Overview

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.