Alpha elastic scattering angular distributions of the 106Cd(alpha,alpha)106Cd reaction were measured at three energies around the Coulomb barrier to provide a sensitive test for the alpha + nucleus optical potential parameter sets. Furthermore, the n
ew high precision angular distributions, together with the data available from the literature were used to study the energy dependence of the locally optimized {alpha}+nucleus optical potential in a wide energy region ranging from E_Lab = 27.0 MeV down to 16.1 MeV. The potentials under study are a basic prerequisite for the prediction of alpha-induced reaction cross sections and thus, for the calculation of stellar reaction rates used for the astrophysical gamma 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.
The $gamma$-process in core-collapse and/or type Ia supernova explosions is thought to explain the origin of the majority of the so-called $p$ nuclei (the 35 proton-rich isotopes between Se and Hg). Reaction rates for $gamma$-process reaction network
studies have to be predicted using Hauser-Feshbach statistical model calculations. Recent investigations have shown problems in the prediction of $alpha$-widths at astrophysical energies which are an essential input for the statistical model. It has an impact on the reliability of abundance predictions in the upper mass range of the $p$ nuclei. With the measurement of the $^{164,166}$Er($alpha$,n)$^{167,169}$Yb reaction cross sections at energies close to the astrophysically relevant energy range we tested the recently suggested low energy modification of the $alpha$+nucleus optical potential in a mass region where $gamma$-process calculations exhibit an underproduction of the $p$ nuclei. Using the same optical potential for the $alpha$-width which was derived from combined $^{162}$Er($alpha$,n) and $^{162}$Er($alpha$,$gamma$) measurement makes it plausible that a low-energy modification of the optical $alpha$+nucleus potential is needed.
The cross sections of the 162Er(a,g,)166Yb and 162Er(a,n)165Yb reactions have been measured for the first time. The radiative alpha capture reaction cross section was measured from Ec.m. = 16.09 down to Ec.m. = 11.21 MeV, close to the astrophysically
relevant region (which lies between 7.8 and 11.48 MeV at 3 GK stellar temperature). The 162Er(a,n)165Yb reaction was studied above the reaction threshold between Ec.m. = 12.19 and 16.09 MeV. The fact that the 162Er(a,g)166Yb cross sections were measured below the (a,n) threshold at first time in this mass region opens the opportunity to study directly the a-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.
The elastic scattering cross sections for the reactions $^{110,116}$Cd($alpha,alpha$)$^{110,116}$Cd at energies above and below the Coulomb barrier are presented to provide a sensitive test for the alpha-nucleus optical potential parameter sets. Addi
tional constraints for the optical potential are taken from the analysis of elastic scattering excitation functions at backward angles which are available in literature. Moreover, the variation of the elastic alpha scattering cross sections along the $Z = 48$ isotopic and $N = 62$ isotonic chain is investigated by the study of the ratios of the of $^{106,110,116}$Cd($alpha,alpha$)$^{106,110,116}$Cd scattering cross sections at E$_{c.m.} approx$ 15.6 and 18.8 MeV and the ratio of the $^{110}$Cd($alpha,alpha$)$^{110}$Cd and $^{112}$Sn($alpha,alpha$)$^{112}$Sn reaction cross sections at E$_{c.m.} approx$ 18.8 MeV, respectively. These ratios are sensitive probes for the alpha-nucleus optical potential parameterizations. The potentials under study are a basic prerequisite for the prediction of $alpha$-induced reaction cross sections, e.g. for the calculation of stellar reaction rates in the astrophysical $p$- or $gamma$-process.
The $gamma$ process in supernova explosions is thought to explain the origin of proton-rich isotopes between Se and Hg, the so-called $p$ nuclei. The majority of the reaction rates for $gamma$ process reaction network studies has to be predicted in H
auser-Feshbach statistical model calculations using global optical potential parameterizations. While the nucleon+nucleus optical potential is fairly known, for the $alpha$+nucleus optical potential several different parameterizations exist and large deviations are found between the predictions calculated using different parameter sets. By the measurement of elastic $alpha$-scattering angular distributions at energies around the Coulomb barrier a comprehensive test for the different global $alpha$+nucleus optical potential parameter sets is provided. Between 20$^{circ}$ and 175$^{circ}$ complete elastic alpha scattering angular distributions were measured on the $^{113}$In textit{p} nucleus with high precision at E$_{c.m.}$ = 15.59 and 18.82 MeV. The elastic scattering cross sections of the $^{113}$In($alpha$,$alpha$)$^{113}$In reaction were measured for the first time at energies close to the astrophysically relevant energy region. The high precision experimental data were used to evaluate the predictions of the recent global and regional $alpha$+nucleus optical potentials. Parameters for a local $alpha$+nucleus optical potential were derived from the measured angular distributions. Predictions for the reaction cross sections of $^{113}$In($alpha,gamma$)$^{117}$Sb and $^{113}$In($alpha$,n)$^{116}$Sb at astrophysically relevant energies were given using the global and local optical potential parameterizations.
(Shorten version of the PRC abstract) Alpha-induced reactions on 127I have been studied using the activation technique in order to provide cross section data for the modeling of the astrophysical gamma process. The relative intensity of the 536.1 keV
gamma transition was measured precisely, its uncertainty was reduced from 13% to 4%. By measuring the yield of the characteristic X-rays, the cross sections of the 127I(alpha,gamma)131Cs reaction have been determined for the first time close to the astrophysically relevant energy region, at energies 9.50 < Ec.m. < 15.15$ MeV. The 127I(alpha,n)130Cs reaction was studied in the range 9.62 < Ec.m. < 15.15 MeV by measuring the yield of the 536.1 keV gamma-ray and at the lower part of this energy range by counting the characteristic X-rays. A comparison of the resulting cross sections to predictions of statistical model calculations confirmed the predictions of the astrophysically relevant averaged alpha width. Nevertheless, the newly derived stellar reaction rates at gamma process temperatures for 127I(alpha,gamma)131$Cs and its reverse reaction are factors 4-10 faster than previous calculations, due to improvements in the reaction model.
Elastic scattering cross sections of the $^{89}$Y($alpha$,$alpha$)$^{89}$Y reaction have been measured at energies E$_{c.m.}$ = 15.51 and 18.63 MeV. The high precision data for the semi-magic $N = 50$ nucleus $^{89}$Y are used to derive a local poten
tial and to evaluate the predictions of global and regional $alpha$-nucleus potentials. The variation of the elastic alpha scattering cross sections along the $N = 50$ isotonic chain is investigated by a study of the ratios of angular distributions for $^{89}$Y($alpha$,$alpha$)$^{89}$Y and $^{92}$Mo($alpha$,$alpha$)$^{92}$Mo at E$_{c.m.} approx$ 15.51 and 18.63 MeV. This ratio is a very sensitive probe at energies close to the Coulomb barrier, where scattering data alone is usually not enough to characterize the different potentials. Furthermore, $alpha$-cluster states in $^{93}$Nb = $^{89}$Y $otimes$ $alpha$ are investigated.
