Giant dipole resonance in highly excited Pb and Th nuclei
The giant dipole resonance (GDR) built on highly excited states was measured in neutron deficient Pb and Th isotopes in order to study nuclear deformation at high excitation energies and spins, and to search for the presence of a compound nucleus GKR even in the heaviest masses. This was achieved by measuring high energy {gamma}-rays in heavy ion fusion reactions. The compound nuclei were formed with {sup 16}O and {sup 19}F beams on W, {sup 181}Ta, and {sup 208}PB targets with excitation energies from 57 to 102MeV and mean spins from 14 to 44{h bar}. In this mass region, fission is a major decay channel and the total {gamma}-ray spectrum is a sum of {gamma}-rays emitted from the compound system and {gamma}-rays emitted from the excited fission fragments. The data analysis was performed using the evaporation code CASCADE, which was extensively modified to calculate the decay of these heavy systems and to include the subsequent decay of the fission fragments. In the Pb isotopes, which are spherical in the ground state, the dipole strength function showed to components indicating a strongly deformed nucleus ({beta} {approx} 0.3). Large {gamma}-ray anisotropies were measured for the compound nucleus GDR from which a deformed shape could be unambiguously established. At 105MeV the fission coincidence data yield a prolate deformation of {beta} {approx} 0.43 in agreement with a predicted superdeformed shape. However, at 141MeV, the ambiguity between the prolate and noncollective oblate shape could not be resolved. The {gamma}-ray energy spectra in the heavy mass region of Th isotopes required an enhancement of the HDR {gamma}-rays over the statistical model predictions from the pre-fission nuclei.
- Research Organization:
- State Univ. of New York, Stony Brook, NY (USA)
- OSTI ID:
- 6051347
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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FLUORINE 19 REACTIONS
HEAVY ION FUSION REACTIONS
LEAD 208 TARGET
OXYGEN 16 REACTIONS
LEAD ISOTOPES
GIANT RESONANCE
TANTALUM 181 TARGET
THORIUM ISOTOPES
ANISOTROPY
COMPOUND NUCLEI
DEFORMED NUCLEI
EXCITED STATES
FISSION FRAGMENTS
GAMMA RADIATION
GAMMA SPECTRA
MASS
ACTINIDE ISOTOPES
CHARGED-PARTICLE REACTIONS
ELECTROMAGNETIC RADIATION
ENERGY LEVELS
HEAVY ION REACTIONS
IONIZING RADIATIONS
ISOTOPES
NUCLEAR FRAGMENTS
NUCLEAR REACTIONS
NUCLEI
RADIATIONS
RESONANCE
SPECTRA
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