From a comparison of absolute intensities of the individual two-step cascades with the known intensities of their primary and secondary transitions, the cascade and total population of about 100 levels has been determined for each of the following nuclei: ⁴⁰K, ⁶⁰Co, ⁷⁴Ge, ¹¹⁴Cd, ¹¹⁸Sn, ¹²⁴Te, ^137,138Ba, ¹⁵⁰Sm, ^156,158Gd, ¹⁶⁵Dy, ¹⁶⁸Er, ¹⁷⁵Yb, ¹⁸¹Hf, ^{183,184,185,187}W, ¹⁹⁶Pt and ²⁰⁰Hg. These experimental results and intensities of two-step cascades to the low-lying levels of these nuclei were reproduced with a good enough accuracy using energy dependence of level density with the clearly expressed ''step-like'' structure and radiative strength functions which were considerably increased for the primary transitions to the region of this structure as compared with predictions of conventional models. Besides, population of levels of nuclei with any nucleon parity below 3-5 MeV could be reproduced only accounting for considerable local strengthening in the radiative strength functions of the secondary transitions to the levels lying in the vicinity of the break point in the energy dependence of level density and rather considerable decrease of wave functions of secondary transitions to low-lying levels of a nucleus. Simultaneous strong local change in both level density and radiative strength functions of two-step gamma-cascades in the small excitation region of a nucleus corresponds to the definition of the second order phase transition.

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