Abstract. The present status of the standard Big Bang Nucleosynthesis (BBN) is here reviewed by comparing the theoretical predictions with the observational estimates of light nuclei abundances. In particular, the analysis reports the expected ranges for the baryon fraction and effective number of the neutrinos as obtained by BBN only. The comparison is also performed in case of a more detailed analysis of neutrino decoupling by assuming initial degenerate neutrino distributions and oscillation mechanism as well. As a result one gets the upper bound to the radiation content in terms of neutrinos of primordial plasma.

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