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

A systematic study of the damping of the giant dipole resonance (GDR) in ⁹⁰Zr, ¹²⁰Sn and ²⁰⁸Pb 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.     

The effect of p-h corrections on the proton pairing vibrations at Z=50

Recent experimental results from Cd(³He, n)Sn reactions on a variety of Cd targets indicate that the proton pairing vibration lies at an excitation energy nearly 2 MeV below the value suggested by binding energy systematics. It is shown here that this large discrepancy, which is in contrast to the case of neutron pairing vibrations, may be explained by the effects of particle-hole (p-h) interactions which are large because of the Coulomb contribution. The p-h matrix elements are obtained empirically from observed p-h separations and also calculated theoretically for both Coulomb and nuclear contributions. These average empirical matrix elements from the Cd experiments give excellent agreement to the 2p-1h states in the ¹¹⁵In(³He, n) experiment populated via L=0 transfers. The agreement in the latter case indicates a simple scaling of the interaction with the number of particles and holes.     

Dynamics of single-particle and collective excitations in heavy nuclei

The propagation of single-particle and small-amplitude collective excitations in a heavy nucleus is considered. We calculate perturbatively corrections to the mean-field approximation induced by the coupling of one-particle and collective motion via the residual particle-hole interaction. Special attention is paid to the energy variation of the quasiparticle effective mass near Fermi energy. We conclude from the calculation that particles and holes excited in low multipolarity giant resonances have average effective masses of the order of 0.8 m rather than m. The mechanism for the decrease is provided by the enforced decoupling of the quasiparticles from surface oscillations due to the high frequency of the giant resonances. We also study the role of surface modes in the decay of giant resonances. Considerable reduction of the damping into 2p-2h states expected from the absorptive part of the optical potential is found. The correlated particle-hole pairs interact with each other by exchanging surface oscillations which adds a destructive interference term to the decay widths of giant resonances. The reduction depends on the multipolarity of the mode and is only large for low angular momenta.     

States of intermediate charge symmetry as low-lying, 0 collective excitations of medium weight nuclei

A method for calculating the states of the charge-independent pairing hamiltonian that have intermediate charge symmetry is presented. The states are shown to be collective 0⁺ excitations with energies that fall well within the gap in the single-particle spectrum.     

Influence of a dynamical coupling between single particle and collective states on the density distribution of the breathing mode

The effects of a dynamical effective mass in the unperturbed p-h spectrum fof the breathing mode are discussed. Consequences on the transition density of ²⁰⁸Pb are investigated and related to the inelastic scattering cross sections for high energetic α-particles and electrons.     

Collective coordinates in Fermi systems

The problem of developing a consistent perturbation theory for a Fermi system in the case in which the unperturbed system exhibits dynamical symmetry breaking is discussed, by using collective coordinate methods. By adapting to this problem the methods used in the quantization of gauge theories, it is shown how to deal with composite zero-frequency excitations in such a way that the resulting perturbation theory is free of infrared divergencies. Explicit calculations are carried out in the case of a simple quantum mechanical model representing a superfluid Fermi system.     

Description of isovector giant dipole resonances in relativistic Vlasov equation at small amplitude limit

A more general relativistic Vlasov equation has been derived in the framework of relativistic quantum hadron dynamical theory. In the small amplitude limit we use this Vlasov equation to study the isovector giant dipole resonances built on groundstate in spherical nuclei¹⁶O,⁴⁰Ca,⁹⁰Zn and²⁰⁸Pb. The results show that the spin-orbit coupling and the non-linear terms of scalar meson can influence the resonance energies to a certain extent comparing with those obtained from the non-relativistic Vlasov equation approach and are in good agreement with the experimental ones, especially for the case which vacuum fluctuation is included.     

Study of the giant dipole resonance of 232Th and 238U using elastic and raman photon scattering

Differential cross sections for elastic and Raman scattering of photons from ²³²Th and ²³⁸U targets were measured. Eight photon energies in the range 7.9–11.4 MeV were used and were obtained from thermal neutron capture in Fe, Cr, Cu and Ni. The angular distribution of the elastic and Raman scattered radiation from ²³²Th was measured. The results are compared with calculations of the simple rotator model and the dynamical collective model of the giant dipole resonance after incorporating the effect of Delbruck scattering.     

对关联对核基态和集体激发态性质的影响

基于相对论平均场和BCS理论,研究了共振连续对奇特核对关联性质的影响. 利用S矩阵方法，通过设定合理的散射态边界条件来得到单粒子共振态的能量和宽度. 通过引入连续态能级密度的方法来处理共振态宽度对核对关联的贡献. 计算结果显示合理地处理共振态对对关联性质的贡献在研究滴线附近核性质时很重要. 它可以影响中子的对隙、费米能级、对关联能以及总结合能. 其次,基于RMF+BCS基态,采用线性响应理论给出了描述开壳核集体激发态性质的准粒子相对论无规位相近似理论. 并且将该方法应用于开壳核120Sn的各种同位旋标量集体激发态性质的研究中. 研究表明：对关联对核的集体激发性质的影响主要表现在低能集体激发态上,考虑对关联后的相对论无规位相近似理论能够很好地再现低能集体激发的实验结果.     

Spin waves in Hubbard model

Gutzwiller's variational method has been used to study the spin waves in the ferromagnetic state of a narrow band. The spin wave energies are investigated in both the nondegenerate and the doubly degenerate bands. The electron correlation restricts the spin excitations and so improves the RPA solutions of the magnon energies. It is found that the bare intra-atomic interaction energies in the RPA solutions are replaced by smaller effective ones. In the case of a degenerate band model, contrary to the constant value as predicted by RPA, the Stoner gap parameter is reduced by the correlation effect.     

Relativistic Continuum Random Phase Approximation and Applications II. Applications

The fully consistent relativistic continuum random phase approximation （RCRPA） has been constructed in the momentum representation in the first part of this paper. In this part we describe the numerical details for solving the Bethe-Salpeter equation. The numerical results are checked by the inverse energy weighted sum rules in the isoscalar giant monopole resonance, which are obtained from the constraint relativistic mean field theory and also calculated with the integration of the RCRPA strengths. Good agreement between them is achieved. We study the effects of the self-consistency violation, particularly the currents and Coulomb interaction to various collective multipole excitations. Using the fully consistent RCRPA method, we investigate the properties of isoscalar and isovector collective multipole excitations for some stable and exotic from light to heavy nuclei. The properties of the resonances, such as the centroid energies and strength distributions are compared with the experimental data as well as with results calculated in other models.     

The role of collective inertias in heavy ion fusion

The role of collective inertias in determining the fusion excitation function for heavy ions is investigated. We use a generalized trajectory calculation which allows for a fully dynamical treatment of collective deformations. It is shown that for high bombarding energies, the cross section is sensitive to the choice of collective inertias. For comparison with experiment we chose the symmetric system ⁴⁰Ca+⁴⁰Ca.     

The level structures of the nuclei232Th and238U

Time-of-flight gating techniques have been used to study the decay γ-rays from states excited by inelastic scattering of neutrons from²³²Th and²³⁸U. Neutron energies up to 1900 MeV have been used. From accurate determinations of the γ-ray energies, intensities and thresholds, detailed level and decay schemes have been obtained for²³²Th and²³⁸U. New levels in both nuclei are observed at larger excitations than before and the present work is incompatible with some previously accepted spin and collective band assignments derived from Coulomb excitation studies.     

Dynamical instability of the XY spiral state of ferromagnetic condensates

We calculate the spectrum of collective excitations of the XY spiral state prepared adiabatically or suddenly from a uniform ferromagnetic F=1 condensate. For spiral wave vectors past a critical value, spin wave excitation energies become imaginary indicating a dynamical instability. We construct phase diagrams as functions of spiral wave vector and quadratic Zeeman energy.     

Anomaly of specific heat due to kinks

Finite temperature corrections to classical kink free energies for the sine-Gordon and ø⁴ chains are obtained analytically by means of the transfer integral method. These corrections reveal that kink excitations cause a Schottky-type anomaly of specific heat at low temperatures. The numerical results of Schneider and Stoll are explained qualitatively.     

Isospin symmetry and giant resonance in nuclei of mass number <Emphasis Type="Italic">A</Emphasis> = 14

An analysis of the cross sections for photon absorption by isobar nuclei ¹⁴C and ¹⁴N in the giant-dipole-resonance region demonstrates a high degree of isospin symmetry for this type of collective excitations in the above nuclei. Giant resonances in A = 14 isobar nuclei are related by a simple rescaling procedure that is based on the fact that, for these nuclei, the isospin remains a good quantum number in the process of dipole excitations of energy up to about 40 MeV. The features of the isospin splitting of the giant resonance in the ¹⁴C nucleus are refined. The shape of the cross section for photoabsorption in the ¹⁴C nucleus—in particular, a large width of the giant resonance in this nucleus—is exhaustively explained.     

Giant resonances on excited states

We derive modified RPA equations for small vibrations about excited states. The temperature dependence of collective excitations is examined. The formalism is applied to the ground state and the first excited state of ⁹⁰Zr in order to confirm a hypothesis which states that not only the ground state but every excited state of a nucleus has a giant resonance built upon it.