Decay Modes of the Isoscalar Giant Quadrupole Resonance in NICKEL-58 and the Zinc Isotopes.
Abstract
The particle decay of the isoscalar GQR has been studied in medium-mass nuclei in order to obtain information relevant to the nuclear structure of the resonance and to understand the total width of the resonance observed in inelastic scattering spectra. Particle-particle coincidence measurements have been performed for the charged particle decay channels of the GQR excited in ('58)Ni via 140 MeV inelastic alpha particle scattering. The branching ratio was found to be 59 (+OR-) 12% for proton decay and 12 (+OR -) 4% for alpha particle decay. This corresponds to 30 (+OR-) 6% and 6 (+OR-) 2% of the isoscalar E2 energy-weighted sum-rule strength, respectively. These values were found to be very similar to those of the continuum underlying the GQR and to statistical model predictions. Qualitative evidence for the neutron decay of the GQR was also found. The angular correlations of the total proton and total alpha decay of the GQR region of excitation (GQR peak plus underlying continuum) are identical in shape to those of a continuum region adjacent to the GQR. Combined with the above results, this indicates that the GQR and the surrounding continuum in ('58)Ni decay in a similar way and that the GQR decay may therefore be strongly influenced by statistical effects. In the RCM system, the alpha particle decay angular correlation of the GQR region is strongly peaked along the ('58)Ni GQR recoil direction due to a large contribution from quasi-free alpha particle knockout. The proton angular correlation function is nearly symmetric about 90(DEGREES) relative to the recoil direction, but its (TURN)23% anisotropy could be interpreted as a direct proton emission component in the decay process. To further investigate the importance of statistical effects, a coincidence experiment has been performed to look for the strong isotopic (particle emission threshold) dependence of the GQR decay in Zn which is predicted by Hauser-Feshbach calculations. The total GQR proton, neutron, and alpha particle decay branching ratios have been measured on ('64)Zn, ('66)Zn, and ('68)Zn. They are again similar to those of the underlying continuum and to statistical model predictions, within the experimental uncertainties. The Zn coincidence spectra also exhibit a dependence on particle emission thresholds and barriers and on particle multiplicities. The results indicate a strong statistical influence on the particle decay from the entire GQR region of excitation in the Zn isotopes.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1980
- Bibcode:
- 1980PhDT.......140C
- Keywords:
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- Physics: Nuclear