Nucleosynthesis in γ-ray bursts outflows

It is shown that fusion of neutrons and protons to 4He nuclei occurs in ray burst outflows in a process similar to big-bang nucleosynthesis in the early Universe. Only the surviving free neutrons can then decouple kinematically from the charged fluid so that the multi-GeV neutrino signal predicted from inelastic nuclear n-p collisions is significantly reduced. It is also argued that a sizeable fraction of ultra-high energy cosmic rays accelerated in ray bursts should be 4He nuclei.