Microscopic description of the low lying and high lying electric dipole strength in stable Ca isotopes

Tertychny, G.; Tselyaev, V.; Kamerdzhiev, S. P.; Grümmer, F.; Krewald, S.; Speth, J.; Авдеенков, А. В.; Литвинова, Елена

doi:10.1016/j.physletb.2007.01.069

Cited by 23 publications

(19 citation statements)

References 26 publications

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“…In particular, the coupling to lowlying vibrations is known already for decades [23] as a very important mechanism of the formation of nuclear excited states and serves as a foundation for the so-called (quasi)particle-phonon coupling model. Implementations of this concept on the base of the modern density functionals have been extensively elaborated in non-relativistic [32,[52][53][54][55][56][57] and relativistic [45-51, 58, 59] frameworks.…”

Section: Relativistic Quasiparticle Time Blocking Approximation: mentioning

confidence: 99%

Nuclear response theory with multiphonon coupling in a covariant framework

Литвинова¹

2015

Phys. Rev. C

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Background: Nuclear excited states within a wide range of excitation energies are formally described by the linear response theory. Besides its conventional formulation within the quasiparticle random phase approximation (QRPA) representing excited states as two correlated quasiparticles (2q), there exist extensions for 4q configurations. Such extended approaches are quite successful in the description of gross properties of nuclear spectra, however, accounting for many of their fine features requires further extension of the configuration space. Purpose: This work aims at the development of an approach which is capable of such an extension as well as of reproducing and predicting fine spectral properties, which are of special interest at low energies. Method: The method is based on the covariant density functional theory and time blocking approximation, which is extended for couplings between quasiparticles and multiphonon excitations. Results: The covariant multiphonon response theory is developed and adopted for nuclear structure calculations in medium-mass and heavy nuclei. The equations are formulated in both general and coupled forms in the spherical basis. Conclusions: The developed covariant multiphonon response theory represents a new generation of the approaches to nuclear response, which aims at a unified description of both high-frequency collective states and low-energy spectroscopy in medium-mass and heavy nuclei.

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Section: Relativistic Quasiparticle Time Blocking Approximation: mentioning

confidence: 99%

Nuclear response theory with multiphonon coupling in a covariant framework

Литвинова¹

2015

Phys. Rev. C

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“…[18,19,25] and references therein) and theoretical (see Refs. [5][6][7]21,[26][27][28] and references therein) studies. Even if the total E1 strength of the PDR is small, if it is located well below the neutron separation energy, it can significantly increase the radiative neutron capture cross section, especially for neutron-rich nuclei [14,15,23].…”

Section: Introductionmentioning

confidence: 99%

Self-consistent calculations of the strength function and radiative neutron capture cross section for stable and unstable tin isotopes

Авдеенков

Goriely²,

Kamerdzhiev

et al. 2011

Phys. Rev. C

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The E1 strength function for 15 stable and unstable Sn even-even isotopes from A = 100 to A = 176 are calculated using a self-consistent microscopic theory which, in addition to the standard (quasiparticle) randomphase approximation [(Q)RPA] approach, takes into account phonon coupling and the single-particle continuum (by means of the discretization procedure) with a cutoff of 100 MeV. Our analysis shows two distinct regions for which the integral characteristics of both the giant and pygmy resonances behave rather differently. For neutron-rich nuclei, starting from 132 Sn, we obtain a giant E1 resonance which significantly deviates from the widely used systematics extrapolated from experimental data in the β-stability valley. We show that the inclusion of phonon coupling is necessary for a proper description of the low-energy pygmy resonances and the corresponding transition densities for A < 132 nuclei, while in the A > 132 region the influence of phonon coupling is significantly smaller. The radiative neutron capture cross sections leading to the stable 124 Sn and unstable 132 Sn and 150 Sn nuclei are calculated with both the (Q)RPA and the beyond-(Q)RPA strength functions and shown to be sensitive to both the predicted low-lying strength and the phonon-coupling contribution. The comparison with the widely used phenomenological generalized Lorentzian approach shows considerable differences both for the strength function and the radiative neutron capture cross section. In particular, for the neutron-rich 150 Sn, the reaction cross section is found to be increased by a factor greater than 20. We conclude that the present approach may provide a complete and coherent description of the γ -ray-strength function for astrophysics applications. In particular, such calculations are highly recommended for a reliable estimate of the electromagnetic properties of exotic nuclei.

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“…In hydrodynamic and collective approaches, it was suggested that an oscillation of a small portion of neutron-rich nuclear matter relative to the rest of the nucleus is responsible for the generation of pygmy resonances [11,12]. Further, in microscopic models based on the quasiparticle-random-phase approximation, relativistic (RQRPA) and nonrelativistic (QRPA), the position and the distribution of the PDR have been investigated [13][14][15][16]. From the analysis of transition densities, the unique behavior of the PDR mode is revealed, making it distinct from the well-known giant dipole resonance (GDR) [17].…”

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confidence: 99%

Spectral Structure of the Pygmy Dipole Resonance

et al. 2010

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High-sensitivity studies of E1 and M1 transitions observed in the reaction 138 Bað; 0 Þ at energies below the one-neutron separation energy have been performed using the nearly monoenergetic and 100% linearly polarized photon beams of the HIS facility. The electric dipole character of the so-called ''pygmy'' dipole resonance was experimentally verified for excitations from 4.0 to 8.6 MeV. The fine structure of the M1 ''spin-flip'' mode was observed for the first time in N ¼ 82 nuclei. DOI: 10.1103/PhysRevLett.104.072501 PACS numbers: 21.10.Hw, 21.60.Àn, 23.20.En, 24.70.+s In stable and unstable neutron-rich nuclei a resonancelike concentration of dipole strength is observed at excitation energies around the neutron-separation energy [1][2][3][4][5][6][7][8][9][10]. This clustering of strong dipole transitions has been named the pygmy dipole resonance (PDR). In hydrodynamic and collective approaches, it was suggested that an oscillation of a small portion of neutron-rich nuclear matter relative to the rest of the nucleus is responsible for the generation of pygmy resonances [11,12]. Further, in microscopic models based on the quasiparticle-random-phase approximation, relativistic (RQRPA) and nonrelativistic (QRPA), the position and the distribution of the PDR have been investigated [13][14][15][16]. From the analysis of transition densities, the unique behavior of the PDR mode is revealed, making it distinct from the well-known giant dipole resonance (GDR) [17]. The systematic studies of the PDR over isotonic and isotopic chains of nuclei indicate a correlation between the observed total BðE1Þ strength of the PDR and the neutron-to-proton ratio N=Z [5,8,14,15]. In addition, it has been suggested that the PDR is independent of the type of nucleon excess (neutron or proton) [13,15].The existence of the PDR mode near the neutron threshold has also important astrophysical implications. For example, the reaction rate of the (, n) and (n, ) reactions in explosive nucleosynthesis of certain neutron deficient heavy nuclei may be significantly enhanced by the PDR [18]. Furthermore, for very neutron-rich exotic nuclei, the PDR is an important topic of study at the new generation of radioactive ion beam facilities [19].In many cases the interpretation of the PDR excitation is based on the assumption of negative parity for the majority of the J ¼ 1 states. However, there has not been a systematic experimental verification that all the dipole states observed in the entire PDR region are indeed 1 À states. The parity was measured directly in certain energy intervals, e.g., off-axis bremsstrahlung or Compton polarimetry [20]. The advantage of using 100% linearly polarized photon beams for parity identification has been recently demonstrated [21][22][23][24], which opens new opportunities for unveiling the character of the nuclear dipole response.On the other hand, in heavy mass nuclei there should be M1 strength located in the same excitation energy region as the PDR, i.e., in the low-energy tail of the GDR [17]. A major ex...

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Microscopic description of the low lying and high lying electric dipole strength in stable Ca isotopes

Cited by 23 publications

References 26 publications

Nuclear response theory with multiphonon coupling in a covariant framework

Nuclear response theory with multiphonon coupling in a covariant framework

Self-consistent calculations of the strength function and radiative neutron capture cross section for stable and unstable tin isotopes

Spectral Structure of the Pygmy Dipole Resonance

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