Solar neutrino fluxes depend both on astrophysical and on nuclear physics inputs, namely on the cross sections of the reactions responsible for neutrino production inside the Solar core. While the flux of solar B-8 neutrinos has been recently measured at Superkamiokande with a 3.5% uncertainty and a precise measurement of Be-7 neutrino flux is foreseen in the next future, the predicted fluxes are still affected by larger errors. The largest nuclear physics uncertainty to determine the fluxes of B-8 and Be-7 neutrinos comes from the He-3(alpha,gamma)Be-7 reaction. The uncertainty on its S-factor is due to an average discrepancy in results obtained using two different experimental approaches: the detection of the delayed gamma rays from Be-7 decay and the measurement of the prompt gamma emission. Here we report on a new high precision experiment performed with both techniques at the same time. Thanks to the low background conditions of the Gran Sasso LUNA accelerator facility, the cross section has been measured at E-c.m.=170, 106, and 93 keV, the latter being the lowest interaction energy ever reached. The S-factors from the two methods do not show any discrepancy within the experimental errors. An extrapolated S(0) = 0.560 +/- 0.017 keV barn is obtained. Moreover, branching ratios between the two prompt gamma-transitions have been measured with 5-8% accuracy.
|Titolo:||Astrophysical S factor of the 3He(alpha,gamma)7Be reaction measured at low energy via detection of prompt and delayed gamma rays|
|Autori interni:||GUGLIELMETTI, ALESSANDRA|
|Parole Chiave:||Capture reaction HE-3(alpha, gamma)BE-7 ; absolute cross-section ; solar-neutrino problem ; HE-3(HE-4, gamma)BE-7 reaction ; gas-target ; nuclei ; rates ; BE7|
|Settore Scientifico Disciplinare:||Settore FIS/04 - Fisica Nucleare e Subnucleare|
|Data di pubblicazione:||2007|
|Digital Object Identifier (DOI):||10.1103/PhysRevC.75.065803|
|Appare nelle tipologie:||01 - Articolo su periodico|