Why are there so many resonances energetically close to open reaction channels?

Prof. Lee Sobotka, Department of Chemistry and Physics, Washington University
March 30, 2018 at 12:00 pm
241 Compton
Event Description 

We can be here because the Hoyle state has a mass must above that of 8Be + α, which is just above the mass of 3α’s. The s-process can occur because there is a state in 17O almost exactly coinciding in mass with that of 13C+ α (and that there is also an open neutron-decay channel). Sure there is an Anthropic rationalization (i.e. if this were not the case we could not be around to talk about it), but what is the real "go of it"? The "it" being: why are so many resonances energetically close to open reaction channels? Of course nuclear clustering, complex wave functions that have considerable similarity to a fewer particle – but clustered – many-body system, is important. But is there more going on?

Ten years ago, highly-excited states were found in 9Li and 10Be a few hundred kilovolts above the respective proton-decay thresholds. These physical states are too low in energy to be the isospin-stretched configuration of the decay channel. However these states can be understood by a continuum-cognizant shell model as strongly mixed states of lower isospin, where the mixing is largely mediated by the open neutron channels but ushered in energy to be just above the proton threshold. Do these cases shed light on the general question of why there are so many resonances near open channels?