[en] The CNO cycles are fusion processes in stars that convert hydrogen to helium. These hydrogen burning processes occur in several sites and stages of stellar evolution, such as red giants, asymptotic giant branch (AGB) stars, massive stars, and classical novae.

One of the important reactions in the CNO-III and CNO-IV cycles is ¹⁷O(p,γ)¹⁸F [1]. The only available total cross section measurement in a wide energy range for this reaction dates back to several decades ago [2] which makes the theoretical extrapolation to astrophysical energies more difficult and introduces uncertainty.

The aim of the present work is to provide precise total cross section data in the energy range between about 500 keV and the 2MeV using the activation method. The experimental campaign at the new tandetron accelerator of Atomki is in progress. (paper)

[en] Complete text of publication follows. The 35 stable nuclei located on the proton rich side of the valley of stability whose production cannot be explained in the framework of the slow and rapid neutron capture process are called the p-nuclei. In order to reproduce the abundance distribution of these isotopes, an extensive reaction network is needed, in which reactions with alpha particles in their entrance or exit channels play an important role. Therefore, the determination of the alpha-nucleus optical potentials is essential for the calculation of reaction cross sections. The experimental data, which is obtained by alpha elastic scattering, can provide a direct test for the global alpha-nucleus optical potential parameterizations and thus makes the improvement of the statistical models possible. In previous years several (α, α) reactions on heavy nuclei have been studied at ATOMKI. As a continuation of this systematic study, we measured the angular distribution of the ⁶⁴Zn(α, α)⁶⁴Zn reaction at laboratory energies: 12.00 MeV and 16.15 MeV. The experimental setup was an updated version of the scattering chamber which is presented e.g. in [1]. The angular distribution of the scattered alpha particles was recorded by 9 Si particle detectors. The physical dimensions of experimental setup made the investigation of 20-175 deg angular range possible. During the experiment around 700 spectra were acquired by the 9 detectors. The evaluation of the spectra was done with the help of commercial and self-developed programs. The angular distribution of scattering cross section was first calculated in the laboratory frame then it was converted into the center of mass system and normalized to the Rutherford scattering. The results at energies of 12.00 and 16.15 MeV can be found in Fig. 1 and 2 respectively. Due to the high precision measurements the overall uncertainties of the obtained data were less than 5 %. The next stage of the analysis will involve the comparison of the experimental data with cross sections supplied by global optical potentials and the construction of a local optical potential.

[en] Full text: Low energy alpha-nucleus optical potentials are an important ingredient of reaction cross section calculations relevant in various processes of heavy element nucleosynthesis, such as the astrophysical γ -process. The optical potential can be studied directly by high precision alpha elastic scattering experiments. In the Institute for Nuclear Research (Atomki) a systematic study of the optical potential has been carried in the last 15 years. One of the last studied isotope was the ⁶⁴Zn, where complete angular distributions were measured at two energies close above the Coulomb barrier. Through the example of this study, the experimental techniques needed for a precise alpha elastic scattering measurement will be presented. This research was realized in the frames of TAMOP 4.2.4. A/2-11-1-2012-0001 'National Excellence Program Elaborating and operating an inland student and researcher personal support system' The project was subsidized by the European Union and co-financed by the European Social Fund.

[en] Full text: The p-nuclei are a particular set of 35 stable nuclei heavier than iron located at the proton-rich side of the valley of β-stability. These are thought to be considerably produced by a series of photodisintegration reactions from neutron rich isotopes, previously produced by neutron capture processes. The process of creating these p-nuclei, the so-called γ-process is believed to occur e.g. in the O/Ne layers of Type II Supernovae at temperatures of a few GK. In order to run a γ-process network calculation, the p-nuclei abundances and the rates of reactions involved have to be known. However, the α-nucleus optical potential is one of the most uncertain parameters of the theoretical reaction rate calculation. As such, the experimental study of the low energy α-nucleus optical potential is of crucial importance. In this work we present the results from the analysis of the experimentally measured angular distributions of the reactions ⁶⁴Zn(α,α)⁶⁴Zn and ¹⁰⁶Cd(α,α)¹⁰⁶Cd at energies above and below the Coulomb barrier. The difficulties that arise in the study of the α-nuclear potential and the so-called Family Problem are also addressed in this work.

[en] Complete text of publication follows. The 35 stable nuclei located on the proton rich side of the valley of stability whose production cannot be explained in the framework of the slow and rapid neutron capture process are called the p-nuclei. These are thought to be produced by photodisintegration reactions on the neutron rich stable isotopes under high temperatures (T₉ ∼ 2-3, billion Kelvin) and short time intervals to avoid complete photodisintegration to the nickel and iron isotopes. A possible site for these reactions are the C,N,O layers of a Type II Supernovae. A full understanding of the explosion mechanisms of Type II Supernovae is required to more precisely determine where the necessary conditions for the process can be found. The ¹⁰⁶Cd isotope is an important piece of the puzzle and the study of the ¹⁰⁶Cd alpha-nuclear potential is a necessary requirement to better describe the full reaction network. The aim of this work is to extend the knowledge of the alpha nucleus potentials for p-nuclei at energies close to the astrophysically relevant window for the photodisintegration reaction (γ, α). The elastic scattering of α particles has been observed at different energies above and below the Coulomb barrier of the p-nucleus ¹⁰⁶Cd at the ATOMKI cyclotron laboratory. The main problem in the study of ¹⁰⁶Cd α-nucleus potential is the 'Family Problem' which implies there are several different potentials that describe the experimental data with similar precision. The problem was presented in previous articles and was treated with more detail in. The current results from the Family Problem can be seen in Fig. 1. The families obtained provide a better description of the capture data than the McFadden global α-nuclear potential. Further analysis of the families will allow for the determination of the most suited family to describe the experimental data. The ¹⁰⁶Cd family problem is currently being treated in a full length article, soon to be published, where the obtained families are compared with further global α-nucleus potentials and χ²/F table will also be presented to further strengthen the results.

[en] In this work we present the continuation of the reported analysis [1] of the experimentally measured angular distributions of the reaction ¹⁰⁶Cd(α, α)¹⁰⁶Cd at several different energies around the Coulomb barrier. The difficulties that arise in the study of ¹⁰⁶Cd-α-nuclear potential and the so called Family Problem are addressed.

[en] Elastic alpha scattering cross sections on the even-odd "1"1"5In nucleus have been measured at energies E_l_a_b_. = 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. (paper)

[en] Alpha 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 $E_{\mathit{Lab}}=27.0\text{MeV}$ 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.