Analysis of the two-step cascade intensities, that are excited in thermal neutrons capture, for approximately 40 nuclei from the mass region 40 A 200, gives maximally reliable today values of the level density for the fixed spin window and the sums of the radiative strength functions of cascade gamma-transitions. The maximum reliability of these data is provided by the experiment conditions: minimally possible transfer coefficients of errors and practically unique extraction of the process parameters from the measured spectra.
Step-like structures in the level density at the excitation energy less than 3-4 MeV with good precision are described within the framework of this idea as the superposition of two- (three-quasiparticle in odd A nuclei) and vibration excitations with the coefficient of a collective enhancement in the density K_coll 10-20. To them corresponds the correlated on the excitation energy maximal enhancement of radiative strength functions of primary gamma-transitions.
The level density at the higher excitation energies is reproduced well upon consideration of the break of two more, as the minimum, Cooper pairs of nucleons. The unconditional decrease of the radiative strength functions of the primary gamma-transitions of the compound-state decay corresponds to an increase in the number of quasiparticles excited in the nucleus. But a maximally possible value of partial widths of primary transitions with the decrease of their energy regularly grows. A certain ambiguity of results of approximation and divergence with the existing theoretical ideas about the energy dependence of the correlation functions of nucleons in the excited nucleus indicates the possibility of direct obtaining from the experiment of fundamentally new information about the structure of the nucleus excited levels in the range of the neutron binding energy and, first of all, the possibility of obtaining the parameters of the dependence of the correlation functions of nucleons on the excitation energy of nucleus.

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