First Measurement of the Cascade Transition via the 6.049-MeV State of ^16O in the ^12C(,)^16O Reaction

The cascade through the 6.049-MeV state of ^16O has rarely been discussed as contributing to the ^12C (α,γ)^16O cross section at low energies largely due to experimental difficulties in observing this transition. We report here first measurements of this transition in ^12C(α,γ)^16O using the DRAGON separator facility at TRIUMF. The experiment was performed in inverse kinematics with an incident ^12C beam on a windowless ^4He gas target. The coincidence setup included a BGO array around the gas target and a DSSSD detector for the detection of ^16O recoils. The acceptance of DRAGON including the BGO array has been simulated in GEANT as well as measured directly. The transition strength has been derived and analyzed in the R- matrix formalism. We find an extrapolated value of S_6.05(300)=25±16 keVb showing that this transition is likely the most important cascade contribution for ^12C (α,γ)^16O.