Mahmoud Yahia Ismail

We systematically investigated the behavior of the α-decay half-lives (Tα) for 20 isotopic chains of even–even nuclei, from 78Pt to 116Lv. Tα is calculated within the preformed cluster model. The α-core potential is determined by the double-folding model based on the M3Y-Reid nucleon–nucleon interaction. The Coulomb potential is also microscopically calculated by the folding procedure. To confirm our results, we used four different parameterizations of the involved proton and neutron densities, which are consistent with extensive microscopic calculations and electron scattering data. The results correlate the logTα behavior for the isotopes of an element with their proton energy levels. We found a clear similarity in the behavior of logTα with the number of neutrons of the daughter nuclei (Nd) for specific isotopic chains. The proton pairs forming the α-particles that emitted from the isotopes of the similar chains belong to the same proton energy level. We pointed out some neutron magic and semi-magic numbers corresponding to characteristic minima in the logTα variation with Nd. We interpreted these magic (semi-magic) numbers as the total number of neutrons filling the upper neutron level in the parent nucleus.

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 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..

In view of the role of nuclear deformations in the fusion between spherical and deformed nuclei to form super-heavy elements, we try to understand how a cancellation of the different nuclear deformations could arise. We first investigated the correlation between the orientation variation of the deformed nucleus radius and the orientation Coulomb barrier distribution in presence of the higher order deformation components, β 6 and β 8, in addition to the lower order ones. This correlation has been reported in our previous work (Ismail and Seif, 2010) [1] in presence of the lower order (β 2, β 3 and β 4) deformations. Even if there are higher deformations, we found here that the simple expression which describes the deformed target nucleus can be used to predict with good accuracy the behavior of the fusion Coulomb barrier with both orientation and deformation as well as the optimum (cold or hot) fusion configurations. It can predict the orientations of compact and elongated configurations of the interaction and whether they are equatorial or polar or none of them. The value and sign of the deformation parameters ratios with respect to one of them have been used to classify these configurations. We applied the same correlation to predict successfully the mutual cancellation effects between the different deformation components up to β 8. Illustrative examples are given in which the cancellation, at some orientations, brings the fusion barrier back to the spherical case or keeps only the effect of quadrupole deformation, or the effects of both β 2 and β 4. © 2011 Elsevier B.V.

A simple straightforward method has been presented to predict the dependence of barrier distributions at arbitrary orientations on different deformations. The proposed interpretation is developed independently of the complicated numerical calculations. It is related to the change of half-density radius of the deformed nucleus, in the direction of the separation vector. The microscopic calculations of Coulomb barrier are carried out by using a realistic density dependent nucleon-nucleon (NN) interaction, BDM3Y, for the interaction between spherical, Ca48, and deformed, Pu244, nuclei, as an example. To do so, the double-folding model for the interaction of spherical-deformed nuclei is put in a suitable computational form for the calculation of the potential at several separation distances and orientation angles using the density dependent NN force without consuming computational time. We found that the orientation distributions of the Coulomb barrier parameters show similar patterns to those of the interacting deformed nucleus radius. It is found that the orientation distribution of the Coulomb barrier radius follows the same variation of the deformed nucleus radius while the barrier height distribution follows it inversely. This correlation (anticorrelation) allows a simple evaluation of the orientation barrier distribution which would be very helpful to estimate when the barrier parameters will increase or decrease and at which orientations they will be independent of the deformation. This also allows us to estimate the compact and elongated configurations of the interacting nuclei which lead to hot and cold fusion, respectively. © 2010 The American Physical Society.

The effect of octupole deformation, β 3, and the higher multipole deformations, β 6 and β 8, on the distribution of barriers in orientation degrees of freedom, is studied. Coulomb barriers are derived in the frame work of the double folding model with the realistic M3Y nucleon-nucleon interaction and its density dependent version. 48Ca + 244Pu spherical-deformed nuclear interacting pair is considered, as an example, to study the effect of deformation parameters on the height and position of the Coulomb barrier. Although the dependence of the Coulomb barrier parameters on the higher deformations is complicated, numerically, if it is treated in microscopic way, we found a simple linear variation of barrier parameters with the different orders of deformation. We found that the variation of the barrier parameters with deformation exactly follows the change of the half density radius of the deformed nucleus in the direction of the separation vector between the centers of mass of the interacting nuclei. This suggests a simple and straightforward way to predict the behavior of the barrier parameters with different orders of deformations. We compared the results of present work with a similar recent study of the same quantities based on simple expression derived by Wong for the Coulomb part and proximity approach for the nuclear part of heavy ion potential, respectively. © 2009 Elsevier B.V. All rights reserved.

The interaction potential for a deformed-spherical pair of nuclei is calculated using the folding model derived from different range nucleon-nucleon (NN) interactions. Five spherical projectiles of different mass numbers scattered on the 238U deformed target are considered. The error in the heavy ion (HI) potential by using the truncated multipole density expansion is evaluated for each case. We find systematic trends of the percentage error in the HI potential depending on the number of multipoles considered; this percentage decreases if the mass number of the projectile or the range of the NN force increases, and it becomes smaller for small values of the separation distance between two nuclei or when higher deformation parameters vanish. The maximum error in using the truncated density expansion is estimated in the case of two deformed interacting nuclei. © 2008 IOP Publishing Ltd.

The Coulomb interaction for a spherical-deformed interacting pair is derived assuming realistic nuclear charge distributions. The effect of a finite diffuseness parameter is described either by the folding product of spherical or deformed sharp-surface distribution and a spherical short-range function or by using a Fermi two-parameter distribution function. The approximate solutions obtained using these categories of charge distributions are then compared to the numerical solution obtained within the framework of the double-folding model. We found that the finite surface diffuseness parameter affects slightly the inner region of the total Coulomb potential, while it produces large errors in calculating the Coulomb form factors used frequently in nuclear reactions and fusion numerical codes. © Nauka/Interperiodica 2006.

The deformation and orientation dependence of the real part of the interaction potential is studied for two heavy deformed nuclei using the Hamiltonian energy density approach derived from the well-known Skyrme NN interaction with two parameter sets SIII and SkM*. We studied the real part of the heavy ion (HI) potential for U238+U238 pair considering quadrupole and hexadecapole deformations in both nuclei and taking into consideration all the possible orientations, coplanar and noncoplanar, of the two interacting nuclei. We found strong orientation dependence for the physically significant region of the HI potential. The orientation dependence increases with adding the hexadecapole deformation. The azimuthal angle dependence is found to be strong for some orientations. This shows that taking the two system axes in one plane produces a large error in calculating the physical quantities. © 2005 The American Physical Society.

A method is described to calculate the heavy ion reaction cross section σ R when one of the two nuclei is deformed. This method is based on both the double folding model and the optical limit approximation to Glauber theory. Both finite range of the nucleon-nucleon (NN) interaction and in-medium effects of NN cross section are included. The interacting pair 12C -238U is taken to study orientation, energy, and deformation dependence of σ R. The finite range force increases the value of σ R by about 5%. In-medium NN cross section decreases σ R by about 1.9% compared to the free NN cross section.

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.

A method is presented to calculate the exact HI Coulomb potential between spherical and deformed nuclei in the framework of the double folding model. We used realistic density distributions taking the deformations of the target into account. We have compared between our calculations and one of the more recent analytical expressions based on assuming sharp surface of the interacting nuclei. We have found that the finite surface diffuseness affects strongly the HI Coulomb interaction in the inner region and has a smaller effect in the tail region. Moreover, neglecting non-linear higher order terms in the analytical expressions produces errors in the outer region of the Coulomb interaction. © 2003 Published by Elsevier Science B.V.

The interaction potential for a deformed-spherical pair is calculated, and the error in using the truncated multipole expansion is evaluated for different numbers of terms of the expansion considered. It was found for the internal region of the nuclear part that three terms are sufficient, but for the surface and tail region up to five terms are necessary, while for the Coulomb potential three terms were found to be sufficient.