Meitnerium – facts and properties

Position in the periodic table

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Occurrence and extraction

Meitnerium exists only in laboratories. Every known isotope is radioactive and short-lived. For the longest-lived one, meitnerium-278, the literature gives a half-life of a few seconds, but the value is uncertain because so few atoms have been observed. The first isotope found, meitnerium-266, lasts only milliseconds.

In 1982 a GSI team around Peter Armbruster and Gottfried Münzenberg bombarded a thin layer of bismuth-209 with iron-58 ions. After a long irradiation the detector recorded one single atom. It decayed by alpha emission to bohrium-262, which the same team had found a year earlier, and that link made the event unambiguous. Later experiments confirmed the element.

The method is called cold fusion, and it has nothing to do with the claimed nuclear fusion at room temperature that was never confirmed. Here "cold" refers to the excitation energy of the new nucleus. When two nuclei merge, the energy of the collision ends up in the product, and the more of it there is, the more likely the nucleus is to fly apart or boil off neutrons. Lead-208 and bismuth-209 are unusually tightly bound nuclei. If a medium-heavy projectile such as iron-58 strikes one of them, the merged nucleus stays comparatively cool and usually loses only a single neutron. The price is a tiny yield, because the positively charged nuclei repel each other. The ions come from the UNILAC linear accelerator, and the separator SHIP sorts the fusion products from the beam particles by their speed. The counterpart is hot fusion, which uses calcium-48 and actinide targets and led to the still heavier elements in Dubna.

The name honours Lise Meitner (1878–1968), born in Vienna. She worked for decades in Berlin with the chemist Otto Hahn and had to flee to Sweden in 1938 because of her Jewish background. When Hahn and Fritz Strassmann found barium after bombarding uranium at the end of 1938, Meitner and Otto Robert Frisch interpreted it as the splitting of the uranium nucleus. The 1944 Nobel Prize in Chemistry for the discovery of nuclear fission went to Hahn alone, and historians have long criticised that Meitner was passed over. Meitnerium is the only element dedicated solely to a historical woman, while curium commemorates Marie and Pierre Curie together.

Properties and reactions

Meitnerium is in period 7 and group 9, below iridium, with rhodium and cobalt above. Its electron configuration [Rn] 5f¹⁴ 6d⁷ 7s² is a prediction. The atomic mass entry 278 u is no average but the mass number of meitnerium-278.

Nobody has ever seen a piece of the metal, and the melting point, boiling point and density have not been measured. Calculations predict a solid, very dense and very noble metal, possibly denser than iridium.

No chemical experiment with meitnerium has been done. Its isotopes live for seconds or less, and at most single atoms form per experiment. Any expectation therefore rests on the position in the periodic table alone.

The atoms decay by alpha emission or spontaneous fission. The tiny quantities pose no danger.

Research and synthesis

Outside research meitnerium has no use, and there is no amount one could collect. From half-life and decay mode, researchers draw conclusions about how nuclei are built. Meitnerium isotopes also appear in the decay chains of heavier elements, for instance that of nihonium, and help to interpret such chains.

Meitnerium also shows a limit of cold fusion. The heavier the projectile, the lower the yield. At GSI hassium, darmstadtium, roentgenium and copernicium followed this way, and nihonium in Japan. Beyond that the probability becomes so small that researchers turn to hot fusion.

Quick question

What is the atomic number of meitnerium (Mt)?

FAQ