Superheavy elements*

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 48 Ca 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 × 10 7 years, they can be found in natural objects. The experiments were carried out during [2001][2002][2003] in the Flerov Laboratory of Nuclear Reactions (JINR, Dubna) in collaboration with the Analytical and Nuclear Chemistry Division (LLNL, Livermore)