Elastic scattering cross sections of the ${}^{89}\mathrm{Y}$$(\alpha ,\alpha )$${}^{89}\mathrm{Y}$ reaction have been measured at energies $E_{\mathrm{c}.\mathrm{m}.}=15.51$ and $18.63$ MeV. The high-precision data for the semimagic $N=50$ nucleus ${}^{89}\mathrm{Y}$ are used to derive a local potential and to evaluate the predictions of global and regional $\alpha$-nucleus potentials. The variation of the elastic $\alpha$-scattering cross sections along the $N=50$ isotonic chain is investigated by a study of the ratios of angular distributions for ${}^{89}\mathrm{Y}$$(\alpha ,\alpha )$${}^{89}\mathrm{Y}$ and ${}^{92}\mathrm{Mo}$$(\alpha ,\alpha )$${}^{92}\mathrm{Mo}$ at $E_{\mathrm{c}.\mathrm{m}.}\approx 15.51$ and $18.63$ MeV. This ratio is a very sensitive probe at energies close to the Coulomb barrier, where scattering data alone is usually not enough to characterize the different potentials. Furthermore, $\alpha$-cluster states in ${}^{93}\mathrm{Nb}$$=$${}^{89}\mathrm{Y}$$\otimes \alpha$ are investigated.

• Received 18 August 2009

DOI:https://doi.org/10.1103/PhysRevC.80.045807