Mahmoud Yahia Ismail

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 energy dependence of the ion-ion reaction cross section has been investigated using the eikonal approximation to study the effects of the Pauli blocking and surface contribution to the optical potential. This leads to theoretical cross sections lower than the data. If the collective surface contribution is added to the volume part, one obtains reasonable agreement with experiment at higher energies.

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 real and imaginary parts of the optical model potential for several pairs of magic nuclei have been calculated by a double folding procedure. The complex effective interaction is calculated from the Reid soft core potential by solving the Bethe-Goldstone equation in two colliding nuclear matters. The calculated potentials were approximated with a Woods-Saxon shape. We studied the dependence of the parameters of these Woods-Saxon forms on the masses of the interacting nuclei. © 1984 Springer-Verlag.

The Coulomb and nuclear heavy ion (HI) potentials are derived for an interacting pair of deformed nuclei assuming sharp surface model for each nucleus. The orientation and separation dependences of the Coulomb and nuclear interactions are studied. It is assumed 238U + 238U as an example, and the effect of quadrupole term is investigated. For the nuclear potential part based on M3Y nucleonnucleon interaction, the sharp surface model shows much difference compared with the more accurate frequently used multipole expansion method while the success of this model in calculating the Coulomb potential between this deformed pair of nuclei exists in the physically important surface region. © 2010 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%.

The energy density method was employed to calculate the real part of the 40Ca-40Ca interaction potential in the sudden approximation. A simple effective two-body force as well as the Skyrme and Negele interactions were used to derive the energy density functional. The real part of the 40Ca-40Ca potential calculated using Negele's (1970) force agrees well with the experimental results.

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 azimuthal angle (φ) dependence of the Coulomb barrier parameters (height V b and position R b) are studied in the framework of the double-folding model with the realistic M3Y nucleon-nucleon interaction. Different pairs of axially symmetric, deformed nuclei are considered. For the interaction between medium and heavy nuclei, the maximum percentage of φ dependence is studied as a function of relative orientations of the interacting nuclei. It appreciably increases as the values of the deformation parameters increase and is sensitive to the hexadecapole deformation. The smallest φ variation is found for the relative orientations θ P= θ T=90. The φ variation of the Coulomb barrier parameters, as calculated in the present paper, is completely different in both magnitude and behavior from those deduced in the widely used proximity approach. © 2011 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 optical limit approximation to Glauber theory was used to calculate the reaction cross-section, σ R, for a deformed target nucleus. A method is presented to include both density dependence of NN reaction cross-section and higher order deformations of the target nucleus. We studied orientation, energy and deformation dependence of σ R for C 12-N 17 and C 12-U 238 interacting pairs. We found that the orientation dependence of σ R for the heavy target U 238 depends on the value and sign of hexadecapole deformation and it is more than 2.2 times compared to the light deformed target nucleus N 17. The presence of hexadecapole deformation does not affect the value of σ R averaged over all orientation of the target nucleus. A geometrical model was proposed to account for the orientation dependence of σ R. We found that the error in this model is less than 10%.

The authors have investigated proximity scaling for Pb+U and U+U potentials calculated recently from the collision of two infinite nuclear matters flowing through each other. They have found that the proximity theorem is satisfied to a good extent for the Pb+U system. for the U+U system a deviation between the proximity approach and the energy-density method has been found.

The effect of both rotation and vibration of a deformed target nucleus on the fusion cross-section and barrier distributions was studied. This was done in the framework of the microscopically derived heavy-ion (HI) potential. Moreover, the effect of target deformation up to β6 and the density dependence of the NN force on the fusion process was studied in the presence of vibrational excitations of the target. The results obtained were compared with experimental data.

The azimuthal angle variation of the Coulomb and nuclear heavy ion (HI) potentials is studied in the framework of the double folding model, which is derived from realistic nuclear density distributions and a nucleon-nucleon (NN) interaction. The present calculation shows that the variation of HI potentials with the azimuthal angle depends strongly on the range of the NN forces. For the long-range Coulomb force, the maximum variation with is about 0.9%, and for HI potential derived from zero-range NN interaction the variation can reach up to 90.0%. Our calculations are compared with the recent dependence of the HI potential derived from proximity method. The present realistic dependence calculations of the HI potential is completely different from the results of the proximity calculations. © 2007 The American Physical Society.

A simple density-dependent effective nucleon-nucleon interaction is used to show the effect of compressibility of nuclear matter on the real part of the n+ 40Ca optical-model potential. It is found that the half-strength radius of the optical-model real potential decreases as the compression of nuclear matter increases.