Studies of the 2 alpha and 3 alpha channels of the C-12 + C-12 reaction in the range of E-c.m.=8.9 MeV to 21 MeV using the active target Time Projection Chamber

The C-12+C-12 fusion reaction was studied in the range of E-c.m.=8.9 to 21 MeV using the active-target Time Projection Chamber. With full information on all tracks of the reaction products, cross sections of the C-12(C-12, Be-8)O-16(g.s.) channel and the C-12(C-12, 3 alpha)C-12 channel could be measured down to the level of a few milibarns. The C-12(C-12, Be-8)O-16(g.s.) reaction channel was determined to be 10(-8)(+24) mb at E-c.m. = 11.1 MeV, supporting the direct alpha transfer reaction mechanism. The C-12(C-12, 3 alpha)C-12 reaction channel was studied for the first time using an exclusive measurement. Our result does not confirm the anomaly behavior reported in the previous inclusive measurement by Kolata et al. [Phys. Rev. C 21, 579 (1980)]. Our comparisons with statistical model calculations suggest that the 3 alpha channel is dominated by the fusion evaporation process at E-c.m. > 19 MeV. The additional contribution of the 3 alpha channel increases the fusion reaction cross section by 10% at energies above 20 MeV. We also find that an additional reaction mechanism is needed to explain the measured cross section at E-c.m. < 15 MeV at which point the statistical model prediction vanishes.