Low energy measurement of the 14N(p,γ)15O total cross section at the LUNA underground facility

Deep underground in Gran Sasso National Laboratory (Italy), at the LUNA facility, the cross section of the N-14(p, gamma) O-15, the slowest process of the CNO cycle, has been measured at energies much lower than achieved before. Using a 400 kV accelerator, a windowless gas target and a 4 pi BGO summing detector, direct cross section data has been obtained down to 70 keV, reaching a value of 0.24 picobarn, corresponding to an S-factor of 1.74 +/- 0.14(stat) +/- 0.14(syst) keV barn. The Gamow peak has been covered by direct experimental data for several scenarios of stable and explosive hydrogen burning. The wy strength of the 259 keV resonance has been re-measured obtaining 12.8 +/- 0.3(stat) +/- 0.4(syst) meV. The stellar reaction rate has been calculated for temperatures 0.09 x 10(9) - 0.3 x 10(9) K. A complete description of the experiment is here presented, including the impact of the present data on nucleosynthesis in AGB stars

Energy loss of deuterons in 3He gas: a threshold effect

The energy loss of deuterons in 3He gas was measured at E d = 15 to 100 keV using the 3He pressure dependence of the 3He(d,p)4He cross-section at a given incident energy. At the highest energies, the observed energy loss is in good agreement with a standard compilation. However, with decreasing energy the experimental values drop steadily below the theoretical values and near E d = 18 keV they drop sharply (within 1 keV) reaching the domain of nuclear stopping power. This threshold behavior is due to the minimum 1s → 2s electron excitation of the He target atoms, i.e. it is a quantum effect. Some consequences are discussed