Back-angle elastic alpha scattering from 89Y and 909194Zr

Excitation functions and angular distributions for elastic α scattering from target nuclei around A = 90 have been measured in an effort to obtain a precise picture of the cross sections at backward angles. Excitation functions between E/sub alpha/(lab) = 18 through 25 MeV for α + 89Y and α + 909194Zr have been measured in steps of 500 keV or less at angles between 1410 and 1760 (lab). Near 1800, narrow (about 1 MeV minima, with a drop in cross section by more than an order of magnitude, are observed around E/sub alpha/ = 23 MeV for the α + 89Y and α + 9091Zr elastic scattering. A similar, but less pronounced, structure is seen in the excitation function for α + 94Zr. Angular distributions between 48.50 and 1760 (lab) measured at several energies in 2.50 steps show a regular, diffractionlike pattern over the entire angular range. A standard four-parameter Woods-Saxon potential is found to be sufficient to provide a detailed fit to the experimental data including the minima in the excitation functions at back angles