Superheavy elements
Yu. Ts. Oganessian
Flerov Laboratory of Nuclear Reactions, Joint Institute
for Nuclear Research, 141980 Dubna, Moscow, Russia
Abstract: One of the fundamental outcomes of nuclear theory
is the predicted existence of increased stability in the region of unknown
superheavy elements. This hypothesis, proposed more than 35 years ago
and intensively developed during all this time, significantly extends
the limits of existence of chemical elements. �Magic �nuclei with closed
proton and neutron shells possess maximum binding energy. For the heaviest
nuclides, a considerable stability is predicted close to the deformed
shells with Z = 108, N = 162. Even higher stability is expected
for the neutron-rich nuclei close to the spherical shells with Z = 114
(possibly also at Z = 120, 122) and N = 184, coming next to the
well-known �doubly magic �nucleus 208 Pb. The present paper describes
the experiments aimed at the synthesis of nuclides with Z = 113�116,
118 and N = 170�177, produced in the fusion reactions of the
heavy isotopes of Pu, Am, Cm, and Cf with 48Ca projectiles.The
energies and half-lives of the new nuclides, as well as those of their
daughter nuclei (Z < 113) qualitatively agree with the theoretical predictions.
The question, which is the nucleus, among the superheavy ones, that
has the longest half-life is also considered. It has been shown that,
if the lifetime of the most stable isotopes, in particular, the isotopes
of element 108 (Hs), is > 5 �107 years, they can
be found in natu ral objects. The experiments were carried out during
2001�2003 in the Flerov Laboratory of Nuclear Reactions (JINR, Dubna)
in collaboration with the Analytical and Nuclear Chemistry Division
(LLNL, Livermore).
*Plenary lecture presented at the XVII Mendeleev Congress on General and Applied Chemistry, Kazan, Tatarstan, Russia, 21 -26 September 2003. Other presentations are published in this issue, pp. 1605-1798.
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