  The mechanism of beta decay in nature is not understood yet. Mirrored energy
spectra of electron and antineutrino can clarify the situation. A special
experiment is needed to measure antineutrino spectrum from known beta-decaying
isotope to compare it with the beta one. One of ongoing experiments with large
volume detector can be chosen to make the experiment. Another possibility is to
make a special experiment close to a powerful source of mixture of known
beta-decaying isotopes. If sufficient differences in shape will be observed the
method of antineutrino spectrum calculation should be revised.
