We report on a new measurement of the 14N(p,γ) 15O capture cross section at Ep=140 to 400 keV using the 400 kV LUNA accelerator facility at the Laboratori Nazionali del Gran Sasso (LNGS). The uncertainties have been reduced with respect to previous measurements and their analysis. We have analyzed the data using the R-matrix method and we find that the ground state transition accounts for about 15% of the total S-factor. The main contribution to the S-factor is given by the transition to the 6.79 MeV state. We find a total S(0)=1.7±0.2 keVb, in agreement with recent extrapolations. The result has important consequences for the solar neutrino spectrum as well as for the age of globular clusters. © 2004 Elsevier B.V. All rights reserved.info:eu-repo/semantics/publishe

We give the LUNA results on the $\sigma \left(E\right)$ cross section measurement of a key reaction of the proton-proton chain strongly affecting the calculated neutrino luminosity from the Sun: ${}^3\mathrm{He}{(}^3\mathrm{He},2p{)}^4\mathrm{He}$. Because of the cosmic ray suppression provided by the Gran Sasso underground laboratory, it has been possible to measure $\sigma \left(E\right)$ throughout the energy range in which this reaction occurs in the Sun, i.e., down to $16.5\mathrm{keV}$ center of mass energy. The data clearly show the cross section increase due to the electron screening effect but they do not exhibit any evidence for a narrow resonance suggested to explain the ${}^8\mathrm{B}$ and ${}^7\mathrm{Be}$ solar neutrino flux reduction.

The nuclear physics input from the ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$ cross section is a major uncertainty in the fluxes of ${}^7\mathrm{Be}$ and ${}^8\mathrm{B}$ neutrinos from the Sun predicted by solar models and in the ${}^7\mathrm{Li}$ abundance obtained in big-bang nucleosynthesis calculations. The present work reports on a new precision experiment using the activation technique at energies directly relevant to big-bang nucleosynthesis. Previously such low energies had been reached experimentally only by the prompt-$\gamma$ technique and with inferior precision. Using a windowless gas target, high beam intensity, and low background $\gamma$-counting facilities, the ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$ cross section has been determined at 127, 148, and 169 keV center-of-mass energy with a total uncertainty of 4%. The sources of systematic uncertainty are discussed in detail. The present data can be used in big-bang nucleosynthesis calculations and to constrain the extrapolation of the ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$ astrophysical $S$ factor to solar energies.