Speaker
Description
The understanding of stellar structure and evolution is strictly related to the possibility of energy production in a star. Indeed, nuclear processes generate the energy that makes stars shine. The same nuclear processes in stars are responsible for the synthesis of the elements. The theory of this building of elements is called nucleosynthesis and it is remarkably successful in predicting how these processes are based on the quantum mechanical properties of atomic nuclei. Nucleosynthesis, nuclear energy generation in stars, and other topics at the intersection of nuclear physics and astrophysics make up the science of nuclear astrophysics. The conditions under which the majority of astrophysical reactions proceed in stellar en- vironments make it difficult or impossible to measure them under the same conditions in the laboratory. For example, the astrophysical reactions between charged nuclei occur at ener- gies much lower than the Coulomb barrier, therefore, the cross sections of these processes are very small (of the order of nano-picobarn) in the energy windows of astrophysical interest. It seems evident that the experimental determination of these cross sections is greatly hampered by the effects of penetration of the Coulomb barrier, which generally reduces the number of useful events for the experimental investigation. The behaviour of the direct cross sections is usually extrapolated from higher energies to the astrophysical interest region by using the definition of the astrophysical factor S(E) = Eσ(E)exp(2πµ) which varies smoothly with energies. Nevertheless this extrapolation procedure can introduce some uncertainties due, for example, to the presence of unexpected subthreshold resonances. In order to avoid the extrapolation procedure, a number of experimental solutions were proposed in direct mea- surements for enhancing the signal-to-noise ratio. However, the measurements in laboratory
at ultralow energies suffer from the complication due to the effects of electron screening.
To overcome the experimental difficulties, in the last decades many indirect techniques and alternative methods have been developed to determine reaction rates of astrophysical interest. A selection of these methods, mainly used among the INFN groups, will be presented.
