Lawrencium, Lr

an artificially produced radioactive chemical element of the actinide series; atomic number, 103. No stable isotopes of Lawrencium are known to exist.

The first experiments to synthesize element 103 were carried out in 1961 by a team of American scientists headed by A. Ghiorso. The results of the experiments were not subsequently confirmed, although the name given by the research team to element 103 in honor of E. Lawrence is still retained. The latter designation is given in parentheses in the D. I. Mendeleev periodic system of elements.

The first reliable data about the isotope ²⁵⁶Lr were obtained in 1965 by Soviet physicists at the Joint Institute for Nuclear Research in Dubna. They obtained 256Lr nuclei by irradiating an americium (²⁴³Am) target with accelerated ¹⁸O ions. It was established that ²⁵⁶Lr nuclei emit a-particles and that the half-life is approximately 35 sec. The second lawrencium isotope, ²⁵⁵Lr, was also first obtained at Dubna in 1969. In 1971 a team of American physicists working in Berkeley reported the synthesis of lawrencium isotopes with mass numbers 257-260; isotope ²⁶⁰Lr was found to have the longest half-life, approximately 3 min. All the lawrencium isotopes were obtained in negligible quantities.

The chemical properties of lawrencium should be similar to those of other heavy actinides, and therefore the characteristic oxidation number for lawrencium should be +3. The results of numerous studies of the properties of lawrencium support this assumption.