Isovector E2 matrix elements from electromagnetic transitions in the s-d shell: Experiment and shell-model calculations

All available B(E2) values in the mass region 8< or =Z, N< or =20 relevant to the isovector electric quadrupole operator are compared to the theoretical B(E2) values based on Chung-Wildenthal 0d/sub 5/2/-1s/sub 1/2/-0d/sub 3/2/ shell-model wave functions with harmonic oscillator radial wave functions, and some selected cases are compared with local and energy dependent Woods-Saxon potential wave functions. The empirical effective charges deduced from these comparisons are insensitive to differences in mass, state, and dominant single-nucleon orbit. The value for the effective charge parameter e/sub p/-e/sub n/ extracted in the harmonic oscillator approximation is consistent with 1.0e. The values extracted with local and energy-dependent Woods-Saxon potentials, which are more meaningfully related to the underlying structure of the isovector polarizability, are consistent with 0.7e and 0.6e, respectively. Some inadequacies in the experimental data and theoretical models are discussed and improvements are suggested