  At the early stage of the Universe evolution, when photons and neutrinos are
no longer able to prevent nucleosynthesis, the key role is given to neutron
component of matter. Neutron component creates a certain variety of the
lightest chemical elements and disappears leaving a sufficient portion of
Helium isotopes and some tiny portions of Li and Be isotopes. Free neutrons
disappear in energetic flame of these reactions not using even a quarter of
their own lifetime. Further the Universe matter has been evolving smoothly
without free neutrons.
  The following physical principle is taken as a basis: interactions of the
most fast component in speed are considered as main and taken into account
first. Substance component that meets this requirement provides a thermodynamic
equilibrium in the system. It is obvious that fast component of the substance
is the neutrons. Other components cause slow change as compared with actions of
the main one.
  Thermodynamic description of nucleus matter is carried out in the same way as
it is made in the well-known problem of ``ionization equilibrium'' of atomic
plasma.
