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FIZIKA B 20 (2011) 3, 203-222
 
INVESTIGATION OF DIPOLE EXCITATIONS BELOW THE GIANT DIPOLE RESONANCE
IN 89Y USING THE ELBE FACILITY
N. BENOUARETa,b, R. SCHWENGNERb, G. RUSEVb,d,
F. DÖNAUb, R. BEYERb, M. ERHARDb, E. GROSSEb,c,
A. R. JUNGHANSb, K. KOSEVb, C. NAIRb, K. D. SCHILLINGb
and A. WAGNERb
aFaculté de physique, Université des Sciences et de la Technologie d'Alger, Algerie
bInstitut für Strahlenphysik, Forschungszentrum Dresden-Rossendorf, Dresden, Germany
cInstitut für Kern-und Teilchenphysik, Technische Universität Dresden, Dresden, Germany
dPresent address: Department of Physics, Duke University, Triangle Universities Nuclear Laboratory, Durham, NC 27708, U. S. A.
Received 20 December 2010; Accepted 14 December 2011
Online 3 February 2012
We have investigated the dipole response of the stable N=50
nucleus 89Y up to the excitation energy of the giant dipole
resonance (GDR) using the bremsstrahlung facility at the ELBE
accelerator at the research center Dresden-Rossendorf. After
eliminating background radiation from atomic processes as well
as inelastic transitions in the spectra by using statistical
methods, the photoabsorption cross section could be deduced
from the photon-scattering data. This cross section was
combined with that known from (γ,n) experiments.
An excess of the cross section relative to a simple Lorentz
approximation of the tail of the GDR is found in the energy
range from about 6 MeV up to 11 MeV.
The comparison with predictions of a quasiparticle-random-phase
approximation (QRPA) showed that the corresponding excitations
may be caused by an oscillation of the excessive neutrons
forming a so-called pygmy dipole resonance (PDR) as it was
found for the neighbouring isotones 88Sr and 90Zr.
PACS numbers: 25.20.Dc, 23.20.-g
UDC 539.143, 539.166
Keywords: photon scattering, dipole resonances in 89Y,
up to giant dipole resonance, quasiparticle-random-phase approximation, pygmy dipole resonances
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