  Comparative analysis of different types of initial mass spectra of primordial
black holes (PBHs) is carried out. It is assumed that primordial density
fluctuations have power law spectrum and the spectral index is constant
throughout all scales. It is shown that densities of background radiations
(neutrinos, gamma-quanta) from PBH evaporations strongly depend on the type of
gravitational collapse and on the way of taking into account the spread of
horizon masses at which PBHs can form. Constraints on spectral index values
based on PBH evaporation process and on atmospheric and solar neutrino data are
obtained.
