Near-threshold resonances and the beta-delayed proton emission of the halo nucleus ¹¹Be

There are numerous examples of narrow resonances in light nuclei that can be found in the proximity of particle decay thresholds. Probably the most famous resonance of this kind is the excited 0⁺ Hoyle state of ¹²C very close to the alpha-particle separation energy. Based on studies in the shell model embedded in the continuum, it has been conjectured that the coupling to the decay channel(s) leads to a new kind of near-threshold collectivity, which may result in a formation of a single "aligned eigenstate" of the system that carries many characteristics of a nearby decay channel. This mechanism provides a general explanation, based on the configuration mixing approach to open quantum systems, of the widespread appearance of cluster or correlated states in the vicinity of cluster emission thresholds.

A splendid example of a threshold resonance is the 1/2⁺ state in ¹¹B that explains the beta-delayed proton decay of a neutron-rich nucleus ¹¹Be. In this presentation, I will use the lenses of real-energy continuum shell model to describe this "conveniently located" state in ¹¹B, and other threshold resonances in light nuclei.