Nobelium
Atomic Number: 102
Atomic Symbol: No
Atomic Weight: 259
Electron Configuration: [Rn]7s²5f¹⁴
History
(Alfred Nobel, discoverer of dynamite) Nobelium was unambiguiously 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
254-102 with a 55-s half-life,
252-102 with a 2.3-s half-life, and 257-102 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 -- 255-102 -- has a half-life of
3 minutes.