Meitnerium (Mt) is a synthetic element with the atomic number 109. This highly radioactive transactinide metal does not exist in nature. A team of German scientists successfully synthesized the first atom in 1982 at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany. The discovery marked a significant step in exploring the boundaries of the periodic table.
The Scientists and the Laboratory
The successful synthesis of element 109 was achieved by a research group at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, West Germany. The team was primarily led by physicists Peter Armbruster and Gottfried Münzenberg. GSI, which features the powerful Universal Linear Accelerator (UNILAC), was already a leading center for creating superheavy elements, having previously discovered elements 107 (bohrium) and 108 (hassium). The first atom of element 109 was conclusively detected on August 29, 1982.
The experiment relied on the specialized equipment and expertise available at the GSI laboratory. The Darmstadt team developed sophisticated techniques for accelerating and colliding heavy atomic nuclei. Precisely managing the energy of the colliding particles was instrumental in facilitating the required nuclear fusion. Identifying the extremely short-lived new atom necessitated advanced detection and separation methods, including the Separator for Heavy Ion Reaction Products (SHIP).
The Nuclear Reaction: Creating Element 109
The synthesis of Meitnerium involved heavy ion fusion, specifically employing “cold fusion.” This method is preferred because it produces a compound nucleus with less internal excitation energy. A lower excitation energy means the resulting superheavy nucleus is more likely to survive fission and remain intact. The GSI team used the \(\text{Bi}^{209}\) isotope of bismuth as the target material, which was bombarded with a beam of \(\text{Fe}^{58}\) nuclei, a stable isotope of iron.
The specific nuclear reaction fused the bismuth nucleus (83 protons) with the iron nucleus (26 protons). This fusion created a nucleus with 109 protons, defining it as Meitnerium, along with the emission of a single neutron. The resulting isotope was Meitnerium-266 (\(\text{Mt}^{266}\)), represented by the equation \(\text{Bi}^{209} + \text{Fe}^{58} \rightarrow \text{Mt}^{266} + n\). This process is incredibly inefficient, requiring the GSI team to bombard the target for approximately one week to generate and detect a single atom.
The synthesized \(\text{Mt}^{266}\) isotope proved extremely unstable, exhibiting a half-life of only a few milliseconds (around 3.8 to 5 ms) before undergoing alpha decay. Detection relied on observing the characteristic chain of alpha decays following the creation of the Meitnerium atom. While \(\text{Mt}^{266}\) was the isotope first discovered, subsequent experiments identified Meitnerium-278 as the longest-lived isotope, with a half-life of about 4.5 to 8 seconds.
The Naming of Meitnerium
The element’s name, Meitnerium, honors the Austrian-Swedish physicist Lise Meitner, whose contributions to nuclear physics were profound. Meitner was instrumental in the discovery and theoretical explanation of nuclear fission. Working with chemist Otto Hahn, she helped discover protactinium. After fleeing Nazi Germany in 1938, she provided the physical interpretation for the experimental results showing that uranium nuclei could be split.
Meitner and her nephew, Otto Robert Frisch, were the first to use the term “fission” to describe this process. Despite her foundational role, she was controversially overlooked when Hahn was solely awarded the 1944 Nobel Prize for Chemistry. The GSI team proposed the name Meitnerium in September 1992 to formally recognize her scientific legacy.
Prior to the official naming, element 109 was temporarily known by the systematic name unnilennium, or Une, following IUPAC nomenclature rules. The process of officially recognizing the names of elements 104 to 109 was lengthy and involved some controversy. However, the name Meitnerium was recommended by IUPAC in 1994 and officially adopted in 1997, permanently linking Lise Meitner’s name to the periodic table.