[en] Measured differential cross sections for deuteron induced γ-ray emission from the reactions "1"2C(d,pγ)"1"3C, (E_γ = 3089 keV), "1"4N(d,pγ)"1"5N (E_γ = 8310 keV) and "1"6O(d,pγ)"1"7O (E_γ = 871 keV) available in the literature were assessed. In order to cross check the assessed γ-ray production cross section data, thick target γ-yields calculated from the differential cross sections were compared with available measured thick target yields. Recommended differential cross section data for each reaction were deduced for particle induced γ-ray emission (PIGE) applications.

[en] The CNO cycle is one of the fundamental processes of hydrogen burning in stars. The first reaction of the cycle is the radiative proton capture on ${}^{12}$C and the rate of this ${}^{12}$C(p,γ)${}^{13}$N reaction is related to the ${}^{12}$C/${}^{13}$C ratio observed e.g. in the Solar System. The low-energy cross section of this reaction was measured several times in the past, however, the experimental data are scarce in a wide energy range especially around the resonance at 1.7 MeV. In the present work the ${}^{12}$C(p,γ)${}^{13}$N cross section was measured between 300 and 1900 keV using the activation method. This method was only used several decades ago in the low-energy region. As the activation method provides the total cross section and has uncertainties different from those of the in-beam γ-spectroscopy technique, the present results provide a largely independent data set for future low-energy extrapolations and thus for astrophysical reaction rate calculations.

[en] For the better understanding of the astrophysical γ-process the experimental determination of low energy proton- and α-capture cross sections on heavy isotopes is required. The existing data for the ⁹²Mo(p,γ)⁹³Tc reaction are contradictory and strong fluctuation of the cross section is observed which cannot be explained by the statistical model. In this paper a new determination of the ⁹²Mo(p,γ)⁹³Tc and ⁹⁸Mo(p,γ)^99mTc cross sections based on thick target yield measurements are presented and the results are compared with existing data and model calculations. Reaction rates of ⁹²Mo(p,γ)⁹³Tc at temperatures relevant for the γ-process are derived directly from the measured thick target yields. The obtained rates are a factor of 2 lower than the ones used in astrophysical network calculations. It is argued that in the case of fluctuating cross sections the thick target yield measurement can be more suited for a reliable reaction rate determination

[en] The astrophysically important ³He(α,γ)⁷Be reaction was studied at high energies where the available experimental data are in contradiction. A thin window ³He gas cell was used and the cross section was measured with the activation method. The obtained cross sections at energies between E_c.m.=1.5 and 2.5 MeV are compared with the available data and theoretical calculations. The present results support the validity of the high energy cross section energy dependence observed by recent experiments

[en] Complete text of publication follows. The ⁶⁶Ga radioisotope is important e.g. in the high energy efficiency calibration of γ-detectors. Therefore, the precise knowledge of its half-life is crucial. In 2004 a critical review was published about the half-lives of radionuclides considered to be important for detector efficiency calibrations. It was found that the precision of the ⁶⁶Ga half-life is by far not enough for the requirements posed by the International Atomic Energy Agency. Since 2004 two new high precision half-life measurement of ⁶⁶Ga became available whose results disagree by about six standard deviations. This strong deviation indicates that the knowledge of the ⁶⁶Ga half-life is still very far from the required precision, therefore, new experiments are clearly needed. In the present work the half-life of ⁶⁶Ga has been measured based on counting the γ-radiation following the β⁺ decay. Special emphasis was put to the experimental implementation of the measurements to reduce the systematic uncertainties and to increase the reliability of the measured half-life value. Six sources were produced at the cyclotron of Atomki by the ⁶⁶Zn(p,n)⁶⁶Ga and ⁶³Cu(α,n)⁶⁶Ga reactions. Evaporated Zn targets and thick Cu disks were used for these two reactions, respectively. The γ-radiation following the β⁺ decay of ⁶⁶Ga was measured with three shielded HPGe detectors. A sufficiently long waiting time was inserted between the source preparation and the beginning of the counting in order to reduce the initial dead time of the counting setups below 2 %. The reliability of the dead time values provided by the data acquisition system was checked by measuring the decay of one source in parallel with two different acquisition systems. In order to check the longterm stability of the counting systems, longlived reference sources were measured together with the ⁶⁶Ga sources. The reference isotopes were ⁵⁶Co, ⁶⁵Zn and ¹³⁷Cs. The ⁶⁶Ga half-life was determined based on the analysis of the seven strongest γ-transitions. The decay was followed for up to 87 hours (about 9 half-lives) and the spectra were recorded in every 30 minutes. The half-life was determined from the parameters of the exponential curve fitted to the peak area vs. time function. The final value was calculated as the weighted average of 37 individual half-life values (six sources with six or seven γ-transitions). The obtained half-life value is t_1/2 =(9.312±0.032) h. The quoted uncertainty include the statistical uncertainty as well as systematic uncertainties from the stability of the counting systems, dead time determination and peak integration. Further details of the experiments and the data analysis can be found in [5]. The obtained half-life value supports the validity of one of the recent measurements while it is in contradiction with the other one.

[en] In this paper we describe our experiment determining the half-life of ^133mCe. An activation-based nuclear-reaction cross-section measurement has been carried out for the ¹³⁰Ba(α, n)^133mCe reaction, in order to improve our knowledge of the astrophysical p-process. For the analysis of such a measurement, the precise knowledge of the decay half-life of the reaction product is desired. In the case of ^133mCe the literature half-life value has only been known with a high relative uncertainty. A measurement utilizing γ -spectrometry has been carried out to refine the half-life of ^133mCe. As a result, the new recommended half-life is t_1/2 = (5.326±0.011) h. This value has been found to be consistent with the previous literature value, while its uncertainty has been reduced by more than a factor of 30. (orig.)

[en] Complete text of publication follows. Supernova simulations aim to explain the nucleosynthesis of heavy elements. These simulations rely heavily on nuclear physics input. This input comes either directly from nuclear measurements or from theoretical calculations, where the theories are constrained by the results of nuclear experiments. In order to support the theoretical work on the astrophysical γ process, we planned to measure the cross section of α induced reactions on ¹³⁰Ba, as experimental data on these reactions are absent in the literature. The (α, γ) reaction cross section can directly be used to enhance γ process models, while the (α, n) reaction is used to constrain the Hauser - Feshbach model calculations used in such models. We used the activation technique in our measurement: we activated the ¹³⁰Ba target with an α beam and detected the γ photons emitted by the decaying reaction products. In order to perform the cross section measurement one needs the precise half-lives of the created nuclei. We discovered that the half life of one of the products of the ¹³⁰Ba + α reaction, ^133mCe is known with high uncertainty (t_1/2^lit = 4.9 h ± 0.4 h). We also found evidence that this half-life value is underestimated. As the compilations are based on a single measurement published back in 1967, we decided to perform a recent half-life measurement of ^133mCe the precision of which is suitable for our needs. The irradiations were performed at the cyclotron of Atomki and the decay of ^133mCe was followed with a γ detector. By analysing the 58.4 keV, 130.8 keV and 477.2 keV peaks we found the half-life to be t_1/2 = 5.326 h±0.011 h. As this value is consistent with the literature value and its uncertainty is lower by a factor of 30, we have suggested its use in the nuclear data compilations to-come. This new half-life value was successfully used in the cross section measurement of the ¹³⁰Ba(α, n)^133mCe reaction.

[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] Highlights: • Based on gamma-spectroscopy the half-life of 65Ga is measured. • Systematic uncertainties are carefully studied. • The obtained result is (15.133 +- 0.028)min. • This results is in agreement with the only available value in literature, but almost one order of magnitude more precise. - Abstract: The literature half-life value of ⁶⁵Ga is based on only one experiment carried out more than 60 years ago and it has a relatively large uncertainty. In the present work this half-life is determined based on the counting of the γ-rays following the β-decay of ⁶⁵Ga. Our new recommended half-life is t_1/2 = (15.133 ± 0.028) min which is in agreement with the literature value but almost one order of magnitude more precise.

[en] The study of nuclear physics in stellar explosions is a strong driving force for the development of modern radioactive ion beam (RIB) facilities. Indeed, in explosive astrophysical processes isotopes far from the valley of stability are created and they can only be studied with RIB facilities. Low energy reactions on heavy stable isotopes, on the other hand, are still important as the relevant experimental database is very limited even at stability. Nucleosynthesis model calculations have therefore to rely on theoretical reaction rates, which often prove to be unreliable. In the last twenty years the experimental study of the astrophysical γ-process has been one of the most important research topics of the Atomki nuclear astrophysics group. Cross sections of proton and α-induced reactions are systematically measured in order to provide data for the assessment of theoretical calculations. As one of the key nuclear physics ingredient, the low energy α-nucleus optical potential was investigated with special emphasis. In this talk, some recent experiments and results related to the γ-process will be presented. In order to give a comprehensive overview, the group's other activities will also be shortly summarized. (author)