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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 C (α , n) 16 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 γ rays emitted by the 13 C (p , γ) 14 N radiative capture reaction. This approach was used to monitor 13 C target degradation in situ during the 13 C (α , n) 16 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 C (α , n) 16 O reaction cross-section at one beam energy is also reported. [ABSTRACT FROM AUTHOR]

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 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: 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]