Inelastic and Elastic Scattering of 187-Mev Electrons from Selected Even-Even Nuclei

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Abstract

A survey has been made of the differential scattering cross sections for 187-Mev electrons on the even-even nuclei $_{12}\mathrm{Mg}^{24}$, $_{14}\mathrm{Si}^{28}$, $_{16}\mathrm{S}^{32}$, $_{18}\mathrm{A}^{40}$, and $_{28}\mathrm{Sr}^{88}$. It has been possible to separate the elastic scattering from the inelastic in all cases and to resolve the inelastic groups from specific nuclear levels for at least one level in all cases. A simple Born-approximation analysis of the elastic data yields values of the effective radii and surface thicknesses of the nuclear charge densities which (if suitably corrected for failure of the Born approximation) are in substantial agreement with the results of Hahn, Ravenhall, and Hofstadter; i.e., a radius parameter of $c\ensuremath{\cong}1.08 {A}^{\frac{1}{3}}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ cm (radius to half-maximum of the charge distribution) and a surface thickness of $t\ensuremath{\cong}2.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ cm (thickness from 10% to 90% of the maximum of the charge distribution). Phenomenological analysis of the inelastic scattering along the lines laid down by Schiff yields some tentative multipolarity assignments, and application of some results of Ravenhall yields estimates of (radiative) partial level widths; for the $E2$ transitions these correspond to lifetimes of \ensuremath{\sim}19\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ sec (Mg 1.37 Mev) to \ensuremath{\sim}1.4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ sec (Sr 1.85 Mev). The observed strengths of the transitions are compared to those predicted by Weisskopf theory.