Decay modes of the isoscalar giant quadrupole resonance in 58Ni and the Zn isotopes

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 58Ni via 140 MeV inelastic alpha particle scattering. The branching ratio was found to be 59 +- 12% for proton decay and 12 +- 4% for alpha particle decay. This corresponds to 30 +- 6% and 6 +- 2% of the isoscalar E2 energy-weighted sum-rule strength, respectively. 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 58Ni 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 58Ni GQR recoil direction due to a large contribution from quasi-free alpha particle knockout. The proton angular correlation function is nearly symmetric about 900 relative to the recoil direction, but its approx. 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 emisssion 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 64Zn, 66Zn, and 68Zn