Saturation of the width of the giant dipole resonance at high temperature

Bracco, A.; Gaardhøje, J. J.; Bruce, A. M.; Garrett, J.D.; Herskind, B.; Pignanelli, M.; Barnéoud, D.; Nifenecker, H.; Pinston, J.A.; Ristori, C.; Schüßler, F.; Bacelar, J. C. S.; Hofmann, Helmut

doi:10.1103/physrevlett.62.2080

Cited by 137 publications

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“…In particular Giant Resonances have been observed in hot nuclei formed by fusion [13,14]. This demonstrates the survival of ordered vibrations in very excited systems, which are known to be chaotic, even if some Giant Resonance characteristics like the width are affected by the temperature [15,16]. Moreover, the strong couplings between various collective modes which occur for Giant Resonances built on the ground state [17,18] are still present in fusion reactions [10,19].…”

Section: Introductionmentioning

confidence: 99%

Fusion process studied with a preequilibrium giant dipole resonance in time-dependent Hartree-Fock theory

2007

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The equilibration of macroscopic degrees of freedom during the fusion of heavy nuclei, like the charge and the shape, are studied in the Time-Dependent Hartree-Fock theory. The preequilibrium Giant Dipole Resonance (GDR) is used to probe the fusion path. It is shown that such isovector collective state is excited in N/Z asymmetric fusion and to a less extent in mass asymmetric systems. The characteristics of this GDR are governed by the structure of the fused system in its preequilibrium phase, like its deformation, rotation and vibration. In particular, we show that a lowering of the preequilibrium GDR energy is expected as compared to the statistical one. Revisiting experimental data, we extract an evidence of this lowering for the first time. We also quantify the fusion-evaporation enhancement due to γ-ray emission from the preequilibrium GDR. This cooling mechanism along the fusion path may be suitable to synthesize in the future super heavy elements using radioactive beams with strong N/Z asymmetries in the entrance channel.

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Section: Introductionmentioning

confidence: 99%

Fusion process studied with a preequilibrium giant dipole resonance in time-dependent Hartree-Fock theory

2007

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“…To improve the sensitivity of such experiments to the fusion-evaporation reaction channel, typical gates such as, e.g., γ-multiplicity filters [17], detection of heavy evaporation residues [18], and detection of evaporated, light charged particles such as protons or α particles [19] can be performed. The resulting γ-ray spectra are more exclusive, not only in terms of the product nuclei from which high-energy γ rays are emitted, but also in terms of the spin and the excitation-energy range investigated.…”

Section: Experimental Techniquesmentioning

confidence: 99%

Compilation of giant electric dipole resonances built on excited states

Schiller

Thoennessen

2007

Atomic Data and Nuclear Data Tables

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“…The general way to excite such modes is to use rapidly varying electromagnetic fields associated with photons or generated by fast electrically charged particles. The collective vibrations can also be thermally excited as it was clearly demonstrated in the studies of the γ -emission from hot nuclei [3][4][5][6]. It has been recently proposed that fusion reactions with N/Z asymmetric nuclei may lead to the excitation of a dipole mode because of the presence of a net dipole moment in the entrance channel [7][8][9].…”

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Quantum Calculation of the Dipole Excitation in Fusion Reactions

2001

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The excitation of the giant dipole resonance induced by fusion reaction is studied with N/Z asymmetry in the entrance channel. The Time Dependant Hartree Fock solution exhibits a strong dipole vibration which can be associated to a giant vibration along the main axis of the deformed compound nucleus. This dipole motion appears to be non linearly coupled to the shape oscillation leading to a strong modulation of its frequency. These phenomenons can be detected in the gamma-ray emission from hot compound nuclei.Ordered collective motions are a general property of mesoscopic systems. In metallic clusters, electron vibrations are plasmon excitations. In atomic nuclei, oscillations of protons against neutrons generate giant dipole resonances [1,2]. The general way to excite such modes is to use rapidly varying electromagnetic fields associated with photons or generated by fast electrically charged particles. The collective vibrations can also be thermally excited as it was clearly demonstrated in the studies of the γ -emission from hot nuclei [3][4][5][6]. It has been recently proposed that fusion reactions with N/Z asymmetric nuclei may lead to the excitation of a dipole mode because of the presence of a net dipole moment in the entrance channel [7][8][9]. The first experimental indications on the possible existence of such new phenomenon have been reported in [10] for fusion reactions and in [11] for deep inelastic collisions. However, the real nature of such a vibration is still unclear both from the experimental and the theoretical point of view. In particular only semiclassical approaches or schematic models have been used to infer the properties of the generated dipole mode.In this letter, we present the first quantum calculation of pre-equilibrium giant collective vibrations using the time dependent Hartree Fock (TDHF) approach [12][13][14][15]17]. TDHF corresponds to an independent propagation of each single particle wave function in the mean field generated by the ensemble of particles. It does not incorporate the dissipation due to two-body interaction [19][20][21], but takes into account one body mechanisms such as Landau spreading and evaporation damping [22]. The quantal nature of the single particle dynamics is explicitely preserved, which is crucial at low energy both because of shell effects and of the wave dynamics. Moreover TDHF is a strongly non linear theory. Hence it can exhibit new couplings between collective modes.In the time dependent Hartree-Fock (TDHF) approach, the evolution of the single particle density matrix ρ(t) = N n=1 |ϕ n ϕ n | is determined by a Liouville equation,where h(ρ) is the mean-field Hamiltonian. We have used the code built by P. Bonche and coworkers with an effective Skyrme mean-field and SLy 4 parameters [23]. The effect of the isospin asymmmetry in the entrance channel has been first studied in the 20 O + 20 M g fusion reactions at energies close to the Coulomb barrier. Strong quantum effects are expected in these mirror-nuclei reactions leading to the N=Z 40 Ca compou...

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Saturation of the width of the giant dipole resonance at high temperature

Cited by 137 publications

References 14 publications

Fusion process studied with a preequilibrium giant dipole resonance in time-dependent Hartree-Fock theory

Fusion process studied with a preequilibrium giant dipole resonance in time-dependent Hartree-Fock theory

Compilation of giant electric dipole resonances built on excited states

Quantum Calculation of the Dipole Excitation in Fusion Reactions

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