Alpha induced reaction cross section measurements on 162Er for the astrophysical γ process

Funding Details: NSF, National Science Foundation. ©2014 Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/). Funded by SCOAP3The cross sections of the Er162(α,γ)Yb166 and Er162(α,n)Yb165 reactions have been measured for the first time. The radiative alpha capture reaction cross section was measured from Ec.m.=16.09MeV down to Ec.m.=11.21MeV, close to the astrophysically relevant region (which lies between 7.8 and 11.48 MeV at 3 GK stellar temperature). The Er162(α,n)Yb165 reaction was studied above the reaction threshold between Ec.m.=12.19 and 16.09MeV. The fact that the Er162(α,γ)Yb166 cross sections were measured below the (α,n) threshold at first time in this mass region opens the opportunity to study directly the α-widths required for the determination of astrophysical reaction rates. The data clearly show that compound nucleus formation in this reaction proceeds differently than previously predicted. © 2014 Elsevier B.V.Peer reviewedFinal Published versio

Coulomb suppression of the stellar enhancement factor

It is commonly assumed that reaction measurements for astrophysics should be preferably performed in the direction of positive Q value to minimize the impact of the stellar enhancement factor, i.e. the difference between the laboratory rate and the actual stellar rate. We show that the stellar effects can be minimized in the charged particle channel, even when the reaction Q value is negative. As a demonstration, the cross section of the astrophysically relevant 85Rb(p,n)85Sr reaction has been measured by activation between 2.16 < Ec.m. < 3.96 MeV and the astrophysical reaction rate for (p,n) as well as (n,p) is directly inferred from the data. The presented arguments are also relevant for other alpha and proton-induced reactions in the p and rp processes. Additionally, our results confirm a previously derived modification of a global optical proton potential.Comment: submitted to PR

The 106Cd(α, α)106Cd elastic scattering in a wide energy range for γ process studies

Date of Acceptance: 15/04/2015Alpha elastic scattering angular distributions of the 106Cd(α, α)106Cd reaction were measured at three energies around the Coulomb barrier to provide a sensitive test for the α + nucleus optical potential parameter sets. Furthermore, the new high precision angular distributions, together with the data available from the literature were used to study the energy dependence of the locally optimized α + nucleus optical potential in a wide energy region ranging from ELab=27.0MeV down to 16.1 MeV.The potentials under study are a basic prerequisite for the prediction of α-induced reaction cross sections and thus, for the calculation of stellar reaction rates used for the astrophysical γ process. Therefore, statistical model predictions using as input the optical potentials discussed in the present work are compared to the available 106Cd + alpha cross section data.Peer reviewe

70Ge(p,gamma)71As and 76Ge(p,n)76As cross sections for the astrophysical p process: sensitivity of the optical proton potential at low energies

The cross sections of the 70Ge(p,gamma)71As and 76Ge(p,n)76As reactions have been measured with the activation method in the Gamow window for the astrophysical p process. The experiments were carried out at the Van de Graaff and cyclotron accelerators of ATOMKI. The cross sections have been derived by measuring the decay gamma-radiation of the reaction products. The results are compared to the predictions of Hauser-Feshbach statistical model calculations using the code NON-SMOKER. Good agreement between theoretical and experimental S factors is found. Based on the new data, modifications of the optical potential used for low-energy protons are discussed.Comment: Accepted for publication in Phys. Rev.