Determination of Pr-141(alpha, n)Pm-144 cross sections at energies of relevance for the astrophysical p process using the gamma gamma coincidence method

The reaction Pr-141(alpha, n)Pm-144 was investigated between E-alpha = 11 MeV and 15 MeV with the activation method using the gamma gamma coincidence method with a segmented clover-type high-purity Germanium (HPGe) detector. Measurements with four other HPGe detectors were additionally made. The comparison proves that the gamma gamma coincidence method is an excellent tool to investigate cross sections down to the microbarn range. The (alpha, n) reaction at low energy is especially suited to test alpha + nucleus optical-model potentials for application in the astrophysical p process. The experimentally determined cross sections were compared to Hauser-Feshbach statistical model calculations using different optical potentials and generally an unsatisfactory reproduction of the data was found. A local potential was constructed to improve the description of the data. The consequences of applying the same potential to calculate astrophysical (gamma, alpha) rates for Pm-145 and Gd-148 were explored. In summary, the data and further results underline the problems in global predictions of alpha + nucleus optical potentials at astrophysically relevant energies.