Fermium

Fermium was discovered in 1952, like einsteinium, in the fallout of the first hydrogen-bomb test, and identified by Albert Ghiorso's team; its discovery too was kept secret for several years. It was named after the Italian-American physicist Enrico Fermi. Fermium is an intensely radioactive synthetic metal, the heaviest element that can be formed by successive neutron capture and the heaviest that has been made in weighable, if still invisibly small, amounts by that route. Its longest-lived isotope survives about a hundred days, and it can be produced only in trace, invisible quantities; no bulk sample has ever existed, and what little is known of its chemistry comes from experiments on a few atoms dissolved in solution.

Fermium marks what nuclear physicists call the fermium gap: beyond this point, spontaneous fission becomes so overwhelmingly fast that no heavier element can be built simply by adding neutrons one at a time to a lighter nucleus, since the nucleus tends to fly apart before it can capture enough additional neutrons. This hard physical limit is why every element heavier than fermium has instead been made by fusing two lighter nuclei together in an accelerator, a fundamentally different and far more difficult technique that has defined the frontier of element-making ever since.

Fermium honours Enrico Fermi, the physicist who built the first nuclear reactor and was one of the towering figures of twentieth-century physics, and who had died in 1954, shortly before the element's naming was made public. It shares its dramatic birth with einsteinium, both elements condensing out of the hydrogen bomb's flash as light nuclei swallowed neutron after neutron; fermium, at element 100, marks the practical ceiling of that process, for still heavier elements must be built by fusing whole nuclei together rather than by adding neutrons one at a time. Fermium has no ancient or esoteric tradition, being a synthetic element of the atomic age; its name pairs it with einsteinium as a tribute to two of the physicists whose work made the nuclear era, and its discovery, possible.

Fermi had fled Fascist Italy for the United States in 1938, partly because his wife Laura was Jewish and increasingly at risk under Mussolini's racial laws, arriving just in time to lead the team that achieved the first self-sustaining nuclear chain reaction beneath the stands of a disused football stadium at the University of Chicago in December 1942, the Chicago Pile-1 experiment that opened the reactor age his namesake element's own discovery would later depend on.