Speaker
Description
Carbon burning is the third stage of stellar evolution, influencing the fate of both massive stars and low-mass stars in binary systems.
Stellar carbon burning primarily occurs through the 12C(12C, α)20Ne and 12C(12C, p)23Na reactions. While these reactions have been studied over a wide energy range, direct measurements below 2.1 MeV (the astrophysical range) are lacking. Indirect data, such as those from the Trojan Horse approach, are available at astrophysical energies but carry uncertainties in renormalization. Thus, direct measurements are crucial for stellar evolution models and interpreting indirect results.
Currently, the LUNA collaboration is conducting direct studies at the Bellotti ion beam facility in the Laboratori Nazionali del Gran Sasso (LNGS), Italy, using intense carbon beams with excellent energy resolution. The goal is to directly measure the 12C+12C cross-section at astrophysical energies using γ-ray spectroscopy. The detection setup includes NaI scintillators surrounding a 150% HPGe detector ensuring high efficiency and preserving HPGe resolution (1.2 keV at 1.33 MeV). The NaI array also acts as a veto for background radiation. The detectors are shielded with 2 cm of copper and 25 cm of lead to reduce environmental background by over two orders of magnitude.
This setup will achieve unprecedented sensitivity, with an expected background four orders of magnitude lower than previous direct measurements at low energies. It will also allow exploration of the 24Mg level density through de-excitation of 20Ne and 23Na nuclei, potentially revealing cluster structures in the 24Mg nucleus. In particular, we will focus on the 1.5-3.5 MeV energy range (15.44 MeV to 17.94 MeV in the Q-value window), where cluster states might influence the 12C+12C reaction rate.
I will present recent developments in the setup, including simulations and detailed characterization of the HPGe detector’s active volume, as well as preliminary results from beam-on-target tests for target characterization, detector efficiency, and 12C+12C measurements at higher energies (Ep > 2 MeV).
