Meitnerium is a chemical element with symbol Mt and atomic number 109. It is an extremely radioactive synthetic element (an element not found in nature that can be created in a laboratory). The most stable known isotope, meitnerium-278, has a half-life of 7.6 seconds. The GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany, first created this element in 1982.Symbol: Mt
Atomic number: 109
Discovered: 1982
CAS ID: 54038-01-6
Van der Waals radius: 200 pm
Atomic mass: 268 u