Scientists from the Helmholtz Center Dresden-Rossendorf (HZDR), together with researchers from Italy, Hungary and Scotland, have discovered that one of the main thermonuclear reactions that occurs inside stars takes place slower than previously thought. The research results published in Physical Review C will help improve models of processes in stars, including the Sun.
The hydrogen combustion reaction, recreated at the Felsenkeller accelerator in Dresden, is important for the formation of elements in massive stars and is also the first step in the CNO cycle. The CNO cycle combines four protons, using carbon, nitrogen and oxygen isotopes as catalysts. The final product is one alpha particle (stable helium nucleus), two positrons, and two electron neutrinos.
Scientists used tantalum discs containing carbon on the surface as targets. They are bombarded with protons emitted from the 5 MV Pelletron accelerator, which can cover a fairly wide energy range. The gamma rays produced by the reaction can be detected using 20 high-purity germanium detectors. During the experiment, the reaction cross-section that determines the probability of a reaction occurring was determined with unprecedented precision. As a result, the previously accepted value had to be adjusted by approximately 25%.
It turns out that the reaction takes longer and neutrino emission from nitrogen occurs closer to the center of the Sun. The new data also helps to more accurately predict the ratio of 12C and 13C carbon isotopes.