Back-angle elastic alpha scattering fromY89andZr90,91,94

Abstract
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 Eα(lab)=18 through 25 MeV for α+Y89 and α+Zr90,91,94 have been measured in steps of 500 keV or less at angles between 141° and 176° (lab). Near 180°, narrow (about 1 MeV) minima, with a drop in cross section by more than an order of magnitude, are observed around Eα=23 MeV for the α+Y89 and α+Zr90,91 elastic scattering. A similar, but less pronounced, structure is seen in the excitation function for α+Zr94. Angular distributions between 48.5° and 176° (lab) measured at several energies in 2.5° 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.