The 13.9-MeV angular distributions for the ${\mathrm{C}}^{12}({\mathrm{He}}^3,\alpha ){\mathrm{C}}^{11}$ reactions which produce the ground, 2.00-, 4.32-, and 4.81-MeV states of ${\mathrm{C}}^{11}$ were measured, using silicon surface-barrier detectors. The differential cross sections were determined at 2.5° intervals over a laboratory angular range from about 15° to 100°. The angular distributions display features which suggest that a direct-reaction mechanism is operative. The ground-state angular distribution is strongly peaked at forward angles with a weak washed-out oscillatory structure, and those for the excited states are also forward-peaked, but have a strong, well-defined oscillatory nature. The integrated cross sections over the common center-of-mass angular range (32° to 112°) for the ground and first three excited states are 30.5, 9.2, 9.7, and 11.9 mb, respectively. Each angular distribution was analyzed in terms of both zero-range distorted-wave Born-approximation knockout and pickup models. Reasonable correspondence between theory and experiment for the ground-state (${\frac{3}{2}}^{-}$) and second-excited-state (${\frac{5}{2}}^{-}$) angular distributions was achieved only with the pickup model, while only the knockout model provided a reasonable representation of the angular distributions corresponding to the first (${\mathrm{½}}^{-}$) and third (${\frac{3}{2}}^{-}$) excited states.

• Received 27 December 1967

DOI:https://doi.org/10.1103/PhysRev.170.924