Extended theory of finite Fermi systems: Application to the collective and noncollective E1 strength in {sup 208}Pb
Abstract
The Extended Theory of Finite Fermi Systems is based on the conventional LandauMigdal theory and includes the coupling to the lowlying phonons in a consistent way. The phonons give rise to a fragmentation of the singleparticle strength and to a compression of the singleparticle spectrum. Both effects are crucial for a quantitative understanding of nuclear structure properties. We demonstrate the effects on the electric dipole states in {sup 208}Pb (which possesses 50% more neutrons then protons) where we calculated the lowlying noncollective spectrum as well as the highlying collective resonances. Below 8 MeV, where one expects the socalled isovector pygmy resonances, we also find a strong admixture of isoscalar strength that comes from the coupling to the highlying isoscalar electric dipole resonance, which we obtain at about 22 MeV. The transition density of this resonance is very similar to the breathing mode, which we also calculated. We shall show that the extended theory is the correct approach for selfconsistent calculations, where one starts with effective Lagrangians and effective Hamiltonians, respectively, if one wishes to describe simultaneously collective and noncollective properties of the nuclear spectrum. In all cases for which experimental data exist the agreement with the present theory results ismore »
 Authors:
 Institut fuer Kernphysik, Forschungszentrum Juelich, D52425 Juelich (Germany)
 (Russian Federation)
 (Poland)
 Institute of Physics and Power Engineering, RU249020 Obninsk (Russian Federation)
 Publication Date:
 OSTI Identifier:
 20990954
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 75; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevC.75.014315; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; COUPLING; DENSITY; ELECTRIC DIPOLES; HAMILTONIANS; ISOVECTORS; LAGRANGIAN FUNCTION; LEAD 208; MEV RANGE; MIGDAL THEORY; NEUTRONS; NUCLEAR STRUCTURE; PARTICLES; PHONONS; PROTONS; RESONANCE; SPECTRA
Citation Formats
Tselyaev, V., Institute of Physics, St. Petersburg University, St. Petersburg, Speth, J., Institute of Nuclear Physics, PAN, PL31342 Cracow, Gruemmer, F., Krewald, S., Avdeenkov, A., Tertychny, G., Institute of Physics and Power Engineering, RU249020 Obninsk, and Litvinova, E. Extended theory of finite Fermi systems: Application to the collective and noncollective E1 strength in {sup 208}Pb. United States: N. p., 2007.
Web. doi:10.1103/PHYSREVC.75.014315.
Tselyaev, V., Institute of Physics, St. Petersburg University, St. Petersburg, Speth, J., Institute of Nuclear Physics, PAN, PL31342 Cracow, Gruemmer, F., Krewald, S., Avdeenkov, A., Tertychny, G., Institute of Physics and Power Engineering, RU249020 Obninsk, & Litvinova, E. Extended theory of finite Fermi systems: Application to the collective and noncollective E1 strength in {sup 208}Pb. United States. doi:10.1103/PHYSREVC.75.014315.
Tselyaev, V., Institute of Physics, St. Petersburg University, St. Petersburg, Speth, J., Institute of Nuclear Physics, PAN, PL31342 Cracow, Gruemmer, F., Krewald, S., Avdeenkov, A., Tertychny, G., Institute of Physics and Power Engineering, RU249020 Obninsk, and Litvinova, E. Mon .
"Extended theory of finite Fermi systems: Application to the collective and noncollective E1 strength in {sup 208}Pb". United States.
doi:10.1103/PHYSREVC.75.014315.
@article{osti_20990954,
title = {Extended theory of finite Fermi systems: Application to the collective and noncollective E1 strength in {sup 208}Pb},
author = {Tselyaev, V. and Institute of Physics, St. Petersburg University, St. Petersburg and Speth, J. and Institute of Nuclear Physics, PAN, PL31342 Cracow and Gruemmer, F. and Krewald, S. and Avdeenkov, A. and Tertychny, G. and Institute of Physics and Power Engineering, RU249020 Obninsk and Litvinova, E.},
abstractNote = {The Extended Theory of Finite Fermi Systems is based on the conventional LandauMigdal theory and includes the coupling to the lowlying phonons in a consistent way. The phonons give rise to a fragmentation of the singleparticle strength and to a compression of the singleparticle spectrum. Both effects are crucial for a quantitative understanding of nuclear structure properties. We demonstrate the effects on the electric dipole states in {sup 208}Pb (which possesses 50% more neutrons then protons) where we calculated the lowlying noncollective spectrum as well as the highlying collective resonances. Below 8 MeV, where one expects the socalled isovector pygmy resonances, we also find a strong admixture of isoscalar strength that comes from the coupling to the highlying isoscalar electric dipole resonance, which we obtain at about 22 MeV. The transition density of this resonance is very similar to the breathing mode, which we also calculated. We shall show that the extended theory is the correct approach for selfconsistent calculations, where one starts with effective Lagrangians and effective Hamiltonians, respectively, if one wishes to describe simultaneously collective and noncollective properties of the nuclear spectrum. In all cases for which experimental data exist the agreement with the present theory results is good.},
doi = {10.1103/PHYSREVC.75.014315},
journal = {Physical Review. C, Nuclear Physics},
number = 1,
volume = 75,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}

The dipole response of the doubly magic nuclide {sup 208}Pb was studied in photonscattering experiments at the electron linear accelerator ELBE with bremsstrahlung produced at kinetic electron energies of 9.0 and 15.0 MeV. The present (gamma,gamma{sup '}) data combined with (gamma,n) data from the literature are compared with results of shellmodel calculations and calculations using a quasiparticle randomphase approximation. The shellmodel calculations including (2p2h) excitations describe the experimental E1 strength well and reproduce the spreading of the giant dipole resonance by applying a small smearing width only.

Evidence for collective M1 strength in /sup 208/Pb between 8 and 10 MeV
Veryhighenergyresolution photoneutron timeofflight measurements in combination with highresolution measurements of photoneutron polarizations from the reaction /sup 208/Pb(..gamma..,n/sub 0/(spin up)/sup 207/Pb have enabled us to identify seven probable 1/sup +/ resonances at excitations between 8.2 and 9.5 MeV. These resonances have a total strength B (M1)(spin up) approximatelygreaterthan (8.5 + 0.5) ..mu../sub 0//sup 2/. This strength plus that previously reported at 7 at 8 MeV can account for the M1 sum rule in /sup 208/Pb.