Breakup channels for 12C triple-α continuum states

The triple-α-particle breakup of states in the triple-α continuum of 12C has been investigated by way of coincident detection of all three α particles of the breakup. The states have been fed in the β decay of 12N and 12B, and the α particles measured using a setup that covers all of the triple-α phase space. Contributions from the breakup through the 8Be(0+) ground state as well as other channels--interpreted as breakup through excited energies in 8Be--have been identified. Spins and parities of 12C triple-α continuum states are deduced from the measured phase-space distributions for breakup through 8Be above the ground state by comparison to a fully symmetrized sequential R-matrix description of the breakup. At around 10 MeV in 12C, the breakup is found to be dominated by 0+ strength breaking up through the ghost of the 8Be(0+) ground state with L=0 angular momentum between the first emitted α particle and the intermediate 8Be nucleus. For 12C energies above the 12.7 MeV 1+ state, however, L=2 breakup of a 12C 2+ state through the 8Be(2+) excited state dominates. Furthermore, the possibility of a 2+ excited state in the 9-12 MeV region of 12C is investigated.