[en] This study presents the laboratory background measurement of a Clover-type composite γ-detector equipped with a BGO escape-suppression shield. Recently, such a detector had been used in an in-beam γ-spectroscopy measurement of the ¹⁴N(p,γ)¹⁵O reaction deep underground. Here the laboratory γ-ray background of that detector is studied in three different environments: overground, in a shallow underground laboratory and deep underground. In addition, the effect of the escape-suppression shield on the cosmic-ray induced background has been studied in all three cases. The measurements have been performed at LUNA site in the Gran Sasso National Laboratory, Assergi, Italy (deep underground), at the Felsenkeller Laboratory, Dresden, Germany (shallow underground) and ATOMKI, Debrecen, Hungary (Earth's surface).

[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. 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] 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. The precise knowledge of the half-life of the reaction product is of crucial importance for a nuclear reaction cross section measurement carried out with the activation technique. The cross section of the ¹⁵¹Eu(α,n)¹⁵⁴Tb reaction has been measured recently using the activation method, however, the half-life of the m1 isomer in ¹⁵⁴Tb has a relatively high uncertainty (T_1/2^m1 9.4±0.4 h) and ambiguous values can be found in the literature. This uncertainty introduces an error in the measured cross section and therefore the precise determination of the half-life is highly needed. For the half-life determination, several ¹⁵⁴Tb sources have been prepared by the ¹⁵¹Eu(α,n)¹⁵⁴Tb reaction. Highly enriched ¹⁵¹Eu targets have been irradiated with the alpha-beam of the cyclotron of ATOMKI. The targets have been prepared by vacuum evaporation. By choosing different bombarding energies and irradiation times, source activities in the range of 1-100 kBq have been obtained. The γ-radiation following the β-decay of ¹⁵⁴Tb has been measured with a shielded 40% relative efficiency HPGe detector. The length of the countings varied between 20 and 60 hours (more than 6 half-lives) and the spectra were stored in every hour. For the analysis the 540 keV line, the strongest γ-radiation which comes exclusively for the m1 isomer of ¹⁵⁴Tb has been selected. In order to obtain a high precision half life value, all possible systematic uncertainties have been carefully investigated. The five measured sources gave the same half-life value within their statistical uncertainty. This shows the robustness of the counting system. However, to increase the reliability of the measurements, the half-life of a reference source is also determined. During α-bombardment the ⁶³Cu(α,n) reaction takes place with high cross section in the target backing producing ⁶⁶Ga. The half-life of this isotope is similar to that of ¹⁵⁴Tb^m1 (9.49±0.07 h) and it is precisely known. The obtained half-life results for this reference isotope are in all cases in good agreement with the literature value, which shows the reliability of the measurement. Further systematic uncertainties may arise from the complicated decay scheme of ¹⁵⁴Tb. The m2 isomer (T_1/2^m2 =22.7±0.5 h) is known to have a weak decay branch to the m1 state. This contribution has been taken into account by measuring the production ratio of the two isomers. Although the 540 keV radiation has been reported to come exclusively from the m1 isomer, a hypothetical contribution of the ¹⁵⁴Tb ground state decay to this γ-line has been considered. Using a χ² analysis, an upper limit could be assigned to this contribution. A final result of T_1/2 =9.994±0.039 h has been obtained for the half-life of the m1 isomer in ¹⁵⁴Tb. Compared to the literature value, the half-life is increased significantly and its uncertainty is reduced by one order of magnitude. With this precise measurement one source of uncertainty of the ¹⁵¹Eu(α,n)¹⁵⁴Tb cross section measurement is avoided. Further details can be found in Ref. 1.

[en] The stable proton-rich nuclei between Se and Hg are the so called p-nuclei. The main stellar mechanism synthesizing these nuclei - the so called g process - is initiated by (γ,n) photodisintegration reactions on preexisting neutron-rich seed nuclei. As the neutron separation energy increases along the (γ,n) path towards more neutron deficient isotopes, (γ,p) and (γ,α) reactions become stronger and process the material towards lower masses. To calculate the p-nuclei abundance, the reaction rates involved in the g process have to be known. Stellar rates for (g,a) photodisintegration reactions should always be derived from alpha-capture to maximize the experimental constraint on the rate. Above the A>100 region very few (a,g) cross sections relevant for the g process were measured. This way, the g process network calculations rely mostly on theoretical cross sections calculated using the Hauser-Feshbach statistical model. By the measurement of thick target yield of a induced reactions on iridium, the reliability of the statistical model calculations in this heaviest mass range is checked. The thick target yield of four reactions /¹⁹¹Ir(α,γ)¹⁹⁴Au, ¹⁹¹Ir(α,n)¹⁹⁵Au, ¹⁹³Ir(α,n)^196m2Au, ¹⁹³Ir(α,n)¹⁹⁶Au/ was determined in the energy range of E_α = 13.4 - 17 MeV by the activation technique using γ- and X-ray counting. Preliminary results of the measurements will be presented. (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].

[en] Complete text of publication follows. In many cases in nuclear astrophysics, the investigated quantity is proportional to the yield of the emitted γ-radiation. At relatively small energies, which occur in a stellar environment, this yield is tiny. If a study is performed close to these energies, the knowledge of the laboratory γ-ray background is crucial. It is important to keep the background as low as possible, to reach higher sensitivity. In this work, the effect of an active shield (veto detector), and a passive shield (underground location) on the background is shown. For the present studies, a Clover detector has been used. It is equipped with a surrounding bismuth germanate (BGO) scintillator. With anticoincidence electronics, the BGO is used as an escape-suppression veto detector. It can also act as an efficient veto against muons penetrating the germanium detector volume. The underground site where the background measurements were performed is the Felsenkeller. It is a shallow underground laboratory with 45m thick rock cover (110m water equivalent). As a comparison the spectra taken from recorded at Laboratori Nazionali del Gran Sasso (LNGS) are also shown. LNGS is a deep underground laboratory with 1400m rock coverage (3400m water equivalent). For in-beam experiments, the counting rate in the high energy continuum is of paramount importance, because γ-rays from reactions with high Q-values can be emitted. In this region cosmic ray induced events dominate the laboratory background. On the Earth's surface and at the Felsenkeller, the main source of this background is the energy loss of penetrating muons in the germanium. Deep underground, because of the factor of 10⁶ reduction in the muon flux, the main background sources are neutron reactions, producing high energy gammas. In the present study, the BGO veto leads to a factor of 160 reduction in the continuum counting rates, which combined with the muon flux reduction (factor of 40) at Felsenkeller leads to a background counting rate comparable to that of LNGS. (Fig. 1.). In summary, using an active shield in a shallow underground environment, a background level comparable to that of a deep underground laboratory can be reached. Further details about the laboratory background investigations can be found in [5]. T.S. acknowledges a Herbert Quandt fellowship at Technical University Dresden.

[en] Complete text of publication follows. The main stellar mechanism synthesizing the stable proton-rich nuclei with charge number Z≥34 is the so-called γ process. It is initiated by (γ,n) photodisintegration reactions on preexisting more neutron-rich seed nuclei. As the neutron separation energy increases along the (γ,n) path, (γ,p) and (γ,α) reactions become dominant and push the material towards lower masses. Recently, consistent studies of the γ process nucleosynthesis proved that in the production of the heavy proton-rich nuclei (γ,α) reactions play a crucial role. To predict the stellar (γ,α) rates measurements of (α,γ) cross sections are required. Our systematic study of reactions relevant for the γ process was continued with the cross section measurement of ¹²⁷I(α,γ)¹³¹Cs and ¹²⁷I(α,n)¹³⁰Cs reactions using the activation method. Both reactions have been studied close to the astrophysically relevant energy range. The decay of the (α,n) reaction product is followed by emission of γ-rays. By counting these, the reaction cross section can be derived. The (α,γ) reaction product decays exclusively by electron capture followed by the emission of characteristic X-rays, but no γ-rays. For determination of the radiative α-capture cross sections the yield of these characteristic X-rays was measured, using the technique described in Ref. [2]. For the target preparation KI compound was evaporated onto thin Al foils. The target thickness was determined by PIXE method using the 5-MV VdG accelerator of ATOMKI. The targets were irradiated with α beams from the MGC20 cyclotron of ATOMKI. The investigated energy range between 9.8MeV and 15.5MeV was covered about 0.5MeV steps. For the γ counting a shielded HPGe detector was used, while the X-ray countings were carried out using a shielded low-energy photon spectrometer (LEPS). The obtained results were compared with statistical model predictions calculated by the code SMARAGD (version 0.8.4s). It is found that the calculations overestimate the experimental values by a factor of 2 at the upper end of the investigated energy range and a factor of about 6 at the lower end. (see fig 1.) In the measured energy range the predicted (α,γ) cross sections are sensitive to the α, neutron and γ widths. Therefore it is impossible to further disentangle the different contributions of the widths to the total deviation from experiments and to draw strong conclusions on the basis of the experimental capture data alone. The predicted (α,n) cross sections at the upper part of the measured energy range is only sensitive to the α width. Here the predictions and the measurements are in good agreement. It is to be concluded, therefore, that the α width is predicted well by the SMARAGD code. The deviations in the (α,γ) case are caused by problems in the neutron and/or γ widths. Further details of the experiment, the data analysis and the astrophysical discussion can be found in Ref. [3].