Mt · Element 109 · Transition metal
Named for Lise Meitner, who explained nuclear fission but was left off the Nobel Prize.
Structure
Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.
Measured values
Every bar shows where meitnerium sits among all 118 elements for that property.
Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.
Same element, different neutrons
All meitnerium atoms have the same number of protons, 109, and differ only in their number of neutrons: those variants are its isotopes. None of them is stable. The longest-lived known isotope, Mt-282, has 173 neutrons and a half-life of ~1.1 min.
| ISOTOPE | Neutrons | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|---|
| Mt-270 | 161 | — | ~0.48 sec | α |
| Mt-274 | 165 | — | ~0.44 sec | α |
| Mt-276 | 167 | — | 0.69 sec | α |
| Mt-278 | 169 | — | 4.5 sec | α |
| Mt-282 longest-lived | 173 | — | ~1.1 min | α, SF |
Periodic tables list 276 for meitnerium: the mass number of one long-lived isotope, not an average, so mass minus atomic number gives 167, the neutron count of Mt-276.
Decay modes
~ marks a half-life whose published uncertainty is larger than the value itself.
Data: IAEA Nuclear Data Section, LiveChart of Nuclides, ground-state evaluations, retrieved October 10, 2026. Abundance is the share of atoms in the natural element; a dash means the isotope has no standard natural abundance.
Size, to scale
Radius 247 pm — that is 0.247 nm, so about 2.02 million of them side by side would span a millimetre.
Thermal range
Neither transition has been measured for meitnerium — too few atoms have ever existed at once.
The story
Named for Lise Meitner, who explained nuclear fission but was left off the Nobel Prize.
Meitnerium was first synthesized in 1982 by a German research team led by Peter Armbruster and Gottfried Münzenberg at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany, using their advanced heavy-ion linear accelerator facility. The discovery involved bombarding bismuth-209 targets with iron-58 ions accelerated to extremely high energies, successfully creating meitnerium-266 through nuclear fusion and detecting its characteristic alpha decay signature. The German team used sophisticated detection equipment to identify meitnerium atoms through their unique radioactive decay chains, confirming the synthesis of element 109 through careful statistical analysis of nuclear events occurring over milliseconds. The element was initially assigned the systematic name "unnilennium" (meaning "one-zero-nine" in Latin) according to International Union of Pure and Applied Chemistry (IUPAC) conventions for temporarily naming undiscovered elements. The German researchers proposed the name "meitnerium" in honor of Austrian-Swedish physicist Lise Meitner, who made fundamental contributions to nuclear physics and co-discovered nuclear fission, recognizing her pioneering work in understanding nuclear processes. Lise Meitner was a particularly appropriate choice for this honor, as she had been overlooked for the Nobel Prize in Physics despite her crucial role in discovering nuclear fission, making this a belated recognition of her scientific contributions. The discovery represented a significant technical achievement, requiring years of development in accelerator technology, target preparation techniques, and ultra-sensitive detection methods for studying extremely short-lived nuclear species. IUPAC officially approved the name "meitnerium" with the symbol "Mt" in 1997 after thorough review of the experimental evidence and confirmation that the German team had successfully synthesized element 109. The successful creation of meitnerium demonstrated the feasibility of extending the periodic table beyond the actinide series and provided crucial experimental data for testing theories about superheavy element stability. This discovery opened new avenues for research into even heavier elements and contributed significantly to our understanding of nuclear physics at the limits of atomic mass and nuclear charge. The achievement required international collaboration and represented the culmination of decades of advancement in nuclear physics technology and experimental methodology.
Applications
Meitnerium, being an extremely short-lived synthetic superheavy element with half-lives from milliseconds up to about a minute, has no practical applications outside of fundamental nuclear physics research and theoretical studies of atomic structure. The element serves exclusively to advance our scientific understanding of superheavy nuclei and test theoretical predictions about the limits of nuclear stability and the proposed island of stability. Research with meitnerium contributes to validating nuclear shell models and magic number theories that predict how protons and neutrons organize themselves in very heavy atomic nuclei. The element is used as a testing ground for sophisticated computational models that attempt to predict the chemical and physical properties of superheavy elements based on relativistic quantum mechanical calculations. Meitnerium research helps scientists understand how chemical properties evolve as elements become increasingly heavy and how relativistic effects influence atomic behavior at the limits of the periodic table. The techniques developed for detecting and studying meitnerium have advanced nuclear physics instrumentation and contributed to improvements in particle detection technology used in various scientific applications. Studies of meitnerium provide crucial data for understanding stellar nucleosynthesis processes and how the heaviest elements in the universe are created in high-energy astrophysical environments. The element's research contributes to training nuclear physicists and developing new experimental methods for studying rare nuclear phenomena that occur at the limits of current technology. While meitnerium itself has no practical uses, the fundamental research it enables advances our understanding of nuclear processes that underlie many important technologies in medicine, energy, and materials science. The international collaborative efforts required for meitnerium research promote scientific cooperation and knowledge sharing in the global nuclear physics community. Future discoveries of longer-lived meitnerium isotopes or related superheavy elements might reveal unique properties with potential applications in advanced technologies. The element represents a testament to human ability to explore the fundamental limits of matter and atomic structure through advanced scientific instrumentation.
Meitnerium has no applications in everyday life, industry, or practical technology due to its extremely short half-lives of at most about a minute and the fact that only a few atoms can be produced at a time in specialized accelerator facilities. The element is used exclusively in advanced nuclear physics research at major international laboratories equipped with heavy-ion accelerators and sophisticated detection systems. Research institutions study meitnerium to explore fundamental questions about the maximum number of protons that can exist in a stable atomic nucleus and the theoretical limits of matter. Nuclear physicists use meitnerium as a benchmark for testing theoretical models that predict the behavior of superheavy elements and their placement in extended versions of the periodic table. The element serves as a testing ground for computational chemistry methods that attempt to predict chemical properties through relativistic quantum mechanical calculations rather than experimental measurement. Educational programs in nuclear physics use meitnerium as an example of advanced research into the fundamental nature of atomic structure and the ongoing quest to understand matter at its limits. Scientific databases maintain records of meitnerium's properties to ensure comprehensive documentation of all known chemical elements, even those that exist only briefly in laboratory conditions. International scientific collaborations study meitnerium to advance global understanding of superheavy element physics and share knowledge about nuclear research at the frontiers of science. The element's study contributes to developing new experimental techniques and instrumentation for detecting and analyzing extremely rare nuclear events. While meitnerium cannot be used practically, research into its properties advances fundamental science that underlies nuclear technologies used in medical imaging, cancer treatment, and nuclear power generation. The methodologies developed for meitnerium research contribute to improvements in particle physics instrumentation and nuclear analysis techniques. The element demonstrates the current limits of artificial element synthesis and represents a high point of achievement in creating new forms of matter through nuclear physics.
Where it comes from
0 mg/kg of Earth's crust · more abundant than 0% of elements
Meitnerium has never been found in nature and has only been made artificially through nuclear fusion reactions in the advanced particle accelerator facilities on Earth. The element is synthesized by bombarding heavy target nuclei with lighter projectile nuclei at extremely high energies, typically using bismuth-209 targets and iron-58 projectiles to create meitnerium-266 through nuclear fusion. Production requires sophisticated heavy-ion accelerators capable of accelerating ions to precise energies while maintaining high accuracy in beam focusing and target positioning systems. Only one or two atoms of meitnerium can be produced per hour even with the advanced accelerator technology available, and these atoms decay within milliseconds of their creation. Meitnerium-278, one of the longest-lived known isotopes, has a half-life of approximately 4.5 seconds, while the other known isotopes range from about 2 milliseconds to under a second, apart from meitnerium-282, listed at about 1.1 minutes, making detection and study extremely challenging. The element's production is limited to perhaps half a dozen specialized research facilities worldwide, including GSI in Germany, RIKEN in Japan, and similar institutions with appropriate superheavy element research capabilities. Meitnerium has no geological occurrence and no environmental presence; whether the r-process in neutron star mergers briefly makes it is an open question. All meitnerium research must be conducted on individual atoms detected through their characteristic decay signatures, requiring very sensitive detection equipment capable of identifying single nuclear events against background radiation. The total amount of meitnerium ever created by humanity would be far too small to measure by any conventional means, representing perhaps a few hundred atoms produced over decades of intensive research. Environmental concentrations of meitnerium are effectively zero, as the element cannot persist in nature because of its rapid radioactive decay. The element exists only momentarily in the highly controlled environment of nuclear physics laboratories before decaying into lighter elements within seconds or milliseconds. Future production capabilities might increase marginally as accelerator technology advances, but meitnerium will remain among the rarest and most ephemeral substances that can be created through human technology.
Handling
Meitnerium is radioactive. It has no stable isotope — every nucleus decays. Handling requires appropriate shielding and licensing.
Meitnerium is radioactive, but it is made only a few atoms at a time in heavy-ion accelerators. Its isotopes decay by alpha emission and spontaneous fission: meitnerium-276 has a half-life of about 0.7 seconds and meitnerium-278 about 4.5 seconds, and meitnerium-282 is listed at about 1.1 minutes. No weighable amount of meitnerium has ever existed, so the atoms themselves cannot deliver a meaningful radiation dose to anyone. The hazards in this research come from the experiment, not the element: the accelerator beam, radioactive targets and activated equipment, and the waste these produce, which is managed as radioactive waste under national radiation protection rules. Staff follow the standard occupational radiation rules: annual dose limits, personal dose monitoring and keeping doses as low as reasonably achievable (ALARA). Workers under 18 face much lower dose limits than adults: one tenth of the adult limits under US Nuclear Regulatory Commission rules (10 CFR 20.1207), and 1 mSv a year at US Department of Energy laboratories (10 CFR 835.207). A worker who declares a pregnancy is limited to 5 mSv to the fetus over the whole pregnancy (10 CFR 20.1208 and 835.206).
Quick answers
Meitnerium (symbol Mt) is element 109 on the periodic table, a transition metal in period 7, group 9. Named for Lise Meitner, who explained nuclear fission but was left off the Nobel Prize. At room temperature it is a solid, and it is radioactive.
[Rn] 5f¹⁴ 6d⁷ 7s², giving 7 occupied shells with the distribution 2, 8, 18, 32, 32, 15, 2.Meitnerium has no stable isotope, so it has no standard atomic weight. The figure quoted, 276, is the mass number of Mt-276, the isotope periodic tables usually list; the longest-lived one in the IAEA data is Mt-282.
Meitnerium has no stable isotope. Its longest-lived known isotope, Mt-282, has 173 neutrons (mass number 282 minus atomic number 109) and a half-life of ~1.1 min. Periodic tables list 276 for meitnerium, the mass number of one long-lived isotope, so mass minus atomic number gives 167, the neutron count of Mt-276.
Meitnerium is predicted to have a density of about 37.4 g/cm³, though no sample large enough to weigh has ever been made. Water is 1.0 g/cm³ for comparison.
Meitnerium was discovered in 1982 by GSI Darmstadt. Origin of the name: Lise Meitner.
Meitnerium does not occur naturally on Earth in any meaningful quantity — it is made in a reactor or an accelerator.
Yes. Meitnerium has no stable isotope — every one of its nuclei decays. It does not occur in usable quantities in nature and must be synthesised.