Electroexcitation of the Giant Resonance ofC13

The giant resonance of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ has been investigated by means of inelastic electron scattering. The incident energies and scattering angles employed were 77.0 MeV (75°), 106.0 MeV (75°), 55.4 MeV (145.7°), and 81.0 MeV (145.7°). The data show a distinct splitting of the resonance into two large peaks near 20.5 and 24.5 MeV. Some fine structure is observed which correlates well with the position of excitations calculated by Easlea. Considerable strength is observed in the region of 14-MeV excitation which may correspond to the "pygmy" resonance seen in the photonuclear work of Cook. Data were also taken consecutively on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. The form factors for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ are compared. The presence of the extra neutron in ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ results in a major restructuring of the giant-resonance strength. The possibility of an isotopic splitting in the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ giant resonance is discussed.