Pygmy dipole resonance in
stable nuclei
P VON NEUMANN-COSEL
Institut für Kernphysik,
Technische
E-mail: vnc@ikp.tu-darmstadt.de
Abstract. Two
examples of recent work on the structure of low-energy
electric dipole modes are
presented. The first part discusses the
systematics
of the pygmy dipole resonance (PDR) in stable tin
isotopes deduced from
high-resolution ($\gamma,\gamma'$)
experiments. These help to
distinguish between microscopic QRPA
calculations based on either a
relativistic or a non-relativistic
mean-field description, predicting
significantly different
properties of the PDR. The second
part presents a novel approach to
measure the complete electric
dipole strength distribution from
excitation energies starting at
about 5 MeV across the giant dipole
resonance (GDR) with
high-resolution inelastic proton scattering
under $0^\circ$ at energies of a
few 100 MeV/nucleon. The case of
$^{208}$Pb
is discussed in detail and first result from a recent
experiment on $^{120}$Sn is presented.
Keywords. $^{112,120}$Sn$(\gamma,\gamma')$; deduced systematics
of
the pygmy dipole resonance in
$^{112-124}$Sn; $^{120}$Sn;
$^{208}$Pb($\vec{p},\vec{p}\,'$) at $0^\circ$;
deduced complete
$B(E1)$ strength.
PACS Nos 24.30.Gd; 25.20.Dc; 21.60.Jz; 27.60.+j