α-decay of excited states in ¹¹C and ¹¹B

Studies of the 16 O(⁹Be,α⁷Be)¹⁴ C and ⁷ Li(⁹Be,α⁷Be)⁵ He reactions at E_beam=70 MeV have been performed using resonant particle spectroscopy techniques. The ¹¹ C excited states decaying into α + Be ⁷ (gs) are observed at 8.65, 9.85, 10.7 and 12.1 MeV as well as possible states at 12.6 and 13.4 MeV. This result is the first observation of α -decay for excited states above 9 MeV. The α + Li ⁷ (gs) decay of ¹¹ B excited states at 9.2, 10.3, 10.55, 11.2, (11.4), 11.8, 12.5, (13.0), 13.1, (14.0), 14.35, (17.4) and (18.6) MeV is observed. The decay processes are used to indicate the possible three-centre 2 α + ³ He (³H) cluster structure of observed states. Two rotational bands corresponding to very deformed structures are suggested for the positive-parity states. Excitations of some observed T = 1/2 resonances coincide with the energies of T = 3/2 states which are the isobaric analogs of the lowest ¹¹ Be states. Some of these states may have mixed isospin.