[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 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)

[en] Complete text of publication follows. The synthesis of the chemical elements heavier than iron is the focal point of nuclear astrophysics. The origin of about 99% of the heavier elements observed in the Universe are well described by the classical r- and s-processes. Nevertheless, the genesis of the remaining 1% is rather interesting: because of the shielding effect of the stable elements, they can not be created via neutron-capture reactions. These are the so-called p-isotopes and their producing mechanism is referred to as the astrophysical p-process. The validation of nucleosynthesis theories are based mainly on experiments, i.e. on the extensive knowledge about the reaction cross sections. For this reason there is a great demand to high precision measurements. Particularly, among the p-elements there are some, where the experimental results are totally missing. This report shows some results of the α-induced reaction cross section measurements on ¹³⁰Ba, which is one from these above mentioned isotopes. In the astrophysical relevant energy range - in the Gamow-window, in this case between 5.3 and 8.1 MeV - the ¹³⁰Ba's (α,γ) and (α,γ) reaction cross sections are very low, thus they are non-measurable in laboratory environment. The cross section must be measured 'higher' energy and the results must be interpolated to the lower range. The α-capture on ¹³⁰Ba leads to the radioactive ¹³⁴Ce and decays to ¹³⁴La with 75.9h half-life. The produced ¹³⁴La decays to the stable ¹³⁴Ba with a half-life of 6.67min. Besides this radiative capture, the ¹³⁰Ba (α,n)¹³³Ce can be measured parallel, because both the ground state and the isomeric state of the ¹³³Ce also have a suitable half-life (5.3h, 97min respectively). The natural abundance of the p-nucleus ¹³⁰Ba is very low, consequently, enriched target should be used. Targets have been prepared by evaporating BaCO₃ onto thin Al foils. The target stability was continuously monitored during the irradiation process. The uncertainty of the measured values has been calculated from the following components: counting statistics (≤5%), number of target atoms (≤ 8%), detector efficiency and summing correction (≤ 5%) and current integration (≤ 3%). The experimental cross sections were compared to theoretical predictions based on the Hauser-Fesbach statistical model. The predictions overestimates the experimental values by factors 2-3 in the measured energy range.

[en] Complete text of publication follows. In our γ-process related studies charge particle capture cross sections are measured, from which the photodisintegration rates can be calculated applying the principle of detailed balance. Many of these reactions can be measured via the activation method, where the sample is irradiated by the ion beam provided by an accelerator, the activated sample is transported to a shielded detector for activity measurement. From the detected activity, the reaction cross section can be derived. This method was successfully applied for the determination of several α induced reaction cross sections for the astrophysical γ-process at ATOMKI. Recently, to determine the accumulated activity not only γ-ray but X-ray counting was performed. To measure these X-rays a low energy photon spectrometer (LEPS) was used, which consists of a thin crystal of high purity germanium (HPGe). It has high efficiency for low energy γ- and X-rays and insensitive to the high energy γ-s. With a graded shield (4mm Cu, 2mm Cd, 8 cm Pb) it is more suited for the low energy counting experiments, compared to a coaxial HPGe detector in a 10 cm lead shield lined with 1mm copper and 1mm cadmium. The minimum detectable activity (MDA) is a measure to test the performance of a counting system. The MDA is inversely proportional to the absolute detection efficiency (ε), and proportional to the square root of the background (B) and to the full width at half maximum (FWHM) energy resolution. MDA ∞ √BxFWHM/ε. The ratio of two MDAs is a good measure to compare the two counting systems, because it is independent from the source and counting parameters, only depends on the detectors. The following MDA ratio is calculated and shown in figure 1: MDA_LEPS/MDA_HPGe = √B_LEPS/B_HPGe ε_HPGe/ε_LEPS FWHM_LEPS/FWHM_HPGe. It turned out that the LEPS for γ- or X-ray counting is preferable up to 350 keV. In the X-ray region (up to 100 keV) the LEPS can measure 4 time less activity. Between 100 keV and 250 keV it is still better than a factor of 2. This finding opens the way to measure lower cross sections for the astrophysical γ-process, if the source emits high intensity γ- or X-rays in the low energy region.

[en] Compete text of publication follows. The uncertainty of the S₃₄(0) value for the ₃He+₄He→⁷Be+γ reaction is the nuclear physics biggest uncertainty contributing to the neutrino flux in the SSM (Standard Solar Model) from the decay of ⁷Be from the Sun]; so that a possible reduction of this uncertainty will significantly reduce the uncertainty in the calculated flux in the frame of the SSM and which the BOREXINO and KamLAND experiments are supposed to observe. In the last 50 years, this experiment produced a lot of data somehow in conflict (see the prompt and delayed gamma rays measurements in). For the last 10 years, new data was produced due to high precision measurements, new technology and new methods to reduce the background. Theoretical models didn't yet solve the astrophysical factor fitting issue. New perspectives on the low-energy behavior investigations for the astrophysical S-factor for radiative captures have been recently introduced with extraordinarily good results for the reaction modern data. Controversy is still waiting for other similar experiments data and new experimental data on this reaction as well. In the new NuPPEC Range Plan 2010 there is a recommendation for a future better absolute cross section measurement for this reaction. The goal is to determine the astrophysical factor S₃₄(0) for the ³He+⁴He reaction within a ± 5% error using the activation method for the radiative capture reaction. This experiment is planned to be fulfilled at ATOMKI in the next two years. Its accomplishment became a necessity after the last most recent results coming from LUNA, Seattle, ERNA and Weizmann. The new approach consists in building a gas target chamber in ATOMKI for this experiment and all the enclosed systems required for a good operation, such as gas manipulation and gas pressure monitoring. A first step had been done at the Van de Graaff accelerator for the contaminants check using an alpha beam of 3.8 MeV energy and 200 nA intensity impinging on Cu and Al stopping foils of high purity. After several hours of gamma rays collection using the ORTEC Maestro detection system the data analysis revealed that the chance to create extra ⁷Be coming from parasitic reactions is under the background value in the energy region close to 478 keV. Acknowledgements. This project is financially supported by OTKA and NKTH through the HUMAN-MB-08-B mobility project NKTH-OTKA-EU FP7 (Marie Curie). Many thanks to the accelerator people for their support.

[en] Complete text of publication follows. In order to construct a gas cell target and perform experiments for E_CM from 1.2 to 3.0MeV on the ³He(⁴He,γ)⁷Be reaction we continued our feasibility tests for the contaminants at the ATOMKI cyclotron at E_α = 8.0MeV. The decision was to use Cu OFHC as a stopper. 1 μm thick nickel windows from LeBow for the gas cell were checked for their surface cleanliness and the sealing capability. A special system was manufactured and most of the foils were tested for pressure difference of over 300mbar in long measurements. No pinholes or loss through the glue were detected. The thickness and the uniformity along the Ni foils surface were measured using the ORTEC Soloist system. A moveable 2mm diameter collimator was put between a ²⁴¹Am source and the foil at different positions of the foil. From α-spectra taken by a particle detector it was found that the nominal thicknesses agree with SRIM calculations within 4% and their uniformity all over the surface changes less than 5 %. One foil was checked at the cyclotron with ⁴He⁺⁺ beam at E_α = 6.3MeV with maximum beam intensity of 520 nA. No any damage of the window was detected. For the activation part, the HPGe efficiency was measured using standard gamma sources ¹³³Ba, ¹⁵²Eu, ²²Na, ⁶⁰Co and ¹³⁷Cs at 27 cm. An extended (diameter of 5 mm) ⁷Be test source was prepared at the Van de Graaff accelerator through ⁷Li(p,n)⁷Be reaction at E_p = 2.3MeV. This source, placed at 1 cm from the detector, was moved in steps of 5mm parallel to the detector surface with up to 15mm from the center. The position change affects the detection counting by less than 1 %, also confirmed by GEANT4. Three measurements for the ³He+⁴He reaction at E_α = 4.0MeV, 5.4MeV and 6.32MeV were performed at the cyclotron. The beam impinged on the ³He (99.99 %) gas target, at around 300 mbar pressure, collecting each time about 20 mC. The current and pressure were monitored during the irradiations. The stopper was cooled using water. LN₂ in the cooling trap was used to minimize the Carbon buildup. After the irradiation, Cu OFHC stopper was put in front of the 100% HPGe detector at 1 cm distance and the activity was measured for about 7 days (see Figure 1.). The activity was determined using a home made fitting program and GEANT4. The results agreed within the error. The work was presented at the Nordic Conference for Nuclear Physics in Stockholm 2011. Acknowledgements. This project is financially supported by OTKA and NKTH through the HUMAN-MB-08-B mobility project NKTH-OTKA-EU FP7 (Marie Curie).

[en] The so-called γ-process is responsible for the production of the majority of the proton rich stable nuclei which are unreachable by the neutron capture reactions in the heavy element nucleosynthesis. The γ-process network calculations still fails to reproduce the observed abundances partially due to their uncertain nuclear physics input. These inputs are provided by statistical model calculations which need to be validated. To maximize the experimental constrain on the stellar rate entering into the reaction network calculation, charged particle capture reaction cross sections have to be measured [2,3]. The database of such reactions are growing, but still scarce. This work presents alpha capture reaction cross section measurements on ¹⁹⁷Au. Beside the radiative capture the (α,n) and (α,2n) reactions was also investigated. Since the reaction products are radioactive the activation technique was employed using γ- and X-ray countings. Thanks to the high sensitivity of the X-ray counting method, 1.5 orders of magnitude lower radiative capture cross section and 2 orders of magnitude lower (α,n) cross sections was successfully measured, compared to the recent precision dataset in the literature. (author)

[en] Compete text of publication follows. The astrophysical γ-process is the main production mechanism of the p-isotopes, the heavy, proton-rich nuclei not produced by neutron capture reactions in the astrophysical sand r-processes. The γ-process is a poorly known process of nucleosynthesis, the models are not able to reproduce well the p-isotope abundances observed in nature. Experimental data on nuclear reactions involved in γ-process reaction networks are clearly needed to provide input for a more reliable γ-process network calculation. As a continuation of our systematic study of reactions relevant for the γ-process, the cross sections of the ¹⁵¹Eu(α, γ)¹⁵⁵Tb and ¹⁵¹Eu(α,n)¹⁵⁴Tb reactions have been measured. These reactions have been chosen because α-induced cross section data in the region of heavy p-isotopes are almost completely missing although the calculations show a strong influence of these cross section on the resulting abundances. Since the reaction products of both reactions are radioactive, the cross sections have been measured using the activation technique. The targets have been prepared by evaporating Eu₂O₃ enriched to 99.2% in ¹⁵¹Eu onto thin Al foils. The target thicknesses have been measured by weighing and Rutherford Backscattering Spectroscopy. The targets have been irradiated by typically 1-2 μA intensity α-beams from the cyclotron of ATOMKI. The investigated energy range between 12 and 17 MeV was covered with 0.5 MeV steps. This energy range is somewhat higher than the astrophysically relevant one, but the cross section at astrophysical energies is so low that the measurements are not possible there. The γ- activity of the reaction products has been measured by a shielded HPGe detector. The absolute efficiency of the detector was measured with several calibration sources. Since ¹⁵⁴Tb has two long lived isomeric states, partial cross sections of the ¹⁵¹Eu(α,n)¹⁵⁴Tb reaction leading to the ground and isomeric states could be determined separately. The obtained results are compared with the predictions of the statistical model code NON-SMOKER^WEB version v5.8.1 which is widely used in γ-process network calculations. 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 α+nucleus channel. A factor of two reduction of the reaction rate of ¹⁵¹Eu(α, γ)¹⁵⁵Tb in γ-process network calculations with respect to theoretical rates using the standard optical potential by McFadden and Satchler (1966) is recommended. Further details of the experiment, the data analysis and the astrophysical discussion can be found in [3].