Nuclear reactions for Astrophysics and the opportunity of indirect methods featuring Marco La Cognata (INFN LNS, Italy)

Hosted by: Jakub Skowronski (University of Padua, Italy)

Abstract: Nuclear reactions among charged particles in stars take place at energies generally well below the Coulomb barrier, so the Coulomb barrier penetration factor exponentially suppresses the cross sections down to values as small as few nanobarns or picobarns. Therefore, approaching astrophysical energies opens new challenges and calls for new approaches. 

I will introduce the mission of nuclear astrophysics and discuss how experiments are usually conducted. Then, I will focus on the use of indirect methods as complementary approaches to direct measurements, discussing in detail the asymptotic normalization coefficient (ANC) and the Trojan Horse Method (THM). These methods are used to deduce the astrophysical factors of reactions with photons and charged particles in the exit channel, respectively, with no need of extrapolation. 

I will present recent results of the application of the two methods as examples. First, I will discuss the 6Li(3He,d)7Be measurement used to deduced the ANC’s of the 3He+4He->7Be and p+6Li->7Be channels and the corresponding radiative capture astrophysical factors. Then, I will illustrate the THM measurement of the 27Al(p,a)24Mg astrophysical factor through the 2H(27Al,a24Mg)n reaction. The reaction rate of the 27Al(p,g)28Si reaction was also deduced thanks to the determination of the proton partial widths. 

Both the ANC and the THM applications made it possible to assess the occurrence or exclude the presence of resonances that could be responsible significant changes of the reaction rates at temperatures of astrophysical interest.