[en] Paper describes β-decay of polarized neutron with regard to electromagnetic interaction. The effect of γ-radiation turns to be essential to determine B asymmetry factor of antineutrino angular distribution in the experiments devoted to β-decay of polarized neutrons when one records p electron pulse directed along x axis and P_x projection proton pulse for this direction of x, while ξ neutron polarization vector is directed along or opposite x. As γ-radiation is not recorded in such experiments the kinematics of antineutrino may be recovered in the average, that is why, the antineutrino pulse distribution averaged by γ-radiation pulse distribution, is studied. Respectively, on the basis of these experiments the true value of B may be estimated in the average. Unavoidable uncertainties as to the estimation of B constitute several percents. With regard to electromagnetic interactions one may use measurement of pulse distribution of electrons and protons to estimate with high accuracy the value of g_A - axial amplitude of β-decay