Scattering of 14.1 MeV neutrons from 11 B

Angular distributions of the differential cross sections and integrated cross sections for the scattering of 14.1 MeV neutrons from 11B for the 0, 2.12, 4.44, 5.02, (6.74+6.79) and 7.30 MeV levels have been measured. Two targets (81.17% 11B, 18.83% 10B (natural boron) and 91.35% 10B, 8.65% 11B) were used. A Monte-Carlo program, which calculated the time-of-flight spectra for the two targets, was used to obtain the best value of the cross sections. The elastic scattering has been analysed with the optical model. Differential cross sections for the four lower excited states show some discrepancies with respect to the predictions of the excited-core model (12C(0+ —> 2+)+1p3/2 hole) and collective DWBA calculations. However, they agree well with those derived from the unified model of 11B, which takes into account the strong coupling scheme for these levels by assuming a 1p3/2 —> 1p1/2. hole transition superimposed on collective excitations. On the basis of this model, the spin of the 5.02 MeV level is found to be 3/2