Target Characterization for 12C+12C Fusion Measurements at LUNA

The 12C + 12C fusion reaction has a central role in nuclear astrophysics, being the fundamental process of the carbon burning phase in massive stars and influencing key phenomena such as the synthesis of intermediate-mass elements and the evolution toward explosive scenarios. In particular, the reaction rate at energies within the Gamow window (E ≃ 1–3 MeV) has a direct impact on the determination of the critical mass parameter Mup, which separates stars that undergo carbon ignition from those evolving toward degenerate configurations. Despite its importance, the behavior of the cross section at these energies remains highly uncertain due to the presence of resonant structures and the experimental challenges associated with extremely low reaction yields. In this work, a preliminary study of the 12C + 12C reaction has been performed by the LUNA (Laboratory for Underground Nuclear Astrophysics) collaboration at Laboratori Nazionali del Gran Sasso (LNGS). The underground location of the experiment, combined with a detection setup based on high-resolution HPGe detectors and a graded shielding, allows for a strong suppression of the γ-ray background, enabling measurements at low energies. The main objective of this work is the characterization of four different carbon targets, i.e. AXF, ZXF, HOPG, and Glassy Carbon, to identify the most suitable configuration for future low-energy measurements. A dedicated experimental test campaign was carried out in December 2024, during which particular attention was committed to the identification of contaminant-induced reactions and their impact on the extracted yields. Taking into account the performance of the targets during irradiation and the evolution of their contaminant content, it was possible to determine ZXF as the best candidate for the 12C + 12C cross section measurements. With future campaigns and the resulting data, it will be possible to establish the validity of the chosen targets or the need for further research to identify better solutions.