O-16 resonances near the 4 alpha threshold through the C-12(Li-6, d) reaction

Background: Resonances around x alpha thresholds in light nuclei are recognized to be important in basic aspects of nuclear structure. However, there is scarce experimental information associated with them. Purpose: We study the alpha-clustering phenomenon in resonant states around the 4 alpha threshold (14.44 MeV) in the O-16 nucleus. Method: The C-12(Li-6, d)(16)Oreactionwas investigated with an unprecedented resolution at a bombarding energy of 25.5 MeV by employing the Sao Paulo Pelletron-Enge-Spectrograph facility and the nuclear emulsion technique. Results: Several narrow resonances were populated and the energy resolution of 15 keV allows for the separation of doublet states that were not resolved previously. The upper limits for the resonance widths in this region were extracted. The angular distributions of the absolute differential cross section associated with four natural parity quasibound states are presented and compared to distorted wave Born approximation predictions. Conclusions: Narrow resonances not previously reported in the literature were observed. This indicates that the alpha-cluster structure information in this region should be revised.