  On the basis of the concept of the growing role of nonadiabatic effects of
the non-conservation of the quantum number $K,$ a theory has been developed of
the phenomenon which has been given the name of backbending. Above the
transition point, for $J\geq J_c$, all the values $-J\leq K\leq J$ are equally
probable. An investigation is made of the singularities possessed by the
ordering parameter (proportional to the spectroscopic quadrupole moment of a
nonspherical nucleus), the rotational angular velocity and the moment of
inertia of a nucleus at the Curie point. Formulas have been derived for the
intensity of quadrupole radiation in the more symmetric $n$-phase $J> J_c$. By
analyzing the experimental values of the moments of inertia belonging to the
$n$-phase, the radius of the mass distribution in the nucleus was determined.
It agrees with the radius of the proton distribution derived from data on the
scattering of electrons by nuclei. On the basis of the simplest form of the
singularity of the parametric derivative of the Hamiltonian of the system a
general theory of zero-temperature second-order phase transitions is developed
in the Appendix.
