Electroexcitation of even-parity states inAl27

Abstract

Inelastic electron scattering form factors were measured for the even-parity states of $^{27}\mathrm{Al}$ below 7 MeV. The data span a momentum transfer range of $q\ensuremath{\simeq}0.57\ensuremath{-}2.80$ ${\mathrm{fm}}^{\ensuremath{-}1}$. Separate longitudinal and transverse information was obtained, especially for the lowest-energy excitations. For excitations below 3.7 MeV, the longitudinal form factors were found to be well described by shell model calculations provided appropriate effective charges were introduced. These effective charges appear to exhibit little dependence on momentum transfer up to $q\ensuremath{\simeq}2$ ${\mathrm{fm}}^{\ensuremath{-}1}$. In contrast, effective charges or magnetic moments were not required to account for the corresponding transverse form factors. The shell model was somewhat less successful in its description of the higher-energy excitations, although tentative ${J}^{\ensuremath{\pi}}$ assignments were made for some currently ambiguous states on the basis of a comparison with the theoretical predictions.NUCLEAR REACTIONS $^{27}\mathrm{Al}(e, {e}^{\ensuremath{'}})$, $E=60\ensuremath{-}340$ MeV, $\ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{}, 160\ifmmode^\circ\else\textdegree\fi{}, 180\ifmmode^\circ\else\textdegree\fi{}$; measured $\ensuremath{\sigma}(E, \ensuremath{\theta})$, $\ensuremath{\pi}=+1$ levels, ${E}_{x}\ensuremath{\le}7$ MeV. Shell model theory.