Investigation of alpha-induced reactions on Ba-130 and Ba-132 and their importance for the synthesis of heavy p nuclei

Abstract

Captures of a particles on the proton-richest barium isotope, Ba-130, have been studied in order to provide cross-section data for the modeling of the astrophysical gamma process. The cross sections of the Ba-130(alpha,gamma)Ce-134 and Ba-130(alpha, n)Ce-133 reactions have been measured with the activation technique in the center-of mass energy range between 11.6 and 16 MeV, close above the astrophysically relevant energies. As a side result, the cross section of the Ba-132(alpha, n)Ce-135 reaction has also been measured. The results are compared with the prediction of statistical model calculations, using different input parameters such as alpha + nucleus optical potentials. It is found that the (a, n) data can be reproduced by employing the standard a + nucleus optical potential widely used in astrophysical applications. Assuming its validity also in the astrophysically relevant energy window, we present new stellar reaction rates for Ba-130(alpha,gamma)Ce-134 and Ba-132(alpha,gamma)Ce-136 and their inverse reactions calculated with the SMARAGD statistical model code. The highly increased Ce-136(gamma, alpha)Ba-132 rate implies that the p nucleus Ba-130 cannot directly receive contributions from the Ce isotopic chain. Further measurements are required to better constrain this result.