Nuclear astrophysics studies with radioactive beams at Louvain-la-Neuve

The radioactive beam facility of Louvain-la-Neuve, based on a two-cyclotron scheme, currently produces post-accelerated beams of 6He, 13N, 18Ne and 19Ne. In the past two years the main effort has been concentrated on measurements dealing with the 13N(p,γ)14O cross section, which opens the hot CNO cycle as an alternative to the standard cold CNO cycle. First of all, the authors measured the 13N(p,γ)14O cross section, which at stellar energies, is dominated by a resonance corresponding to the first excited state of 14O (Eexc = 5.17 MeV), which subsequently decays by γ radiation to the ground state with a probability of about 10-4. The p + 13N elastic scattering was measured to better determine the resonance energy and width. Finally the measurement of the 13N(d,n) 14O reaction provided some knowledge on the nonresonant 13N(p,γ)14O cross section. The same set of measurements will soon be performed on the 19Ne(p,γ)20Na reaction, responsible for the breakout from the hot CNO cycle. The excited states of 20Na which are the most important for astrophysics are not yet known, due to the uncertainty on the spin, parity, and partial widths of the levels between threshold (2.2 MeV) and 3.1 MeV excitation energy in 20Na. Two different techniques will be used to measure the 19Ne(p,γ)20Na cross section: detection of the positrons from the decay of 20Na; or of the delayed α particles from the decay of some 20Ne* levels fed by the decay of 20Na. The p+19Ne elastic scattering will be studied with a large silicon strip detector covering a solid angle of 2π in the centre of mass frame