[en] Ultrahigh-energy neutrons and pions are likely to be produced in particle interactions inside cosmic ray sources and subsequently decay to neutrinos and other secondary particles [π^±→μ^±ν_μ(ν_μ), μ^±→e^±ν_μ(ν_μ)ν_e(ν_e)]. In high magnetic fields of the cosmic acceleration sites, the ultrahigh-energy-charged particles may lose energy significantly due to synchrotron radiation before decay. We show that for gamma-ray bursts in the internal shock model, the flux of very high-energy antineutrinos (ν_e) produced from decaying ultrahigh-energy neutrons can be more than the total neutrino flux produced in pion decay depending on the values of their Lorentz factors, luminosities, and variability times.