Resonance effects in elastic and first excited level inelastic neutron scattering on 12C from 15.0 to 18.25 MeV

In order to investigate the reaction mechanisms for elastic and first excited level (Isup(π) = 2+, Esub(x) = 4.44 MeV) inelastic n-12C scattering, angular distributions of several observables have been measured: differential elastic cross sections at Esub(n) = 15.0, 15.85 and 18.25 MeV, elastic polarizations at Esub(n) = 15.85 MeV, differential inelastic cross sections and spin-flip probabilities at Esub(n) = 15.0, 15.85, 16.9 and 18.25 MeV, and inelastic analyzing powers and spin-flip analyzing powers at Esub(n) = 15.85 MeV. Neutron time-of-flight techniques with a scintillating scatterer have been used. Spin-flip data have been determined by means of the (n,n'γsub(transverse)) correlation. Detailed comparisons of the experimental results were made with the predictions of collective-model CC calculations using the full Thomas form for the deformed spin-orbit potential. Large and energy-dependent spin-orbit deformations (β2sup(s.o.) > approx. 3 β2sup(c)) were neeeded indicating nuclear structure effects. The fit to the 15.85 MeV polarization data was considerably improved by adding dsub(3/2) and fsub(5/2) Breit-Wigner resonance amplitudes to the optical-model amplitudes. Inelastic scattering data were analyzed in terms of a microscopic antisymmetrized DWA in which high-lying resonance states are incorporated explicitly as doorway states. Higher-order processes are described by the addition of a phenomenological imaginary part to the transition potential. These analyses reveal the presence of a quadrupole resonance at about 21 MeV excitation in 12C. The results are also influenced to a lesser extent by the E1 giant dipole resonance and a dipole resonance at Esub(x) approx. 19.5 MeV. (orig.)