Mahmoud Yahia Ismail

We study the role of the projectile breakup in the fusion process by example of the 6Li reactions with the 59Co, 144Sm and 209Bi targets in vicinity of the Coulomb barrier. The coupled channel and distorted wave approaches are employed in order to calculate the complete fusion and the breakup cross sections, respectively. The partial cross sections in both the channels are compared in order to estimate the breakup fraction responsible for the suppression of complete fusion. The calculations are compared with available experimental data. The conclusions and recommendations are made.

The influence of nuclear deformation on α -decay half-lives is taken into account in the deformed density-dependent cluster model. The microscopic potential between the spherical α particle and the deformed daughter nucleus is evaluated numerically from the double-folding model by the multipole expansion method. A realistic density-dependent nucleon-nucleon (NN ) interaction with finite-range exchange part, which produces the nuclear matter saturation curve and the energy dependence of the nucleon-nucleus optical potential model is used. The ordinary zero-range exchange NN force, which is commonly used in α decay, is also considered in the present work. We systematically investigate the influence of nuclear deformations on the α -particle preformation probability of the deformed medium and heavy nuclei from the ground state to ground-state α transitions within the framework of the Wentzel-Kramers-Brillouin method by considering the Bohr-Sommerfeld quantization condition. Taking the deformation of daughter nuclei into account changes the behavior of the preformation probability, S α , by an amount depending on the Q value, the order, values, and signs of deformation parameters. Calculations have been conducted for the spherical nuclei in order to present clearly the effect of the deformation on the preformation probability. The combined effect of both finite-range force and deformation can reduce the value of S α by about an order of magnitude.

The interactions of 48Ca spherical nucleus are considered with the deformed targets 224Ra and 244Pu to form the super heavy elements 272Hs and 292114 (292Fl), respectively. The double folding model with effective density dependent M3Y-NN force, and the energy density functional method based on Skyrme force are used to derive the nucleus–nucleus interaction. The effect of deformation and orientation on the Coulomb barrier parameters is studied, and the results are compared with the corresponding quantities derived from a simple model based on the proximity approach for the nuclear part and simple analytical formula for the Coulomb interaction. Consistent behavior of the results is obtained at certain ranges for deformation parameters and orientations.

The preformation probability of an α cluster inside radioactive parent nuclei is investigated. The calculations are employed in the framework of the density-dependent cluster model for both even-even and odd-A isotopes with 74≤Z≤83 . A realistic density-dependent nucleon-nucleon (NN ) interaction with a finite-range exchange part is used to calculate the microscopic α -nucleus potential in the well-established double-folding model. The main effect of antisymmetrization under exchange of nucleons between the α and daughter nuclei has been included in the folding model through the finite-range exchange part of the NN interaction. The calculated potential is then implemented to find both the assault frequency and the penetration probability of the α particle by means of the Wentzel-Kramers-Brillouin approximation in combination with the Bohr-Sommerfeld quantization condition. We investigated the correlation between the α -particle preformation probability, S α , and the energy levels of the parent nucleus for α emitters with atomic number 74≤Z≤83 . Based on the similarity in the behavior of S α with the neutron number for two nuclei, we try to predict or confirm the unknown or doubted nuclear spins and parities in this mass region.

We assume a simple model to describe the ion-ion potential with dynamical change in its surface diffuseness. In particular, this model is used to calculate the heavy-ion fusion cross-section using different values of the surface diffuseness. Both the static and dynamic nuclear Woods-Saxon potentials with diffuseness values ranging between 0.65 fm and 1.3 fm are used to reproduce the fusion cross-sections data of the 19F+208Pb and 16O+154Sm reactions. The results estimate that there are different physical processes which could contribute to the fusion cross-section with different weights at each energy value. Each of these processes has its own nuclear potential. © 2013 World Scientific Publishing Company.

The study show the effect of the local density and the accuracy of neglecting s-dependence on direct part of α-α interaction potential. The large error in neglecting s-dependence produced at (R<2 fm) for BDM3Y3 -Ried force. In the surface and tail region (R≥3) the error is less than 50%.

A new averaging process of the calculation of α-decay half-lives for heavy and superheavy nuclei is studied in the framework of a deformed density-dependent cluster model. The potential between a spherical α particle and a deformed daughter nucleus is calculated numerically from the double-folding model by the multipole expansion method. The nuclear potential is calculated at each α-particle emission angle applying the Bohr-Sommerfeld condition at each case. The penetration factors and the half-lives for all the emission angles are evaluated with the new averaging process and compared with older values based on a fixed value of the nuclear potential depth. Finally, the half-lives of 83 even-even heavy nuclei in the atomic-number range 82-118 are calculated by the two methods and compared with their experimental values and the corresponding half-lives of the spherical daughter nuclei. © 2012 American Physical Society.

In the present paper we discuss the differences between the fusion barrier parameters (the height of Coulomb barrier V B and its radius R B) computed by two methods namely; the proximity approach for coplanar and non-coplanar systems of interacting nuclei and double folding model. The minimum separation distance, s, between the deformed surfaces of interacting nuclei was determined exactly from numerical calculations and the results of Coulomb parameters were compared with previous calculations based on approximate determination of s. We considered the three interaction systems 48Ar+ 238Pu, 150Nd+ 150Nd and 86Kr+ 180Hf and found that V B and R B, evaluated by using the proximity approach, have too strong Φ-dependence for the system 150Nd+ 150Nd at relative orientation angles of the nuclei symmetry axes θ 1=θ 2=90°. © 2012 Elsevier B.V.

A realistic density-dependent nucleon-nucleon (NN) interaction with a finite-range exchange part which produces the nuclear matter saturation curve and the energy dependence of the nucleon-nucleus optical potential model is used to calculate the preformation probability, S α, of α decay from Po isotopes to superheavy nuclei. The variation of S α with the neutron number for the isotopes of Po, Rn, Ra, Th, and U elements is studied below and above the magic neutron number N=126. We found a strong correlation between the behavior of S α and the energy levels of the parent nucleus at and just below the Fermi level. S α has a regular behavior with the neutron number if the neutron pair of α particles, emitted from adjacent isotopes, comes from the same energy level or from a group of levels, assuming that the order of levels in this group is not changed. Irregular behavior of S α with the neutron number occurs if the levels of the adjacent isotopes change or holes are present in lower levels. © 2012 American Physical Society.

The role of neutron transfer is investigated in the fusion process near and below the Coulomb barrier within the empirical channel coupling approach. The possibility of neutron transfer with positive Q-values considerably increases the barrier penetrability. The enhancement of fusion cross sections for 58Ni+ 64Ni, 32S+ 64Ni, 40Ca+ 48Ca, and 40Ca+ 124Sn is well reproduced at subbarrier energies by the empirical channel coupling approach including the coupling to the neutron-transfer channels. The predictions of the fusion cross sections for several combinations of colliding nuclei are also proposed which may shed additional light on the effect of neutron transfer in fusion processes. A huge enhancement of deep subbarrier fusion probability was found for light neutron-rich weakly bound nuclei. This may be quite important for astrophysical primordial and supernova nucleosynthesis. © 2012 Elsevier B.V..

{The shell and pairing correction energies are calculated for heavy and superheavy nuclei (SHN) by means of the Strutinsky's method. The single-particle (s.p.) energy levels are obtained from the diagonalization of the WoodsSaxon s.p. Hamiltonian in the deformed harmonic oscillator basis for both neutrons and protons. The residual pairing interaction is calculated by means of the usual BardeenCooperSchrieffer (BCS) approximation. A two-dimensional deformation space describing axially and reflection-symmetric shapes of nuclei has been used. Based on the shell and pairing correction energies, the signatures of the magic numbers appear at the spherical shell closures Z = 82, 114, 164 and N = 126, 184, 228 and 308. There are also signatures for some other shell closures at, e.g.