Properties Of Giant Dipole Resonance Research Articles

Finite-temperature calculation of the isovector giant dipole resonance in Sn120 using self-consistent inputs

Background: Although microscopic models are frequently used to investigate giant resonances built on the ground state of a nucleus, similar calculations at nonzero temperature are limited. Approaches based on the classical thermal shape-fluctuation model (TSFM) are often utilized to analyze the properties of giant dipole resonance at finite temperature. However, TSFM fails to predict the correct trend of resonance width over a wide range of temperature starting from zero.Purpose: To study the isovector giant dipole resonance (IVGDR) at finite temperature, we present an improved version of TSFM, where driving potential and IVGDR centroid energies are obtained self-consistently using the nuclear energy density functional formalism. The temperature dependence of IVGDR width in $^{120}\mathrm{Sn}$ is calculated to benchmark the proposed method.Method: Nuclear free energy surfaces and entropy surfaces are simulated at different temperatures for two different parametrizations of Skyrme energy density functionals. Moreover, IVGDR centroid energies are calculated by incorporating nuclear deformations extracted from the corresponding self-consistent densities. Subsequently, IVGDR widths are obtained within TSFM. Also, we demonstrate the role of pairing fluctuation in improving the low temperature behavior of IVGDR width.Result: We found good overall agreement of our results with the measured IVGDR widths. Specifically, except at a very low temperature, unprecedented accuracy has been achieved in TSFM. Calculated IVGDR widths are shown to be robust against the choices of driving potential and Skyrme parametrization.Conclusion: The present paper provides guidance on using TSFM based calculations in predicting the IVGDR width over a broad range of temperature. For a more consistent calculation, pairing fluctuations are required to be included as additional degrees of freedom.

Properties of giant dipole resonances within an extended pairing model with a focus on spectral statistics

In this paper, we report on a study of the spectral features associated with dipole resonances in medium-mass nuclei $(E\ensuremath{\le}12 \mathrm{MeV})$, as revealed in the framework of the spd-interacting boson model. The effect of pairing correlations on the theory follows from solutions obtained through an application of the Bethe ansatz equation. In general, calculated spectra around the critical point of the vibrational to $\ensuremath{\gamma}$-soft transitions appear to approach those of a Gaussian orthogonal ensemble, while near the rotational and vibrational limits of the theory the spectra show more regular behavior. Specifically, the results reveal that the statistical features of the spectra are sensitive to the vector boson pairing strength ${c}_{p}$ in the transition region; that is, when ${c}_{p}$ is zero, or when the system approaches one of its dynamical symmetry limits, the spectra display regular features, while for stronger ${c}_{p}$ values, or when near to the critical phase transition region, the spectral features show more chaotic behavior. Overall, our results indicate that the statistical features are governed by the interplay between dipole resonant energies, pairing correlations, and interactions between and among the single and vector boson modes of the theory. As part of this work we also found out that chaoticity occurred when results were fit to a Berry-Robnik distribution. Throughout our analyses, we used experimentally known information about both positive- and negative-parity states. Our findings suggest that dipole resonances appear to be best-described by Poisson statistics for $A\ensuremath{\approx}32--138$ nuclei.

Giant Dipole Resonance of Nuclei with the Number of Nucleons 12–65

The properties of giant dipole resonance (GDR) of a large group of light atomic nuclei are analyzed. The analysis is based on the systematics of photoabsorption cross sections for 31 nuclei with 12 to 65 nucleons, created from experimental data available in the scientific literature. Such effects as configurational and isospin splitting of GDR are clearly manifested in the cross sections included in the systematics. These cross sections are recommended for testing modern theories of GDR.

Properties of giant dipole resonance and the elimination of center-of-mass motion

The accuracy of eliminating the spurious state from the E1-transition strength distribution is investigated within the random-phase approximation with separabelized Skyrme forces. The E1-transition strength distribution in 132Sn is considered as an example.

Excitation of multiple giant dipole resonances: from spherical to deformed nuclei

The effect of deformation on the excitation of multiple giant dipole resonances is studied. Analytical expressions are derived in the framework of the interacting boson model for the energies and E1 properties of giant dipole resonances in spherical and deformed nuclei, and a numerical treatment of transitional nuclei is proposed. Coulomb-excitation cross sections are calculated in 238 U and in the samarium isotopes.

Pre-equilibrium effects on properties of hot giant dipole resonances

In this article we analyse how the presence of a pre-equilibrium dipole strength can affect the properties of the giant dipole resonance (GDR) built on hot nuclei. We show that a little amount of GDR phonons still excited when the compound nucleus is formed will substantially modify the γ-decay from the giant resonance region. Also on the basis of microscopic calculations of the reaction dynamics we propose to study the effect of the N over Z ratio in the entrance channel. This analysis could bring independent information on the problem of the GDR disappearing at high excitation energy.

Finite Temperature Giant Resonances

The properties of Giant Dipole Resonances (GDR) built on excited nuclear states are sensitive to the structure of heated and rotating nuclei. Experiments measuring the spectral and strength distribution of the high energy gamma rays emitted in the decay of excited state GDR's can thus provide information on the deformations and fluctuations of the shapes of hot rotating nuclei, and on the characteristics and limits of collective motion at high temperatures.

GIANT RESONANCES BUILT ON HIGHLY EXCITED STATES

The properties of giant dipole resonances built on excited nuclear states are reviewed, with emphasis on recent results. Nonstatistical (p,γ) reactions in light nuclei, and statistical complex-particle reactions in light and heavy nuclei are discussed.