The [formula omitted] reaction at 100–140 MeV

Abstract

Transitions to negative-parity states in 11C below E x = 6.48 MeV were studied in the 12 C( 3 He, α) 11 C reaction at incident energies of 99.4, 119.1 and 139.6 MeV in an angular range of θ c. m. ∼ 1°–60°. A magnetic quadrupole spectrometer was used for the measurement at the very forward angle. The observed angular distributions for the transitions to 4.26 ( 5 2 −) and 6.48 ( 7 2 −) MeV states in 11C (forbidden transitions in terms of the simple shell model) show a remarkable fall-off at the very forward angle, whereas those to 0.0 ( 3 2 −), 1.94 ( 1 2 − ) and 4.74 ( 3 2 −) MeV states transitions) show forward-peaked behaviour. The experimental angular distributions were analysed in terms of the zero-range DWBA including two-step processes via inelastic scattering both in the entrance and exit channels. With the spectroscopic amplitudes of the deformed nucleus model and a normalization constant of D 2 0 = 20 × 10 4 fm 3 · MeV 2 which is usually used in the analysis of the ( 3 He, α) reactions on heavier targets, the observed cross sections were considerably well reproduced by the DWBA calculations, especially for the allowed transitions. Some deviation from the DWBA predictions was found in the excitation functions of the cross sections for the forbidden transitions. This suggests that another reaction model is further required in understanding the reaction mechanism in the present incident energy region.