Meitnerium (Mt)

On the evening of 29 August 1982, a detector at the heavy-ion laboratory outside Darmstadt recorded one decay chain that had never been seen before. That was the entire discovery of element 109: a single atom, which existed for a few milliseconds and then took itself apart in a sequence of alpha decays ending in nuclides already on the charts.

Announcing an element on the strength of one event required confidence that the chain could not be anything else. Peter Armbruster and Gottfried Münzenberg's group had it, because the velocity filter feeding the detector rejected essentially everything except the fused nucleus they were after, and because every step of the observed chain matched a known nuclide in energy and in timing. Nobody disputed the claim. Nobody has ever disputed anything about element 109.

Forty-eight nominations

Lise Meitner spent thirty years working with Otto Hahn in Berlin. In 1938, being Jewish and by then stateless after the Anschluss stripped her of Austrian citizenship, she fled Germany with almost nothing. From Sweden she continued to correspond with Hahn about the puzzling barium he and Fritz Strassmann kept finding in irradiated uranium.

It was Meitner, with her nephew Otto Frisch over Christmas 1938, who worked out what was happening: the uranium nucleus was splitting, and the energy released could be calculated from the mass difference using Einstein's relation. They gave the process its name — fission, borrowed from biology. Hahn published the chemistry; Meitner and Frisch published the interpretation.

The 1944 Nobel Prize in Chemistry went to Hahn alone. Meitner was nominated forty-eight times across her career, nineteen times in chemistry and twenty-nine in physics, and received nothing. She died in 1968. Her epitaph, written by Frisch, reads: "a physicist who never lost her humanity."

Meitnerium is the only element named exclusively in honour of a woman. Curium honours Marie Curie alongside her husband, and no other square carries a woman's name at all.

The name nobody fought over

The naming of elements 104 through 108 consumed the better part of three decades, generated competing national conventions, and required IUPAC to issue a draft recommendation, withdraw it, and issue another.

Element 109 passed through all of that untouched. The Darmstadt group proposed meitnerium immediately, in 1982. The name appeared in IUPAC's contested 1994 draft as meitnerium. It appeared in the final 1997 settlement as meitnerium. Across the whole of the naming dispute, it is the one element about which every party agreed from the beginning.

There is a reasonable argument that this was the periodic table making a correction. A field that had been slow to acknowledge Meitner's part in the discovery of fission was, by the 1980s, conscious of the fact, and the proposal was received as overdue rather than contentious.

What is known, and what is only calculated

The honest summary of meitnerium's properties is that almost nothing has been measured.

No chemical experiment has ever been performed on element 109. Not one. The isotopes available are too short-lived and produced too rarely — meitnerium-278, the most durable, survives a few seconds, and the total number of atoms ever made runs to a few dozen. Everything in the tables beyond atomic number and observed decay properties is theoretical.

What theory says, clearly labelled as prediction: meitnerium should be a group 9 metal resembling iridium, with the +3 oxidation state prominent and possibly a stable +1 state that iridium lacks, the latter arising from relativistic stabilisation of the 7s orbital.

Density is where the calculations disagree with each other, and the disagreement is worth knowing about. The figure that circulates most widely, close to 37 grams per cubic centimetre, comes from the early relativistic extrapolations of the 1970s; more recent solid-state work argues for something nearer the high twenties. What both agree on is the shape of the row rather than its scale — meitnerium and hassium come out at the top of it, mirroring iridium and osmium directly above, because that is where a partly filled d shell binds a metal most tightly. Meitnerium is also expected to melt far above 1000 K.

None of these numbers has been checked against an experiment, and none can be until an isotope is found that lasts long enough to react with something.

The decay chains are the exception. Those are measured, and they are how element 109 makes itself useful: meitnerium isotopes appear partway down the chains of elements 111 and 113, so a meitnerium decay of known energy is one of the signposts by which the discovery of a heavier element is confirmed.