Search citation statements
Paper Sections
Citation Types
Year Published
Publication Types
Relationship
Authors
Journals
We consider the propagation and damping of isovector excitations in heated nuclear matter within the Landau Fermi-liquid theory. Results obtained for nuclear matter are applied to calculate the Giant Dipole Resonance (GDR) at finite temperature in heavy spherical nuclei within Steinwedel and Jensen model. The centroid energy of the GDR slightly decreases with increasing temperature and the width increases as T 2 for temperatures T < 5 MeV in agreement with recent experimental data for GDR in 208 Pb and 120 Sn.The validity of the method for other Fermi fluids is finally suggested.PACS numbers: 24.30. Cz, 21.60.Ev, 21.65.+f In recent years the GDR built on highly excited states is in the center of many experimental and theoretical studies (c.f. [1] and references therein). In this context, one of the most important open problems is the behaviour of the GDR width in nonrotating nuclei as a function of temperature. There are two essentially different theoretical approaches to this problem. The first one [2] explains the temperature increasing of the width as an effect of the adiabatic coupling of the GDR to thermal shape deformations. In the second approach [3,4,5] the thermal contribution to the damping width arises from 1 an increasing nucleon-nucleon collision rate (2p2h excitations) plus a Landau spreading due to thermally allowed ph transitions [6,7,8,9].In the present work, following the ideology of the second approach, we consider isovector volume vibrations in spin-isospin symmetrical nuclear matter at finite temperature. A similar problem was considered in Refs. [7,8] within the RPA method. However the Landau damping mechanism of the dissipation of a propagating mode due to thermal smearing of Fermi distribution is too weak to be responsible for the fast increase of the observed GDR width with temperature [7,8,11]. This problem can be solved by taking into account the two-body dissipation through the collision integral of the Landau-Vlasov equation [3]. The use of a quantum kinetic equation leads to memory effects in the collision term in order to include off energy-shell contributions [12]. Moreover it was shown in Refs. [13,14], that memory effects are essentially increasing the widths of multipole resonances at small temperatures. In this Rapid Communication we calculate the isovector strength function of nuclear matter taking into account both thermal Landau damping and two-body collisional dissipation, including the quantum memory contribution.The isovector response of uniform nuclear matter is described by the linearized Landau-Vlasov equation with a collision term treated in the relaxation time approximation [4,9,14] where δf ≡ δf n −δf p and δU ≡ δU n −δU p are differences between neutron and proton distribution functions (d.f.) and mean fields respectively, δV ≡ δV n − δV p is external field (δV q = τ q δV, τ n = +1,) is the equilibrium finite temperature Fermi distribution, and the notation l ≥ 1 means that the perturbation of the d.f. δf | l≥1 in collision integral includes only Fermi ...
We consider the propagation and damping of isovector excitations in heated nuclear matter within the Landau Fermi-liquid theory. Results obtained for nuclear matter are applied to calculate the Giant Dipole Resonance (GDR) at finite temperature in heavy spherical nuclei within Steinwedel and Jensen model. The centroid energy of the GDR slightly decreases with increasing temperature and the width increases as T 2 for temperatures T < 5 MeV in agreement with recent experimental data for GDR in 208 Pb and 120 Sn.The validity of the method for other Fermi fluids is finally suggested.PACS numbers: 24.30. Cz, 21.60.Ev, 21.65.+f In recent years the GDR built on highly excited states is in the center of many experimental and theoretical studies (c.f. [1] and references therein). In this context, one of the most important open problems is the behaviour of the GDR width in nonrotating nuclei as a function of temperature. There are two essentially different theoretical approaches to this problem. The first one [2] explains the temperature increasing of the width as an effect of the adiabatic coupling of the GDR to thermal shape deformations. In the second approach [3,4,5] the thermal contribution to the damping width arises from 1 an increasing nucleon-nucleon collision rate (2p2h excitations) plus a Landau spreading due to thermally allowed ph transitions [6,7,8,9].In the present work, following the ideology of the second approach, we consider isovector volume vibrations in spin-isospin symmetrical nuclear matter at finite temperature. A similar problem was considered in Refs. [7,8] within the RPA method. However the Landau damping mechanism of the dissipation of a propagating mode due to thermal smearing of Fermi distribution is too weak to be responsible for the fast increase of the observed GDR width with temperature [7,8,11]. This problem can be solved by taking into account the two-body dissipation through the collision integral of the Landau-Vlasov equation [3]. The use of a quantum kinetic equation leads to memory effects in the collision term in order to include off energy-shell contributions [12]. Moreover it was shown in Refs. [13,14], that memory effects are essentially increasing the widths of multipole resonances at small temperatures. In this Rapid Communication we calculate the isovector strength function of nuclear matter taking into account both thermal Landau damping and two-body collisional dissipation, including the quantum memory contribution.The isovector response of uniform nuclear matter is described by the linearized Landau-Vlasov equation with a collision term treated in the relaxation time approximation [4,9,14] where δf ≡ δf n −δf p and δU ≡ δU n −δU p are differences between neutron and proton distribution functions (d.f.) and mean fields respectively, δV ≡ δV n − δV p is external field (δV q = τ q δV, τ n = +1,) is the equilibrium finite temperature Fermi distribution, and the notation l ≥ 1 means that the perturbation of the d.f. δf | l≥1 in collision integral includes only Fermi ...
We investigate the collective response function and the energy-weighted sums (EWS) $m_k$ for isovector mode in hot nuclei. The approach is based on the collisional kinetic theory and takes into consideration the temperature and the relaxation effects. We have evaluated the temperature dependence of the adiabatic, $E_1=\sqrt{m_1/m_{-1}}$, and scaling, $E_3=\sqrt{m_3/m_1}$, energy centroids of the isovector giant dipole resonances (IVGDR). The centroid energy $E_3$ is significantly influenced by the Fermi surface distortion effects and, in contrast to the isoscalar mode, shows much weaker variation with temperature. Taking into account a connection between the isovector sound mode and the corresponding surface vibrations we have established the $A$-dependence of the IVGDR centroid energy which is in a good agreement with experimental data. We have shown that the enhancement factor for the "model independent" sum $m_1$ is only slightly sensitive to the temperature change.Comment: 28 pages, 8 figures, revised versio
Level density [Formula: see text] is derived within the micro-macroscopic approximation (MMA) for a system of strongly interacting Fermi particles with the energy E and additional integrals of motion Q, in line with several topics of the universal and fruitful activity of A. S. Davydov. Within the extended Thomas Fermi and semiclassical periodic orbit theory beyond the Fermi-gas saddle-point method, we obtain [Formula: see text], where Iν ( S) is the modified Bessel function of the entropy S. For small shell-structure contribution, one finds ν = κ/2 + 1, where κ is the number of additional integrals of motion. This integer number is a dimension of Q, Q = { N, Z, …} for the case of two-component atomic nuclei, where N and Z are the numbers of neutrons and protons, respectively. For much larger shell structure contributions, one obtains ν = κ /2 + 2. The MMA level density ρ reaches the well-known Fermi gas asymptote for large excitation energies and the finite micro-canonical combinatoric limit for low excitation energies. The additional integrals of motion can also be the projection of the angular momentum of a nuclear system for nuclear rotations of deformed nuclei, number of excitons for collective dynamics, and so on. Fitting the MMA total level density ρ( E, Q) for a set of the integrals of motion Q = { N, Z}, to experimental data on a long nuclear isotope chain for low excitation energies, one obtains the results for the inverse level-density parameter K, which differs significantly from those of neutron resonances due to shell, isotopic asymmetry, and pairing effects.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.