In stars, four hydrogen nuclei are converted into a helium nucleus by two competing nuclear fusion processes: the proton - proton chain (p-p) and the carbon - nitrogen - oxygen (CNO) cycle. At temperatures higher than 2 middot 107 K, the CNO cycle dominates the energy production. In particular, its rate is determined by the slowest reaction: 14N(p, gamma )15O. Direct measurement in a laboratory at the surface of the Earth is hampered by the background due to the cosmic rays. Here we report on an experiment performed with the LUNA (Laboratory for Underground Nuclear Astrophysics) accelerator placed deep underground in the Gran Sasso laboratory (Italy). Thanks to the cosmic ray suppression provided by the mountain shield, we could measure the 14N(p, gamma )15O cross section for the first time directly at energies corresponding to stellar temperatures and with unprecedented accuracy. The results are strictly related to carbon stars formation, an independent lower limit on the age of the universe and solar neutrinos flux. The 13N and 15O neutrinos coming from the CNO cycle are strictly correlated to the 14N(p, gamma )15O S-factor and their flux will play an important role in some future solar neutrino experiment, such as Borexino.
|Titolo:||Underground measurement of 14N(p,gamma)15O astrophysical factor at low energy|
|Parole Chiave:||cosmic ray interactions ; cosmic ray neutrinos ; nuclear fusion ; nuclei with mass number 6 to 19 ; proton radiative capture ; solar cosmic ray particles ; solar interior ; star formation ; stellar internal processes|
|Settore Scientifico Disciplinare:||Settore FIS/04 - Fisica Nucleare e Subnucleare|
|Data di pubblicazione:||2006|
|Digital Object Identifier (DOI):||10.1088/1742-6596/39/1/063|
|Appare nelle tipologie:||01 - Articolo su periodico|