Spectral structure of the pygmy dipole resonance.

Duke University, Durham, North Carolina 27708-0308, USA.
Physical Review Letters (Impact Factor: 7.73). 02/2010; 104(7):072501. DOI: 10.1103/PHYSREVLETT.104.072501
Source: PubMed

ABSTRACT High-sensitivity studies of E1 and M1 transitions observed in the reaction 138Ba(gamma,gamma{'}) at energies below the one-neutron separation energy have been performed using the nearly monoenergetic and 100% linearly polarized photon beams of the HIgammaS 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=82 nuclei.

1 Bookmark
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effect of a neutron skin on the collective states of medium and heavy-mass nuclei is discussed. We consider two well-known collective modes which correspond to the motion of neutrons with respect to protons, namely, the {ital M}1 (scissors) and the isovector {ital E}1 (giant dipole) resonance. For nuclei with a sufficient excess of neutrons the behavior of the pygmy resonance'' is also discussed.
    Physical Review C 02/1992; 45(1):R13-R16. · 3.72 Impact Factor
  • Source
    Physical Review Letters 95(13):132501. · 7.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We review recent studies of the evolution of collective excitations in atomic nuclei far from the valley of $\beta$-stability. Collective degrees of freedom govern essential aspects of nuclear structure, and for several decades the study of collective modes such as rotations and vibrations has played a vital role in our understanding of complex properties of nuclei. The multipole response of unstable nuclei and the possible occurrence of new exotic modes of excitation in weakly-bound nuclear systems, present a rapidly growing field of research, but only few experimental studies of these phenomena have been reported so far. Valuable data on the evolution of the low-energy dipole response in unstable neutron-rich nuclei have been gathered in recent experiments, but the available information is not sufficient to determine the nature of observed excitations. Even in stable nuclei various modes of giant collective oscillations had been predicted by theory years before they were observed, and for that reason it is very important to perform detailed theoretical studies of the evolution of collective modes of excitation in nuclei far from stability. We therefore discuss the modern theoretical tools that have been developed in recent years for the description of collective excitations in weakly-bound nuclei. The review focuses on the applications of these models to studies of the evolution of low-energy dipole modes from stable nuclei to systems near the particle emission threshold, to analyses of various isoscalar modes, those for which data are already available, as well as those that could be observed in future experiments, to a description of charge-exchange modes and their evolution in neutron-rich nuclei, and to studies of the role of exotic low-energy modes in astrophysical processes. Comment: 123 pages, 59 figures, submitted to Reports on Progress in Physics
    Reports on Progress in Physics 01/2007; 70:691. · 13.23 Impact Factor

Full-text (2 Sources)

Available from
May 20, 2014