Components of antineutrino emission in nuclear reactor

New ⊻ e e scattering experiments aimed at sensitive searches for the ν e magnetic moment and projects to explore small mixing angle neutrino oscillations at reactors require a better understanding of the reactor antineutrino spectrum. Six components which contribute to the total ⊻ e spectrum generated in a nuclear reactor are considered. They are beta decays of the fission fragments of 235 U, 239 Pu, 238 U, and 241 Pu and decays of beta emitters produced as a result of neutron capture in 238 U and in accumulated fission fragments which perturb the spectrum. For antineutrino energies of less than 3.5 MeV and for each of the four fissile isotopes, the time evolution of ⊻ e spectra is given during fuel irradiation and after the irradiation is stopped. The relevant uncertainties are estimated. Small corrections to the ILL spectra are considered.