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The total cross section of the 3He(α,γ)7Be reaction was measured by the activation technique in the energy range of Ecm = 2.6 - 3.1 MeV, covering the first known resonance in the reaction. Consistent results were obtained with the only one available literature dataset in this energy range.

One of the main neutron sources for the astrophysical s process is the reaction ^{13}C(α,n)^{16}O, taking place in thermally pulsing asymptotic giant branch stars at temperatures around 90 MK. To model the nucleosynthesis during this process the reaction cross section needs to be known in the 150-230 keV energy window (Gamow peak). At these sub-Coulomb energies, cross section direct measurements are severely affected by the low event rate, making us rely on input from indirect methods and extrapolations from higher-energy direct data. This leads to an uncertainty in the cross section at the relevant energies too high to reliably constrain the nuclear physics input to s-process calculations. We present the results from a new deep-underground measurement of ^{13}C(α,n)^{16}O, covering the energy range 230-300 keV, with drastically reduced uncertainties over previous measurements and for the first time providing data directly inside the s-process Gamow peak. Selected stellar models have been computed to estimate the impact of our revised reaction rate. For stars of nearly solar composition, we find sizeable variations of some isotopes, whose production is influenced by the activation of close-by branching points that are sensitive to the neutron density, in particular, the two radioactive nuclei ^{60}Fe and ^{205}Pb, as well as ^{152}Gd.

Background: Light ($30\ensuremath{\le}Z\ensuremath{\le}45$) neutron-rich isotopes are thought to be synthesized in the neutrino-driven ejecta of core-collapse supernovae explosions via the weak $r$ process. Recent nucleosynthesis studies have demonstrated that $(\ensuremath{\alpha},xn)$ reactions play a particularly important role in the production of these isotopes. $\ensuremath{\alpha}$-nucleus optical model potentials ($\ensuremath{\alpha}$-OMPs) are used to model this nucleosynthesis scenario.Purpose: The different $\ensuremath{\alpha}$-OMP model parameters can affect the calculated cross sections by more than an order of magnitude in the relevant energy regions, which affects the production of light neutron-rich isotopes. Consequently, to constrain the astrophysical conditions characterizing the supernovae ejecta, the uncertainty of the nuclear physics input has to be reduced.Methods: The cross section of the $^{100}\mathrm{Mo}(\ensuremath{\alpha},n)^{103}\mathrm{Ru}$ reaction was measured by means of the activation method. 0.5 mm thick molybdenum disks were irradiated with ${E}_{\ensuremath{\alpha}}$ = 7.0 to ${E}_{\ensuremath{\alpha}}$ = 13.0 MeV $\ensuremath{\alpha}$ beams. Thick target yields and reaction cross sections were determined via $\ensuremath{\gamma}$-ray spectroscopy.Results: Cross sections at several energies below the Coulomb barrier were measured, reaching the astrophysically relevant energy region. Large discrepancies between the experimental values and statistical model predictions calculated using the well-known $\ensuremath{\alpha}$-OMPs were found. The measured cross section data could be excellently described by the Atomki-V2 potential. Therefore, this $\ensuremath{\alpha}$-OMP was used to derive the astrophysical reaction rates as a function of temperature.Conclusions: The successful reproduction of the measured cross sections in a wide energy region confirm the reliability of the Atomki-V2 potential. The usage of the new $^{100}\mathrm{Mo}(\ensuremath{\alpha},n)^{103}\mathrm{Ru}$ experimental data along with the Atomki-V2 potential reduces the nuclear uncertainties of the weak $r$-process production yields of nuclei with $36\ensuremath{\le}Z\ensuremath{\le}50$ to a marginal level.

The synthesis of heavy, proton rich isotopes is a poorly understood astrophysical process. Thermonuclear (type Ia) supernova explosions are among the suggested sites and the abundance of some isotopes present in the early solar system may be used to test the models. 92Nb is such an isotope and one of the reactions playing a role in its synthesis is 91Zr(p,gamma)92Nb. As no experimental cross sections were available for this reaction so far, nucleosynthesis models had to solely rely on theoretical calculations. In the present work the cross section of 91Zr(p,gamma)92mNb has been measured at astrophysical energies by activation. The results excellently confirm the predictions of cross sections and reaction rates for 91Zr(p,gamma)92Nb, as used in astrophysical simulations., Accepted for publication in Journal of Physics G

Background: Shell hydrogen burning during the asymptotic giant branch (AGB) phase through the oxygen isotopes has been indicated as a key process that is needed to understand the observed O 18 / O 16 relative abundance in presolar grains and in stellar atmospheres. This ratio is strongly influenced by the relative strengths of the reactions O 18 ( p , α ) N 15 and O 18 ( p , γ ) F 19 in low-mass AGB stars. While the former channel has been the focus of a large number of measurements, the ( p , γ ) reaction path has only recently received some attention and its stellar reaction rate over a wide temperature range rests on only one measurement. Purpose: Our aim is the direct measurement of states in F 19 as populated through the reaction O 18 ( p , γ ) F 19 to better determine their influence on the astrophysical reaction rate, and more generally to improve the understanding of the nuclear structure of F 19 .Method: Branchings and resonance strengths were measured in the proton energy range E p lab = 150 – 400 keV , using a high-purity germanium detector inside a massive lead shield. The measurement took place in the ultra-low-background environment of the Laboratory for Underground Nuclear Astrophysics (LUNA) experiment at the Gran Sasso National Laboratory, leading to a highly increased sensitivity. Results: The uncertainty of the γ branchings and strengths was improved for all four resonances in the studied energy range; many new transitions were observed in the case of the 334 keV resonance, and individual γ decays of the 215 keV resonance were measured for the first time. In addition a number of transitions to intermediate states that decay through α emission were identified. The strengths of the observed resonances are generally in agreement with literature values. Conclusions: Our measurements substantially confirm previous determinations of the relevant resonance strengths. Therefore the O 18 ( p , γ ) F 19 reaction rate does not change with respect to the reaction rate reported in the compilations commonly adopted in the extant computations of red-giant branch and AGB stellar models. Nevertheless, our measurements definitely exclude a nonstandard scenario for the fluorine nucleosynthesis and a nuclear physics solution for the O 18 depletion observed in Group 2 oxygen-rich stardust grains.

Background: The Li 6 ( p , γ ) Be 7 cross section influences a variety of astrophysical scenarios, including big-bang and stellar nucleosynthesis. In recent years, conflicting results of direct measurements have been published, reporting contradictory low-energy trends. Purpose: To shed light on the contradiction between the existing data sets, the reaction was studied using the asymptotic normalization coefficient (ANC) technique which was up-to-now never used for this reaction. Methods: To derive the ANC, the Li 6 ( He 3 , d ) Be 7 transfer reaction, studied at the Department of Physics and Astronomy of the University of Catania and at the John. D. Fox Superconducting Accelerator Laboratory at Florida State University, was re-analyzed, focusing on the proton transfer mechanism [the α transfer process is discussed by Kiss et al. [Phys. Lett. B 807, 135606 (2020)]. The energy of the He 3 beam impinging on a Li 6 target was E lab = 3 MeV and E lab = 5 MeV. The yield of the emitted deuterons was measured with high precision by using silicon Δ E - E telescopes. Results: From the DWBA analysis of the angular distributions of the emitted deuterons populating the ground ( E * = 0.0 MeV; 3 2 − ) and the first excited ( E * = 0.429 MeV ; 1 2 − ) states of Be 7 , the ANCs for the Li 6 + p → Be 7 system were deduced. Furthermore, the recently measured Li 6 ( p , γ ) Be 7 reaction cross sections [Piatti , Phys. Rev. C 102, 052802 (2020)] were also analyzed within this theoretical framework. Excellent agreement was found between ANC values derived indirectly and those determined from the direct data, which strengthens the conclusion of the present work. The astrophysical S factor—at energies characterizing the Sun—for the Li 6 ( p , γ ) Be 7 reaction was calculated using the weighted mean of the experimentally derived ANC values. Conclusions: The result of the present comprehensive study supports the extrapolation of Piatti [Phys. Rev. C 102, 052802 (2020)], Dong [J. Phys. G Nucl. Partic. 44, 045201 (2017)], and Gnech and Marcucci [Nucl. Phys. A 987, 1 (2019)], and thus disfavors the conclusions drawn by He [Phys. Lett. B 725, 287 (2013)] and Xu [Nucl. Phys. A 918, 61 (2013)].

The muon intensity and angular distribution in the shallow-underground laboratory Felsenkeller in Dresden, Germany have been studied using a portable muon detector based on the close cathode chamber design. Data has been taken at four positions in Felsenkeller tunnels VIII and IX, where a new 5 MV underground ion accelerator is being installed, and in addition at four positions in Felsenkeller tunnel IV, which hosts a low-radioactivity counting facility. At each of the eight positions studied, seven different orientations of the detector were used to compile a map of the upper hemisphere with 0.85{\deg} angular resolution. The muon intensity is found to be suppressed by a factor of 40 due to the 45 m thick rock overburden, corresponding to 140 meters water equivalent. The angular data are matched by two different simulations taking into account the known geodetic features of the terrain: First, simply by determining the cutoff energy using the projected slant depth in rock and the known muon energy spectrum, and second, in a Geant4 simulation propagating the muons through a column of rock equal to the known slant depth. The present data are instrumental for studying muon-induced effects at these depths and also in the planning of an active veto for accelerator-based underground nuclear astrophysics experiments., Comment: Submitted to Astroparticle Physics

In order to provide data for the simulation of the astrophysical $\gamma$-process, the cross section measurement of the $^{124}$Xe(p,$\gamma$)$^{125}$Cs reaction is in progress at MTA Atomki using the activation technique. Precise information on the decay characteristics of the reaction products is of crucial importance for measurements carried out using this method. The half-lives of the produced $^{125}$Cs and its daughter $^{125}$Xe are published in previous works, but with large uncertainties and ambiguous values. To make these nuclear parameters more precise, the half-lives have been re-measured with high precision using $\gamma$-spectroscopy. The obtained new half-life values are t$_{1/2}$ = 44.35 $\pm$ 0.29 minutes for $^{125}$Cs and t$_{1/2}$ = 16.87 $\pm$ 0.08 hours for $^{125}$Xe.

The 18O(p,α)15N reaction affects the synthesis of 15N, 18O and 19F isotopes, whose abundances can be used to probe the nucleosynthesis and mixing processes occurring deep inside asymptotic giant branch (AGB) stars. We performed a low-background direct measurement of the 18O(p,α)15N reaction cross-section at the Laboratory for Underground Nuclear Astrophysics (LUNA) from center of mass energy Ec.m.=340 keV down to Ec.m.=55 keV, the lowest energy measured to date corresponding to a cross-section of less than 1 picobarn/sr. The strength of a key resonance at center of mass energy Er=90 keV was found to be a factor of 10 higher than previously reported. A multi-channel R-matrix analysis of our and other data available in the literature was performed. Over a wide temperature range, T=0.01–1.00 GK, our new astrophysical rate is both more accurate and precise than recent evaluations. Stronger constraints can now be placed on the physical processes controlling nucleosynthesis in AGB stars with interesting consequences on the abundance of 18O in these stars and in stardust grains, specifically on the production sites of oxygen-rich Group II grains., SCOPUS: ar.j, info:eu-repo/semantics/published

Recent astronomical data have provided the primordial deuterium abundance with percent precision. As a result, big bang nucleosynthesis may provide a constraint on the universal baryon to photon ratio that is as precise as, but independent from, analyses of the cosmic microwave background. However, such a constraint requires that the nuclear reaction rates governing the production and destruction of primordial deuterium are sufficiently well known. Here, a new measurement of the $^{2}\mathrm{H}{(p,\ensuremath{\gamma})}^{3}\mathrm{He}$ cross-section is reported. This nuclear reaction dominates the error on the predicted big bang deuterium abundance. A proton beam of 400--1650 keV beam energy was incident on solid titanium deuteride targets, and the emitted $\ensuremath{\gamma}$ rays were detected in two high-purity germanium detectors at angles of ${55}^{\ensuremath{\circ}}$ and ${90}^{\ensuremath{\circ}}$, respectively. The deuterium content of the targets has been obtained in situ by the $^{2}\mathrm{H}(^{3}\mathrm{He},p)^{4}\mathrm{He}$ reaction and offline using the elastic recoil detection method. The astrophysical $S$ factor has been determined at center of mass energies between 265 and 1094 keV, addressing the uppermost part of the relevant energy range for big bang nucleosynthesis and complementary to ongoing work at lower energies. The new data support a higher $S$ factor at big bang temperatures than previously assumed, reducing the predicted deuterium abundance.

The electron capture process was studied for Xe$^{54+}$ colliding with H$_2$ molecules at the internal gas target of the ESR storage ring at GSI, Darmstadt. Cross section values for electron capture into excited projectile states were deduced from the observed emission cross section of Lyman radiation, being emitted by the hydrogen-like ions subsequent to the capture of a target electron. The ion beam energy range was varied between 5.5 MeV/u and 30.9 MeV/u by applying the deceleration mode of the ESR. Thus, electron capture data was recorded at the intermediate and in particular the low collision energy regime, well below the beam energy necessary to produce bare xenon ions. The obtained data is found to be in reasonable qualitative agreement with theoretical approaches, while a commonly applied empirical formula significantly overestimates the experimental findings.

Ambient neutrons may cause significant background for underground experiments. Therefore, it is necessary to investigate their flux and energy spectrum in order to devise a proper shielding. Here, two sets of altogether ten moderated He-3 neutron counters are used for a detailed study of the ambient neutron background in tunnel IV of the Felsenkeller facility, underground below 45 m of rock in Dresden/Germany. One of the moderators is lined with lead and thus sensitive to neutrons of energies higher than 10 MeV. For each He-3 counter moderator assembly, the energy-dependent neutron sensitivity was calculated with the FLUKA code. The count rates of the ten detectors were then fitted with the MAXED and GRAVEL packages. As a result, both the neutron energy spectrum from 10(-9) to 300 MeV and the flux integrated over the same energy range were determined experimentally. The data show that at a given depth, both the flux and the spectrum vary significantly depending on local conditions. Energy-integrated fluxes of (0.61 +/- 0.05), (1.96 +/- 0.15), and (4.6 +/- 0.4) x 10(-4) cm(-2) s(-1), respectively, are measured for three sites within Felsenkeller tunnel IV which have similar muon flux but different shielding wall configurations. The integrated neutron flux data and the obtained spectra for the three sites are matched reasonably well by FLUKA Monte Carlo calculations that are based on the known muon flux and composition of the measurement room walls.

The prediction of stellar ($\gamma$,$\alpha$) reaction rates for heavy nuclei is based on the calculation of ($\alpha$,$\gamma$) cross sections at sub-Coulomb energies. These rates are essential for modeling the nucleosynthesis of so-called $p$-nuclei. The standard calculations in the statistical model show a dramatic sensitivity to the chosen $\alpha$-nucleus potential. The present study explains the reason for this dramatic sensitivity which results from the tail of the imaginary $\alpha$-nucleus potential in the underlying optical model calculation of the total reaction cross section. As an alternative to the optical model, a simple barrier transmission model is suggested. It is shown that this simple model in combination with a well-chosen $\alpha$-nucleus potential is able to predict total $\alpha$-induced reaction cross sections for a wide range of heavy target nuclei above $A \gtrsim 150$ with uncertainties below a factor of two. The new predictions from the simple model do not require any adjustment of parameters to experimental reaction cross sections whereas in previous statistical model calculations all predictions remained very uncertain because the parameters of the $\alpha$-nucleus potential had to be adjusted to experimental data. The new model allows to predict the reaction rate of the astrophysically important $^{176}$W($\alpha$,$\gamma$)$^{180}$Os reaction with reduced uncertainties, leading to a significantly lower reaction rate at low temperatures. The new approach could also be validated for a broad range of target nuclei from $A \approx 60$ up to $A \gtrsim 200$., Comment: 6 pages, 3 figures; 6 pages supplement with 3 additional figures and 3 tables; Physical Review Letters, accepted for publication

Direct measurements of reaction cross-sections at astrophysical energies often require the use of solid targets able to withstand high ion beam currents for extended periods of time. Thus, monitoring target thickness, isotopic composition, and target stoichiometry during data taking is critical to account for possible target modifications and to reduce uncertainties in the final cross-section results. A common technique used for these purposes is the Nuclear Resonant Reaction Analysis (NRRA), which however requires that a narrow resonance be available inside the dynamic range of the accelerator used. In cases when this is not possible, as for example the $$^{13}\hbox {C}(\alpha ,\hbox {n})^{16}\hbox {O}$$ reaction recently studied at low energies at the Laboratory for Underground Nuclear Astrophysics (LUNA) in Italy, alternative approaches must be found. Here, we present a new application of the shape analysis of primary $$\gamma $$ rays emitted by the $$^{13}\hbox {C}(\hbox {p},\gamma )^{14}\hbox {N}$$ radiative capture reaction. This approach was used to monitor $$^{13}\hbox {C}$$ target degradation in situ during the $$^{13}\hbox {C}(\alpha ,\hbox {n})^{16}\hbox {O}$$ data taking campaign. The results obtained are in agreement with evaluations subsequently performed at Atomki (Hungary) using the NRRA method. A preliminary application for the extraction of the $$^{13}\hbox {C}(\alpha ,\hbox {n})^{16}\hbox {O}$$ reaction cross-section at one beam energy is also reported.

Light elements were produced in the first few minutes of the Universe through a sequence of nuclear reactions known as Big Bang nucleosynthesis (BBN)1,2. Among the light elements produced during BBN1,2, deuterium is an excellent indicator of cosmological parameters because its abundance is highly sensitive to the primordial baryon density and also depends on the number of neutrino species permeating the early Universe. Although astronomical observations of primordial deuterium abundance have reached percent accuracy3, theoretical predictions4,5,6 based on BBN are hampered by large uncertainties on the cross-section of the deuterium burning D(p,γ)3He reaction. Here we show that our improved cross-sections of this reaction lead to BBN estimates of the baryon density at the 1.6 percent level, in excellent agreement with a recent analysis of the cosmic microwave background7. Improved cross-section data were obtained by exploiting the negligible cosmic-ray background deep underground at the Laboratory for Underground Nuclear Astrophysics (LUNA) of the Laboratori Nazionali del Gran Sasso (Italy)8,9. We bombarded a high-purity deuterium gas target10 with an intense proton beam from the LUNA 400-kilovolt accelerator11 and detected the γ-rays from the nuclear reaction under study with a high-purity germanium detector. Our experimental results settle the most uncertain nuclear physics input to BBN calculations and substantially improve the reliability of using primordial abundances to probe the physics of the early Universe.

The detection of the neutrinos produced in the p − p chain and in the CNO cycle can be used to test the Standard Solar Model. The 3He( α , γ )7Be reaction is the first reaction of the 2nd and 3rd branch of the p − p chain, therefore, the uncertainty of its cross section sensitively influences the prediction of the 7Be and 8B neutrino fluxes. Despite its importance and the large number of experimental and theoretical works devoted to this reaction, the knowledge on the reaction cross section at energies characterizing the core of the Sun (15 keV - 30 keV) is limited and further experimental efforts are needed to reach the desired (≈ 3%) accuracy. The precise knowledge on the external capture contribution to the 3He( α , γ )7Be reaction cross section is crucial for the theoretical description of the reaction mechanism. In the present work the indirect measurement of this external capture contribution using the Asymptotic Normalization Coefficient (ANC) technique is reported. To extract the ANC, the angular distributions of deuterons emitted in the 6Li(3He,d)7Be α-transfer reaction were measured with high precision at E H 3 e = 3.0 MeV and E H 3 e = 5.0 MeV. The ANCs were then extracted from comparison of DWBA calculations to the measured data and the zero energy astrophysical S-factor for 3He( α , γ )7Be reaction was found to be 0.534 ± 0.025 keVb.

Luminosity is a measure of the colliding frequency between beam and target and it is a crucial parameter for the measurement of absolute values, such as reaction cross sections. In this paper, we make use of experimental data from the ESR storage ring to demonstrate that the luminosity can be precisely determined by modelling the measured Rutherford scattering distribution. The obtained results are in good agreement with an independent measurement based on the x-ray normalization method. Our new method provides an alternative way to precisely measure the luminosity in low-energy stored-beam configurations. This can be of great value in particular in dedicated low-energy storage rings where established methods are difficult or impossible to apply., 8 pages, 5 figures

The 16O(n, α)13C reaction was proposed to be measured at the neutron time-of-flight (n_TOF) facility of CERN. To this purpose, a Double Frisch Grid Ionization Chamber (DFGIC) containing the oxygen atoms as a component in the counting gas coupled with a switch device in order to prevent the charge collection from the so-called γ-flash has been developed at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), in Germany. The first 16O(n, α)13C measurement without seeing the charge of the γ-flash at n_TOF has been performed in November 2018. After the electronics did not suffer from the y-flash any more, another huge charge collection was discovered. Due to the high instantaneous flux at the n_TOF facility [1] the amount of that induced charge from neutron induced background reactions was piling up so much that the recognition of 16O(n, α)13C reactions from that background was very difficult. For that reason another 16O(n, α)13C measurement at the time-of-flight facility nELBE at HZDR which has a low instantaneous flux [2], has been performed in April 2019. Both measurements from n_TOF and nELBE will be presented here.

Among the reactions involved in the production and destruction of deuterium during Big Bang Nucleosynthesis, the deuterium-burning D(p,$$\gamma $$)$$^3$$He reaction has the largest uncertainty and limits the precision of theoretical estimates of primordial deuterium abundance. Here we report the results of a careful commissioning of the experimental setup used to measure the cross-section of the D(p,$$\gamma $$)$$^3$$He reaction at the Laboratory for Underground Nuclear Astrophysics of the Gran Sasso Laboratory (Italy). The commissioning was aimed at minimising all sources of systematic uncertainty in the measured cross sections. The overall systematic error achieved ($$< 3\%$$) will enable improved predictions of BBN deuterium abundance.

The 3He(α,γ)7Be reaction plays an important role in two astrophysical scenarios. It is a key reaction in lithium production during the Big Bang Nucleosynthesis and one of the central reaction in the p-p chain in stars. In the case of the former event, the Gamow energy of the reaction is around 0.2 MeV, while in the case of the p-p chain in the Sun, an order of magnitude less, around 0.023 MeV. Experimental investigation at such low energies is very difficult, if possible at all, thus low energy extrapolation inevitable to predict the reaction rate at these energies. The extrapolation and its uncertainty are influenced by the precision and covered energy range of the data used. There are many precision datasets between Ec.m. = 0.3–3.1 MeV, but only one below and one above. At higher energies known levels of 7Be exist, which motivates the study of that energy range. Therefore, we performed investigations in the energy range of Ec.m. = 4.3–8.3 MeV, where the radiative cross section has not been studied so far. For the cross section determination, the activation technique was used utilising a thin-windowed gas cell and the MGC-20 cyclotron of ATOMKI.

The so-called $\ensuremath{\gamma}$ process is responsible for the production of the majority of the heavy proton-rich stable nuclei. For modeling the extended reaction network of the process, the reaction rates are derived mainly from statistical model calculations, which are validated with experimental $\ensuremath{\alpha}$-induced reaction cross sections. In the present work, the key parameter of the statistical model is constrained by measuring cross sections a hundred times smaller than those in previous experiments, reaching down to the relevant stellar energies. It is expected that this work will reduce the uncertainty in the calculation of stellar production of these proton-rich nuclei.

The new Atomki-V2 α -nucleus potential is applied to calculate astrophysical reaction rates N A 〈 σ v 〉 of intermediate mass and heavy target nuclei from iron ( Z = 26 ) up to bismuth ( Z = 83 ). Overall, reaction rates of α -induced reactions are provided for 4359 target nuclei, covering as well neutron-deficient as extremely neutron-rich target nuclei from the proton to the neutron dripline. Contrary to previous rate compilations, these new calculations include all relevant exit channels with the dominating ( α , xn) reactions for neutron-rich target nuclei.

The crisis demonstrated that the role of the accounting standards applicable to fair valuation may be particularly important in the credit institution sector. The paper examines the influence exerted on the balance sheets of the Hungarian credit institutions by the fair valuation and the international and the Hungarian economic policy regulatory changes relating to valuation. We place special emphasis on examining whether the foreign-owned credit institution subsidiaries operating in Hungary and their parent banks responded differently to the challenges posed by the crisis. We elaborated a method for the measurement of the real involvement and using this we examine how the fair value involvement of the Hungarian credit institution sector has changed before, during and after the crisis. Generalising the problem, we found that the degree of the fair value involvement may represent an additional risk factor upon assessing the credit institutions’ operational efficiency and that the Hungarian subsidiaries followed a slightly different path than their parent banks.

The relevant interaction energies for astrophysical radiative capture reactions are very low, much below the repulsive Coulomb barrier. This leads to low cross sections, low counting rates in $\gamma$-ray detectors, and therefore the need to perform such experiments at ion accelerators placed in underground settings, shielded from cosmic rays. Here, the feasibility of such experiments in the new shallow-underground accelerator laboratory in tunnels VIII and IX of the Felsenkeller site in Dresden, Germany, is evaluated. To this end, the no-beam background in three different types of germanium detectors, i.e. a Euroball/Miniball triple cluster and two large monolithic detectors, is measured over periods of 26-66 days. The cosmic-ray induced background is found to be reduced by a factor of 500-2400, by the combined effects of, first, the 140 meters water equivalent overburden attenuating the cosmic muon flux by a factor of 40, and second, scintillation veto detectors gating out most of the remaining muon-induced effects. The new background data are compared to spectra taken with the same detectors at the Earth's surface and at other underground sites. Subsequently, the beam intensity from the cesium sputter ion source installed in Felsenkeller has been studied over periods of several hours. Based on the background and beam intensity data reported here, for the example of the $^{12}$C($\alpha$,$\gamma$)$^{16}$O reaction it is shown that highly sensitive experiments will be possible., Comment: Submitted to Eur. Phys. J. A

The observation of oxygen isotopes in giant stars sheds light on mixing processes operating in their interiors. Due to the very strong correlation between nuclear burning and mixing processes it is very important to reduce the uncertainty on the cross sections of the nuclear reactions that are involved. In this paper we focus our attention on the reaction O 18 ( p , γ ) 19 F . While the O 18 ( p , α ) 15 N channel is thought to be dominant, the (p,γ) channel can still be an important component in stellar burning in giants, depending on the low energy cross section. So far only extrapolations from higher-energy measurements exist and recent estimates vary by orders of magnitude. These large uncertainties call for an experimental reinvestigation of this reaction. We present a direct measurement of the O 18 ( p , γ ) 19 F cross section using a high-efficiency 4π BGO summing detector at the Laboratory for Underground Nuclear Astrophysics (LUNA). The reaction cross section has been directly determined for the first time from 140 keV down to 85 keV and the different cross section components have been obtained individually. The previously highly uncertain strength of the 90 keV resonance was found to be 0.53 ± 0.07 neV, three orders of magnitude lower than an indirect estimate based on nuclear properties of the resonant state and a factor of 20 lower than a recently established upper limit, excluding the possibility that the 90 keV resonance can contribute significantly to the stellar reaction rate.

Background: The $^{14}\mathrm{N}(p,\ensuremath{\gamma})^{15}\mathrm{O}$ reaction plays a vital role in various astrophysical scenarios. Its reaction rate must be accurately known in the present era of high precision astrophysics. The cross section of the reaction is often measured relative to a low energy resonance, the strength of which must therefore be determined precisely.Purpose: The activation method, based on the measurement of $^{15}\mathrm{O}$ decay, has not been used in modern measurements of the $^{14}\mathrm{N}(p,\ensuremath{\gamma})^{15}\mathrm{O}$ reaction. The aim of the present work is to provide strength data for two resonances in the $^{14}\mathrm{N}(p,\ensuremath{\gamma})^{15}\mathrm{O}$ reaction using the activation method. The obtained values are largely independent from previous data measured by in-beam $\ensuremath{\gamma}$ spectroscopy and are free from some of their systematic uncertainties.Method: Solid state TiN targets were irradiated with a proton beam provided by the Tandetron accelerator of Atomki using a cyclic activation. The decay of the produced $^{15}\mathrm{O}$ isotopes was measured by detecting the 511 keV positron annihilation $\ensuremath{\gamma}$ rays.Results: The strength of the ${\mathrm{E}}_{p}=278\phantom{\rule{0.16em}{0ex}}\mathrm{keV}$ resonance was measured to be $\ensuremath{\omega}{\ensuremath{\gamma}}_{278}=(13.4\ifmmode\pm\else\textpm\fi{}0.8)\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ while for the ${\mathrm{E}}_{p}=1058\phantom{\rule{0.16em}{0ex}}\mathrm{keV}$ resonance $\ensuremath{\omega}{\ensuremath{\gamma}}_{1058}=(442\ifmmode\pm\else\textpm\fi{}27)\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$.Conclusions: The obtained ${E}_{p}=278$ keV resonance strength is in fair agreement with the values recommended by two recent works. However, the ${E}_{p}=1058\phantom{\rule{0.16em}{0ex}}\mathrm{keV}$ resonance strength is about 20% higher than the previous value. The discrepancy may be caused in part by a previously neglected finite target thickness correction. As only the low energy resonance is used as a normalization point for cross section measurements, the calculated astrophysical reaction rate of the $^{14}\mathrm{N}(p,\ensuremath{\gamma})^{15}\mathrm{O}$ reaction and therefore the astrophysical consequences are not changed by the present results.

Background: The $^{3}\mathrm{He}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Be}$ reaction is a widely studied nuclear reaction; however, it is still not understood with the required precision. It has a great importance both in Big Bang nucleosynthesis and in solar hydrogen burning. The low mass number of the reaction partners makes it also suitable for testing microscopic calculations.Purpose: Despite the high number of experimental studies, none of them addresses the $^{3}\mathrm{He}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Be}$ reaction cross sections above 3.1-MeV center-of-mass energy. Recently, a previously unobserved resonance in the $^{6}\mathrm{Li}(\mathrm{p},\ensuremath{\gamma})^{7}\mathrm{Be}$ reaction suggested a new level in $^{7}\mathrm{Be}$, which would also have an impact on the $^{3}\mathrm{He}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Be}$ reaction in the energy range above 4.0 MeV. The aim of the present experiment is to measure the $^{3}\mathrm{He}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Be}$ reaction cross section in the energy range of the proposed level.Method: For this investigation the activation technique was used. A thin window gas-cell target confining $^{3}\mathrm{He}$ gas was irradiated using an $\ensuremath{\alpha}$ beam. The $^{7}\mathrm{Be}$ produced was implanted into the exit foil. The $^{7}\mathrm{Be}$ activity was determined by counting the $\ensuremath{\gamma}$ rays following its decay by a well-shielded high-purity germanium detector.Results: Reaction cross sections have been determined between ${E}_{\text{cm}}=4.0\phantom{\rule{4.pt}{0ex}}\text{and}\phantom{\rule{4.pt}{0ex}}4.4$ MeV with 0.04-MeV steps covering the energy range of the proposed nuclear level. One lower-energy cross-section point was also determined to be able to compare the results with previous studies.Conclusions: A constant cross section of around 10.5 $\ensuremath{\mu}\mathrm{b}$ was observed around the $^{7}\mathrm{Be}$ proton separation energy. An upper limit of 45 neV for the strength of a $^{3}\mathrm{He}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Be}$ resonance is derived.

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 t1/2 = (15.133 ± 0.028) min which is in agreement with the literature value but almost one order of magnitude more precise.

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 682841 “ASTRUm”). This work is supported by the Helmholtz International Center for FAIR (HIC for FAIR), by the Bundesministerium fur Bildung und Forschung (BMBF) (05P15RFFAA, 05P15RGFAA), by the Science and Technology Facilities Council (STFC) UK (ST/L005824/1, ST/M001652/1, ST/M006085), by the Helmholtz-CAS Joint Research Group (HCJRG-108), and by the Helmholtz-OCPC Postdoctoral Program (GSI08). C. L. W. acknowledges support by the European Research Council (Grant Agreement ERC-2015-StG No. 677497 “DoRES”). S. D. gratefully acknowledges the support provided by the Alexander von Humboldt Foundation and the Jordanian Scientific Research Support Fund under Grant No. Bas/2/4/2014. S. Yu. T. acknowledges the support by the DAAD through Mendeleev Grant, SPbU(28999675). C. L. and J. G. thank the ExtreMe Matter Institute EMMI at GSI, Darmstadt, and JINA-CEE (NSF Grant No. PHY-1430152) for support in the framework of the EMMI/JINA-CEE Workshop “NARRS” during which this work was discussed.

New measurements of the neutron scattering double differential cross section of iron were carried out at the neutron time-of-flight facilities GELINA and nELBE. A neutron spectrometer consisting of an array of up to 32 liquid organic scintillators was employed, which was designed to measure the scattering differential cross section at eight scattering angles and to simultaneously determine the integral cross section via numerical quadrature. The separation of elastic from inelastic scattering was achieved by analyzing the time-of-flight-dependent light-output distributions to determine the scattered neutron energy. The method was validated by studying elastic scattering on carbon and it was proved to work well for the determination of the elastic cross section. Here, the possibility to extend it to inelastic scattering was investigated too. For these experiments a sample of natural iron was used and the results cover the incident neutron energy range from 2 to 6 MeV. Both the differential and the integral elastic cross sections were produced for $^{\mathrm{nat}}\mathrm{Fe}$, while for inelastic scattering, partial angular distributions for scattering from the first excited level of $^{56}\mathrm{Fe}$ could be determined.

The NeNa and the MgAl cycles play a fundamental role in the nucleosynthesis of asymptotic giant branch stars undergoing hot bottom burning. The Na 23 ( p , γ ) 24 Mg reaction links these two cycles and a precise determination of its rate is required to correctly estimate the contribution of these stars to the chemical evolution of various isotopes of Na, Mg and Al. At temperatures of 50 ≲ T ≲ 110 MK , narrow resonances at E p = 140 and 251 keV are the main contributors to the reaction rate, in addition to the direct capture that dominates in the lower part of the temperature range. We present new measurements of the strengths of these resonances at the Laboratory for Underground Nuclear Astrophysics (LUNA). We have used two complementary detection approaches: high efficiency with a 4π BGO detector for the 140 keV resonance, and high resolution with a HPGe detector for the 251 keV resonance. Thanks to the reduced cosmic ray background of LUNA, we were able to determine the resonance strength of the 251 keV resonance as ω γ = 482 ( 82 ) μ eV and observed new gamma ray transitions for the decay of the corresponding state in Mg 24 at E x = 11931 keV . With the highly efficient BGO detector, we observed a signal for the 140 keV resonance for the first time in a direct measurement, resulting in a strength of ω γ 140 = 1.46 − 0.53 + 0.58 neV (68% CL). Our measurement reduces the uncertainty of the Na 23 ( p , γ ) 24 Mg reaction rate in the temperature range from 0.05 to 0.1 GK to at most − 35 % + 50 % at 0.07 GK. Accordingly, our results imply a significant reduction of the uncertainties in the nucleosynthesis calculations.

We introduce the LUNA neutron detector array developed for the investigation of the 13C( α , n )16O reaction towards its astrophysical s -process Gamow peak in the low-background environment of the Laboratori Nazionali del Gran Sasso (LNGS). Eighteen 3He counters are arranged in two different configurations (in a vertical and a horizontal orientation) to optimize neutron detection efficiency, target handling and target cooling over the investigated energy range E α , lab = 300 − 400 keV (E n = 2 . 2 − 2 . 6 MeV in emitted neutron energy). As a result of the deep underground location, the passive shielding of the setup and active background suppression using pulse shape discrimination, we reached a total background rate of 1 . 23 ± 0 . 12 counts/hour. This resulted in an improvement of two orders of magnitude over the state of the art allowing a direct measurement of the 13C( α , n )16O cross-section down to E α , lab = 300 keV. The absolute neutron detection efficiency of the setup was determined using the 51V(p,n)51Cr reaction and an AmBe radioactive source, and completed with a Geant4 simulation. We determined a (34 ± 3)% and (38 ± 3)% detection efficiency for the vertical and horizontal configurations, respectively, for E n = 2 . 4 MeV neutrons.

Cross sections of ( α,γ), (α,n), and (α,2n) reactions for 197Au were measured below the Coulomb barrier using the activation technique. The new data are analyzed in the statistical model and in a simple barrier transmission model. Sensitivities of the resulting cross sections on the underlying parameters are discussed. It is found that the cross sections in the statistical model depend sensitively on the tail of the imaginary α-nucleus potential at large radii outside the colliding nuclei. Contrary, the cross sections in the barrier transmission model depend only on the real part of the α-nucleus potential. The calculated cross sections in the barrier transmission model agree nicely with the new experimental data. Furthermore, the available experimental data for heavy targets above A ≈150 are also well reproduced within the barrier transmission model.

The ^{22}Ne(p,γ)^{23}Na reaction, part of the neon-sodium cycle of hydrogen burning, may explain the observed anticorrelation between sodium and oxygen abundances in globular cluster stars. Its rate is controlled by a number of low-energy resonances and a slowly varying nonresonant component. Three new resonances at E_{p}=156.2, 189.5, and 259.7 keV have recently been observed and confirmed. However, significant uncertainty on the reaction rate remains due to the nonresonant process and to two suggested resonances at E_{p}=71 and 105 keV. Here, new ^{22}Ne(p,γ)^{23}Na data with high statistics and low background are reported. Stringent upper limits of 6×10^{-11} and 7×10^{-11} eV (90% confidence level), respectively, are placed on the two suggested resonances. In addition, the off-resonant S factor has been measured at unprecedented low energy, constraining the contributions from a subthreshold resonance and the direct capture process. As a result, at a temperature of 0.1 GK the error bar of the ^{22}Ne(p,γ)^{23}Na rate is now reduced by 3 orders of magnitude.

The field of nuclear astrophysics is devoted to the study of the creation of the chemical elements. By nature, it is deeply intertwined with the physics of the Sun. The nuclear reactions of the proton-proton cycle of hydrogen burning, including the 3He({\alpha},{\gamma})7Be reaction, provide the necessary nuclear energy to prevent the gravitational collapse of the Sun and give rise to the by now well-studied pp, 7Be, and 8B solar neutrinos. The not yet measured flux of 13N, 15O, and 17F neutrinos from the carbon-nitrogen-oxygen cycle is affected in rate by the 14N(p,{\gamma})15O reaction and in emission profile by the 12C(p,{\gamma})13N reaction. The nucleosynthetic output of the subsequent phase in stellar evolution, helium burning, is controlled by the 12C({\alpha},{\gamma})16O reaction. In order to properly interpret the existing and upcoming solar neutrino data, precise nuclear physics information is needed. For nuclear reactions between light, stable nuclei, the best available technique are experiments with small ion accelerators in underground, low-background settings. The pioneering work in this regard has been done by the LUNA collaboration at Gran Sasso/Italy, using a 0.4 MV accelerator. The present contribution reports on a higher-energy, 5.0 MV, underground accelerator in the Felsenkeller underground site in Dresden/Germany. Results from {\gamma}-ray, neutron, and muon background measurements in the Felsenkeller underground site in Dresden, Germany, show that the background conditions are satisfactory for nuclear astrophysics purposes. The accelerator is in the commissioning phase and will provide intense, up to 50{\mu}A, beams of 1H+, 4He+ , and 12C+ ions, enabling research on astrophysically relevant nuclear reactions with unprecedented sensitivity., Comment: Submitted to the Proceedings of the 5th International Solar Neutrino Conference, Dresden/Germany, 11-14 June 2018, to appear on World Scientific -- updated version (Figure 2 and relevant discussion updated, co-author A. Domula added)

Background: $\ensuremath{\alpha}$-nucleus optical potentials are basic ingredients of statistical model calculations used in nucleosynthesis simulations. While the nucleon+nucleus optical potential is fairly well known, for the $\ensuremath{\alpha}$+nucleus optical potential several different parameter sets exist and large deviations, reaching sometimes even an order of magnitude, are found between the cross section predictions calculated using different parameter sets.Purpose: A measurement of the radiative $\ensuremath{\alpha}$-capture and the $\ensuremath{\alpha}$-induced reaction cross sections on the nucleus $^{115}\mathrm{In}$ at low energies allows a stringent test of statistical model predictions. Since experimental data are scarce in this mass region, this measurement can be an important input to test the global applicability of $\ensuremath{\alpha}$+nucleus optical model potentials and further ingredients of the statistical model.Methods: The reaction cross sections were measured by means of the activation method. The produced activities were determined by off-line detection of the $\ensuremath{\gamma}$ rays and characteristic x rays emitted during the electron capture decay of the produced Sb isotopes. The $^{115}\mathrm{In}(\ensuremath{\alpha},\ensuremath{\gamma})^{119}\mathrm{Sb}$ and $^{115}\mathrm{In}(\ensuremath{\alpha},n)\phantom{\rule{0.16em}{0ex}}^{118}\mathrm{Sb}^{m}$ reaction cross sections were measured between ${E}_{\mathrm{c}.\mathrm{m}.}=8.83$ and 15.58 MeV, and the $^{115}\mathrm{In}(\ensuremath{\alpha},n)\phantom{\rule{0.16em}{0ex}}^{118}\mathrm{Sb}^{g}$ reaction was studied between ${E}_{\mathrm{c}.\mathrm{m}.}=11.10$ and 15.58 MeV. The theoretical analysis was performed within the statistical model.Results: The simultaneous measurement of the ($\ensuremath{\alpha},\ensuremath{\gamma}$) and ($\ensuremath{\alpha},n$) cross sections allowed us to determine a best-fit combination of all parameters for the statistical model. The $\ensuremath{\alpha}$+nucleus optical potential is identified as the most important input for the statistical model. The best fit is obtained for the new Atomki-V1 potential, and good reproduction of the experimental data is also achieved for the first version of the Demetriou potentials and the simple McFadden-Satchler potential. The nucleon optical potential, the $\ensuremath{\gamma}$-ray strength function, and the level density parametrization are also constrained by the data although there is no unique best-fit combination.Conclusions: The best-fit calculations allow us to extrapolate the low-energy ($\ensuremath{\alpha},\ensuremath{\gamma}$) cross section of $^{115}\mathrm{In}$ to the astrophysical Gamow window with reasonable uncertainties. However, still further improvements of the $\ensuremath{\alpha}$-nucleus potential are required for a global description of elastic ($\ensuremath{\alpha},\ensuremath{\alpha}$) scattering and $\ensuremath{\alpha}$-induced reactions in a wide range of masses and energies.

Neutron total cross sections of natFe, 197Au and natW have been measured at the n ELBE neutron time-of-flight facility in the energy range 0.15-8MeV with an uncertainty due to counting statistics of up to 2% and a total uncertainty due to systematic effects of 1%. The neutrons are produced with the superconducting electron accelerator ELBE using a liquid lead circuit as photo-neutron target. By periodical sample-in-sample-out measurements the transmission of the sample materials has been determined using a low-threshold plastic scintillation detector. The resulting effective total cross sections show good agreement with previously measured data that cover only part of the energy range available at n ELBE. The results have also been compared to evaluated library files and recent calculations based on a dispersive coupled channel optical model potential.

This document is the Accepted Manuscript version of the following article: Z. Korkulu, et al, ‘Investigation of α-induced reactions on Sb isotopes relevant to the astrophysical γ process’, Physical Review C, Vol. 97(4): 045803, April 2018, available online at DOI: https://doi.org/10.1103/PhysRevC.97.045803 © 2018 American Physical Society.

The angular distribution of $ \gamma$ -rays emitted after inelastic scattering of fast neutrons from iron was determined at the n ELBE neutron time-of-flight facility. An iron sample of natural isotopic composition was irradiated by a continuous photo-neutron spectrum in the energy range from about 0.1 up to 10 MeV. The de-excitation $\gamma$ -rays of the four lowest excited states of 56Fe and the first excited state of 54Fe were detected using a setup of five high-purity germanium (HPGe) detectors and five LaBr3 scintillation detectors positioned around the sample at $ 30^\circ$ , $55^{\circ}$ , $90^{\circ}$ , $ 125^{\circ}$ and $150^{\circ}$ with respect to the incoming neutron beam. The resulting angular distributions were fitted by Legendre polynomials up to 4th order and the angular distribution coefficients $a_{2}$ and $ a_{4}$ were extracted. The angular distribution coefficients of three transitions in 56Fe are reported here for the first time. The results are applied to a previous measurement of the inelastic scattering cross section determined using a single HPGe detector positioned at $125^{\circ}$ . Using the updated $\gamma$ -ray angular distribution, the previous cross section results are in good agreement with reference data.

The N14(p,γ)O15 reaction is the slowest reaction of the carbon-nitrogen cycle of hydrogen burning and thus determines its rate. The precise knowledge of its rate is required to correctly model hydr ...

Low-background experiments with stable ion beams are an important tool for putting the model of stellar hydrogen, helium, and carbon burning on a solid experimental foundation. The pioneering work in this regard has been done by the LUNA collaboration at Gran Sasso, using a 0.4 MV accelerator. The present contribution reviews the status of the project for a higher-energy underground accelerator in Felsenkeller, Germany. Results from γ-ray, neutron, and muon background measurements in the Felsenkeller underground site in Dresden, Germany, show that the background conditions are satisfactory. Two tunnels of the Felsenkeller site have recently been refurbished for the installation of a 5MV high-current Pelletron accelerator. Civil construction work has completed in March 2018. The accelerator will provide intense, 50 μA, beams of 1H+, 4He+, and 12C+ ions, enabling research on astrophysically relevant nuclear reactions with unprecedented sensitivity.