fermium fer·mi·um (fûr'mē-əm, fěr'-)
A synthetic radioactive metallic element whose most stable isotope is Fm 257 with a half-life of [approx] 100 days. Atomic number 100.
(Fm), synthetic chemical element of the actinoid series of the periodic table, atomic number 100. Fermium (as the isotope fermium-255) is produced by the intense neutron irradiation of uranium-238 and was first positively identified by Albert Ghiorso and coworkers at Berkeley, Calif., in debris taken from the first thermonuclear or hydrogen-bomb test explosion (November 1952), in the South Pacific. All fermium isotopes are radioactive. Mixtures of the isotopes fermium-254 (3.24-hour half-life), fermium-255 (20.1-hour half-life), fermium-256 (2.7-hour half-life), and fermium-257 (80-day half-life) can be produced by the intensive slow-neutron irradiation of elements of lower atomic number, such as plutonium.
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