M. Fey

Astrophysical Reaction Rate of 12C(α, γ)16O

A new astrophysical reaction rate of 12C(α, γ)16O has been calculated based on our recent determination of the E1- and E2-capture cross sections. The R-matrix method has been applied to describe the SE1- and SE2-factor functions as well as the data of elastic α scattering and the β-delayed α decay of 16N from other experiments. The resulting reaction rate for stellar temperatures of T9 = 0.04-10 is presented in both tabular form and an analytic expression. A new temperature dependence of the reaction rate was obtained when compared with reported evaluations. The associated uncertainties were reduced considerably in comparison to previous determinations.

The key reactions in Stellar helium burning: 12C(α,γ)16O and 22Ne(α,n)25Mg

Abstract The excitation functions of 12C(α,γ)16O and 22Ne(α,n)25Mg have been determined with a yet unequaled experimental sensitivity of 10−11 b. From γ-angular distributions the SE1-and SE2-factors for 12C(α,γ)16O have been deduced and extrapolated into the range of helium burning temperatures using the R-matrix method. An improved reaction rate has been calculated: NA〈σν〉=(7.9±2.5)x10−15cm3(mols)−1 at T9 = 0.2. For a more precise extrapolation the excitation function has to be measured with better statistics. Therefore a new experiment on 12C(α,γ)16O with a better suited setup has been started recently. The accuracy of the 22Ne(α,n)25Mg reaction rate could be improved considerably compared to previous compilations: NA〈σν〉 = (0.88−0.3+2.6) x 10−16cm3(mols)−1 at T9 = 0.2.

A systematic study of proton capture reactions in the SeSb region at energies relevant to the p process

Abstract A systematic investigation of (p,γ) cross sections of nuclei from Se to Sb is presented. In-beam cross section measurements were carried out at E p = 1.4–5 MeV by using an array of 4 HPGe detectors of 100% relative efficiency shielded with BGO crystals. The S factors obtained are compared with the predictions of the statistical model code MOST.