Highly Excited Nuclear Residual States in the (γ, π+) Reaction in the Threshold Region

Energy distributions of π + electroproduced on 6 Li, 9 Be and 28 Si were measured at the electron energy of about 200 MeV. The photon difference method was applied to these (e, π + ) spectra in order to extract the (γ, π + ) cross sections. Present results and previously obtained data show considerable contribution from several discrete levels of the residual nuclei. The spin-isospin flip giant resonance in residual nuclei could be studied up to about 20 MeV residual excitation except in 6 Li which showed a small quasi-free and/or continuum contribution. In 9 Be and 28 Si, the present results show giant resonances in the residual nuclei with a width of about 15 MeV in the gross shape.