Nobelium - Discovery Profile

Discovery Profile

The discovery of element 102 was first announced by physicists at the Nobel Institute in Sweden in 1957. The team reported that they created an isotope with a half-life of 10 minutes, decaying by emission of an 8.5 MeV alpha particle, after bombarding 244Cm with 13C nuclei. The activity was assigned to 251No or 253No. The scientists proposed the name nobelium (No) for the new element. Later they retracted their claim and associated the activity to background effects.

The synthesis of element 102 was then claimed in April 1958 at the University of California, Berkeley by Albert Ghiorso, Glenn T. Seaborg, John R. Walton and Torbjørn Sikkeland. The team used the new heavy-ion linear accelerator (HILAC) to bombard a curium target (95% 244Cm and 5% 246Cm) with 13C and 12C ions. They were unable to confirm the 8.5 MeV activity claimed by the Swedes but were instead able to detect decays from 250Fm, supposedly the daughter of 254102, which had an apparent half-life of ~3 s. In 1959 the team continued their studies and claimed that they were able to produce an isotope that decayed predominantly by emission of an 8.3 MeV alpha particle, with a half-life of 3 s with an associated 30% spontaneous fission branch. The activity was initially assigned to 254No but later changed to 252No. The Berkeley team decided to adopt the name nobelium for the element.

244
96Cm + 12
6C → 256
102No*
→ 252
102No + 4 1
0n

Further work in 1961 on the attempted synthesis of element 103 produced evidence for a Z=102 alpha activity decaying by emission of an 8.2 MeV particle with a half-life of 15 s, and assigned to 255No.

Following initial work between 1958–1964, in 1966, a team at the Flerov Laboratory of Nuclear Reactions (FLNR) reported that they had been able to detect 250Fm from the decay of a parent nucleus (254No) with a half-life of ~50s, in contradiction to the Berkeley claim. Furthermore, they were able to show that the parent decayed by emission of 8.1 MeV alpha particles with a half-life of ~35 s.

238
92U + 22
10Ne → 260
102No*
→ 254
102No + 6 1
0n

In 1969, the Dubna team carried out chemical experiments on element 102 and concluded that it behaved as the heavier homologue of ytterbium. The Russian scientists proposed the name joliotium (Jo) for the new element.

Later work in 1967 at Berkeley and 1971 at Oak Ridge fully confirmed the discovery of element 102 and clarified earlier observations.

In 1992, the IUPAC-IUPAP Transfermium Working Group (TWG) assessed the claims of discovery and concluded that only the Dubna work from 1966 correctly detected and assigned decays to Z=102 nuclei at the time. The Dubna team are therefore officially recognised as the discoverers of nobelium although it is possible that it was detected at Berkeley in 1959.