A. V. Karpov

DECAY PROPERTIES AND STABILITY OF HEAVIEST ELEMENTS

Decay properties and stability of heaviest nuclei with Z≤132 are studied within the macro-microscopical approach for nuclear ground state masses and phenomenological relations for the half-lives with respect to α-decay, β-decay and spontaneous fission. We found that at existing experimental facilities the synthesis and detection of nuclei with Z>120 produced in fusion reactions may be difficult due to their short half-lives (shorter than 1 μs). The nearest (more neutron-rich) isotopes of superheavy elements with 111≤Z≤115 to those synthesized recently in Dubna in 48Ca-induced fusion reactions are found to be β+-decaying. This fact may significantly complicate their experimental identification. However it gives a chance to synthesize in fusion reactions the most stable superheavy nuclei located at the center of the island of stability. Our calculations yield that the β-stable isotopes 291Cn and 293Cn with a half-life of about 100 years are the longest-living superheavy nuclei located at the island of stability.

True ternary fission of superheavy nuclei

True ternary fission with formation of a heavy third fragment is quite possible for superheavy nuclei because of the strong shell effects leading to a three-body clusterization with the two doubly magic tinlike cores. The simplest way to discover this phenomenon in the decay of excited superheavy nuclei is a detection of two tinlike clusters with appropriate kinematics in low-energy collisions of medium-mass nuclei with actinide targets. The three-body quasi-fission process could be even more pronounced for giant nuclear systems formed in collisions of heavy actinide nuclei. In this case a three-body clusterization might be proved experimentally by the detection of two coincident leadlike fragments in low-energy U + U collisions.

Systematic study of decay properties of heaviest elements

Decay properties and stability of heaviest nuclei with Z ≤ 132 are studied within the macro-microscopical approach for nuclear ground-state masses. We use phenomenological relations for the half-lives with respect to α-decay, β-decay and spontaneous fission. Our calculations demonstrate that the β-stable isotopes 291Cn and 293Cn with a half-life of about 100 years are the longest-living superheavy nuclei located on the first island of stability. We found the second island of stability of superheavy nuclei in the region of Z ≈ 124 and N ≈ 198. It is separated from the “continent” by the “gulf” of short-living nuclei with half-lives shorted than 1 μs.

Effect of neutron transfer channels in fusion reactions with weakly bound nuclei at subbarrier energies

The role of neutron transfer in fusion reactions of weakly-bound nuclei at subbarrier energies is studied within the empirical model of channel coupling. The results from calculating the fusion cross sections for the 7Li + 209Bi, 9, 11Li + 208, 206Pb, 6, 7, 9, 11Li + 152Sm reactions are presented. Good agreement with the available experimental data is shown. Several combinations of colliding nuclei for which the strong enhancement of subbarrier fusion due to the effect of neutron transfer processes are predicted.

Does neutron rearrangement enhance the cross sections of the subbarrier fusion of atomic nuclei

The effect neutron rearrangement channels have on nuclear fusion at energies below the Coulomb barrier is considered. The latest experimental data, which reveal no enhancement of the fusion cross section at subbarrier energies despite the presence of rearrangement channels for neutrons with Q > 0 are explained using the empirical channel coupling model. The mechanism of neutron rearrangement in fusion reactions is studied in detail. The conditions required for additional enhancement (complementary to the one associated with the effect of collective excitation channels) of the subbarrier fusion cross section are formulated.

Superheavy Nuclei: Decay and Stability

Decay properties of superheavy nuclei are required for exploring the nuclei from the upper part of the nuclear map. The stability of nuclei with \(Z\le 132\) is studied with respect to \(\alpha \)-decay, \(\beta \)-decay and spontaneous fission. Performed calculations allow us to conclude that at existing experimental facilities the synthesis and detection of nuclei with \(Z>120\) produced in fusion reactions may be difficult due to their short half-lives (shorter than 1 \(\upmu \)s). We found for the first time the region of \(\beta ^{+}\)-decaying superheavy nuclei with \(111\le Z\le 115\) located to the “right” (more neutron-rich) to those synthesized recently in Dubna in \(\mathrm{^{48}}\mathrm{Ca}\)-induced fusion reactions. This fact may significantly complicate their experimental identification. However it gives a chance to synthesize in fusion reactions the most stable superheavy nuclei located at the center of the island of stability. Our calculations yield that the \(\beta \)-stable isotopes \(^{291}\)Cn and \(^{293}\)Cn with a half-life of about 100 years are the longest-living superheavy nuclei located at the island of stability.

Effect of neutron transfer in the fusion process near and below the Coulomb barrier

Near-barrier and sub-barrier fusion of weakly bound neutron-rich isotopes of lithium is explored within the empirical channel coupling model. Several combinations of colliding nuclei are proposed, for which strong enhancement of the sub-barrier fusion is predicted owing to coupling with neutron transfer channels.

Formation of Neutron-Enriched Heavy and Superheavy Nuclei in Fusion Reactions

The formation of new isotopes of heavy and superheavy elements in the fusion of neutron-enriched projectiles with actinide targets is discussed. Cross sections for the formation of evaporation residues in fusion reactions is predicted for several combinations of colliding nuclei.

Study of deep inelastic collisions within multidimensional dynamical model

Energy, angle, and charge distributions of binary products of the deep inelastic collisions of heavy ions are studied in the framework of a multidimensional dynamical model of nucleus-nucleus collisions based on the Langevin equations. The model is verified on the example of the 136Xe + 209Bi system at several above barrier energies.

Perspectives of Heavy and Superheavy Nuclei Research

Low values of the fusion cross sections and very short half-lives of nuclei with \(Z>120\) put obstacles in synthesis of new elements. However the fusion reactions of medium mass projectiles (including RIB) with different actinide targets still can be used for the production of the not-yet-synthesized SH nuclei. The gap of unknown SH nuclei, located between the isotopes which were produced earlier in the cold and hot fusion reactions, could be filled in fusion reactions of \(^{48}\)Ca with available lighter isotopes of Pu, Am, and Cm. The neutron-enriched isotopes of SH elements may be produced with the use of a \({}^{48}\)Ca beam if a \(^{250}\)Cm target would be prepared. In this case we get a real chance to reach the island of stability owing to a possible electron capture in \(^{291}\)Fl nucleus formed in the 3n evaporation channel of this reaction with a cross section of about 0.8 pb. Multi-nucleon transfer processes at near barrier collisions of heavy (and very heavy, U-like) ions seem to be the most realistic reaction mechanism allowing one to produce new neutron enriched heavy nuclei located in the unexplored upper part of the nuclear map. The predictions for the production of new neutron rich heavy nuclei in multinucleon transfer reactions will be given. A special attention will be paid to the “inverse” quasi-fission mechanism leading to formation of reaction fragments with masses lighter than projectile and heavier than target masses.