Clarification of the Three-Body Decay ofC12(12.71 MeV)

Abstract

Using decays of a clean source of 12 N produced at the IGISOL facility, we have measured the breakup of the 12 C (12.71 MeV) state into three particles with a segmented particle detector setup. The high quality of the data permits solving the question of the breakup mechanism of the 12.71 MeV state, a longstanding problem in few-body nuclear physics. Among existing models, a modified sequential model fits the data best, but systematic deviations indicate that a three-body description is needed.

Breakup channels forC12triple-αcontinuum states

“…The first is the broad profiles of some of the 12 C resonances that makes it hard to single them out in even the most selective spectra. The second is the very high α-clustering present in * cd550@york.ac.uk all relevant 8 Be ("double-α") states, implying that all these states couple strongly to the continuum.…”

“…One of the open questions that has attracted recent interest is the resonances in 12 C with pronounced α-particle structure, in particular the 0 + and 2 + states above the Hoyle state. It has become clear that the third 0 + state (0 + 3 ) is situated at 10-to 11-MeV excitation energy [2][3][4] although a consistent picture incorporating all data is still not established.…”

“…The triple-α-particle breakup of states in the triple-α continuum of 12 C 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 12 N and 12 B, and the α particles measured using a setup that covers all of the triple-α phase space.…”

“…Contributions from the breakup through the 8 Be(0 + ) ground state as well as other channels-interpreted as breakup through excited energies in 8 Be-have been identified. Spins and parities of 12 C triple-α continuum states are deduced from the measured phase-space distributions for breakup through 8 Be above the ground state by comparison to a fully symmetrized sequential R-matrix description of the breakup. At around 10 MeV in 12 C, the breakup is found to be dominated by 0 + strength breaking up through the ghost of the 8 Be(0 + ) ground state with L = 0 angular momentum between the first emitted α particle and the intermediate 8 …”

“…The states have been fed in the β decay of 12 N and 12 B, and the α particles measured using a setup that covers all of the triple-α phase space. Contributions from the breakup through the 8 Be(0 + ) ground state as well as other channels-interpreted as breakup through excited energies in 8 Be-have been identified.…”