Microscopic three-cluster study of 21-nucleon systems

The three-cluster generator coordinate method is applied to different properties of T=1/2 21-nucleon systems. The 21Ne and 21Na nuclei are described by mixing of different 16O+α+n or 16O+α+p configurations. A fair agreement with experiment is found for energy spectra and for electromagnetic transition probabilities. We present 17O+α and 20Ne+n elastic phase shifts, as well as 17O(α,γ)21Ne and 17O(α,n)20Ne low-energy cross sections. The ratio between the corresponding reaction rates is predicted 5 orders of magnitude lower than values currently used in astrophysics. We also compare 20Ne(p,p')20Ne(2+), 20Ne(p,α)17F, and 20Ne (p,γ)21Na theoretical cross sections with experimental data. For the proton capture reaction, important in stellar evolution, we do not suggest significant differences with the existing reaction rate