Fermium, Mendelevium, Nobelium, and Lawrencium

The first isotope of element 100 was discovered in heavy-element samples obtained after the ‘Mike’ thermonuclear explosion of 1952, during the same set of experiments that resulted in the discovery of element 99. A joint effort by the researchers from the Lawrence Berkeley National Laboratory, the Argonne National Laboratory, and the Los Alamos National Laboratory resulted in the chemical isolation and identification of the 20 h half-life isotope ²⁵⁵Fm (Ghiorso et al., 1955a). The production involved rapid, multiple neutron capture by uranium nuclei in the nuclear device to form neutron-rich uranium isotopes of heavy mass followed by beta decay to elements of higher atomic number. The ²⁵⁵Fm in the samples, produced from the beta decay of the longer-lived ²⁵⁵Es, was purified and chemically identified by cation-exchange chromatography and detected through the use of alpha particle energy analysis. The name, fermium, was proposed in 1955 in honor of the leader in nuclear science, Enrico Fermi, and the name was subsequently accepted by the IUPAC.