Meitnerium

Meitnerium is a synthetic chemical element with atomic number 109 and symbol Mt. Its known isotopes are radioactive, and its name honors physicist Lise Meitner.

Chemical element: A substance whose atoms all have the same number of protons. Meitnerium is defined by its 109 protons, regardless of its isotope.
Nuclear fusion: A nuclear reaction in which two atomic nuclei combine to form a heavier nucleus. Meitnerium-producing reactions fuse projectile and target nuclei.
GSI Helmholtz Centre for Heavy Ion Research: A German research center in Darmstadt that conducts experiments with heavy-ion accelerators. Its team produced and identified the first accepted atoms of meitnerium.
Superheavy element: A chemical element with atomic number 104 or greater, typically produced artificially and strongly radioactive. Meitnerium belongs to the superheavy elements studied through single-atom experiments.
Island of stability: A predicted region of relatively long-lived superheavy nuclei associated with closed proton and neutron shells. Meitnerium isotopes help constrain how nuclear stability changes beyond known heavy elements.
Atomic number: The number of protons in an atom's nucleus, which determines its chemical element. The value 109 distinguishes meitnerium from every other element.
Cold fusion: A heavy-ion fusion method using near-barrier-energy projectiles and targets, often leaving relatively low excitation energy. The first claimed synthesis used this route with a bismuth target and iron ions.
Peter Armbruster: A German nuclear physicist known for research on heavy elements and nuclear fission. He co-led the GSI team that reported element 109's discovery.
Element synthesis: The production of atomic nuclei with specified proton numbers through nuclear reactions. Making meitnerium extends the experimentally known periodic table.
Relativistic effect: A change in physical behavior caused by relativistic corrections to particles moving at substantial fractions of light speed. Strong nuclear charge may alter meitnerium's electron structure and chemical behavior.

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Group 9 elementBroader topic: Meitnerium completes Group 9, though its chemistry is known mainly from predictions.