R. T. Güray

Odd p isotope In-113 : Measurement of alpha-induced reactions

One of the few p nuclei with an odd number of protons is {sup 113}In. Reaction cross sections of {sup 113}In({alpha},{gamma}){sup 117}Sb and {sup 113}In({alpha},n){sup 116}Sb have been measured with the activation method at center-of-mass energies between 8.66 and 13.64 MeV, close to the astrophysically relevant energy range. The experiments were carried out at the cyclotron accelerator of ATOMKI. The activities were determined by off-line detection of the decay {gamma} rays with a HPGe detector. Measured cross sections and astrophysical S factor results are presented and compared with statistical model calculations using three different {alpha}+nucleus potentials. The comparison indicates that the standard rates used in the majority of network calculations for these reactions were too fast due to the energy dependence of the optical {alpha} potential at low energy.

Alpha-induced reaction cross section measurements on 151Eu for the astrophysical γ-process

In order to extend the experimental database relevant for the astrophysical -process towards the unexplored heavier mass region, the cross sections of the 151 Eu(�,) 155 Tb and 151 Eu(�,n) 154 Tb reactions have been measured at low energies between 12 and 17MeV using the activation technique. The results are compared with the predictions of statistical model calculations and it is found that the calculations overestimate the cross sections by about a factor of two. A sensitivity analysis shows that this discrepancy is caused by the inadequate description of the �+nucleus channel. A factor of two reduction of the reaction rate of 151 Eu(�,) 155 Tb in -process network calculations with respect to theoretical rates using the optical potential by McFadden and Satchler (1966) is recommended.

Cd110,116(α,α)Cd110,116 elastic scattering and systematic investigation of elastic α scattering cross sections along the Z=48 isotopic and N=62 isotonic chains

The elastic scattering cross sections for the reactions 110,116 Cd(α,α) 110,116 Cd at energies above and below the Coulomb barrier are presented to provide a sensitive test for the α-nucleus optical potential parameter sets. Additional 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 α scattering cross sections along the Z = 48 isotopic and N = 62 isotonic chain is investigated by the study of the ratios of the 106,110,116 Cd(α,α) 106,110,116 Cd scattering cross sections at Ecm ≈ 15.6 and 18.8 MeV and the ratio of the 110 Cd(α,α) 110 Cd and 112 Sn(α,α) 112 Sn reaction cross sections at Ecm ≈ 18.8 MeV, respectively. These ratios are sensitive probes for the α-nucleus optical potential parametrizations. The potentials under study are a basic prerequisite for the prediction of α-induced reaction cross sections (e.g., for the calculation of stellar reaction rates in the astrophysical p or γ process).

Measurements of proton-induced reaction cross sections on Te 120 for the astrophysical p process

The total cross sections for the {sup 120}Te(p,{gamma}){sup 121}I and {sup 120}Te(p,n){sup 120}I reactions have been measured by the activation method in the effective center-of-mass energies 2.47 MeV {<=} E{sub c.m.}{sup eff} {<=} 7.93 MeV and 6.44 MeV {<=} E{sub c.m.}{sup eff} {<=} 7.93 MeV, respectively. The targets were prepared by evaporation of 99.4% isotopically enriched {sup 120}Te on aluminum and carbon backing foils, and bombarded with proton beams provided by the FN tandem accelerator at the University of Notre Dame. The cross sections and S factors were deduced from the observed {gamma} ray activity, which was detected off-line by two Clover HPGe detectors mounted in close geometry. The results are presented and compared with the predictions of statistical model calculations using the codes NON-SMOKER and TALYS.

High precision 113In(α,α)113In elastic scattering at energies near the Coulomb barrier for the astrophysical γ process

Background: The γ 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 γ process reaction network studies have to be predicted in Hauser-Feshbach statistical model calculations using global optical potential parametrizations. While the nucleon + nucleus optical potential is fairly well known, for the α + nucleus optical potential several different parametrizations exist and large deviations are found between the predictions calculated using different parameter sets. Purpose: By the measurement of elastic α-scattering angular distributions at energies around the Coulomb barrier a comprehensive test for the different global α + nucleus optical potential parameter sets is provided. Methods: Between 20 ◦ and 175 ◦ complete elastic alpha scattering angular distributions were measured on the 113 In p nucleus with high precision at Ec.m. = 15.59 and 18.82 MeV. Results: The elastic scattering cross sections of the 113 In(α,α) 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 α + nucleus optical potentials. Parameters for a local α + nucleus optical potential were derived from the measured angular distributions. Conclusions: Predictions for the reaction cross sections of 113 In(α, γ ) 117 Sb and 113 In(α,n) 116 Sb at astrophysically relevant energies were given using the global and local optical potential parametrizations.

Test of statistical model cross section calculations for α -induced reactions on Ag 107 at energies of astrophysical interest

Background: Astrophysical reaction rates,which are mostly derived from theoretical cross sections, are necessary ninput to nuclear reaction network simulations for studying the origin of p nuclei. Past experiments have found a considerable difference between theoretical and experimental cross sections in some cases, especially for (α,γ ) reactions at low energy. Therefore, it is important to experimentally test theoretical cross section predictions at low, astrophysically relevant energies. n nPurpose: The aim is to measure reaction cross sections of 107Ag(α,γ )111In and 107Ag(α,n)110In at low energies nin order to extend the experimental database for astrophysical reactions involving α particles towards lower mass numbers. Reaction rate predictions are very sensitive to the optical model parameters and this introduces a large uncertainty into theoretical rates involving α particles at low energy. We have also used Hauser-Feshbach statistical model calculations to study the origin of possible discrepancies between prediction and data. n nMethod: An activation technique has been used to measure the reaction cross sections at effective center of mass nenergies between 7.79 MeV and 12.50 MeV. Isomeric and ground state cross sections of the (α,n) reaction were ndetermined separately. n nResults: The measured cross sections were found to be lower than theoretical predictions for the (α,γ ) reaction. Varying the calculated averaged widths in the Hauser-Feshbach model, it became evident that the data for the (α,γ) and (α,n) reactions can only be simultaneously reproduced when rescaling the ratio of γ to neutron width and using an energy-dependent imaginary part in the optical α + 107Ag potential. n nConclusions: The new data extend the range of measured charged-particle cross sections for astrophysical napplications to lower mass numbers and lower energies. The modifications in the model predictions required to nreproduce the present data are fully consistent with what was found in previous investigations. Thus, our results nconfirm the previously suggested energy-dependent modification of the optical α+nucleus potential.

α scattering and α -induced reaction cross sections of Zn 64 at low energies

Background: α-nucleus potentials play an essential role for the calculation of α-induced reaction cross sections at low energies in the statistical model. Uncertainties of these calculations are related to ambiguities in the adjustment of the potential parameters to experimental elastic scattering angular distributions and to the energy dependence of the effective α-nucleus potentials. Purpose: The present work studies the total reaction cross section σreac of α-induced reactions at low energies which can be determined from the elastic scattering angular distribution or from the sum over the cross sections of all open nonelastic channels. Method: Elastic and inelastic Zn64(α,α)Zn64 angular distributions were measured at two energies around the Coulomb barrier, at 12.1 and 16.1 MeV. Reaction cross sections of the (α,γ), (α,n), and (α,p) reactions were measured at the same energies using the activation technique. The contributions of missing nonelastic channels were estimated from statistical model calculations. Results: The total reaction cross sections from elastic scattering and from the sum of the cross sections over all open nonelastic channels agree well within the uncertainties. This finding confirms the consistency of the experimental data. At the higher energy of 16.1 MeV, the predicted significant contribution of compound-inelastic scattering to the total reaction cross section is confirmed experimentally. As a by-product it is found that most recent global α-nucleus potentials are able to describe the reaction cross sections for Zn64 around the Coulomb barrier. Conclusions: Total reaction cross sections of α-induced reactions can be well determined from elastic scattering angular distributions. The present study proves experimentally that the total cross section from elastic scattering is identical to the sum of nonelastic reaction cross sections. Thus, the statistical model can reliably be used to distribute the total reaction cross section among the different open channels.

High precision elastic α scattering on the even-odd 115In nucleus at low energies

Elastic alpha scattering cross sections on the even-odd 115In nucleus have been measured at energies Elab. = 16.15 MeV and 19.50 MeV. The high precision experimental data are used to derive the parameters of a local a nucleus optical potential.

Alpha capture reaction cross section measurements on Sb isotopes by activation method

Alpha induced reactions on natural and enriched antimony targets were investigated via the activation technique in the energy range from 9.74 MeV to 15.48 MeV, close to the upper end of the Gamow window at a temperature of 3 GK relevant to the γ-process. The experiments were carried out at the Institute for Nuclear Research, the Hungarian Academy of Sciences (MTA Atomki). 121Sb(α,γ)125I, 121Sb(α,n)124I and 123Sb(α,n)126I reactions were measured using a HPGe detector. In this work, the 121Sb(α,n)124 cross section results and the comparison with the theoretical predictions (obtained with standard settings of the statistical model codes NON-SMOKER and TALYS) were presented.

Investigation of α -induced reactions on Sb isotopes relevant to the astrophysical γ process

This document is the Accepted Manuscript version of the following article: Z. Korkulu, et al, ‘Investigation of α-induced reactions on Sb isotopes relevant to the astrophysical γ process’, Physical Review C, Vol. 97(4): 045803, April 2018, available online at DOI: https://doi.org/10.1103/PhysRevC.97.045803