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Register a new userThe first direct measurement of 12C(12C,n)23Mg at stellar energies
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Neutrons produced by the carbon fusion reaction 12C(12C,n)23Mg play an important role in stellar nucleosynthesis. However, past studies have shown large discrepancies between experimental data and theory, leading to an uncertain cross section extrapolation at astrophysical energies. We present the first direct measurement that extends deep into the astrophysical energy range along with a new and improved extrapolation technique based on experimental data from the mirror reaction 12C(12C,p)23Na. The new reaction rate has been determined with a well-defined uncertainty that exceeds the precision required by astrophysics models. Using our constrained rate, we find that 12C(12C,n)23Mg is crucial to the production of Na and Al in Pop-III Pair Instability Supernovae. It also plays a non-negligible role in the production of weak s-process elements as well as in the production of the important galactic gamma-ray emitter 60Fe.
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The 12C+12C fusion reaction is famous for its complication of molecular resonances, and plays an important role in both nuclear structure and astrophysics. It is extremely difficult to measure the cross sections of 12C+12C fusions at energies of astrophysical relevance due to very low reaction yields. To measure the complicated resonant structure existing in this important reaction, an efficient thick target method has been developed and applied for the first time at energies Ec.m.<5.3 MeV. A scan of the cross sections over a relatively wide range of energies can be carried out using only a single beam energy. The result of measurement at Ec.m.= 4.1 MeV is compared with other results from previous work. This method would be useful for searching potentially existing resonances of 12C+12C in the energy range 1 MeV<Ec.m.<3 MeV.
The total cross section of 12C(alpha,gamma)16O was measured for the first time by a direct and ungated detection of the 16O recoils. This measurement in inverse kinematics using the recoil mass separator ERNA in combination with a windowless He gas target allowed to collect data with high precision in the energy range E=1.9 to 4.9 MeV. The data represent new information for the determination of the astrophysical S(E) factor.
New experimental data for the 12C+12C reaction have been measured in the centre-of-mass energy range E_{c.m.}= 40 to 60 MeV. Excitation functions for a number of single and mutual $^{12}$C inelastic channels have been measured which include the 0_{gs}, 2_{1}^+, 0_{2}^+, 3_{1}^-, and 4$_1^+$ 12C states. All of the reactions display largely unstructured excitation functions over this energy range. The absence of further resonances in this energy region for the 12C(12C,2C[3_1^-])12C[3_1^-$] reaction confirms theoretical predictions of the termination of the band of resonances found at lower centre-of-mass energies in this channel.
We present the results of a study of charged pion production in 12C + 12C collisions at incident beam energies of 1A GeV and 2A GeV using the HADES spectrometer at GSI. The main emphasis of the HADES program is on the dielectron signal from the early phase of the collision. Here, however, we discuss the data with respect to the emission of charged hadrons, specifically the production of pi+- mesons, which are related to neutral pions representing a dominant contribution to the dielectron yield. We have performed the first large-angular range measurement of the distribution of pi+- mesons for the 12C + 12C collision system covering a fairly large rapidity interval. The pion yields, transverse-mass and angular distributions are compared with calculations done within a transport model, as well as with existing data from other experiments. The anisotropy of pion production is systematically analyzed.
In this work, angular distribution measurements for the elastic channel were performed for the 9Be+12C reaction at the energies ELab=13.0, 14.5, 17.3, 19.0 and 21.0 MeV, near the Coulomb barrier. The data have been analyzed in the framework of the double folding S~ao Paulo potential. The experimental elastic scattering angular distributions were well described by the optical potential at forward angles for all measured energies. However, for the three highest energies, an enhancement was observed for intermediate and backward angles. This can be explained by the elastic transfer mechanism. Keywords: 9Be+12C, Elastic Scattering, S~aoo Paulo Potential.
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