The 12 C( 16 O,γ) 28 Si radiative capture: Structural and statistical aspects of the γ decay

The heavy-ion radiative capture reaction ${}^{12}$C(${}^{16}$O,$\ensuremath{\gamma}$)${}^{28}$Si has been studied at three energies ${E}_{\mathrm{c}.\mathrm{m}.}=8.5$, 8.8, and 9 MeV which are close to the Coulomb barrier. The weak radiative capture process has been identified by measuring the ${}^{28}$Si recoils in the highly selective 0${}^{\ensuremath{\circ}}$ spectrometer DRAGON at TRIUMF (Vancouver). The coincident $\ensuremath{\gamma}$ rays have been recorded in the associated BGO array. This has allowed a complete measurement of the $\ensuremath{\gamma}$ spectrum and the relative strength of all decay pathways. An important part of the decay through quasibound states close to the particle threshold and the feeding of bound states with particular deformation have been identified for the first time. Comparisons with Monte Carlo simulations allowed the extraction of the full experimental radiative capture cross section. Our results suggest an important contribution of spins ${J}^{\ensuremath{\pi}}={5}^{\ensuremath{-}}$ and 6${}^{+}$ in the entrance channel. The surprisingly large cross sections from 12 $\ensuremath{\mu}$b at ${E}_{\mathrm{c}.\mathrm{m}.}=8.5$ MeV to 25 $\ensuremath{\mu}$b at ${E}_{\mathrm{c}.\mathrm{m}.}=9.0$ MeV for the heavy-ion radiative capture process are discussed in terms of the interplay between statistical and structural aspects of the process.