Nobelium

Author: Robert Husted, Mollie Boorman

History

(Alfred Nobel, discoverer of dynamite) Nobelium was unambiguously discovered and identified in April 1958 at Berkeley by A. Ghiorso, T. Sikkeland, J.R. Walton, and G.T. Seaborg, who used a new double-recoil technique. A heavy-ion linear accelerator (HILAC) was used to bombard a thin target of curium (95% ²⁴⁴Cm and 4.5% ²⁴⁶Cm) with ¹²C ions to produce ¹⁰²No according to the ²⁴⁶Cm(¹²C, 4n) reaction.

In 1957 workers in the United States, Britain, and Sweden announced the discovery of an isotope of element 102 with a 10-minute half-life at 8.5 MeV, as a result of bombarding ²⁴⁴Cm with ¹³C nuclei. On the basis of this experiment, the name nobelium was assigned and accepted by the Commission on Atomic Weights of the International Union of Pure and Applied Chemistry.

The acceptance of the name was premature because both Russian and American efforts now completely rule out the possibility of any isotope of Element 102 having a half-life of 10 min in the vicinity of 8.5 MeV. Early work in 1957 on the search for this element, in Russia at the Kurchatov Institute, was marred by the assignment of 8.9 +/- 0.4 MeV alpha radiation with a half-life of 2 to 40 sec, which was too indefinite to support discovery claims.

Confirmatory experiments at Berkeley in 1966 have shown the existence of ²⁵⁴102 with a 55-s half-life, ²⁵²102 with a 2.3-s half-life, and ²⁵⁷102 with a 23-s half-life.

Following tradition giving the right to name an element to the discoverer(s), the Berkeley group in 1967, suggested that the hastily given name nobelium along with the symbol No , be retained.

Isotopes

Ten isotopes are now recognized, one of which -- ²⁵⁵102 -- has a half-life of 3 minutes.