The Hoyle Family: The Search for Alpha-Condensate States in Light Nuclei

Our present understanding of the structure of the Hoyle state in ^12 C and other near-threshold states in α -conjugate nuclei is reviewed in the framework of the α -condensate model. The ^12 C Hoyle state, in particular, is a candidate for α -condensation, due to its large radius and α -cluster structure. The predicted features of nuclear α -particle condensates are reviewed along with a discussion of their experimental indicators, with a focus on precision break-up measurements. Two experiments are discussed in detail, firstly concerning the break-up of ^12 C and then the decays of heavier nuclei. With more theoretical input, and increasingly complex detector setups, precision break-up measurements can, in principle, provide insight into the structures of states in α -conjugate nuclei. However, the commonly-held belief that the decay of a condensate state will result in N α -particles is challenged. We further conclude that unambiguously characterising excited states built on α -condensates is difficult, despite improvements in detector technology.