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We report on a new measurement of the 14N(p,γ)15O capture cross section at Ep=140 to 400 keV using the 400 kV LUNA accelerator facility at the Laboratori Nazionali del Gran Sasso (LNGS). The uncertainties have been reduced with respect to previous measurements and their analysis. We have analyzed the data using the R-matrix method and we find that the ground state transition accounts for about 15% of the total S-factor. The main contribution to the S-factor is given by the transition to the 6.79 MeV state. We find a total S(0)=1.7±0.2 keV b, in agreement with recent extrapolations. The result has important consequences for the solar neutrino spectrum as well as for the age of globular clusters. [Copyright &y& Elsevier]

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 4 π 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. [ABSTRACT FROM AUTHOR]

Abstract: We report here on the direct generation of a CN− ion beam for the production of a N ion beam to be used in nuclear astrophysics measurements. The procedure relies on the production of CN− ion beam with a SNICS source starting from several appropriate substrates containing CN− triple bond. Several of the investigated substrates showed a higher beam intensity with respect to the common N beam production from a cathode of BN plus graphite. Best results in terms of analyzed beam intensity were observed with K3Fe(CN)6 and KSCN cathodes. Use of the latter compound is particularly appealing because of the easy availability of mass-15 enriched molecule. [Copyright &y& Elsevier]

Abstract: In the present work we report on a new measurement of resonance strengths ωγ in the reaction 25Mg(p, γ)26Al at and 189 keV. This study was performed at the LUNA facility in the Gran Sasso underground laboratory using a 4π BGO summing crystal. For the first time the 92 keV resonance was directly observed and a resonance strength was determined. Additionally, the γ-ray branchings and strength of the 189 keV resonance were studied with a high resolution HPGe detector yielding an ωγ value in agreement with the BGO measurement, but 20% larger compared to previous works. [Copyright &y& Elsevier]

Abstract: The radiative capture reaction has been investigated in the energy range to 4.5 MeV. This experiment focused in particular on the cascade transition to the 0+ state at in 16O and was performed by detecting the capture γ-rays with a NaI detector array at the windowless 4He gas target of the recoil mass separator ERNA in coincidence with the 16O ejectiles. The 6.05 MeV transition has been considered recently as a component accounting for up to 15% of the total cross section at astrophysical energies. The arrangement of the detector array yielded additional information on the γ-ray multipolarity, i.e. the ratio , and it was found that the 6.05 MeV transition is entirely E2 in the studied energy range. The results for this transition are analyzed in an R-matrix formalism and extrapolated to the relevant Gamow energy of stellar helium burning, . In contrast to a previous analysis, the present extrapolation suggests a negligible contribution from this amplitude, . Additional data for cascade transitions to excited states at , 6.92, and 7.12 MeV, respectively, as well as to the ground state were obtained and the corresponding S factors in the studied energy range are given. [Copyright &y& Elsevier]

Abstract: The process is a key reaction in both Big-Bang nucleosynthesis and p–p chain of Hydrogen Burning in Stars. A new measurement of the cross section has been performed at the INFN Gran Sasso underground laboratory by both the activation and the prompt γ detection methods. The present work reports full details of the prompt γ detection experiment, focusing on the determination of the systematic uncertainty. The final data, including activation measurements at LUNA, are compared with the results of the last generation experiments and two different theoretical models are used to obtain the S-factor at solar energies. [Copyright &y& Elsevier]

Abstract: The reaction plays a key role for the understanding of the production of 7Li in Big Bang nucleosynthesis as well as for the high energy component of the solar neutrino spectrum. The uncertainty in its absolute cross-section arises from systematic differences of the available data sets. In various experiments the cross-section was measured by the detection of the prompt -rays or by the off-line observation of the -rays following the 7Be electron capture; in a few cases both observations were carried out. We report on a new approach based on the use of the recoil separator ERNA (European Recoil separator for Nuclear Astrophysics) to detect directly the 7Be recoils as well as the prompt -rays in coincidence with the recoils. We present technical details of the experimental setup, such as a recirculating 3He gas target, a TOF-E end detector, and a NaI detector array. In addition, the measurement of the separator acceptance is discussed and compared to the expected recoil emittance. The feasibility of the approach is demonstrated by sample spectra, indicating cross-section determinations of in the energy range with high precision and accuracy. [Copyright &y& Elsevier]

Abstract: Deep underground in Gran Sasso National Laboratory (Italy), at the LUNA facility, the cross section of the 14N(p, γ)15O, the slowest process of the CNO cycle, has been measured at energies much lower than achieved before. Using a 400 kV accelerator, a windowless gas target and a 4π BGO summing detector, direct cross section data has been obtained down to 70 keV, reaching a value of 0.24 picobarn, corresponding to an S-factor of barn. The Gamow peak has been covered by direct experimental data for several scenarios of stable and explosive hydrogen burning. The ωγ strength of the 259 keV resonance has been re-measured obtaining . The stellar reaction rate has been calculated for temperatures . A complete description of the experiment is here presented, including the impact of the present data on nucleosynthesis in AGB stars. [Copyright &y& Elsevier]

Abstract: In stars with temperatures above , hydrogen burning is dominated by the CNO cycle. Its rate is determined by the slowest process, the 14N(p, γ)15O reaction. Deep underground in Italy''s Gran Sasso laboratory, at the LUNA 400 kV accelerator, the cross section of this reaction has been measured at energies much lower than ever achieved before. Using a windowless gas target and a 4π BGO summing detector, direct cross section data has been obtained down to 70 keV, reaching a value of 0.24 picobarn. The Gamow peak has been covered by experimental data for several scenarios of stable and explosive hydrogen burning. In addition, the strength of the 259 keV resonance has been remeasured. The thermonuclear reaction rate has been calculated for temperatures , for the first time with negligible impact from extrapolations. [Copyright &y& Elsevier]

The electron capture half life of 7Be implanted into different metals has been measured with high precision in order to search for a possible dependence of the decay rate on the electron configuration around the 7Be atoms. In order to reduce systematic errors, the half life in different metals is measured by three laboratories simultaneously using different experimental setups. The measurements and data analysis are in progress, preliminary results are presented. [Copyright &y& Elsevier]

The 14N(p,γ)15O reaction has been investigated by LUNA at the National Laboratory of Gran Sasso (LNGS) using two different techniques. The first study has been performed using a solid target and detecting the γ-rays coming from the single transitions with a HPGe detector in very close geometry to the target. In a second phase a windowless gas target sorrounded by a nearly 4π BGO summing crystal has been used and the total S-factor has been measured down to . [Copyright &y& Elsevier]

The reaction 12C(α, γ)16O plays a key role in determining the C/O ratio in the stellar core at the end of helium burning, which in turn influences the further evolution and nucleosynthesis. The determination of the cross section at the relevant astrophysical energy , which is of the order of 10−17 b, requires extrapolation of the S factor determined from data collected with high precision and accuracy at higher energy. A new experimental approach has been undertaken in order to study this reaction for the first time by the direct detection of the 16O nuclides using the recoil mass separator ERNA. [Copyright &y& Elsevier]

A 7Be ion beam of several particle pA at 8 MeV has been produced at the TTT3 tandem of the University “Federico II” in Naples. The 7Be nuclides were formed via the 7Li(p,n)7Be reaction using a metallic Li target and an 11.4 MeV proton beam of 20 μA intensity, delivered by the cyclotron in Debrecen. Methods of hot chemistry were used to extract the 7Be nuclides from the Li matrix and to prepare the 7Be cathodes for the ion sputter source of the tandem. Examples of 7Be beam applications are given. [Copyright &y& Elsevier]

Using the 50 kV LUNA accelerator facility at the Gran Sasso underground laboratory we measured, with an accuracy of the order of 10%, the d(p, γ)3He cross section from 22 down to 2.5 keV c.m. energy, well below the solar Gamow peak. The experimental set-up was based on a large solid angle, segmented BGO detector and a renewed windowless gas target. The astrophysical S(E) factor within the Gamow peak is in fair agreement with the value of one of the existing extrapolations of data at higher energies. [Copyright &y& Elsevier]

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 4 π 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. [ABSTRACT FROM AUTHOR]