Large-scale continuum random-phase approximation predictions of dipole strength for astrophysical applications

Abstract

Large-scale calculations of the E1 strength are performed within the random phase approximation (RPA) based on the relativistic point-coupling mean field approach in order to derive the radiative neutron capture cross sections for all nuclei of astrophysical interest. While the coupling to the singleparticle continuum is taken into account in an explicit and self-consistent way, additional corrections like the coupling to complex configurations and the temperature and deformation effects are included in a phenomenological way to account for a complete description of the nuclear dynamical problem. It is shown that the resulting E1-strength function based on the PCF1 force is in close agreement with photoabsorption data as well as the available experimental E1 strength data at low energies. For neutron-rich nuclei, as well as light neutron-deficient nuclei, a low-lying so-called pygmy resonance is found systematically in the 5-10 MeV region. The corresponding strength can reach 10% of the giant dipole strength in the neutron-rich region and about 5% in the neutron-deficient region, and is found to be reduced in the vicinity of the shell closures. Finally, the neutron capture reaction rates of neutron-rich nuclei is found to be about 2-5 times larger than those predicted on the basis of the nonrelativistic RPA calculation and about a factor 50 larger than obtained with traditional Lorentzian-type approaches.

Symmetry energy in nuclear density functional theory

“…Other observables, such as Q α -values, δV pn , barrier heights, and low-energy dipole strength [14,59,60] are too strongly impacted by shell effects to be useful as global isovector indicators.…”

“…On the other hand, the low-energy E1 strength, sometimes referred to as the pygmy dipole strength, exhibits weak collectivity. The correlation between the accumulated low-energy strength and the symmetry energy is weak, and depends on the energy cutoff assumed [14,59,60].…”

Finite amplitude method applied to the giant dipole resonance in heavy rare-earth nuclei

“…For example, the centroid energy of GDR, which is well approximated as ω ∼ = 80A MeV for spherical nuclei, can be connected to the symmetry * tomohiro.t.oishi@jyu.fi energy in infinite nuclear matter, which is an important pseudoobservable used to determine the parameters of the nuclear energy density functional (EDF) [6,8,9]. The wide spread of the GDR in neutron-rich nuclei [10] has been understood to originate from the ground state deformation, which has been well reproduced with modern nuclear EDFs [11][12][13][14][15]. Also, the pairing part of the nuclear EDF has been expected to play a significant role in the low-lying dipole excitations of exotic nuclei [16][17][18][19][20].…”

Proton pygmy resonances: Predictions for N = 20 isotones

“…A Gogny-QRPA model preticts a collective low-lying proton excitation in 18 Ne [9]. Largescale continuum quasiparticle random-phase approximation (CQRPA) calculations predict up to five percentage points of the E1 energy-weighted sum to be exhausted by transitions below 10 MeV in various proton-rich nuclei [10]. Recent measurements in 32,34 Ar isotopes [11] will help assess some of the above predictions.…”