Gamma decay of giant resonances excited by heavy ions
Experiments on /sup 208/Pb bombarded by /sup 17/O at 22 MeV/nucleon (ORNL) and 84 MeV nucleon (GANIL) are reviewed. Inelastically scattered projectiles were detected at forward angles in coincidence with gamma rays seen in NaI (ORNL) or in BaF/sub 2/ (GANIL). The /sup 17/O were identified by 6 Si telescopes covering THETA = 11. 5/degree/--14.5/degree/ (ORNL) or by the focal-plane detector system of the energy-loss spectrometer SPEG, set to accept THETA = 1. 5/degree/--5.0/degree/ (GANIL). The ..gamma..-ray data provide information on the multipole character of various parts of the giant resonance region, matrix elements between the GR region and low-lying states in /sup 208/Pb, and the relative contribution of direct and compound process to ..gamma../sub 0/ decay. At the higher energy the 9--15 MeV GR region is excited very strongly. The isovector giant dipole is dominant over most of the angles studied. Significant contributions from the isoscalar giant quadrupole and monopole resonances are also present. Decomposition of the GR into L = 1, 2, and 0 components was based on coincidences with the overwhelmingly dipole ..gamma../sub 0/ transitions. The magnitude (1.7 +- 0.2%) and energy distribution of the ..gamma../sub 0/ branch can be reproduced well by a parameter-free calculation. The ..gamma../sub 0/ decay of the isoscalar giant quadrupole resonance is more easily observed at the lower energy. The ..gamma../sub 0/ angular correlations confirm the presence of E2 radiation from states in the 9--11 MeV region. The B(E2) implies that the ratio of neutron to proton matrix elements is consistent with the expected value of N/Z. This conclusion is confirmed by evidence form Coulomb-nuclear interference in the singles data at 84 MeV/nucleon. Photon decays to excited states indicate that 4/sup +/ and/or 6/sup +/ strength is present around 9--10 MeV, and are consistent with a monopole contribution from 12.5--15.5 MeV. 20 refs., 14 figs.
- Research Organization:
- Oak Ridge National Lab., TN (USA)
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 6761922
- Report Number(s):
- CONF-880795-2; ON: DE88016810; TRN: 88-036320
- Resource Relation:
- Conference: Tokyo symposium on heavy-ion and nuclear astrophysical problems, Tokyo, Japan, 19 Jul 1988; Other Information: Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BISMUTH 209 TARGET
OXYGEN 17 REACTIONS
GIANT RESONANCE
RADIATIVE DECAY
LEAD 208 TARGET
ANGULAR CORRELATION
COINCIDENCE METHODS
DIFFERENTIAL CROSS SECTIONS
EXCITED STATES
GAMMA RADIATION
HEAVY ION REACTIONS
INELASTIC SCATTERING
MATRIX ELEMENTS
CHARGED-PARTICLE REACTIONS
CORRELATIONS
COUNTING TECHNIQUES
CROSS SECTIONS
ELECTROMAGNETIC RADIATION
ENERGY LEVELS
IONIZING RADIATIONS
NUCLEAR REACTIONS
RADIATIONS
RESONANCE
SCATTERING
TARGETS
651920* - Nuclear Properties & Reactions
A=190-219
Experimental