States of Be11, B11, and C11

Abstract
The gamma-decay of the 4.46- and 5.03-Mev levels of B11 has been determined by (p, γ) coincidences using the reaction Be9(He3, p)B11. The 5.03-Mev level is found to decay with a probability of 0.14±0.03 via the state at 2.13 Mev; the intensity of the branch to the state at 4.46 Mev is less than 3×103. The intensity of the branch from the 4.46-Mev level via that at 2.13 Mev is less than 5×103. The data on these states are reviewed and it is concluded that the present results strongly favor the choices J=12, 52, 32 for the states at 2.13, 4.46, and 5.03 Mev, respectively, without appeal to a model. It is, however, emphasized that the body of data as it stands at the moment might admit J=12+ for the 2.13-Mev state and J=12 for the 5.03-Mev state. The previsions of the independent-particle model (IPM) are then examined and it is concluded that best general agreement between theory and experiment is achieved for aK44.5. The likely relevance of the collective model is remarked upon. It is demonstrated with the aid of the reaction B10(p, γ)C11 that the ordering of the first three excited states of C11 is the same as in B11. The beta-decay of Be11 is reconsidered in the light of the increased firmness of the assignments in B11 and of the previsions of the IPM; it is concluded that Be11 is most probably of even parity.