Excited state halos in Be10

Abstract

The structure of certain bound excited states in Be10 have been shown to have exotic features because of their weak binding and cluster-like configurations. In this article, we investigate E1 and E2 transitions between these states and compare the findings with recent experimental results. We compare the predictions of two types of structure calculations: a microscopic multicluster model and an ab initio no-core shell model. Both predict very similar transition strengths. By considering the relative contributions from the various matrix elements contributing to the transitions arising from the coupling of different Be9×n configurations in the wave functions making up the states, we conclude that the very weak B(E1;2-→21+) can only be understood if the 2- state (with a separation energy of its predominantly 1s1/2 neutron of just 0.548 MeV) is a clear halo state. Other nearby states, such as the 22+, do not exhibit a clear halo signature because of the less than clean decoupling into the well-defined Be9 core plus halo neutron. © 2006 The American Physical Society.