Nguyen Dinh Dang

Damping of isovector giant dipole resonances in hot even-even spherical nuclei

Abstract An approach based on the finite temperature quasiparticle phonon nuclear model (FT-QPNM) with the couplings to (2p2h) states at finite temperature taken into account is suggested for calculations of the damping of giant multipole resonances in hot even-even spherical nuclei. The strength functions for the isovector giant dipole resonance (IV-GDR) are calculated in 58 Ni and 90 Zr for a range of temperatures up to 3 MeV. The results show that the contribution of the interactions with (2p2h) configurations to the IV-GDR spreading width changes weakly with varying temperature. The IV-GDR centroid energy decreases slightly with increasing temperature. The nonvanishing superfluid pairing gap due to thermal fluctuations is included.

Modified Hartree-Fock-Bogoliubov at finite temperature

The modified HFB (MHFB) theory at finite temperature is derived, which conserves the unitarity relation of the particle-density matrix. This is achieved by constructing a modified quasiparticle-density matrix, where the fluctuation of the quasiparticle number is microscopically built in. This matrix can be directly obtained from the usual quasiparticle-density matrix by applying the secondary Bogoliubov transformation, which includes the quasiparticle occupation number. It is shown that, in the limit of constant pairing parameter, the MHFB theory yields the previously obtained modified BCS (MBCS) equations. It is also proved that the modified quasiparticle RPA, which is based on the MBCS quasiparticle excitations, conserves the Ikeda sum rule. The numerical calculations of the pairing gap, heat capacity, level density, and level density parameter within the MBCS theory are carried out for

Temperature dependence of quantal and thermal dampings of the hot giant dipole resonance

^{120}

Study of the Gamow-Teller resonance in 90Nb and 208Bi

Sn. The results show that the superfluid - normal phase transition is completely washed out. The applicability of the MBCS up to a temperature as high as

Transversal E1-Resonance in Spherical Nuclei

T\sim

Damping of multiphonon giant resonances

5 MeV is analyzed in detail.

Influence of particle number fluctuations and vibrational modes on thermodynamic characteristics of a hot nucleus

Abstract A systematic study of the damping of the giant dipole resonance (GDR) in 90 Zr, 120 Sn and 208 Pb as a function of temperature T is performed. The double-time Green function technique is employed to determine the single-particle and GDR dampings. The single-particle energies, obtained in the Woods-Saxon potential for these nuclei, are used in the calculations. The results show that the coupling of collective vibration to the pp and hh excitations, which causes the thermal damping width, is responsible for the enlargement of the total width with increasing temperature up to T ≈ 3MeV and its saturation at higher temperatures. The quantal width, which arises from the coupling of the collective mode to the ph excitations decreases slowly with increasing temperature. The effect of single-particle damping on the GDR width is small. The results are found in an overall agreement with the experimental data for the GDR width, obtained in the inelastic α scattering and heavy-ion fusion reactions at excitation energies E * ⩽ 450 MeV. At high excitation energies ( E * > 400 MeV) a behavior similar to the transition from zero to ordinary sounds is observed.

Comment on “Test of the modified BCS model at finite temperature”

An approach is proposed for studying the spreading properties of the Gamow-Teller resonance (GTR) in heavy nuclei including the coupling to 2p2h configurations and the ground-state correlations beyond RPA. The GTR is generated by a proton p-neutron h (Trp-~h) phonon within the renormalized RPA. The second-order configuration mixing beyond RPA is realized by constructing two-phonon configurations, in which one of two intermediate phonon states is a ~rp-eh phonon. The numerical calculations are performed in the parent nuclei 9°Zr and 2°sPb making use of M3Y nucleon-nucleon interaction and the single-particle wave functions obtained in the standard harmonic oscillator potential. The single-particle energies around the Fermi surface are substituted with the empirical values or those given by a Woods-Saxon potential. The results obtained provide a reasonable account for recent experimental findings on the GTR in these nuclei. The extension of the present approach to highly excited (hot) nuclei is also provided. The GTR is found to be stable against temperatures up to T = 6 MeV. @ 1997 Elsevier Science B.V.

Particle-number conservation within self-consistent random-phase approximation

where ~b‘), K\’) and K

Thermal quasiparticle correlations and continuum coupling in nuclei far from stability

“), K:”) are the isoscalar and isovector The spin-flip El-states in medium and heavy spherical nuclei are investigated within the q;iasiparticlephonon nuclear model. The RPA-calculations predict the existence of a collective 1-state formed by the isovector spin-dipole force. Its excitation energy is about 20MeV. This state is intensively excited by the inelastic electron scattering at momentum transferred q = 0.5-0.7 fm-’, at the scattering angles 0 > 60’ the main contribution to its excitation comes from the transversal form factor. Therefore, it can be recognized as the transversal Elresonance. The interaction with two-phonon states causes a very strong spreading of the resonance, thus making its experimental observation hardly probable.