Generation of high-frequency components in TDHF heavy-ion collisions

TDHF modeling of the ⁴⁰Ca + ⁴⁰Ca scattering experiment at 400 MeV laboratory energy, at grazing impact parameters, has yielded evidence for relatively large collective excitations in the high-energy range where structures have been observed.     

Giant resonances in the fused system induced by 40Ca + 40Ca reactios

The giant quadrupole resonance of the fused system obtained in a ⁴⁰Ca + ⁴⁰Ca reaction is investigated in the framework of the TDHF approximation. A large splitting of the resonance due to the deformation of the composite system is observed. These results are confirmed by a direct fluid-dynamical calculation of the resonance. An estimation of the energy stored in the resonance is also presented.     

Angular momentum dependence of quasifission dynamics in the reaction <Superscript>48</Superscript>Ca+<Superscript>244</Superscript>Pu

The quasifission dynamics in the reaction ⁴⁸Ca+²⁴⁴Pu is investigated in the framework of time-dependent Hartree-Fock (TDHF) theory. The calculations are performed in three-dimensional Cartesian coordinate without any symmetry restrictions. The full Skyrme energy functional is incorporated in our TDHF implementation. The quasifission dynamics is quite sensitive to the angular momentum of colliding system. The contact time of quasifission decreases as a function of angular momentum and then forms a plateau with small oscillations. The quasifission process is accompanied by an important multi-nucleon transfer. The quantum shell effect plays a crucial role in the mass and charge of quasifission fragments. The mass-angle distribution of the fragments is calculated, which can be compared directly with future experiments.     

TDHF study of the He+ collision on atomic He targets at the8Be ground state energy

Experimentally the⁸Be ground state resonance has been studied in He⁺ collisions on atomic He atoms. The nuclear resonance manifests itself by satellite resonance lines corresponding to different electron configurations of the Be ion. Experimentally a large probability for the emission of one electron has been deduced. We study the atomic He⁺+He collision within a model in which the evolution of the electron wavefunction is treated dynamically in the TDHF scheme, and the motion of the nuclei is treated classically. In agreement with experiment we find a large probability for one electron to be emitted into the continuum during the lifetime of the⁸Be ground state resonance.     

A study of short-range correlation effects on nuclear spatial and momentum distribution

The relation between the nuclear spatial and momentum densities is studied by means of their integral representations in terms of uniform distributions. Examples of this approach are given for the harmonic oscillator model of⁴He and¹⁶O, with and without Jastrow correlations, and for the single-particle potential model of⁴⁰Ca.     

Nuclear giant resonances and linear response

We search for nonlinear effects in nuclear giant resonances (GRs), in particular the isovector dipole and the isoscalar quadrupole modes. To that end, we employ a spectral analysis of time-dependent Hartree-Fock (TDHF) dynamics using Skyrme forces. Based on TDHF calculations over a wide range of excitation amplitudes, we explore the collectivity and degree of harmonic motion in these modes. Both GR modes turn out to be highly harmonic in heavy nuclei from A = 100 on. There is no trace of a transition to irregular motion and multiple resonances are predicted. Slight anharmonicities are seen for light nuclei, particularly for ¹⁶O. These are mainly caused by the spin-orbit splitting.     

Isospin aspects in nuclear reactions involving Ca beams at 25 MeV/nucleon

Isospin dependence of dynamical and thermodynamical properties observed in reactions ⁴⁰Ca+ ^40,48Ca and ⁴⁰Ca + ⁴⁶Ti at 25 MeV/nucleon has been studied. We used the CHIMERA multi-detector array. Strong isospin effects are seen in the isotopic distributions of light nuclei and in the competition between different reaction mechanisms in semi-central collisions. We will show also preliminary results obtained in nuclear collision ⁴⁸Ca + ⁴⁸Ca at 25MeV/nucleon, having very high N/Z value in the entrance channel (N/Z = 1.4). The enhancement of evaporation residue production confirms the strong role played by the N/Z degree of freedom in nuclear dynamics.     

Preequilibrium nucleon jets in TDHF calculations of medium-energy,heavy-ion collisions

We study collisions of ¹²C and ¹⁹⁷Au projectiles at E_lab/A_proj = 30 to 85 MeV/A on ¹⁹⁷Au targets, using the 3-dimensional TDHF model. Most of the qualitative phenomena observed experimentally are reproduced by the TDHF calculations. The results are compared with recent data from the 1 GeV ¹²C beam at CERN and show some quantitative deviations from experiment. Possible reasons for these discrepancies are discussed and give valuable insight into intermediate energy collision processes.     

Directed and elliptic flows in 40Ca + 40Ca and 112Sn + 112Sn collisions

The directed and elliptic flows for different light particles and fragments in collisions of ⁴⁰Ca + ⁴⁰Ca and ¹¹²Sn + ¹¹²Sn at energies from 30MeV/nucleon to 100MeV/nucleon were studied in the isospin-dependent quantum molecule dynamics model (IQMD). With increasing incident energy, the directed flow rises from negative to positive, while the elliptic flow decreases with increasing the incident energies. The directed flow for the ⁴⁰Ca + ⁴⁰Ca system is not sensitive to the nuclear equation of states (EOS), but the directed flow for the ¹¹²Sn + ¹¹²Sn system is sensitive to the EOS. However, the elliptic flows for both ⁴⁰Ca + ⁴⁰Ca and ¹¹²Sn + ¹¹²Sn systems are not sensitive to EOS. A study of the dependence of directed and elliptic flows on the fragment charge (mass) is also performed. Received: 15 March 2002 / Accepted: 14 June 2002 / Published online: 19 November 2002 RID="a" ID="a"e-mail: Zhanghy@sinr.ac.cn; Permanent address: Shanghai Institute of Nuclear Research, Chinese Academy of Sciences, P.O. Box 800-204(2), Shanghai 201800, China. Communicated by W. Henning     

Pion-nucleus scattering and systematics of the delta-nucleus potential

A new calculational technique for the isobar-hole model is used to study pion elastic scattering from ¹⁶O, ²⁸Si, and ⁴⁰Ca. The central value of the Δ-nucleus interaction potential is found to be independent of nuclear mass number.     

The temperature dependence of the Hi optical potential

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 ⁴⁰Ca + ⁴⁰Ca and ²⁰⁸Pb + ²⁰⁸Pb. 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.     

Effect of residual interactions on nuclear level densities

We calculate the contribution of residual interactions to nuclear level densities in the framework of the random-phase approximation. We first investigate the case of the schematic model for which analytical formulae can be worked out. More realistic calculations are performed numerically for ⁴⁰Ca and ⁵⁶Ni using oscillator wave functions and a zero-range interaction. In ⁵⁶Ni it is found that residual interactions increase level densities significantly in the random-phase approximation, while small corrections are found in ⁴⁰Ca. A comparison with the results of second-order perturbation theory is presented.     

On the charge distribution of calcium nuclei

The mean square charge radii and the quadrupole moments of Ca nuclei are discussed in the light of theoretical predictions. The very peculiar dependence of the charge radii on the mass number between double magic⁴⁰Ca and double magic⁴⁸Ca can be ascribed to changes of the nuclear deformation, whereas the volume of the nuclear charge remains constant for all the Ca isotopes. Furthermore, correlations between nuclear charge radii and binding energies are discussed.     

Nuclear charge distribution of41Ca

The mean square nuclear charge radius of⁴¹Ca equals the one of double magic⁴⁰Ca within 0.006 fm.     

Microscopic analysis of the breathing mode in 40Ca and 58Ni

Recent experimental studies of the giant electric resonance region in ⁵⁸Ni and ⁴⁰Ca with inelastically scattered α-particles of energy E_α= 240 MeV are analyzed within a microscopic nuclear structure model. The model includes the continuum RPA and more complex 1p1h⊗phonon configurations. By superimposing the contributions of different multipoles up to L = 4 we obtain good agreement with the newest (reanalyzed) data for the isoscalar monopole strength and for the total (α,α′) cross section in ⁵⁸Ni. Agreement with experiment for the isoscalar monopole resonance in ⁴⁰Ca is obtained too. We emphasize the necessity of using microscopic transition densities and discuss consequences for the analyses of such experiments in light and medium mass nuclei. It is shown that the gross structure of the isoscalar monopole resonance in ⁴⁰Ca is caused by the 1p1h⊗phonon configurations. Received: 23 December 1999 / Revised version: 28 February 2000     

Time-dependent hartree-fock study of angular momentum transfer in 6 and 12 MeV/A heavy ion reactions of 86Kr on 166Er

Three-dimensional TDHF calculations are performed for ⁸⁶Kr+¹⁶⁶Er at 6 and 12.2 MeV/A from which we obtain Wilczynski plots and angular momentum loss curves versus incoming angular momentum. These compare well with recent experimental data from GSI and are consistent with the observed fast projectile fission at 12.2 MeV/A. Finite cross sections for capture as nuclear molecules are predicted.     

Dispersion of one-body operators with the Balian-Veneroni variational principle

Using the variational principle proposed by Balian and Veneroni we calculate the dispersion of several one-body observables. Within the Lipkin-Meshkov-Glick model, a comparison with exact results shows that a good agreement on the dispersion is obtained whenever the time-dependent Hartree-Fock (TDHF) method predicts accurately the expectation value of the observable. An application to the more realistic case of a three-dimensional collision of two ¹⁶O nuclei shows a significant increase of the dispersion in the number of transferred nucleons over a simple TDHF prediction.     

Elastic scattering of 32S on 24Mg, 27Al and 40Ca and the effect of nuclear forces on the grazing collision

Elastic scattering of ³²S ions on ²⁴Mg, ²⁷Al and ⁴⁰Ca has been measured at energies between 67 MeV and 120 MeV. Angular distributions were analyzed with the optical model with Woods-Saxon potentials. Strong absorption radii are extracted with and without consideration of the nuclear interaction at the surface. The nuclear potential decreases the otherwise anomalously large strong absorption radii which can then be described by a radius parameter of r₀ = 1.41 fm.