The Hoyle Family: The search for alpha-condensate states in light nuclei

Our present understanding of the structure of the Hoyle state in 12C and other near-threshold states in α-conjugate nuclei is reviewed in the framework of the α-condensate model. The 12C 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 12C and then the decays of heavier nuclei. With more theoretical input, and increasingly complex detector setups, precision breakup 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.