composed of only one isotope, 103Rh. Naturally occurring rhodium is found as the free metal, alloyed...
and iridium
Iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
. This group of transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
s is the first to show lower oxidation states and the +9 state is not known. The latter two members of the group show a maximum oxidation state of +6, whilst the most stable states are +4 and +3 for iridium and +3 for rhodium. Meitnerium is therefore expected to form a stable +3 state but may also portray stable +4 and +6 states.
Chemistry
The +VI state in group 9 is known only for the fluorides which are formed by direct reaction. Therefore, meitnerium should form a hexafluoride, MtF6. This fluoride is expected to be more stable than iridium(VI) fluoride, as the +6 state becomes more stable as the group is descended.In combination with oxygen, rhodium forms Rh2O3 whereas iridium is oxidised to the +4 state in IrO2. Meitnerium may therefore show a dioxide, MtO2, if eka-iridium reactivity is shown.
The +3 state in group 9 is common in the trihalides (except fluorides) formed by direct reaction with 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...
s. Meitnerium should therefore form MtCl3, MtBr3 and MtI3 in an analogous manner to iridium.