  Within the standard V - A theory of weak interactions, Quantum
Electrodynamics (QED) and the linear sigma-model (LsM) of strong low-energy
hadronic interactions we analyse gauge properties of hadronic structure of the
neutron and proton in the neutron radiative beta-decay. We show that the
Feynman diagrams, describing contributions of hadronic structure to the
amplitude of the neutron radiative beta-decay in the tree-approximation for
strong low-energy interactions in the LsM, are gauge invariant. In turn, the
complete set of Feynman diagrams, describing the contributions of hadron-photon
interactions in the one-hadron-loop approximation, is not gauge invariant. In
the infinite limit of the scalar sigma-meson, reproducing the current algebra
results (Weinberg, Phys. Rev. Lett. 18, 188 (1967)), and to leading order in
the large nucleon mass expansion the Feynman diagrams, violating gauge
invariance, do not contribute to the amplitude of the neutron radiative
beta-decay in agreement with Sirlin's analysis of strong low-energy
interactions in neutron beta decays. We assert that the problem of appearance
of gauge non-invariant Feynman diagrams of hadronic structure of the neutron
and proton is related to the following. The vertex of the effective V-A weak
interactions does not belong to the combined quantum field theory including the
LsM and QED. We argue that gauge invariant set of Feynman diagrams of hadrons,
coupled to real and virtual photons in neutron beta decays, can be obtained
within the combined quantum field theory including the Standard Electroweak
Model (SEM) and the LsM, where the effective V-A vertex of weak interactions is
a result of the W^- - electroweak boson exchange.
