The 12C(α, γ)16O reaction at stellar energies☆
Abstract
The most recent experimental data on the 12C(α, γ)16O reaction at energies Ec.m. ≲ 3 MeV have been analysed to determine the astrophysical S-factor. The absolute E2 capture cross section was calculated in a microscopically based direct capture model, while the E1 cross section was described by the hybrid R-matrix model. We find that the E2 rate is less than 4% of the E1 rate at astrophysically important energies. The two sets of data yield S-factors at Ec.m. = 300 keV of 0.15 MeV · b and 0.34 MeV · b.
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The <sup>12</sup>C(α, γ)<sup>16</sup>O cross section at stellar energies
1987, Nuclear Physics, Section AThe capture reaction 12C(α, γ)16O has been investigated at E = 0.94 to 2.84 MeV with the use of an intense α beam and implanted 12C targets of high isotopic purity. The studies involved NaI(Tl) crystals and, for the first time, germanium detectors. The measurement of absolute cross sections, γ-ray angular distributions and excitation functions is reported. A cross section of 48 pb is found at E = 0.94 MeV. The data provide information on the E1 and E2 capture amplitudes involved in the transition to the ground state as well as to excited states. The S-factor at stellar energies has been determined by means of theoretical fits. The results verify the previous report of a substantial higher S-value compared to the value recommended in 1975. The present uncertainty in the S-value as well as possible improvements are discussed. This S-value is of crucial importance to nuclear astrophysics.
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Supported in part by the National Science Foundation [PHY82-07332 and PHY79-23638].
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On leave from the University of Münster.