Seminarium Fizyki Jądra Atomowego

The cross sections of nuclear reactions that take place in different astrophysical scenariosare crucial ingredients to understand the synthesis of the elements and energy generation. In stars, nuclear reactions occur at energies well below the Coulomb barrier. Therefore, theircross sections are often too small and very difficult to be measured in laboratories at theEarth’s surface, where the signal would be covered by the cosmic-ray induced background. An effective solution to suppress the cosmic-ray induced background is to perform experiments in underground laboratories. The extremely low background reached at the Laboratory for Underground Nuclear Astrophysics (LUNA) located deep underground at Gran Sasso National Laboratories (Italy) allows to measure nuclear cross sections directly at the energies of astrophysical interest. In the last 30 years, many crucial reactions involved in different astrophysical scenarios have been measured at LUNA.
The presentation will provide an overview of the measurements of 22Ne(α; γ)26Mg and20Ne(p; γ)21Na reactions ongoing at LUNA. The 22Ne(α; γ)26Mg reaction competes with the22Ne(α; n)25Mg reaction which is the main source of neutrons for the s-process in low-massAsymptotic Giant Branch (AGB) and massive stars. Moreover, it has been found that theuncertainty of the 22Ne(α; γ)26Mg reaction rate affects also the nucleosynthesis of isotopesbetween 26Mg and 31P in intermediate-mass AGB stars. The 22Ne(α; γ)26Mg reaction rate is influenced by the 395 keV resonance which has been studied only indirectly leading to a widerange of possible values for its resonance strength (10-15 - 10-9 eV). For the first time LUNAmeasured directly the resonance at 395 keV. The experimental details and preliminary resultswill be shown, together with their possible impact on the 22Ne(α; γ)26Mg reaction rate.The 20Ne(p; γ)21Na is the first reaction of the NeNa cycle and having the slowest reaction rate it controls the speed of the entire cycle. The rate of the 20Ne(p; γ)21Na reaction, depending on the temperature, is dominated by the high energy tail of a sub-threshold state at ER = 6.7 keV, a direct capture component and a narrow resonance at ER = 366 keV. The first campaign,dedicated to the study of the 366 keV resonance is ongoing at LUNA. The experimentalapproach as well as some "online" analysis will be shown.

Seminarium on-line na platformie zoom:
https://us02web.zoom.us/j/86759935850?pwd=ejZhaHBjUTNncVVDZFJTRnVaYW9MQT09
ID: 867 5993 5850
Passcode: 909432