Study of rlastic and inelastic 11 B +α scattering and search for cluster states of enlarged radius in 11B

Abstract

The differential cross sections for elastic and inelastic 11B + α scattering were measured at the alpha-particle energy of 65 MeV, the inelastic-scattering processes leading to the excitation of known states of 11B up to excitation energies of about 14 MeV. Data on elastic scattering were analyzed together with those that were published earlier for lower energies. The cross sections for inelastic scattering were analyzed on the basis of the distorted-wave method. A modified diffractionmodel was used to determine the root-mean-square radii of excited states. The radii of states whose excitation energies were below about 7MeV were found to agree with radius of the ground state to within 0.1 to 0.15 fm. This result complieswith the traditional idea that the low-lying states of 11B have a shell structure. The possibility that these states belong to the predicted rotational bands, which, if any, are truncated to three states, cannot be ruled out either. The majority of the observed highly excited states are distributed among four rotational bands. The moments of inertia of these bands are close; for the band based on the 3/2− state at E* = 8.56 MeV, they are even higher than those of the Hoyle state in the 12C nucleus. The measured radii of states associated with these bands of 11B are larger than the ground-state radius by 0.7 to 1.0 fm and are also close to the radius of the Hoyle state. The results of the present study agree with the existing predictions that the cluster structure of the 11B nucleus is diverse at high excitation energies. The hypothesis that the 11B nucleus features a “giant” state of size commensurate with those in heavy nuclei was not confirmed.