<Tr> <Td> 99 </Td> <Td> Einsteinium </Td> <Td> 1952 </Td> <Td> A. Ghiorso et al. (Argonne Laboratory, Los Alamos Laboratory and University of California, Berkeley) </Td> <Td> 1952 </Td> <Td> </Td> <Td> Formed in the first thermonuclear explosion in November 1952, by irradiation of uranium with neutrons; kept secret for several years . </Td> </Tr> <Tr> <Td> 100 </Td> <Td> Fermium </Td> <Td> 1952 </Td> <Td> A. Ghiorso et al. (Argonne Laboratory, Los Alamos Laboratory and University of California, Berkeley) </Td> <Td> </Td> <Td> </Td> <Td> Formed in the first thermonuclear explosion in November 1952, by irradiation of uranium with neutrons; kept secret for several years . </Td> </Tr> <Tr> <Td> 101 </Td> <Td> Mendelevium </Td> <Td> 1955 </Td> <Td> A. Ghiorso, G. Harvey, R. Choppin, S.G. Thompson and G.T. Seaborg (Berkeley Radiation Laboratory) </Td> <Td> </Td> <Td> </Td> <Td> Prepared by bombardment of einsteinium with helium . </Td> </Tr> <Tr> <Td> 103 </Td> <Td> Lawrencium </Td> <Td> 1961 </Td> <Td> A. Ghiorso, T. Sikkeland, E. Larsh and M. Latimer (Berkeley Radiation Laboratory) </Td> <Td> </Td> <Td> </Td> <Td> First prepared by bombardment of californium with boron atoms . </Td> </Tr>

By 1985 a total of elements were known