Low-lying dipole response in the stable {sup 40,48}Ca nuclei with the second random-phase approximation

Journal Article · Thu Sep 15 00:00:00 EDT 2011 · Physical Review. C, Nuclear Physics

DOI:https://doi.org/10.1103/PHYSREVC.84.034301· OSTI ID:21596732

Gambacurta, D ^[1]; Grasso, M ^[2]; Catara, F ^[1]

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1. Dipartimento di Fisica e Astronomia and INFN, Via Santa Sofia 64, I-95123 Catania (Italy)
2. Institut de Physique Nucleaire,Universite Paris-Sud, IN2P3-CNRS, F-91406 Orsay Cedex (France)

Low-energy dipole excitations are analyzed for the stable isotopes {sup 40}Ca and {sup 48}Ca in the framework of the Skyrme-second random-phase approximation. The corresponding random-phase approximation calculations provide a negligible strength distribution for both nuclei in the energy region from 5 to 10 MeV. The inclusion and the coupling of 2 particle-2 hole configurations in the second random-phase approximation lead to an appreciable dipole response at low energies for the neutron-rich nucleus {sup 48}Ca. The presence of a neutron skin in the nucleus {sup 48}Ca would suggest the interpretation of the low-lying response in terms of a pygmy excitation. The composition of the excitation modes (content of 1 particle-1 hole and 2 particle-2 hole configurations), their transition densities and their collectivity (number and coherence of the different contributions) are analyzed. This analysis indicates that, in general, these excitations cannot be clearly interpreted in terms of oscillations of the neutron skin against the core with the exception of the peak with the largest B(E1) value, which is located at 9.09 MeV. For this peak the neutron transition density dominates and the neutron and proton transition densities oscillate out of phase in the internal part of the nucleus leading to a strong mixing of isoscalar and isovector components. Therefore, this state shows some features usually associated to pygmy resonances.

• OSTI ID: 21596732
• Journal Information: Physical Review. C, Nuclear Physics, Vol. 84, Issue 3; Other Information: DOI: 10.1103/PhysRevC.84.034301; (c) 2011 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2813
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
CALCIUM 40
CALCIUM 48
COMPUTERIZED SIMULATION
COUPLING
DENSITY
DIPOLES
DISTRIBUTION
E1-TRANSITIONS
EXCITATION
INCLUSIONS
ISOVECTORS
MEV RANGE 01-10
MIXING
NEUTRON-RICH ISOTOPES
NEUTRONS
OSCILLATIONS
RANDOM PHASE APPROXIMATION
RESONANCE
SKYRME POTENTIAL
ALKALINE EARTH ISOTOPES
APPROXIMATIONS
BARYONS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CALCIUM ISOTOPES
CALCULATION METHODS
ELEMENTARY PARTICLES
ENERGY RANGE
ENERGY-LEVEL TRANSITIONS
EVEN-EVEN NUCLEI
FERMIONS
HADRONS
INTERMEDIATE MASS NUCLEI
ISOTOPES
LIGHT NUCLEI
MEV RANGE
MULTIPOLE TRANSITIONS
MULTIPOLES
NUCLEI
NUCLEON-NUCLEON POTENTIAL
NUCLEONS
PHYSICAL PROPERTIES
POTENTIALS
RADIOISOTOPES
SIMULATION
STABLE ISOTOPES
TENSORS
VECTORS