M. Ismail

Photon production in heavy-ion collisions and nuclear equation of state

Abstract Photon-production cross sections in 12 C + 12 C, 40 Ca + 40 Ca and 93 Nb + 93 Nb collisions at E lab = 84 and 200 Me V are calculated within the framework of the quantum molecula dynamics approach. The sensitivity of the photon-production cross section to the different types of nuclear equation of state and the momentum dependence in the in-medium NN interaction is studied in detail. Although we found some difference between the soft and hard equation of state in the calculated photon-production cross section, it is suppressed strongly by the momentum dependence in the interaction. There is a sizeable difference between the results calculated with or without taking into account the momentum dependence in the in-medium interaction. The time dependence of the production of the high-energy photons arising from incoherent pn collisions is also studied. The heavier the masses of colliding nuclei, the more number of energetic photons are produced after the system reaches the maximum density, at the expansion stage. Therefore, the photon-production data for heavy colliding nuclei might provide sc me information on the in-medium NN interaction during the time evolution of the heavy-ion reaction.

Does photon production in heavy-ion collisions depend on the equation of state?

Photon production cross sections in 12C-12C and 40Ca-40Ca collisions at Elab=84 and 200 MeV/A are calculated in the framework of the quantum molecular dynamics approach using the medium-dependent NN cross section obtained from the G matrix. Photons are assumed to be produced by incoherent pn bremsstrahlung and a simple classical expression for the production cross section is used. The effects of the equation of state for nuclear matter on the photon production cross section are studied in detail. In the 12C-12C collision, the authors found little difference in the photon cross section due to differences in the equation of state both at 84 and 200 MeV/A. In the 40Ca-40Ca collision, slightly more high-energy photons are produced in the case of the soft equation of state and the difference is slightly larger at higher incident energies.

The temperature dependence of the Hi optical potential

Abstract Within a realistic effective nucleon-nucleon interaction, derived from the Reid soft-core potential at zero temperature, the dependence on temperature of the heavy ion optical potential is investigated for the systems 40 Ca + 40 Ca and 208 Pb + 208 Pb. The hot nuclear densities are generated using the Thomas-Fermi model at a finite temperature. It is found that both the real and the imaginary parts of the optical potential become more attractive and extend to large distances when the temperature increases. The barrier heights are lowered and shifted outwards.

Pockets in heavy ion potentials for the deformed systems Th + Ta, U + Th and Th + Th

Abstract Using a realistic nucleon-nucleon interaction the optical potentials for the strongly deformed systems Th + Ta, U + Th and Th + Th are calculated at Elab/A ≅ 6 MeV and for different orientations. Pockets exist in the total real potentials (nuclear plus Coulomb potentials) at surface contact. It has been found that the deepest pockets for the U + Th and Th + Th systems exist when the two colliding nuclei are touching with orientation angle β ≅ 45° while for the Th + Ta system the deepest pocket occurs at β = 90° (equator touching).

Relativistic effects on the optical potential of deformed U + U nuclei

Abstract The relativistic energy-density functional derived by Ohtsuka et al. from the Dirac-Brueckner approach to nuclear matter is applied to calculate a relativistic real and imaginary U + U potential. Comparison with non-relativistic calculations are presented and discussed. It was found that the relativistic effects change slightly the imaginary part while changes in the real part depend appreciably on the relative orientations of the two U-nuclei.

Effects of the Pauli blocking and surface contribution to the optical potential on the ion-ion reaction cross section

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.

The effect of nuclear and Coulomb interactions on the nuclear shapes of two colliding208Pb nuclei

Using a complex energy density functional derived from the Reid soft-core potential, the changes in nuclear shapes of two colliding208Pb are investigated. At each separation distanceR, the total binding energy of the Pb + Pb system is minimized w.r.t. the quadrupole deformation and diffuseness parameters of nuclear densities. It is found that the nuclear shapes are strongly affected by the nuclear and Coulomb interactions. A sudden transition occurs from oblate to prolate shapes around R16.8fm and a smooth one from prolate to oblate shapes aroundR≃11.76 fm.

Test of proximity theorem for the nucleus-nucleus potential derived from a realistic NN force

The authors investigate the proximity scaling for the nuclear part of the nucleus-nucleus potential derived from the collision of two infinite nuclear matters flowing through each other. It is found that the proximity theorem is satisfied to a good extent at each value of the projectile energy per nucleon. They simplify the interaction potential between different pairs of nuclei by the product of a geometrical factor, dependent on the radii of the interacting nuclei, and a gaussian distribution whose parameters depend on the projectile energy per nucleon.

The effect of deformation on the nucleus-nucleus optical model potential and how it produces pockets

A recently derived nucleon-nucleon interaction has been used to calculate both the real and imaginary parts of the optical-model potential for the two nuclear pairs Pb+U and U+U. Three different bombarding energies per projectile nucléon (6 MeV, 11.8 MeV and 20.9 MeV) have been considered. We found a dramatic dependence of both the real and imaginary parts of the optical-model potential on relative orientation of the colliding nuclei. For the two considered pairs we predicted pockets whose depths depend strongly on orientation.

Microscopic calculation of the interaction potential between two 12C nuclei

A microscopic calculation of the interaction potential between two 12C ions within the framework of the alpha -particle model has been performed under the assumption that the ground state of each 12C nucleus is a linear chain of three alpha clusters. The potential obtained has been compared with the phenomenological one of Satpathy and Faessler and the agreement between the two potentials is found to be quite good in the tail region.