Study of fusion reactions between heavy nuclei and of the synthesis of super heavy elements by a novel quantum diffusion theory

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1. We developed a new framework of the coupled-channels calculations to evaluate the cross section of heavy-ion fusion reactions at energies around the Coulomb barrier. The new method replaces the.Woods-Saxon potential in the conventional approach by the double folding potential with the M3Y force as the effective nucleon-nucleon interaction. 2. We applied the method to the ^<16>O+^<154>Sm collisions in order to test its validity, and found that the coupled channels calculations including the ground state rotational band of the target nucleus ^<154>Sm reproduce fairly well the experimental data of the fusion excitation function over a wide energy region -including the Coulomb barrier, though some improvements of the theory are required to explain the experimental fusion barrier distribution. 3. We have then examined whether the method is applicable to heavy-ion collisions between heavy nuclei, where the so called extra-push problem is involved. We studied ^<60>Ni+^<154>Sm scattering as … More an example and found that the calculated barrier transmission cross section well agrees with the experimental data of the total fusion-fission like cross section. 4. It is necessary to develop a theory which can quantitatively describe the process from the inside of the fusion barrier to inside of the fission barrier in order to estimate the fusion cross section between two heavy nuclei such as that for the fusion reactions to synthesize super heavy elements. A diffusion theory has been used as a promising approach to this end under the name of the fluctuation-dissipation dynamics. We have developed a novel quantum diffusion theory by paying attention to the fact that super heavy elements should be synthesized at low temperatures, where a quantum effect due to finite barrier curvature cannot be ignored. Our diffusion equation contains various terms which are absent in the standard diffusion equation by reflecting non-Markovian properties originated from the quantum effects. 5. We applied the quantum diffusion theory to the diffusion process along a potential barrier, and found that while the well known fluctuation dissipation theorem between the diffusion and dissipation coefficients holds at high energies, at low temperatures the deviation from that in the absence of the quantum effect is very different from the known deviation in the diffusion process in a potential well. 6. Through analyses with realistic parameters, we found that both quantum and non-Markpvian effects significantly modify the properties of the diffusion process in synthesizing super heavy elements compared with the results of existing theories. Less