Studies of the 2α and 3α channels of the ^(12)C+^(12)C reaction in the range of E_(c.m.)=8.9 MeV to 21 MeV using the active target Time Projection Chamber

The ^(12)C+^(12)C 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^(12)C(^(12)C,^(8)Be)^(16)O_(g.s.)channel and the ^(12)C(^(12)C,3a)^(12)C channel could be measured down to the level of a few milibarns.The ^(12)C(^(12)C,^(8)Be)^(16)O_(g.s.)reaction channel was determined to be 10_(-8)^(+24) mb at E_(c.m.)=11.1 MeV,supporting the direct a transfer reaction mechanism.The ^(12)C(^(12)C,3α)^(12)C 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 a channel is dominated by the fusion evaporation process at E_(c.m.)>19 MeV.The additional contribution of the 3 a 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.

Modified astrophysical S-factor of 12C+12C fusion reaction at sub-barrier energies

The 12C+12C fusion reaction plays a crucial role in stellar evolution and explosions.Its main open reaction channels includeα,p,n,and 8Be.Despite more than a half century of efforts,large differences remain among the experimental data of this reaction measured using various techniques.In this work,we analyze the existing data using a statistical model.Our calculation shows the following:1)the relative systematic uncertainties of the predicted branching ratios decrease as the predicted ratios increase;2)the total modified astrophysical S-factors(S^* factors)of the p andαchannels can be obtained by summing the S^* factors of their corresponding ground-state transitions and the characteristicγrays,while taking into account the contributions of the missing channels to the latter.After applying corrections based on branching ratios predicted by the statistical model,an agreement is achieved among the different data sets at Ecm>4 MeV,while some discrepancies remain at lower energies,suggesting the need for better measurements in the near future.We find that the S^* factor recently obtained from an indirect measurement is inconsistent with the direct measurement value at energies below 2.6 MeV.We recommend upper and lower limits for the 12C+12C S^* factor based on the existing models.A new 12C+12C reaction rate is also recommended.