We report the results of a new accurate evaluation of light nuclei yields i
n primordial nucleosynthesis. All radiative effects, finite nucleon mass, t
hermal and plasma corrections are included in the proton to neutron convers
ion rates. The relic densities of He-4, D and Li-7 have been numerically ob
tained via a new updated Version of the standard BBN code. In particular th
e theoretical uncertainty on He-4 is reduced to the order of 0.1%. (C) 2000
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