Elastic Scattering of Alpha Particles

Abstract

An extensive study of elastic scattering of medium-energy alpha particles at fixed angles has been made for 28 nuclides ranging from Ni to Pu. The sharp-cutoff model is used to evaluate interaction radii, ${R}_{A\ensuremath{\alpha}}$, and a simple graphical method has been developed for these evaluations. A least squares fit to the experimental data of the form ${R}_{A\ensuremath{\alpha}}={r}_{0}{A}^{\frac{1}{3}}+b$ gives ${r}_{0}=(1.414\ifmmode\pm\else\textpm\fi{}0.042)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ cm, $b=(2.19\ifmmode\pm\else\textpm\fi{}0.20)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ cm. The internal consistency of the data is much higher than the stated over-all errors (standard deviations) indicate; the average departure from the least squares curve is 0.75%. The dependence of interaction radius upon scattering angle is slight over the range of angles studied. Significant differences in interaction radius are seen between Pb and Bi and between ${\mathrm{U}}^{235}$ and ${\mathrm{U}}^{238}$, among others. Small changes in either neutron or proton configuration influence the detailed structure of the curves of cross section versus energy, especially in the region of a closed neutron or proton shell. The angular and energy dependence of the structure in cross section curves is qualitatively discussed in terms of the sharp-cutoff model. A modification of this theory is used to estimate the cross section for an ellipsoidally distorted nucleus.