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Damped collisions between very heavy nuclei were studied extensively about twenty years ago. Among others, there had been a great deal of interest in the use of heavy-ion transfer reactions with actinide targets to produce new nuclear species in the transactinide region. The cross sections were found to decrease very rapidly with increasing atomic number of surviving target-like fragments. However, Fm and Md neutron-rich isotopes have been produced at the level of 0.1 μb. Note that superheavy (SH) nuclei obtained in “cold” fusion reactions with Pb or Bi target are along the proton drip line and very neutron-deficient with a short half-life. In fusion of actinides with Ca more neutron-rich SH nuclei are produced with much longer half-life. But they are still far from the center of the predicted first “island of stability” formed by the neutron shell around N=184 (see the nuclear map in Figure 1). In the “cold” fusion, the cross sections of SH nuclei formation decrease very fast with increasing charge of the projectile and become less than 1 pb for Z >112. Heaviest transactinide, Cf, which can be used as a target in the second method, leads to the SH nucleus with Z =118 being fused with Ca. Using the next nearest elements instead of Ca (e.g., Ti, Cr, etc.) in fusion reactions with actinides is expected less encouraging, though experiments of such kind are planned to be performed. In this connection another ways to the production of SH elements in the region of the “island of stability” should be searched for. One more effect, which may be expected in the damped collisions of transactinides, is a formation of giant quasi-atoms with a nucleus consisting of two closely located heavy nuclei. If the lifetime of the composite nuclear system with total charge Z >173 is rather long (~10s) we may expect a spontaneous positron emission from superstrong electric field of quasi-atoms by a static QED process (transition from neutral to charged QED vacuum) (see Figure 2). About twenty years ago a search for such effect were carried out and narrow line structures in the positron spectra were first reported at GSI. Unfortunately these results were not confirmed later, neither in ANL, nor in new experiments performed at GSI (see also hierarchical references therein). Thus the situation remains unclear, while the experimental efforts in this field have ended. We hope that a new analysis, performed within a realistic dynamical model, may shed additional light on this problem and also answer the principal question: are there some reaction features (triggers) testifying to a long reaction delay? If they are, a new experiment could be planned to detect the positrons in the specific reaction channels. Recently a new model has been proposed for simultaneous description of strongly coupled reaction channels of heavy ion collisions: deep inelastic (DI) scattering, quasi-fission (QF), fusion, and regular fission. Reasonable agreement of our first calculations with experimental data on low-energy DI and QF reactions induced by heavy ions stimulated us to study the reaction dynamics of very heavy transactinide nuclei. The purpose is to find an influence of the shell structure of the driving potential (in particular, deep valley caused by the double shell closure Z=82 and N=126) on nucleon rearrangement between Walter Greiner*,a and Valery Zagrebaevb a Frankfurt Institute for Advanced Studies, J.W. Goethe-Universität, 60325 Frankfurt am Main, Germany b Flerov Laboratory of Nuclear Reactions, Joint Institute for Niclear Research, Dubna, Moscow region, 141980, Russia

Long-Lived Superheavy Nuclei and Giant Quasi-Atoms Produced in Damped Collisions of Transactinides