Lawrencium

(Ernest O. Lawrence, inventor of the cyclotron) This member of the 5f transitionelements (actinide series) was discovered in March 1961 by A. Ghiorso, T. Sikkeland, A.E.Larsh, and R.M. Latimer. A 3-Mg californium target, consisting of a mixture of isotopes ofmass number 249, 250, 251, and 252, was bombarded with either 10B or 11B. The electricallycharged transmutation nuclei recoiled with an atmosphere of helium and were collected on athin copper conveyor tape which was then moved to place collected atoms in front of aseries of solid-state detectors. The isotope of element 103 produced in this way decayedby emitting an 8.6 MeV alpha particle with a half-life of 8 s.

In 1967, Flerov and associates at the Dubna Laboratory reported their inability todetect an alpha emitter with a half-life of 8 s which was assigned by the Berkeley groupto 257-103. This assignment has been changed to 258Lr or 259Lr.

In 1965, the Dubna workers found a longer-lived lawrencium isotope, 256Lr, with ahalf-life of 35 s. In 1968, Thiorso and associates at Berkeley used a few atoms of thisisotope to study the oxidation behavior of lawrencium. Using solvent extraction techniquesand working very rapidly, they extracted lawrencium ions from a buffered aqueous solutioninto an organic solvent -- completing each extraction in about 30 s.