Background: Among the several inhomogeneities in the composition of globular cluster stars, an overabundance of 23 Na is interpreted as the signature of the operation of the neon-sodium (NeNa) cycle. One of the hypothesis to explain the observed O-Na anticorrelation invokes massive asymptotic giant branch stars as the main agents. At temperatures relevant for nucleosynthesis in asymptotic giant branch stars the 22 Ne( p , gamma ) 23 Na reaction rate has been the most uncertain so far, giving rise to considerable experimental efforts in recent years. While overall there is a good agreement between reported cross section results, some tensions still remain on the branching ratios of resonance gamma-ray modes and direct capture to excited sates. Purpose: The present paper offers full details and a partial analysis of the high sensitivity study, of both direct capture and low-energy resonances in the 22 Ne( p , gamma ) 23 Na reaction, performed at LUNA, and whose results were previously published in abbreviated form [F. Ferraro et al. , Phys. Rev. Lett. 121 , 172701 (2018)]. Methods: During the LUNA measurement an intense proton beam was delivered to a 22 Ne gas target. The gamma rays from the 22 Ne( p , gamma ) 23 Na reaction were detected by a high efficiency 4 pi , sixfold segmented bismuth germanate (BGO) detector. In the present paper the data from individual detector segments were combined with simulated detector responses to obtain cascade branching ratios. Results: For the three resonances at E p = 156 . 2 and 259.7 keV new gamma-decay branchings are provided. Moreover, partial cross sections for the direct capture to different states of 23 Na are reported down to E p = 188 keV, the lowest energy measured to date. Conclusions: A revised reaction rate has been calculated based on a new R-matrix fit of the recent 22 Ne( p , gamma ) 23 Na S-factor data and results for the resonances. The thermonuclear reaction rate is provided in tabular form to be used in stellar models.

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.

Cross sections of the 107Ag(α, γ)111In and 107Ag(α,n)110In reactions have been measured with the activation method at effective center-of-mass energies between 7.79 MeV and 12.00 MeV close to the astrophysical energy range. The irradiation and counting of the 107Ag targets was carried out at ATOMKI using the cyclotron accelerator and the low background counting facility, respectively. Cross section results are presented and compared with the predictions of Hauser-Feshbach statistical model calculations using the NON-SMOKER and TALYS-1.4 codes. In general, above 10 MeV, the model calculation are able to reproduce reasonably well the experimental data, but below 10 MeV, depending on some input parameters strong deviations are also found.

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.

In this paper we present the ongoing experiments at ATOMKI related to our systematic γ-process studies. These studies are intended to enlarge the limited experimental database from α-induced reactions on nuclei in the heavier mass range of the γ -process. In all presented cases the activation method was used. The details of the cross section measurements and preliminary results on115In(α,n)118mSb, 115In(α,γ)119Sb; 162Er(α,n)165Yb, 162Er(α,γ)166Yb, 164Er(α,n)167Yb, 166Er(α,n)169Yb; 191Ir(α,n)194Au, 191Ir(α,γ)195Au, 193Ir(α,n)196mAu, 193Ir(α,n)196Au reactions are presented.

In 2008 a Starting Grant project supported by the European Research Council titled "Nuclear reaction studies relevant to the astrophysical p-process nucleosynthesis" was launched. After five years of successful research related to the experimental investigation of proton-and alpha-induced nuclear reaction for the astrophysical p-process, the project came to an end. In this paper a summary of the research and the most important achievements is given.

The accurate half-life information for reaction products is very crucial in order to measure the cross section of a reaction via the activation method. Precise and accurate cross section measurement of reactions which are resulting in Pm-144 requires the precise half-life value of this isotope. The adopted half-life of Pm-144 has a relatively high uncertainty and conflicting data can be found in the literature. In order to mitigate this controversy and to reduce the uncertainty, the half-life of Pm-144 is measured with gamma spectroscopy. Experimental methods and preliminary results are presented.

Background: Astrophysical reaction rates, which are mostly derived from theoretical cross sections, are necessary input 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 (alpha,gamma) reactions at low energy. Therefore, it is important to experimentally test theoretical cross section predictions at low, astrophysically relevant energies.Purpose: The aim is to measure reaction cross sections of Ag-107(alpha,gamma)In-111 and Ag-107(alpha,gamma)In-110 at low energies in order to extend the experimental database for astrophysical reactions involving alpha 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 alpha particles at low energy. We have also used Hauser-Feshbach statistical model calculations to study the origin of possible discrepancies between prediction and data.Method: An activation technique has been used to measure the reaction cross sections at effective center of mass energies between 7.79 MeV and 12.50 MeV. Isomeric and ground state cross sections of the (alpha,n) reaction were determined separately.Results: The measured cross sections were found to be lower than theoretical predictions for the (alpha,gamma) reaction. Varying the calculated averaged widths in the Hauser-Feshbach model, it became evident that the data for the (alpha,gamma) and (alpha,n) reactions can only be simultaneously reproduced when rescaling the ratio of gamma to neutron width and using an energy-dependent imaginary part in the optical alpha + Ag-107 potential.Conclusions: The new data extend the range of measured charged-particle cross sections for astrophysical applications to lower mass numbers and lower energies. The modifications in the model predictions required to reproduce the present data are fully consistent with what was found in previous investigations. Thus, our results confirm the previously suggested energy-dependent modification of the optical alpha+nucleus potential.

We report on measurements of resonance strengths and energies for the and 193 keV resonances in the O-18(p,)N-15 and O-17(p,)N-14 reactions, respectively, obtained during commissioning of a new setup for alpha-particle detection studies at the LUNA underground laboratory. Our values, meV and meV, are in excellent agreement with those reported in the literature. New values of resonance energies are keV and keV, respectively, this latter with the highest precision to date. Comparative background measurements in silicon detectors overground and underground were also carried out, yielding up to a factor of 15 in background suppression at LUNA at energies around 200keV. This clearly demonstrates the usefulness of underground measurements in charged-particles experiments, especially at low detection energies.

Alpha elastic scattering angular distributions of the Cd-106(alpha, alpha)Cd-106 reaction were measured at three energies around the Coulomb barrier to provide a sensitive test for the alpha + 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 alpha + nucleus optical potential in a wide energy region ranging from E-Lab = 27.0 MeV down to 16.1 MeV.The potentials under study are a basic prerequisite for the prediction of alpha-induced reaction cross sections and thus, for the calculation of stellar reaction rates used for the astrophysical gamma process. Therefore, statistical model predictions using as input the optical potentials discussed in the present work are compared to the available Cd-106 + alpha cross section data. (C) 2015 Elsevier B.V. All rights reserved.

The total cross sections for the $^{152}$Gd(p,$\gamma$)$^{153}$Tb and $^{152}$Gd(p,n)$^{152}$Tb reactions have been measured by the activation method at effective center-of-mass energies \mbox{$3.47 \leq E_\mathrm{c.m.}^\mathrm{eff}\leq 7.94$ MeV} and \mbox{$4.96 \leq E_\mathrm{c.m.}^\mathrm{eff} \leq 7.94$ MeV}, respectively. The targets were prepared by evaporation of 30.6\% isotopically enriched $^{152}$Gd oxide on aluminum backing foils, and bombarded with proton beams provided by a cyclotron accelerator. The cross sections were deduced from the observed $\gamma$-ray activity, which was detected off-line by a HPGe detector in a low background environment. The results are presented and compared with predictions of statistical model calculations. This comparison supports a modified optical proton+$^{152}$Gd potential suggested earlier.

The γ-process in core-collapse and/or type Ia supernova explosions is thought to explain the origin of the majority of the so-called p nuclei (the 35 proton-rich isotopes between Se and Hg). Reaction rates for γ-process reaction network studies have to be predicted using Hauser-Feshbach statistical model calculations. Recent investigations have shown problems in the prediction of α-widths at astrophysical energies which are an essential input for the statistical model. It has an impact on the reliability of abundance predictions in the upper mass range of the p nuclei. With the measurement of the ^164,166Er(α,n)^167,169Yb reaction cross sections at energies close to the astrophysically relevant energy range we tested the recently suggested low energy modification of the α+nucleus optical potential in a mass region where γ-process calculations exhibit an underproduction of the p nuclei. Using the same optical potential for the α-width which was derived from combined ^162Er(α,n) and ^162Er(α,γ) measurement makes it plausible that a low-energy modification of the optical α+nucleus potential is needed.

The ^{22}Ne(p,γ)^{23}Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle affects the synthesis of the elements between ^{20}Ne and ^{27}Al in asymptotic giant branch stars and novae. The ^{22}Ne(p,γ)^{23}Na reaction rate is very uncertain because of a large number of unobserved resonances lying in the Gamow window. At proton energies below 400 keV, only upper limits exist in the literature for the resonance strengths. Previous reaction rate evaluations differ by large factors. In the present work, the first direct observations of the ^{22}Ne(p,γ)^{23}Na resonances at 156.2, 189.5, and 259.7 keV are reported. Their resonance strengths are derived with 2%-7% uncertainty. In addition, upper limits for three other resonances are greatly reduced. Data are taken using a windowless ^{22}Ne gas target and high-purity germanium detectors at the Laboratory for Underground Nuclear Astrophysics in the Gran Sasso laboratory of the National Institute for Nuclear Physics, Italy, taking advantage of the ultralow background observed deep underground. The new reaction rate is a factor of 20 higher than the recent evaluation at a temperature of 0.1 GK, relevant to nucleosynthesis in asymptotic giant branch stars.

The 22Ne(p,γ)23Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle is active in asymptotic giant branch stars as well as in novae and contributes to the nucleosythesis of neon and sodium isotopes. In order to reduce the uncertainties in the predicted nucleosynthesis yields, new experimental efforts to measure the 22Ne(p,γ)23Na cross section directly at the astrophysically relevant energies are needed. In the present work, a feasibility study for a 22Ne(p,γ)23Na experiment at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator deep underground in the Gran Sasso laboratory, Italy, is reported. The ion-beam-induced γ-ray background has been studied. The feasibility study led to the first observation of the E p=186 keV resonance in a direct experiment. An experimental lower limit of 0.12 × 10−6 eV has been obtained for the resonance strength. Informed by the feasibility study, a dedicated experimental setup for the 22Ne(p,γ)23Na experiment has been developed. The new setup has been characterized by a study of the temperature and pressure profiles. The beam heating effect that reduces the effective neon gas density due to the heating by the incident proton beam has been studied using the resonance scan technique, and the size of this effect has been determined for a neon gas target.

In the model calculations of heavy element nucleosynthesis processes the nuclear reaction rates are taken from statistical model calculations which utilize various nuclear input parameters. It is found that in the case of reactions involving alpha particles the calculations bear a high uncertainty owing to the largely unknown low-energy alpha-nucleus optical potential. Experiments are typically restricted to higher energies and therefore no direct astrophysical consequences can be drawn. In the present work a (p, a) reaction is used for the first time to study the alpha-nucleus optical potential. The measured Zn-64(p, alpha)Cu-61 cross section is uniquely sensitive to the alpha-nucleus potential and the measurement covers the whole astrophysically relevant energy range. By the comparison to model calculations, direct evidence is provided for the incorrectness of global optical potentials used in astrophysical models.

For the better understanding of the astrophysical gamma-process the experimental determination of low energy proton- and alpha-capture cross sections on heavy isotopes is required. The existing data for the 92Mo(p,gamma)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,gamma)93Tc and 98Mo(p,gamma)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,gamma)93Tc at temperatures relevant for the gamma-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.

In this work the differential cross sections for gamma-ray emission from the 14N(d,pγ)15N (Eγ=1885, 2297, 7299 and 8310keV) and from the 28Si(d,pγ)29Si (Eγ=1273, 2028, 2426 and 4934keV) were measured simultaneously with the 14N(d,p4,5,6,7)15N differential cross sections and 14N(d,d)14N elastic scattering cross section using a HPGe detector at 55° and an ion implanted Si detector at 135° with respect to the beam direction in the deuteron energy range 0.65–2.0MeV. The target was a thin silicon-nitride film. Gamma-ray angular distribution measurements were performed to determine the possible anisotropy of the gamma-ray emission, and the measured cross section values were converted into total gamma-ray producing cross sections for most of the gamma-ray emissions. The average uncertainties of nitrogen and silicon gamma-ray production cross sections are 5% and 12%, respectively and 8% concerning the particle production cross section of natN(d,d0)natN and 14N(d,p4,5,6,7)15N reactions.