Above threshold s-wave resonances illustrated by the 1/2+ states in 9Be and 9B

We solve the persistent problem of the structure of the lowest 1/2(+) resonance in Be-9 which is important to bridge the A = 8 gap in nucleosynthesis in stars. We show that the state is a genuine three-body resonance even though it decays entirely into neutron-Be-8 relative s-waves. The necessary barrier is created by dynamical evolution of the wave function as the short-distance alpha-He-5 structure is changed into the large-distance n-Be-8 structure. This decay mechanism leads to a width about two times smaller than table values. The previous interpretations as a virtual state or a two-body resonance are incorrect. The isobaric analog 1/2(+) state in B-9 is found to have energy and width in the vicinity of 2.0 MeV and 1.5 MeV, respectively. We also predict another 1/2(+) resonance in B-9 with similar energy and width. (C) 2010 Elsevier B.V. Ail rights reserved.