Decay modes of the isoscalar giant quadrupole resonance in the Zn isotopes

Particle-particle coincidence measurements have been performed to study directly the particle decay modes of the isoscalar giant quadrupole resonance in ${}_{}{}^{64}{}_{}{}^{}\mathrm{Zn}$, ${}_{}{}^{66}{}_{}{}^{}\mathrm{Zn}$, and ${}_{}{}^{68}{}_{}{}^{}\mathrm{Zn}$. The resonance was excited via inelastic alpha particle scattering at 160 MeV and decay protons, neutrons, and alpha particles were detected in coincidence at a number of angles. The importance of statistical processes in the decay of the giant quadrupole resonance is shown by the similarity of the measured branching ratios to statistical model predictions, which vary systematically across the Zn isotopes. This result is consistent with exciton model calculations which predict that the giant quadrupole resonance width in Zn isotopes is predominantly a spreading width rather than an escape width.

[NUCLEAR REACTIONS ${}_{}{}^{64}{}_{}{}^{}\mathrm{Zn}(\alpha ,\alpha x)$, ${}_{}{}^{66}{}_{}{}^{}\mathrm{Zn}(\alpha ,\alpha x)$, ${}_{}{}^{68}{}_{}{}^{}\mathrm{Zn}(\alpha ,\alpha x)$, $x=p,n,\alpha$, $E_{\alpha }=160\mathrm{}$ MeV; measured $\frac{d^4\sigma }{d{\Omega }_{\alpha }d{\Omega }_{x}d{E}_{\alpha }d{E}_x}$; deduced giant quadrupole resonance branching ratios; compared with branching ratios calculated in statistical model.]