Carbon and oxygen burning reactions, in particular, ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ fusion, are important for the understanding and interpretation of the late phases of stellar evolution as well as the ignition and nucleosynthesis in cataclysmic binary systems such as type Ia supernovae and x-ray superbursts. A new measurement of this reaction has been performed at the University of Notre Dame using particle-$\gamma$ coincidence techniques with SAND (a silicon detector array) at the high-intensity 5U Pelletron accelerator. New results for ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ fusion at low energies relevant to nuclear astrophysics are reported. They show strong disagreement with a recent measurement using the indirect Trojan Horse method. The impact on the carbon burning process under astrophysical scenarios will be discussed.

We investigate the impact of the new LUNA rate for the nuclear reaction ²²Ne(p, γ)²³Na on the chemical ejecta of intermediate-mass stars, with particular focus on the thermally pulsing asymptotic giant branch (TP-AGB) stars that experience hot-bottom burning. To this aim, we use the PARSEC and COLIBRI codes to compute the complete evolution, from the pre-main sequence up to the termination of the TP-AGB phase, of a set of stellar models with initial masses in the range 3.0–6.0 M_⊙ and metallicities Z_i = 0.0005, 0.006 and 0.014. We find that the new LUNA measures have much reduced the nuclear uncertainties of the ²²Ne and ²³Na AGB ejecta that drop from factors of ≃10 to only a factor of few for the lowest metallicity models. Relying on the most recent estimations for the destruction rate of ²³Na, the uncertainties that still affect the ²²Ne and ²³Na AGB ejecta are mainly dominated by the evolutionary aspects (efficiency of mass-loss, third dredge-up, convection). Finally, we discuss how the LUNA results impact on the hypothesis that invokes massive AGB stars as the main agents of the observed O–Na anticorrelation in Galactic globular clusters. We derive quantitative indications on the efficiencies of key physical processes (mass-loss, third dredge-up, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anticorrelation and the observational constraints on the CNO abundance. Results for the corresponding chemical ejecta are made publicly available.

Direct measurements of small nuclear reaction cross sections require a low background in the signal region of interest to achieve the necessary sensitivity. We describe two complementary detector setups that have been used for studies of ( p , γ ) reactions with solid targets at the Laboratory for Underground Nuclear Astrophysics (LUNA): a high-purity germanium detector and a bismuth germanate (BGO) detector. We present the effect of a customised lead shielding on the measured background spectra in the two detector setups at LUNA. We developed a model to describe the contributions of environmental and intrinsic backgrounds in the BGO detector measurements. Furthermore we present an upgrade of the data acquisition system for our BGO detector, which allows us to exploit the features of the segmented detector and overcome some of the limitations encountered in previous experiments. We conclude with a discussion on the improved sensitivity of the presented setups, and the benefits for ongoing and possible future measurements.

Studies of charged-particle reactions for low-energy nuclear astrophysics require high sensitivity, which can be achieved by means of detection setups with high efficiency and low backgrounds, to obtain precise measurements in the energy region of interest for stellar scenarios. High-efficiency total absorption spectroscopy is an established and powerful tool for studying radiative capture reactions, particularly if combined with the cosmic background reduction by several orders of magnitude obtained at the Laboratory for Underground Nuclear Astrophysics (LUNA). We present recent improvements in the detection setup with the Bismuth Germanium Oxide (BGO) detector at LUNA, aiming to reduce high-energy backgrounds and increase the summing detection efficiency. The new design results in enhanced sensitivity of the BGO setup, as we demonstrate and discuss in the context of the first direct measurement of the 65 keV resonance (E _x = 5672 keV) of the ¹⁷O(p,γ)¹⁸F reaction. Moreover, we show two applications of the BGO detector, which exploit its segmentation. In the case of complex γ-ray cascades, e.g. the de-excitation of E _x = 5672 keV in ¹⁸F, the BGO segmentation allows to identify and suppress the beam-induced background signals that mimic the sum peak of interest. We demonstrate another new application for such a detector in form of in situ activation measurements of a reaction with β ⁺ unstable product nuclei, e.g. the ¹⁴N(p,γ)¹⁵O reaction.